diff --git a/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart b/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart
index 5edb79259dd..8085b949548 100644
--- a/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart
+++ b/pkg/front_end/lib/src/fasta/fasta_codes_cfe_generated.dart
@@ -2047,6 +2047,42 @@ Message _withArgumentsMixinInferenceNoMatchingClass(
       arguments: {'name': name, 'name2': name2, 'type': _type});
 }
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Template<
+        Message Function(
+            String name, DartType _type, bool isNonNullableByDefault)>
+    templateNonNullableInNullAware = const Template<
+            Message Function(
+                String name, DartType _type, bool isNonNullableByDefault)>(
+        messageTemplate:
+            r"""Operand of null-aware operation '#name' has type '#type' which excludes null.""",
+        withArguments: _withArgumentsNonNullableInNullAware);
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<
+        Message Function(
+            String name, DartType _type, bool isNonNullableByDefault)>
+    codeNonNullableInNullAware = const Code<
+            Message Function(
+                String name, DartType _type, bool isNonNullableByDefault)>(
+        "NonNullableInNullAware", templateNonNullableInNullAware,
+        severity: Severity.warning);
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+Message _withArgumentsNonNullableInNullAware(
+    String name, DartType _type, bool isNonNullableByDefault) {
+  if (name.isEmpty) throw 'No name provided';
+  name = demangleMixinApplicationName(name);
+  TypeLabeler labeler = new TypeLabeler(isNonNullableByDefault);
+  List<Object> typeParts = labeler.labelType(_type);
+  String type = typeParts.join();
+  return new Message(codeNonNullableInNullAware,
+      message:
+          """Operand of null-aware operation '${name}' has type '${type}' which excludes null.""" +
+              labeler.originMessages,
+      arguments: {'name': name, 'type': _type});
+}
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Template<Message Function(DartType _type, bool isNonNullableByDefault)>
     templateNullableExpressionCallError = const Template<
diff --git a/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart b/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart
index a96fb3e58b8..e1d036baf3d 100644
--- a/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart
@@ -352,6 +352,10 @@ class InferenceVisitor
     ExpressionInferenceResult result = inferrer.inferExpression(
         node.variable.initializer, typeContext, true,
         isVoidAllowed: false);
+    if (node.isNullAware) {
+      reportNonNullableInNullAwareWarningIfNeeded(
+          result.inferredType, "?..", node.fileOffset);
+    }
 
     node.variable.initializer = result.expression..parent = node.variable;
     node.variable.type = result.inferredType;
@@ -1087,6 +1091,8 @@ class InferenceVisitor
     ExpressionInferenceResult lhsResult = inferrer.inferExpression(
         node.left, inferrer.computeNullable(typeContext), true,
         isVoidAllowed: false);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        lhsResult.inferredType, "??", node.left.fileOffset);
 
     Member equalsMember = inferrer
         .findInterfaceMember(
@@ -1280,6 +1286,10 @@ class InferenceVisitor
               <DartType>[inferredTypeArgument]),
           inferenceNeeded || typeChecksNeeded,
           isVoidAllowed: true);
+      if (element.isNullAware) {
+        reportNonNullableInNullAwareWarningIfNeeded(
+            spreadResult.inferredType, "...?", element.expression.fileOffset);
+      }
       element.expression = spreadResult.expression..parent = element;
       DartType spreadType = spreadResult.inferredType;
       inferredSpreadTypes[element.expression] = spreadType;
@@ -1689,6 +1699,10 @@ class InferenceVisitor
       ExpressionInferenceResult spreadResult = inferrer.inferExpression(
           entry.expression, spreadContext, inferenceNeeded || typeChecksNeeded,
           isVoidAllowed: true);
+      if (entry.isNullAware) {
+        reportNonNullableInNullAwareWarningIfNeeded(
+            spreadResult.inferredType, "...?", entry.expression.fileOffset);
+      }
       entry.expression = spreadResult.expression..parent = entry;
       DartType spreadType = spreadResult.inferredType;
       inferredSpreadTypes[entry.expression] = spreadType;
@@ -2376,8 +2390,8 @@ class InferenceVisitor
     ExpressionInferenceResult operandResult = inferrer.inferExpression(
         node.operand, inferrer.computeNullable(typeContext), true);
     node.operand = operandResult.expression..parent = node;
-    // TODO(johnniwinther): Check that the inferred type is potentially
-    //  nullable.
+    reportNonNullableInNullAwareWarningIfNeeded(
+        operandResult.inferredType, "!", node.operand.fileOffset);
     inferrer.flowAnalysis.nonNullAssert_end(node.operand);
     DartType nonNullableResultType =
         inferrer.computeNonNullable(operandResult.inferredType);
@@ -2388,6 +2402,8 @@ class InferenceVisitor
       NullAwareMethodInvocation node, DartType typeContext) {
     Link<NullAwareGuard> nullAwareGuards =
         inferrer.inferSyntheticVariableNullAware(node.variable);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        node.variable.type, "?.", node.variable.fileOffset);
     NullAwareGuard nullAwareGuard =
         inferrer.createNullAwareGuard(node.variable);
     ExpressionInferenceResult invocationResult = inferrer.inferExpression(
@@ -2403,6 +2419,8 @@ class InferenceVisitor
       NullAwarePropertyGet node, DartType typeContext) {
     Link<NullAwareGuard> nullAwareGuards =
         inferrer.inferSyntheticVariableNullAware(node.variable);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        node.variable.type, "?.", node.variable.fileOffset);
     NullAwareGuard nullAwareGuard =
         inferrer.createNullAwareGuard(node.variable);
     ExpressionInferenceResult readResult =
@@ -2417,6 +2435,8 @@ class InferenceVisitor
       NullAwarePropertySet node, DartType typeContext) {
     Link<NullAwareGuard> nullAwareGuards =
         inferrer.inferSyntheticVariableNullAware(node.variable);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        node.variable.type, "?.", node.variable.fileOffset);
     NullAwareGuard nullAwareGuard =
         inferrer.createNullAwareGuard(node.variable);
     ExpressionInferenceResult writeResult =
@@ -2430,6 +2450,8 @@ class InferenceVisitor
   ExpressionInferenceResult visitNullAwareExtension(
       NullAwareExtension node, DartType typeContext) {
     inferrer.inferSyntheticVariable(node.variable);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        node.variable.type, "?.", node.variable.fileOffset);
     NullAwareGuard nullAwareGuard =
         inferrer.createNullAwareGuard(node.variable);
     ExpressionInferenceResult expressionResult =
@@ -2572,6 +2594,8 @@ class InferenceVisitor
     ExpressionInferenceResult readResult = inferrer.inferExpression(
         node.read, const UnknownType(), true,
         isVoidAllowed: true);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        readResult.inferredType, "??=", node.read.fileOffset);
     Expression read = readResult.expression;
     DartType readType = readResult.inferredType;
 
@@ -2633,6 +2657,8 @@ class InferenceVisitor
       IfNullSet node, DartType typeContext) {
     ExpressionInferenceResult readResult =
         inferrer.inferExpression(node.read, const UnknownType(), true);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        readResult.inferredType, "??=", node.read.fileOffset);
     Link<NullAwareGuard> nullAwareGuards;
     Expression read;
     DartType readType;
@@ -2995,6 +3021,8 @@ class InferenceVisitor
 
     ExpressionInferenceResult readResult = _computeIndexGet(node.readOffset,
         readReceiver, receiverType, readTarget, readIndex, checkKind);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        readResult.inferredType, "??=", node.readOffset);
     Expression read = readResult.expression;
     DartType readType = readResult.inferredType;
     inferrer.flowAnalysis.ifNullExpression_rightBegin(read);
@@ -3114,6 +3142,8 @@ class InferenceVisitor
         : const ObjectAccessTarget.missing();
 
     DartType readType = inferrer.getReturnType(readTarget, inferrer.thisType);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        readType, "??=", node.readOffset);
     DartType readIndexType =
         inferrer.getIndexKeyType(readTarget, inferrer.thisType);
 
@@ -3314,6 +3344,8 @@ class InferenceVisitor
         readTarget,
         readIndex,
         MethodContravarianceCheckKind.none);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        readResult.inferredType, "??=", node.readOffset);
     Expression read = readResult.expression;
     DartType readType = readResult.inferredType;
     inferrer.flowAnalysis.ifNullExpression_rightBegin(read);
@@ -4157,6 +4189,8 @@ class InferenceVisitor
     ExpressionInferenceResult receiverResult = inferrer.inferExpression(
         node.receiver, const UnknownType(), true,
         isVoidAllowed: true);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        receiverResult.inferredType, "?.", node.receiver.fileOffset);
 
     Expression receiver;
     DartType receiverType;
@@ -4666,6 +4700,8 @@ class InferenceVisitor
     ExpressionInferenceResult receiverResult = inferrer.inferExpression(
         node.receiver, const UnknownType(), true,
         isVoidAllowed: false);
+    reportNonNullableInNullAwareWarningIfNeeded(
+        receiverResult.inferredType, "?.", node.receiver.fileOffset);
 
     Link<NullAwareGuard> nullAwareGuards;
     Expression receiver;
@@ -5659,6 +5695,20 @@ class InferenceVisitor
     return new ExpressionInferenceResult(
         result.inferredType, result.expression);
   }
+
+  void reportNonNullableInNullAwareWarningIfNeeded(
+      DartType operandType, String operationName, int offset) {
+    if (inferrer.isNonNullableByDefault && inferrer.performNnbdChecks) {
+      if (operandType != InvalidType && !operandType.isPotentiallyNullable) {
+        inferrer.library.addProblem(
+            templateNonNullableInNullAware.withArguments(
+                operationName, operandType, inferrer.isNonNullableByDefault),
+            offset,
+            noLength,
+            inferrer.library.fileUri);
+      }
+    }
+  }
 }
 
 class ForInResult {
diff --git a/pkg/front_end/messages.status b/pkg/front_end/messages.status
index 4ea9e4544b0..65fd57fc6dd 100644
--- a/pkg/front_end/messages.status
+++ b/pkg/front_end/messages.status
@@ -465,6 +465,8 @@ NonConstConstructor/example: Fail
 NonConstFactory/example: Fail
 NonInstanceTypeVariableUse/example: Fail
 NonNullAwareSpreadIsNull/analyzerCode: Fail # There's no analyzer code for that error yet.
+NonNullableInNullAware/analyzerCode: Fail
+NonNullableInNullAware/example: Fail
 NonNullableOptOut/analyzerCode: Fail
 NonNullableOptOut/example: Fail
 NonPartOfDirectiveInPart/part_wrapped_script1: Fail
diff --git a/pkg/front_end/messages.yaml b/pkg/front_end/messages.yaml
index b81fef36270..3a483baebf9 100644
--- a/pkg/front_end/messages.yaml
+++ b/pkg/front_end/messages.yaml
@@ -3906,3 +3906,7 @@ DefaultListConstructorWarning:
   template: "Using the default List constructor."
   tip: "Try using List.filled instead."
   severity: WARNING
+
+NonNullableInNullAware:
+  template: "Operand of null-aware operation '#name' has type '#type' which excludes null."
+  severity: WARNING
diff --git a/pkg/front_end/test/spell_checking_list_common.txt b/pkg/front_end/test/spell_checking_list_common.txt
index f577286a5fa..bfba0036afc 100644
--- a/pkg/front_end/test/spell_checking_list_common.txt
+++ b/pkg/front_end/test/spell_checking_list_common.txt
@@ -1028,6 +1028,7 @@ exceptions
 exclamation
 exclude
 excluded
+excludes
 excluding
 exclusive
 executable
diff --git a/pkg/front_end/testcases/nnbd/issue_39286_2.dart.strong.expect b/pkg/front_end/testcases/nnbd/issue_39286_2.dart.strong.expect
index 57d21df6b5f..4f72c3cef4f 100644
--- a/pkg/front_end/testcases/nnbd/issue_39286_2.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/issue_39286_2.dart.strong.expect
@@ -1,4 +1,16 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/issue_39286_2.dart:15:14: Warning: Operand of null-aware operation '!' has type 'String' which excludes null.
+//   x..f()!.g()['Hi!']!..h()!.y = 2;
+//              ^
+//
+// pkg/front_end/testcases/nnbd/issue_39286_2.dart:15:24: Warning: Operand of null-aware operation '!' has type 'C' which excludes null.
+//  - 'C' is from 'pkg/front_end/testcases/nnbd/issue_39286_2.dart'.
+//   x..f()!.g()['Hi!']!..h()!.y = 2;
+//                        ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/issue_39286_2.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/issue_39286_2.dart.strong.transformed.expect
index 57d21df6b5f..4f72c3cef4f 100644
--- a/pkg/front_end/testcases/nnbd/issue_39286_2.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue_39286_2.dart.strong.transformed.expect
@@ -1,4 +1,16 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/issue_39286_2.dart:15:14: Warning: Operand of null-aware operation '!' has type 'String' which excludes null.
+//   x..f()!.g()['Hi!']!..h()!.y = 2;
+//              ^
+//
+// pkg/front_end/testcases/nnbd/issue_39286_2.dart:15:24: Warning: Operand of null-aware operation '!' has type 'C' which excludes null.
+//  - 'C' is from 'pkg/front_end/testcases/nnbd/issue_39286_2.dart'.
+//   x..f()!.g()['Hi!']!..h()!.y = 2;
+//                        ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/issue_39286_2.dart.weak.expect b/pkg/front_end/testcases/nnbd/issue_39286_2.dart.weak.expect
index 57d21df6b5f..4f72c3cef4f 100644
--- a/pkg/front_end/testcases/nnbd/issue_39286_2.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/issue_39286_2.dart.weak.expect
@@ -1,4 +1,16 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/issue_39286_2.dart:15:14: Warning: Operand of null-aware operation '!' has type 'String' which excludes null.
+//   x..f()!.g()['Hi!']!..h()!.y = 2;
+//              ^
+//
+// pkg/front_end/testcases/nnbd/issue_39286_2.dart:15:24: Warning: Operand of null-aware operation '!' has type 'C' which excludes null.
+//  - 'C' is from 'pkg/front_end/testcases/nnbd/issue_39286_2.dart'.
+//   x..f()!.g()['Hi!']!..h()!.y = 2;
+//                        ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/issue_39286_2.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/issue_39286_2.dart.weak.transformed.expect
index 57d21df6b5f..4f72c3cef4f 100644
--- a/pkg/front_end/testcases/nnbd/issue_39286_2.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/issue_39286_2.dart.weak.transformed.expect
@@ -1,4 +1,16 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/issue_39286_2.dart:15:14: Warning: Operand of null-aware operation '!' has type 'String' which excludes null.
+//   x..f()!.g()['Hi!']!..h()!.y = 2;
+//              ^
+//
+// pkg/front_end/testcases/nnbd/issue_39286_2.dart:15:24: Warning: Operand of null-aware operation '!' has type 'C' which excludes null.
+//  - 'C' is from 'pkg/front_end/testcases/nnbd/issue_39286_2.dart'.
+//   x..f()!.g()['Hi!']!..h()!.y = 2;
+//                        ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/null_access.dart b/pkg/front_end/testcases/nnbd/null_access.dart
index 35b7f16e5ec..6a14198b31c 100644
--- a/pkg/front_end/testcases/nnbd/null_access.dart
+++ b/pkg/front_end/testcases/nnbd/null_access.dart
@@ -9,23 +9,30 @@ class Class {
   void operator []=(int key, int value) {}
   Class get nonNullableClass => this;
   Class call() => this;
+  NullableIndexClass get nonNullableNullableIndexClass => NullableIndexClass();
+}
+
+class NullableIndexClass {
+  int? operator [](int key) => key;
+  void operator []=(int key, int value) {}
 }
 
 main() {}
 
 errors(Class? nullableClass, Class nonNullableClass, int? nullableInt,
-    int nonNullableInt) {
+    int nonNullableInt, NullableIndexClass? nullableNullableIndexClass) {
   -nullableInt; // error
   nullableInt + 2; // error
   nullableClass[nonNullableInt]; // error
   nullableClass[nonNullableInt] = nonNullableInt; // error
   nullableClass[nonNullableInt] += nonNullableInt; // error
-  nullableClass[nonNullableInt] ??= nonNullableInt; // error
+  nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
 
   nullableClass?.nonNullableClass[nonNullableInt]; // ok
   nullableClass?.nonNullableClass[nonNullableInt] = nonNullableInt; // ok
   nullableClass?.nonNullableClass[nonNullableInt] += nonNullableInt; // ok
-  nullableClass?.nonNullableClass[nonNullableInt] ??= nonNullableInt; // ok
+  nullableClass?.nonNullableNullableIndexClass[nonNullableInt] ??=
+      nonNullableInt; // ok
 
   nullableClass.nonNullableField; // error
   nullableClass.nonNullableField = 2; // error
diff --git a/pkg/front_end/testcases/nnbd/null_access.dart.outline.expect b/pkg/front_end/testcases/nnbd/null_access.dart.outline.expect
index a5ae9e34f68..42298883160 100644
--- a/pkg/front_end/testcases/nnbd/null_access.dart.outline.expect
+++ b/pkg/front_end/testcases/nnbd/null_access.dart.outline.expect
@@ -15,8 +15,18 @@ class Class extends core::Object {
     ;
   method call() → self::Class
     ;
+  get nonNullableNullableIndexClass() → self::NullableIndexClass
+    ;
+}
+class NullableIndexClass extends core::Object {
+  synthetic constructor •() → self::NullableIndexClass
+    ;
+  operator [](core::int key) → core::int?
+    ;
+  operator []=(core::int key, core::int value) → void
+    ;
 }
 static method main() → dynamic
   ;
-static method errors(self::Class? nullableClass, self::Class nonNullableClass, core::int? nullableInt, core::int nonNullableInt) → dynamic
+static method errors(self::Class? nullableClass, self::Class nonNullableClass, core::int? nullableInt, core::int nonNullableInt, self::NullableIndexClass? nullableNullableIndexClass) → dynamic
   ;
diff --git a/pkg/front_end/testcases/nnbd/null_access.dart.strong.expect b/pkg/front_end/testcases/nnbd/null_access.dart.strong.expect
index 642146a4980..ac5f13bc290 100644
--- a/pkg/front_end/testcases/nnbd/null_access.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/null_access.dart.strong.expect
@@ -2,82 +2,96 @@ library;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:18:3: Error: Operator 'unary-' cannot be called on 'int?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:24:3: Error: Operator 'unary-' cannot be called on 'int?' because it is potentially null.
 //   -nullableInt; // error
 //   ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:19:15: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:25:15: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
 //   nullableInt + 2; // error
 //               ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:20:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:26:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt]; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:21:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:27:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] = nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:22:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:28:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] += nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:22:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:28:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] += nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:23:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
-//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-//   nullableClass[nonNullableInt] ??= nonNullableInt; // error
-//                ^
+// pkg/front_end/testcases/nnbd/null_access.dart:29:29: Error: Operator '[]' cannot be called on 'NullableIndexClass?' because it is potentially null.
+//  - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+//                             ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:23:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
-//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-//   nullableClass[nonNullableInt] ??= nonNullableInt; // error
-//                ^
+// pkg/front_end/testcases/nnbd/null_access.dart:29:29: Error: Operator '[]=' cannot be called on 'NullableIndexClass?' because it is potentially null.
+//  - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+//                             ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:30:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:37:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:31:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:38:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField = 2; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:32:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:39:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField += 2; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:41:34: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:48:34: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
 //   nonNullableClass.nullableField += 2; // error
 //                                  ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:42:32: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:49:32: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
 //   nullableClass?.nullableField += 2; // error
 //                                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:50:16: Error: Method 'call' cannot be called on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:54:35: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   nullableClass?.nonNullableClass.nonNullableField ??= 0; // ok
+//                                   ^
+//
+// pkg/front_end/testcases/nnbd/null_access.dart:57:16: Error: Method 'call' cannot be called on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try calling using ?. instead.
 //   nullableClass(); // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:50:16: Error: Can't use an expression of type 'Class?' as a function because it's potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:57:16: Error: Can't use an expression of type 'Class?' as a function because it's potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try calling using ?.call instead.
 //   nullableClass(); // error
 //                ^
 //
+// pkg/front_end/testcases/nnbd/null_access.dart:59:3: Warning: Operand of null-aware operation '?.' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nonNullableClass?.nonNullableClass(); // ok
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_access.dart:60:3: Warning: Operand of null-aware operation '?.' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nonNullableClass?.nonNullableClass.nonNullableClass(); // ok
+//   ^
+//
 import self as self;
 import "dart:core" as core;
 
@@ -94,56 +108,66 @@ class Class extends core::Object {
     return this;
   method call() → self::Class
     return this;
+  get nonNullableNullableIndexClass() → self::NullableIndexClass
+    return new self::NullableIndexClass::•();
+}
+class NullableIndexClass extends core::Object {
+  synthetic constructor •() → self::NullableIndexClass
+    : super core::Object::•()
+    ;
+  operator [](core::int key) → core::int?
+    return key;
+  operator []=(core::int key, core::int value) → void {}
 }
 static method main() → dynamic {}
-static method errors(self::Class? nullableClass, self::Class nonNullableClass, core::int? nullableInt, core::int nonNullableInt) → dynamic {
-  let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:18:3: Error: Operator 'unary-' cannot be called on 'int?' because it is potentially null.
+static method errors(self::Class? nullableClass, self::Class nonNullableClass, core::int? nullableInt, core::int nonNullableInt, self::NullableIndexClass? nullableNullableIndexClass) → dynamic {
+  let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:24:3: Error: Operator 'unary-' cannot be called on 'int?' because it is potentially null.
   -nullableInt; // error
   ^" in nullableInt.{core::int::unary-}();
-  let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:19:15: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+  let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:25:15: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
   nullableInt + 2; // error
               ^" in nullableInt.{core::num::+}(2);
-  let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:20:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
+  let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:26:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
   nullableClass[nonNullableInt]; // error
                ^" in nullableClass.{self::Class::[]}(nonNullableInt);
-  let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:21:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
+  let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:27:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
   nullableClass[nonNullableInt] = nonNullableInt; // error
                ^" in nullableClass.{self::Class::[]=}(nonNullableInt, nonNullableInt);
-  let final self::Class? #t5 = nullableClass in let final core::int #t6 = nonNullableInt in let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:22:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
+  let final self::Class? #t5 = nullableClass in let final core::int #t6 = nonNullableInt in let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:28:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
   nullableClass[nonNullableInt] += nonNullableInt; // error
-               ^" in #t5.{self::Class::[]=}(#t6, (let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:22:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
+               ^" in #t5.{self::Class::[]=}(#t6, (let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:28:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
   nullableClass[nonNullableInt] += nonNullableInt; // error
                ^" in #t5.{self::Class::[]}(#t6)).{core::num::+}(nonNullableInt));
-  let final self::Class? #t9 = nullableClass in let final core::int #t10 = nonNullableInt in (let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:23:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
- - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-  nullableClass[nonNullableInt] ??= nonNullableInt; // error
-               ^" in #t9.{self::Class::[]}(#t10)).{core::num::==}(null) ?{core::int} let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:23:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
- - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-  nullableClass[nonNullableInt] ??= nonNullableInt; // error
-               ^" in #t9.{self::Class::[]=}(#t10, nonNullableInt) : null;
+  let final self::NullableIndexClass? #t9 = nullableNullableIndexClass in let final core::int #t10 = nonNullableInt in (let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:29:29: Error: Operator '[]' cannot be called on 'NullableIndexClass?' because it is potentially null.
+ - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+  nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+                            ^" in #t9.{self::NullableIndexClass::[]}(#t10)).{core::num::==}(null) ?{core::int} let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:29:29: Error: Operator '[]=' cannot be called on 'NullableIndexClass?' because it is potentially null.
+ - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+  nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+                            ^" in #t9.{self::NullableIndexClass::[]=}(#t10, nonNullableInt) : null;
   let final self::Class? #t13 = nullableClass in #t13.{core::Object::==}(null) ?{core::int?} null : #t13{self::Class}.{self::Class::nonNullableClass}.{self::Class::[]}(nonNullableInt);
   let final self::Class? #t14 = nullableClass in #t14.{core::Object::==}(null) ?{core::int?} null : #t14{self::Class}.{self::Class::nonNullableClass}.{self::Class::[]=}(nonNullableInt, nonNullableInt);
   let final self::Class? #t15 = nullableClass in #t15.{core::Object::==}(null) ?{core::int?} null : let final self::Class #t16 = #t15{self::Class}.{self::Class::nonNullableClass} in let final core::int #t17 = nonNullableInt in #t16.{self::Class::[]=}(#t17, #t16.{self::Class::[]}(#t17).{core::num::+}(nonNullableInt));
-  let final self::Class? #t18 = nullableClass in #t18.{core::Object::==}(null) ?{core::int?} null : let final self::Class #t19 = #t18{self::Class}.{self::Class::nonNullableClass} in let final core::int #t20 = nonNullableInt in #t19.{self::Class::[]}(#t20).{core::num::==}(null) ?{core::int} #t19.{self::Class::[]=}(#t20, nonNullableInt) : null;
-  let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:30:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+  let final self::Class? #t18 = nullableClass in #t18.{core::Object::==}(null) ?{core::int?} null : let final self::NullableIndexClass #t19 = #t18{self::Class}.{self::Class::nonNullableNullableIndexClass} in let final core::int #t20 = nonNullableInt in #t19.{self::NullableIndexClass::[]}(#t20).{core::num::==}(null) ?{core::int} #t19.{self::NullableIndexClass::[]=}(#t20, nonNullableInt) : null;
+  let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:37:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try accessing using ?. instead.
   nullableClass.nonNullableField; // error
                 ^^^^^^^^^^^^^^^^" in nullableClass.{self::Class::nonNullableField};
-  let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:31:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+  let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:38:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try accessing using ?. instead.
   nullableClass.nonNullableField = 2; // error
                 ^^^^^^^^^^^^^^^^" in nullableClass.{self::Class::nonNullableField} = 2;
-  let final self::Class? #t23 = nullableClass in let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:32:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+  let final self::Class? #t23 = nullableClass in let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:39:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try accessing using ?. instead.
   nullableClass.nonNullableField += 2; // error
-                ^^^^^^^^^^^^^^^^" in #t23.{self::Class::nonNullableField} = (let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:32:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+                ^^^^^^^^^^^^^^^^" in #t23.{self::Class::nonNullableField} = (let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:39:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try accessing using ?. instead.
   nullableClass.nonNullableField += 2; // error
@@ -153,21 +177,21 @@ Try accessing using ?. instead.
   let final self::Class? #t28 = nullableClass in #t28.{core::Object::==}(null) ?{core::int?} null : #t28.{self::Class::nonNullableField} = #t28.{self::Class::nonNullableField}.{core::num::+}(2);
   let final self::Class? #t29 = nullableClass in #t29.{core::Object::==}(null) ?{core::int?} null : #t29{self::Class}.{self::Class::nonNullableClass}.{self::Class::nonNullableField};
   let final self::Class? #t30 = nullableClass in #t30.{core::Object::==}(null) ?{core::int?} null : #t30{self::Class}.{self::Class::nonNullableClass}.{self::Class::nonNullableField} = 2;
-  let final self::Class #t31 = nonNullableClass in #t31.{self::Class::nullableField} = let final<BottomType> #t32 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:41:34: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+  let final self::Class #t31 = nonNullableClass in #t31.{self::Class::nullableField} = let final<BottomType> #t32 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:48:34: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
   nonNullableClass.nullableField += 2; // error
                                  ^" in #t31.{self::Class::nullableField}.{core::num::+}(2);
-  let final self::Class? #t33 = nullableClass in #t33.{core::Object::==}(null) ?{core::int?} null : #t33.{self::Class::nullableField} = let final<BottomType> #t34 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:42:32: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+  let final self::Class? #t33 = nullableClass in #t33.{core::Object::==}(null) ?{core::int?} null : #t33.{self::Class::nullableField} = let final<BottomType> #t34 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:49:32: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
   nullableClass?.nullableField += 2; // error
                                ^" in #t33.{self::Class::nullableField}.{core::num::+}(2);
   let final self::Class? #t35 = nullableClass in #t35.{core::Object::==}(null) ?{core::int?} null : #t35.{self::Class::nonNullableField}.{core::num::==}(null) ?{core::int} #t35.{self::Class::nonNullableField} = 0 : null;
   let final self::Class? #t36 = nullableClass in #t36.{core::Object::==}(null) ?{core::int?} null : #t36.{self::Class::nullableField}.{core::num::==}(null) ?{core::int} #t36.{self::Class::nullableField} = 0 : null;
   let final self::Class? #t37 = nullableClass in #t37.{core::Object::==}(null) ?{core::int?} null : let final self::Class? #t38 = #t37{self::Class}.{self::Class::nonNullableClass} in #t38{self::Class}.{self::Class::nonNullableField}.{core::num::==}(null) ?{core::int} #t38{self::Class}.{self::Class::nonNullableField} = 0 : null;
   let final self::Class? #t39 = nullableClass in #t39.{core::Object::==}(null) ?{core::int?} null : let final self::Class? #t40 = #t39{self::Class}.{self::Class::nonNullableClass} in #t40{self::Class}.{self::Class::nullableField}.{core::num::==}(null) ?{core::int} #t40{self::Class}.{self::Class::nullableField} = 0 : null;
-  let final<BottomType> #t41 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:50:16: Error: Can't use an expression of type 'Class?' as a function because it's potentially null.
+  let final<BottomType> #t41 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:57:16: Error: Can't use an expression of type 'Class?' as a function because it's potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try calling using ?.call instead.
   nullableClass(); // error
-               ^" in let final<BottomType> #t42 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:50:16: Error: Method 'call' cannot be called on 'Class?' because it is potentially null.
+               ^" in let final<BottomType> #t42 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:57:16: Error: Method 'call' cannot be called on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try calling using ?. instead.
   nullableClass(); // error
diff --git a/pkg/front_end/testcases/nnbd/null_access.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/null_access.dart.strong.transformed.expect
index 642146a4980..ac5f13bc290 100644
--- a/pkg/front_end/testcases/nnbd/null_access.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/null_access.dart.strong.transformed.expect
@@ -2,82 +2,96 @@ library;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:18:3: Error: Operator 'unary-' cannot be called on 'int?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:24:3: Error: Operator 'unary-' cannot be called on 'int?' because it is potentially null.
 //   -nullableInt; // error
 //   ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:19:15: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:25:15: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
 //   nullableInt + 2; // error
 //               ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:20:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:26:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt]; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:21:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:27:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] = nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:22:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:28:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] += nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:22:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:28:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] += nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:23:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
-//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-//   nullableClass[nonNullableInt] ??= nonNullableInt; // error
-//                ^
+// pkg/front_end/testcases/nnbd/null_access.dart:29:29: Error: Operator '[]' cannot be called on 'NullableIndexClass?' because it is potentially null.
+//  - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+//                             ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:23:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
-//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-//   nullableClass[nonNullableInt] ??= nonNullableInt; // error
-//                ^
+// pkg/front_end/testcases/nnbd/null_access.dart:29:29: Error: Operator '[]=' cannot be called on 'NullableIndexClass?' because it is potentially null.
+//  - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+//                             ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:30:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:37:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:31:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:38:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField = 2; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:32:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:39:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField += 2; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:41:34: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:48:34: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
 //   nonNullableClass.nullableField += 2; // error
 //                                  ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:42:32: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:49:32: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
 //   nullableClass?.nullableField += 2; // error
 //                                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:50:16: Error: Method 'call' cannot be called on 'Class?' because it is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:54:35: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   nullableClass?.nonNullableClass.nonNullableField ??= 0; // ok
+//                                   ^
+//
+// pkg/front_end/testcases/nnbd/null_access.dart:57:16: Error: Method 'call' cannot be called on 'Class?' because it is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try calling using ?. instead.
 //   nullableClass(); // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:50:16: Error: Can't use an expression of type 'Class?' as a function because it's potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:57:16: Error: Can't use an expression of type 'Class?' as a function because it's potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try calling using ?.call instead.
 //   nullableClass(); // error
 //                ^
 //
+// pkg/front_end/testcases/nnbd/null_access.dart:59:3: Warning: Operand of null-aware operation '?.' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nonNullableClass?.nonNullableClass(); // ok
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_access.dart:60:3: Warning: Operand of null-aware operation '?.' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nonNullableClass?.nonNullableClass.nonNullableClass(); // ok
+//   ^
+//
 import self as self;
 import "dart:core" as core;
 
@@ -94,56 +108,66 @@ class Class extends core::Object {
     return this;
   method call() → self::Class
     return this;
+  get nonNullableNullableIndexClass() → self::NullableIndexClass
+    return new self::NullableIndexClass::•();
+}
+class NullableIndexClass extends core::Object {
+  synthetic constructor •() → self::NullableIndexClass
+    : super core::Object::•()
+    ;
+  operator [](core::int key) → core::int?
+    return key;
+  operator []=(core::int key, core::int value) → void {}
 }
 static method main() → dynamic {}
-static method errors(self::Class? nullableClass, self::Class nonNullableClass, core::int? nullableInt, core::int nonNullableInt) → dynamic {
-  let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:18:3: Error: Operator 'unary-' cannot be called on 'int?' because it is potentially null.
+static method errors(self::Class? nullableClass, self::Class nonNullableClass, core::int? nullableInt, core::int nonNullableInt, self::NullableIndexClass? nullableNullableIndexClass) → dynamic {
+  let final<BottomType> #t1 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:24:3: Error: Operator 'unary-' cannot be called on 'int?' because it is potentially null.
   -nullableInt; // error
   ^" in nullableInt.{core::int::unary-}();
-  let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:19:15: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+  let final<BottomType> #t2 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:25:15: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
   nullableInt + 2; // error
               ^" in nullableInt.{core::num::+}(2);
-  let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:20:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
+  let final<BottomType> #t3 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:26:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
   nullableClass[nonNullableInt]; // error
                ^" in nullableClass.{self::Class::[]}(nonNullableInt);
-  let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:21:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
+  let final<BottomType> #t4 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:27:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
   nullableClass[nonNullableInt] = nonNullableInt; // error
                ^" in nullableClass.{self::Class::[]=}(nonNullableInt, nonNullableInt);
-  let final self::Class? #t5 = nullableClass in let final core::int #t6 = nonNullableInt in let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:22:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
+  let final self::Class? #t5 = nullableClass in let final core::int #t6 = nonNullableInt in let final<BottomType> #t7 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:28:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
   nullableClass[nonNullableInt] += nonNullableInt; // error
-               ^" in #t5.{self::Class::[]=}(#t6, (let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:22:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
+               ^" in #t5.{self::Class::[]=}(#t6, (let final<BottomType> #t8 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:28:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
   nullableClass[nonNullableInt] += nonNullableInt; // error
                ^" in #t5.{self::Class::[]}(#t6)).{core::num::+}(nonNullableInt));
-  let final self::Class? #t9 = nullableClass in let final core::int #t10 = nonNullableInt in (let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:23:16: Error: Operator '[]' cannot be called on 'Class?' because it is potentially null.
- - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-  nullableClass[nonNullableInt] ??= nonNullableInt; // error
-               ^" in #t9.{self::Class::[]}(#t10)).{core::num::==}(null) ?{core::int} let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:23:16: Error: Operator '[]=' cannot be called on 'Class?' because it is potentially null.
- - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-  nullableClass[nonNullableInt] ??= nonNullableInt; // error
-               ^" in #t9.{self::Class::[]=}(#t10, nonNullableInt) : null;
+  let final self::NullableIndexClass? #t9 = nullableNullableIndexClass in let final core::int #t10 = nonNullableInt in (let final<BottomType> #t11 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:29:29: Error: Operator '[]' cannot be called on 'NullableIndexClass?' because it is potentially null.
+ - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+  nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+                            ^" in #t9.{self::NullableIndexClass::[]}(#t10)).{core::num::==}(null) ?{core::int} let final<BottomType> #t12 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:29:29: Error: Operator '[]=' cannot be called on 'NullableIndexClass?' because it is potentially null.
+ - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+  nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+                            ^" in #t9.{self::NullableIndexClass::[]=}(#t10, nonNullableInt) : null;
   let final self::Class? #t13 = nullableClass in #t13.{core::Object::==}(null) ?{core::int?} null : #t13{self::Class}.{self::Class::nonNullableClass}.{self::Class::[]}(nonNullableInt);
   let final self::Class? #t14 = nullableClass in #t14.{core::Object::==}(null) ?{core::int?} null : #t14{self::Class}.{self::Class::nonNullableClass}.{self::Class::[]=}(nonNullableInt, nonNullableInt);
   let final self::Class? #t15 = nullableClass in #t15.{core::Object::==}(null) ?{core::int?} null : let final self::Class #t16 = #t15{self::Class}.{self::Class::nonNullableClass} in let final core::int #t17 = nonNullableInt in #t16.{self::Class::[]=}(#t17, #t16.{self::Class::[]}(#t17).{core::num::+}(nonNullableInt));
-  let final self::Class? #t18 = nullableClass in #t18.{core::Object::==}(null) ?{core::int?} null : let final self::Class #t19 = #t18{self::Class}.{self::Class::nonNullableClass} in let final core::int #t20 = nonNullableInt in #t19.{self::Class::[]}(#t20).{core::num::==}(null) ?{core::int} #t19.{self::Class::[]=}(#t20, nonNullableInt) : null;
-  let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:30:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+  let final self::Class? #t18 = nullableClass in #t18.{core::Object::==}(null) ?{core::int?} null : let final self::NullableIndexClass #t19 = #t18{self::Class}.{self::Class::nonNullableNullableIndexClass} in let final core::int #t20 = nonNullableInt in #t19.{self::NullableIndexClass::[]}(#t20).{core::num::==}(null) ?{core::int} #t19.{self::NullableIndexClass::[]=}(#t20, nonNullableInt) : null;
+  let final<BottomType> #t21 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:37:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try accessing using ?. instead.
   nullableClass.nonNullableField; // error
                 ^^^^^^^^^^^^^^^^" in nullableClass.{self::Class::nonNullableField};
-  let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:31:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+  let final<BottomType> #t22 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:38:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try accessing using ?. instead.
   nullableClass.nonNullableField = 2; // error
                 ^^^^^^^^^^^^^^^^" in nullableClass.{self::Class::nonNullableField} = 2;
-  let final self::Class? #t23 = nullableClass in let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:32:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+  let final self::Class? #t23 = nullableClass in let final<BottomType> #t24 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:39:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try accessing using ?. instead.
   nullableClass.nonNullableField += 2; // error
-                ^^^^^^^^^^^^^^^^" in #t23.{self::Class::nonNullableField} = (let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:32:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
+                ^^^^^^^^^^^^^^^^" in #t23.{self::Class::nonNullableField} = (let final<BottomType> #t25 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:39:17: Error: Property 'nonNullableField' cannot be accessed on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try accessing using ?. instead.
   nullableClass.nonNullableField += 2; // error
@@ -153,21 +177,21 @@ Try accessing using ?. instead.
   let final self::Class? #t28 = nullableClass in #t28.{core::Object::==}(null) ?{core::int?} null : #t28.{self::Class::nonNullableField} = #t28.{self::Class::nonNullableField}.{core::num::+}(2);
   let final self::Class? #t29 = nullableClass in #t29.{core::Object::==}(null) ?{core::int?} null : #t29{self::Class}.{self::Class::nonNullableClass}.{self::Class::nonNullableField};
   let final self::Class? #t30 = nullableClass in #t30.{core::Object::==}(null) ?{core::int?} null : #t30{self::Class}.{self::Class::nonNullableClass}.{self::Class::nonNullableField} = 2;
-  let final self::Class #t31 = nonNullableClass in #t31.{self::Class::nullableField} = let final<BottomType> #t32 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:41:34: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+  let final self::Class #t31 = nonNullableClass in #t31.{self::Class::nullableField} = let final<BottomType> #t32 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:48:34: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
   nonNullableClass.nullableField += 2; // error
                                  ^" in #t31.{self::Class::nullableField}.{core::num::+}(2);
-  let final self::Class? #t33 = nullableClass in #t33.{core::Object::==}(null) ?{core::int?} null : #t33.{self::Class::nullableField} = let final<BottomType> #t34 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:42:32: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
+  let final self::Class? #t33 = nullableClass in #t33.{core::Object::==}(null) ?{core::int?} null : #t33.{self::Class::nullableField} = let final<BottomType> #t34 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:49:32: Error: Operator '+' cannot be called on 'int?' because it is potentially null.
   nullableClass?.nullableField += 2; // error
                                ^" in #t33.{self::Class::nullableField}.{core::num::+}(2);
   let final self::Class? #t35 = nullableClass in #t35.{core::Object::==}(null) ?{core::int?} null : #t35.{self::Class::nonNullableField}.{core::num::==}(null) ?{core::int} #t35.{self::Class::nonNullableField} = 0 : null;
   let final self::Class? #t36 = nullableClass in #t36.{core::Object::==}(null) ?{core::int?} null : #t36.{self::Class::nullableField}.{core::num::==}(null) ?{core::int} #t36.{self::Class::nullableField} = 0 : null;
   let final self::Class? #t37 = nullableClass in #t37.{core::Object::==}(null) ?{core::int?} null : let final self::Class? #t38 = #t37{self::Class}.{self::Class::nonNullableClass} in #t38{self::Class}.{self::Class::nonNullableField}.{core::num::==}(null) ?{core::int} #t38{self::Class}.{self::Class::nonNullableField} = 0 : null;
   let final self::Class? #t39 = nullableClass in #t39.{core::Object::==}(null) ?{core::int?} null : let final self::Class? #t40 = #t39{self::Class}.{self::Class::nonNullableClass} in #t40{self::Class}.{self::Class::nullableField}.{core::num::==}(null) ?{core::int} #t40{self::Class}.{self::Class::nullableField} = 0 : null;
-  let final<BottomType> #t41 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:50:16: Error: Can't use an expression of type 'Class?' as a function because it's potentially null.
+  let final<BottomType> #t41 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:57:16: Error: Can't use an expression of type 'Class?' as a function because it's potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try calling using ?.call instead.
   nullableClass(); // error
-               ^" in let final<BottomType> #t42 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:50:16: Error: Method 'call' cannot be called on 'Class?' because it is potentially null.
+               ^" in let final<BottomType> #t42 = invalid-expression "pkg/front_end/testcases/nnbd/null_access.dart:57:16: Error: Method 'call' cannot be called on 'Class?' because it is potentially null.
  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 Try calling using ?. instead.
   nullableClass(); // error
diff --git a/pkg/front_end/testcases/nnbd/null_access.dart.weak.expect b/pkg/front_end/testcases/nnbd/null_access.dart.weak.expect
index e4fc4d951b6..64118187c06 100644
--- a/pkg/front_end/testcases/nnbd/null_access.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/null_access.dart.weak.expect
@@ -2,82 +2,96 @@ library;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:18:3: Warning: Operator 'unary-' is called on 'int?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:24:3: Warning: Operator 'unary-' is called on 'int?' which is potentially null.
 //   -nullableInt; // error
 //   ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:19:15: Warning: Operator '+' is called on 'int?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:25:15: Warning: Operator '+' is called on 'int?' which is potentially null.
 //   nullableInt + 2; // error
 //               ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:20:16: Warning: Operator '[]' is called on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:26:16: Warning: Operator '[]' is called on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt]; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:21:16: Warning: Operator '[]=' is called on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:27:16: Warning: Operator '[]=' is called on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] = nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:22:16: Warning: Operator '[]' is called on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:28:16: Warning: Operator '[]' is called on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] += nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:22:16: Warning: Operator '[]=' is called on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:28:16: Warning: Operator '[]=' is called on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] += nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:23:16: Warning: Operator '[]' is called on 'Class?' which is potentially null.
-//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-//   nullableClass[nonNullableInt] ??= nonNullableInt; // error
-//                ^
+// pkg/front_end/testcases/nnbd/null_access.dart:29:29: Warning: Operator '[]' is called on 'NullableIndexClass?' which is potentially null.
+//  - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+//                             ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:23:16: Warning: Operator '[]=' is called on 'Class?' which is potentially null.
-//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-//   nullableClass[nonNullableInt] ??= nonNullableInt; // error
-//                ^
+// pkg/front_end/testcases/nnbd/null_access.dart:29:29: Warning: Operator '[]=' is called on 'NullableIndexClass?' which is potentially null.
+//  - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+//                             ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:30:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:37:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:31:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:38:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField = 2; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:32:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:39:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField += 2; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:41:34: Warning: Operator '+' is called on 'int?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:48:34: Warning: Operator '+' is called on 'int?' which is potentially null.
 //   nonNullableClass.nullableField += 2; // error
 //                                  ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:42:32: Warning: Operator '+' is called on 'int?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:49:32: Warning: Operator '+' is called on 'int?' which is potentially null.
 //   nullableClass?.nullableField += 2; // error
 //                                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:50:16: Warning: Method 'call' is called on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:54:35: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   nullableClass?.nonNullableClass.nonNullableField ??= 0; // ok
+//                                   ^
+//
+// pkg/front_end/testcases/nnbd/null_access.dart:57:16: Warning: Method 'call' is called on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try calling using ?. instead.
 //   nullableClass(); // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:50:16: Warning: Expression of type 'Class?' is used as a function, but it's potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:57:16: Warning: Expression of type 'Class?' is used as a function, but it's potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try calling using ?.call instead.
 //   nullableClass(); // error
 //                ^
 //
+// pkg/front_end/testcases/nnbd/null_access.dart:59:3: Warning: Operand of null-aware operation '?.' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nonNullableClass?.nonNullableClass(); // ok
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_access.dart:60:3: Warning: Operand of null-aware operation '?.' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nonNullableClass?.nonNullableClass.nonNullableClass(); // ok
+//   ^
+//
 import self as self;
 import "dart:core" as core;
 
@@ -94,19 +108,29 @@ class Class extends core::Object {
     return this;
   method call() → self::Class
     return this;
+  get nonNullableNullableIndexClass() → self::NullableIndexClass
+    return new self::NullableIndexClass::•();
+}
+class NullableIndexClass extends core::Object {
+  synthetic constructor •() → self::NullableIndexClass
+    : super core::Object::•()
+    ;
+  operator [](core::int key) → core::int?
+    return key;
+  operator []=(core::int key, core::int value) → void {}
 }
 static method main() → dynamic {}
-static method errors(self::Class? nullableClass, self::Class nonNullableClass, core::int? nullableInt, core::int nonNullableInt) → dynamic {
+static method errors(self::Class? nullableClass, self::Class nonNullableClass, core::int? nullableInt, core::int nonNullableInt, self::NullableIndexClass? nullableNullableIndexClass) → dynamic {
   nullableInt.{core::int::unary-}();
   nullableInt.{core::num::+}(2);
   nullableClass.{self::Class::[]}(nonNullableInt);
   nullableClass.{self::Class::[]=}(nonNullableInt, nonNullableInt);
   let final self::Class? #t1 = nullableClass in let final core::int #t2 = nonNullableInt in #t1.{self::Class::[]=}(#t2, #t1.{self::Class::[]}(#t2).{core::num::+}(nonNullableInt));
-  let final self::Class? #t3 = nullableClass in let final core::int #t4 = nonNullableInt in #t3.{self::Class::[]}(#t4).{core::num::==}(null) ?{core::int} #t3.{self::Class::[]=}(#t4, nonNullableInt) : null;
+  let final self::NullableIndexClass? #t3 = nullableNullableIndexClass in let final core::int #t4 = nonNullableInt in #t3.{self::NullableIndexClass::[]}(#t4).{core::num::==}(null) ?{core::int} #t3.{self::NullableIndexClass::[]=}(#t4, nonNullableInt) : null;
   let final self::Class? #t5 = nullableClass in #t5.{core::Object::==}(null) ?{core::int?} null : #t5{self::Class}.{self::Class::nonNullableClass}.{self::Class::[]}(nonNullableInt);
   let final self::Class? #t6 = nullableClass in #t6.{core::Object::==}(null) ?{core::int?} null : #t6{self::Class}.{self::Class::nonNullableClass}.{self::Class::[]=}(nonNullableInt, nonNullableInt);
   let final self::Class? #t7 = nullableClass in #t7.{core::Object::==}(null) ?{core::int?} null : let final self::Class #t8 = #t7{self::Class}.{self::Class::nonNullableClass} in let final core::int #t9 = nonNullableInt in #t8.{self::Class::[]=}(#t9, #t8.{self::Class::[]}(#t9).{core::num::+}(nonNullableInt));
-  let final self::Class? #t10 = nullableClass in #t10.{core::Object::==}(null) ?{core::int?} null : let final self::Class #t11 = #t10{self::Class}.{self::Class::nonNullableClass} in let final core::int #t12 = nonNullableInt in #t11.{self::Class::[]}(#t12).{core::num::==}(null) ?{core::int} #t11.{self::Class::[]=}(#t12, nonNullableInt) : null;
+  let final self::Class? #t10 = nullableClass in #t10.{core::Object::==}(null) ?{core::int?} null : let final self::NullableIndexClass #t11 = #t10{self::Class}.{self::Class::nonNullableNullableIndexClass} in let final core::int #t12 = nonNullableInt in #t11.{self::NullableIndexClass::[]}(#t12).{core::num::==}(null) ?{core::int} #t11.{self::NullableIndexClass::[]=}(#t12, nonNullableInt) : null;
   nullableClass.{self::Class::nonNullableField};
   nullableClass.{self::Class::nonNullableField} = 2;
   let final self::Class? #t13 = nullableClass in #t13.{self::Class::nonNullableField} = #t13.{self::Class::nonNullableField}.{core::num::+}(2);
diff --git a/pkg/front_end/testcases/nnbd/null_access.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/null_access.dart.weak.transformed.expect
index e4fc4d951b6..64118187c06 100644
--- a/pkg/front_end/testcases/nnbd/null_access.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/null_access.dart.weak.transformed.expect
@@ -2,82 +2,96 @@ library;
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:18:3: Warning: Operator 'unary-' is called on 'int?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:24:3: Warning: Operator 'unary-' is called on 'int?' which is potentially null.
 //   -nullableInt; // error
 //   ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:19:15: Warning: Operator '+' is called on 'int?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:25:15: Warning: Operator '+' is called on 'int?' which is potentially null.
 //   nullableInt + 2; // error
 //               ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:20:16: Warning: Operator '[]' is called on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:26:16: Warning: Operator '[]' is called on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt]; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:21:16: Warning: Operator '[]=' is called on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:27:16: Warning: Operator '[]=' is called on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] = nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:22:16: Warning: Operator '[]' is called on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:28:16: Warning: Operator '[]' is called on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] += nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:22:16: Warning: Operator '[]=' is called on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:28:16: Warning: Operator '[]=' is called on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 //   nullableClass[nonNullableInt] += nonNullableInt; // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:23:16: Warning: Operator '[]' is called on 'Class?' which is potentially null.
-//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-//   nullableClass[nonNullableInt] ??= nonNullableInt; // error
-//                ^
+// pkg/front_end/testcases/nnbd/null_access.dart:29:29: Warning: Operator '[]' is called on 'NullableIndexClass?' which is potentially null.
+//  - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+//                             ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:23:16: Warning: Operator '[]=' is called on 'Class?' which is potentially null.
-//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
-//   nullableClass[nonNullableInt] ??= nonNullableInt; // error
-//                ^
+// pkg/front_end/testcases/nnbd/null_access.dart:29:29: Warning: Operator '[]=' is called on 'NullableIndexClass?' which is potentially null.
+//  - 'NullableIndexClass' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nullableNullableIndexClass[nonNullableInt] ??= nonNullableInt; // error
+//                             ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:30:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:37:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:31:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:38:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField = 2; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:32:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:39:17: Warning: Property 'nonNullableField' is accessed on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try accessing using ?. instead.
 //   nullableClass.nonNullableField += 2; // error
 //                 ^^^^^^^^^^^^^^^^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:41:34: Warning: Operator '+' is called on 'int?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:48:34: Warning: Operator '+' is called on 'int?' which is potentially null.
 //   nonNullableClass.nullableField += 2; // error
 //                                  ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:42:32: Warning: Operator '+' is called on 'int?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:49:32: Warning: Operator '+' is called on 'int?' which is potentially null.
 //   nullableClass?.nullableField += 2; // error
 //                                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:50:16: Warning: Method 'call' is called on 'Class?' which is potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:54:35: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   nullableClass?.nonNullableClass.nonNullableField ??= 0; // ok
+//                                   ^
+//
+// pkg/front_end/testcases/nnbd/null_access.dart:57:16: Warning: Method 'call' is called on 'Class?' which is potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try calling using ?. instead.
 //   nullableClass(); // error
 //                ^
 //
-// pkg/front_end/testcases/nnbd/null_access.dart:50:16: Warning: Expression of type 'Class?' is used as a function, but it's potentially null.
+// pkg/front_end/testcases/nnbd/null_access.dart:57:16: Warning: Expression of type 'Class?' is used as a function, but it's potentially null.
 //  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
 // Try calling using ?.call instead.
 //   nullableClass(); // error
 //                ^
 //
+// pkg/front_end/testcases/nnbd/null_access.dart:59:3: Warning: Operand of null-aware operation '?.' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nonNullableClass?.nonNullableClass(); // ok
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_access.dart:60:3: Warning: Operand of null-aware operation '?.' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_access.dart'.
+//   nonNullableClass?.nonNullableClass.nonNullableClass(); // ok
+//   ^
+//
 import self as self;
 import "dart:core" as core;
 
@@ -94,19 +108,29 @@ class Class extends core::Object {
     return this;
   method call() → self::Class
     return this;
+  get nonNullableNullableIndexClass() → self::NullableIndexClass
+    return new self::NullableIndexClass::•();
+}
+class NullableIndexClass extends core::Object {
+  synthetic constructor •() → self::NullableIndexClass
+    : super core::Object::•()
+    ;
+  operator [](core::int key) → core::int?
+    return key;
+  operator []=(core::int key, core::int value) → void {}
 }
 static method main() → dynamic {}
-static method errors(self::Class? nullableClass, self::Class nonNullableClass, core::int? nullableInt, core::int nonNullableInt) → dynamic {
+static method errors(self::Class? nullableClass, self::Class nonNullableClass, core::int? nullableInt, core::int nonNullableInt, self::NullableIndexClass? nullableNullableIndexClass) → dynamic {
   nullableInt.{core::int::unary-}();
   nullableInt.{core::num::+}(2);
   nullableClass.{self::Class::[]}(nonNullableInt);
   nullableClass.{self::Class::[]=}(nonNullableInt, nonNullableInt);
   let final self::Class? #t1 = nullableClass in let final core::int #t2 = nonNullableInt in #t1.{self::Class::[]=}(#t2, #t1.{self::Class::[]}(#t2).{core::num::+}(nonNullableInt));
-  let final self::Class? #t3 = nullableClass in let final core::int #t4 = nonNullableInt in #t3.{self::Class::[]}(#t4).{core::num::==}(null) ?{core::int} #t3.{self::Class::[]=}(#t4, nonNullableInt) : null;
+  let final self::NullableIndexClass? #t3 = nullableNullableIndexClass in let final core::int #t4 = nonNullableInt in #t3.{self::NullableIndexClass::[]}(#t4).{core::num::==}(null) ?{core::int} #t3.{self::NullableIndexClass::[]=}(#t4, nonNullableInt) : null;
   let final self::Class? #t5 = nullableClass in #t5.{core::Object::==}(null) ?{core::int?} null : #t5{self::Class}.{self::Class::nonNullableClass}.{self::Class::[]}(nonNullableInt);
   let final self::Class? #t6 = nullableClass in #t6.{core::Object::==}(null) ?{core::int?} null : #t6{self::Class}.{self::Class::nonNullableClass}.{self::Class::[]=}(nonNullableInt, nonNullableInt);
   let final self::Class? #t7 = nullableClass in #t7.{core::Object::==}(null) ?{core::int?} null : let final self::Class #t8 = #t7{self::Class}.{self::Class::nonNullableClass} in let final core::int #t9 = nonNullableInt in #t8.{self::Class::[]=}(#t9, #t8.{self::Class::[]}(#t9).{core::num::+}(nonNullableInt));
-  let final self::Class? #t10 = nullableClass in #t10.{core::Object::==}(null) ?{core::int?} null : let final self::Class #t11 = #t10{self::Class}.{self::Class::nonNullableClass} in let final core::int #t12 = nonNullableInt in #t11.{self::Class::[]}(#t12).{core::num::==}(null) ?{core::int} #t11.{self::Class::[]=}(#t12, nonNullableInt) : null;
+  let final self::Class? #t10 = nullableClass in #t10.{core::Object::==}(null) ?{core::int?} null : let final self::NullableIndexClass #t11 = #t10{self::Class}.{self::Class::nonNullableNullableIndexClass} in let final core::int #t12 = nonNullableInt in #t11.{self::NullableIndexClass::[]}(#t12).{core::num::==}(null) ?{core::int} #t11.{self::NullableIndexClass::[]=}(#t12, nonNullableInt) : null;
   nullableClass.{self::Class::nonNullableField};
   nullableClass.{self::Class::nonNullableField} = 2;
   let final self::Class? #t13 = nullableClass in #t13.{self::Class::nonNullableField} = #t13.{self::Class::nonNullableField}.{core::num::+}(2);
diff --git a/pkg/front_end/testcases/nnbd/null_check.dart.strong.expect b/pkg/front_end/testcases/nnbd/null_check.dart.strong.expect
index bffb6cef182..28637dd83e3 100644
--- a/pkg/front_end/testcases/nnbd/null_check.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/null_check.dart.strong.expect
@@ -1,4 +1,90 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:14:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:15:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field = 42;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:16:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:17:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:18:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field!.toString();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:19:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method()!.toString();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:20:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:21:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c!;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:21:8: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c!;
+//        ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:22:7: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c + c!;
+//       ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:23:6: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   (c + c)!;
+//      ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:10: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//          ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:17: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//                 ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:18: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//                  ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:5: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:12: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:22: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//                      ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:20: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//                    ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/null_check.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/null_check.dart.strong.transformed.expect
index bffb6cef182..28637dd83e3 100644
--- a/pkg/front_end/testcases/nnbd/null_check.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/null_check.dart.strong.transformed.expect
@@ -1,4 +1,90 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:14:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:15:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field = 42;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:16:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:17:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:18:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field!.toString();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:19:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method()!.toString();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:20:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:21:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c!;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:21:8: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c!;
+//        ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:22:7: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c + c!;
+//       ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:23:6: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   (c + c)!;
+//      ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:10: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//          ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:17: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//                 ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:18: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//                  ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:5: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:12: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:22: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//                      ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:20: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//                    ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/null_check.dart.weak.expect b/pkg/front_end/testcases/nnbd/null_check.dart.weak.expect
index bffb6cef182..28637dd83e3 100644
--- a/pkg/front_end/testcases/nnbd/null_check.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/null_check.dart.weak.expect
@@ -1,4 +1,90 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:14:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:15:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field = 42;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:16:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:17:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:18:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field!.toString();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:19:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method()!.toString();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:20:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:21:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c!;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:21:8: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c!;
+//        ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:22:7: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c + c!;
+//       ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:23:6: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   (c + c)!;
+//      ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:10: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//          ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:17: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//                 ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:18: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//                  ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:5: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:12: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:22: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//                      ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:20: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//                    ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/null_check.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/null_check.dart.weak.transformed.expect
index bffb6cef182..28637dd83e3 100644
--- a/pkg/front_end/testcases/nnbd/null_check.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/null_check.dart.weak.transformed.expect
@@ -1,4 +1,90 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:14:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:15:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field = 42;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:16:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:17:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:18:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.field!.toString();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:19:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c!.method()!.toString();
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:20:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:21:3: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c!;
+//   ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:21:8: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c! + c!;
+//        ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:22:7: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   c + c!;
+//       ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:23:6: Warning: Operand of null-aware operation '!' has type 'Class' which excludes null.
+//  - 'Class' is from 'pkg/front_end/testcases/nnbd/null_check.dart'.
+//   (c + c)!;
+//      ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:10: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//          ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:17: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//                 ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:26:18: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !o! ? !o! : !!o!!;
+//                  ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:5: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:12: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:22: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//                      ^
+//
+// pkg/front_end/testcases/nnbd/null_check.dart:27:20: Warning: Operand of null-aware operation '!' has type 'bool' which excludes null.
+//   !(o!) ? (!o)! : (!(!o)!)!;
+//                    ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/null_shorting_index.dart.strong.expect b/pkg/front_end/testcases/nnbd/null_shorting_index.dart.strong.expect
index 2afae898207..107e73d1837 100644
--- a/pkg/front_end/testcases/nnbd/null_shorting_index.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/null_shorting_index.dart.strong.expect
@@ -1,4 +1,47 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:33:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.[0] ??= 1;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:34:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.[0] ??= 1 + c1[1];
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:46:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c2?.[0] ??= 1;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:47:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c2?.[0] ??= 1 + c2[1];
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:58:16: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c2)?.[0] ??= 1;
+//                ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:59:16: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c2)?.[0] ??= 1 + Extension(c2)[1];
+//                ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:70:12: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.field?.[0] ??= 1;
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:71:12: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.field?.[0] ??= 1 + c1[1];
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:82:23: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c1?.field)?.[0] ??= 1;
+//                       ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:83:23: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c1?.field)?.[0] ??= 1 + Extension(c2)?.[1]!;
+//                       ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/null_shorting_index.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/null_shorting_index.dart.strong.transformed.expect
index 2afae898207..107e73d1837 100644
--- a/pkg/front_end/testcases/nnbd/null_shorting_index.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/null_shorting_index.dart.strong.transformed.expect
@@ -1,4 +1,47 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:33:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.[0] ??= 1;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:34:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.[0] ??= 1 + c1[1];
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:46:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c2?.[0] ??= 1;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:47:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c2?.[0] ??= 1 + c2[1];
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:58:16: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c2)?.[0] ??= 1;
+//                ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:59:16: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c2)?.[0] ??= 1 + Extension(c2)[1];
+//                ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:70:12: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.field?.[0] ??= 1;
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:71:12: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.field?.[0] ??= 1 + c1[1];
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:82:23: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c1?.field)?.[0] ??= 1;
+//                       ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:83:23: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c1?.field)?.[0] ??= 1 + Extension(c2)?.[1]!;
+//                       ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/null_shorting_index.dart.weak.expect b/pkg/front_end/testcases/nnbd/null_shorting_index.dart.weak.expect
index 2afae898207..107e73d1837 100644
--- a/pkg/front_end/testcases/nnbd/null_shorting_index.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/null_shorting_index.dart.weak.expect
@@ -1,4 +1,47 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:33:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.[0] ??= 1;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:34:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.[0] ??= 1 + c1[1];
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:46:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c2?.[0] ??= 1;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:47:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c2?.[0] ??= 1 + c2[1];
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:58:16: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c2)?.[0] ??= 1;
+//                ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:59:16: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c2)?.[0] ??= 1 + Extension(c2)[1];
+//                ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:70:12: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.field?.[0] ??= 1;
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:71:12: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.field?.[0] ??= 1 + c1[1];
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:82:23: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c1?.field)?.[0] ??= 1;
+//                       ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:83:23: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c1?.field)?.[0] ??= 1 + Extension(c2)?.[1]!;
+//                       ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/null_shorting_index.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/null_shorting_index.dart.weak.transformed.expect
index 2afae898207..107e73d1837 100644
--- a/pkg/front_end/testcases/nnbd/null_shorting_index.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/null_shorting_index.dart.weak.transformed.expect
@@ -1,4 +1,47 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:33:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.[0] ??= 1;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:34:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.[0] ??= 1 + c1[1];
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:46:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c2?.[0] ??= 1;
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:47:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c2?.[0] ??= 1 + c2[1];
+//     ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:58:16: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c2)?.[0] ??= 1;
+//                ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:59:16: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c2)?.[0] ??= 1 + Extension(c2)[1];
+//                ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:70:12: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.field?.[0] ??= 1;
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:71:12: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   c1?.field?.[0] ??= 1 + c1[1];
+//            ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:82:23: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c1?.field)?.[0] ??= 1;
+//                       ^
+//
+// pkg/front_end/testcases/nnbd/null_shorting_index.dart:83:23: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   Extension(c1?.field)?.[0] ??= 1 + Extension(c2)?.[1]!;
+//                       ^
+//
 import self as self;
 import "dart:core" as core;
 
diff --git a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart
index 89fe8b07348..1a513c4df6a 100644
--- a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart
+++ b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart
@@ -6,13 +6,44 @@
 // non-nullable types being used in positions typically occupied by those of
 // nullable types, that is, in various null-aware expressions.
 
-warning(String s, List<String> l) {
-  s?.length;
-  s?..length;
-  s ?? "foo";
-  s ??= "foo";
-  [...?l];
-  s!;
+extension E on String {
+  int get foo => 42;
+  void operator[]=(int index, int value) {}
+  int operator[](int index) => 42;
+}
+
+class A {
+  String operator[](int index) => "foo";
+  void operator[]=(int index, String value) {}
+}
+
+class B extends A {
+  void test() {
+    super[42] ??= "bar"; // Warning.
+  }
+}
+
+warning(String s, List<String> l, Map<String, int> m) {
+  s?.length; // Warning.
+  s?..length; // Warning.
+  s ?? "foo"; // Warning.
+  s ??= "foo"; // Warning.
+  [...?l]; // Warning.
+  var a = {...?l}; // Warning.
+  <String>{...?l}; // Warning.
+  var b = {...?m}; // Warning.
+  <String, int>{...?m}; // Warning.
+  s!; // Warning.
+  s?.substring(0, 0); // Warning.
+  l?.length = 42; // Warning.
+  l?.length += 42; // Warning.
+  l?.length ??= 42; // Warning.
+  s?.foo; // Warning.
+  E(s)[42] ??= 42; // Warning.
+  l[42] ??= "foo"; // Warning.
+  l.length ??= 42; // Warning.
+  l?..length = 42; // Warning.
+  l?..length ??= 42; // Warning.
 }
 
 main() {}
diff --git a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.outline.expect b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.outline.expect
index f2afe4813b2..41543538a48 100644
--- a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.outline.expect
+++ b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.outline.expect
@@ -2,7 +2,32 @@ library;
 import self as self;
 import "dart:core" as core;
 
-static method warning(core::String s, core::List<core::String> l) → dynamic
+class A extends core::Object {
+  synthetic constructor •() → self::A
+    ;
+  operator [](core::int index) → core::String
+    ;
+  operator []=(core::int index, core::String value) → void
+    ;
+}
+class B extends self::A {
+  synthetic constructor •() → self::B
+    ;
+  method test() → void
+    ;
+}
+extension E on core::String {
+  get foo = self::E|get#foo;
+  operator []= = self::E|[]=;
+  operator [] = self::E|[];
+}
+static method E|get#foo(final core::String #this) → core::int
+  ;
+static method E|[]=(final core::String #this, core::int index, core::int value) → void
+  ;
+static method E|[](final core::String #this, core::int index) → core::int
+  ;
+static method warning(core::String s, core::List<core::String> l, core::Map<core::String, core::int> m) → dynamic
   ;
 static method main() → dynamic
   ;
diff --git a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.strong.expect b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.strong.expect
index 19938b734a3..39835c2b657 100644
--- a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.strong.expect
+++ b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.strong.expect
@@ -1,19 +1,187 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:22:10: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//     super[42] ??= "bar"; // Warning.
+//          ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:27:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.length; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:28:3: Warning: Operand of null-aware operation '?..' has type 'String' which excludes null.
+//   s?..length; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:29:3: Warning: Operand of null-aware operation '??' has type 'String' which excludes null.
+//   s ?? "foo"; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:30:3: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//   s ??= "foo"; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:31:8: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   [...?l]; // Warning.
+//        ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:32:16: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   var a = {...?l}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:33:16: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   <String>{...?l}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:34:16: Warning: Operand of null-aware operation '...?' has type 'Map<String, int>' which excludes null.
+//  - 'Map' is from 'dart:core'.
+//   var b = {...?m}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:35:21: Warning: Operand of null-aware operation '...?' has type 'Map<String, int>' which excludes null.
+//  - 'Map' is from 'dart:core'.
+//   <String, int>{...?m}; // Warning.
+//                     ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:36:3: Warning: Operand of null-aware operation '!' has type 'String' which excludes null.
+//   s!; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:37:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.substring(0, 0); // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:38:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length = 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:39:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length += 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:40:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length ??= 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:41:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.foo; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:42:7: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   E(s)[42] ??= 42; // Warning.
+//       ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:43:4: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//   l[42] ??= "foo"; // Warning.
+//    ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:44:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   l.length ??= 42; // Warning.
+//     ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:45:3: Warning: Operand of null-aware operation '?..' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?..length = 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:46:3: Warning: Operand of null-aware operation '?..' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?..length ??= 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:46:7: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   l?..length ??= 42; // Warning.
+//       ^
+//
 import self as self;
 import "dart:core" as core;
+import "dart:collection" as col;
 
-static method warning(core::String s, core::List<core::String> l) → dynamic {
-  let final core::String #t1 = s in #t1.{core::String::==}(null) ?{core::int?} null : #t1.{core::String::length};
-  let final core::String #t2 = s in #t2.{core::String::==}(null) ?{core::String} null : let final void #t3 = #t2.{core::String::length} in #t2;
-  let final core::String #t4 = s in #t4.{core::String::==}(null) ?{core::String} "foo" : #t4;
+class A extends core::Object {
+  synthetic constructor •() → self::A
+    : super core::Object::•()
+    ;
+  operator [](core::int index) → core::String
+    return "foo";
+  operator []=(core::int index, core::String value) → void {}
+}
+class B extends self::A {
+  synthetic constructor •() → self::B
+    : super self::A::•()
+    ;
+  method test() → void {
+    let final core::int #t1 = 42 in super.{self::A::[]}(#t1).{core::String::==}(null) ?{core::String} super.{self::A::[]=}(#t1, "bar") : null;
+  }
+}
+extension E on core::String {
+  get foo = self::E|get#foo;
+  operator []= = self::E|[]=;
+  operator [] = self::E|[];
+}
+static method E|get#foo(final core::String #this) → core::int
+  return 42;
+static method E|[]=(final core::String #this, core::int index, core::int value) → void {}
+static method E|[](final core::String #this, core::int index) → core::int
+  return 42;
+static method warning(core::String s, core::List<core::String> l, core::Map<core::String, core::int> m) → dynamic {
+  let final core::String #t2 = s in #t2.{core::String::==}(null) ?{core::int?} null : #t2.{core::String::length};
+  let final core::String #t3 = s in #t3.{core::String::==}(null) ?{core::String} null : let final void #t4 = #t3.{core::String::length} in #t3;
+  let final core::String #t5 = s in #t5.{core::String::==}(null) ?{core::String} "foo" : #t5;
   s.{core::String::==}(null) ?{core::String} s = "foo" : null;
   block {
-    final core::List<core::String> #t5 = <core::String>[];
-    final core::Iterable<core::String>? #t6 = l;
-    if(!#t6.{core::Object::==}(null))
-      for (final core::String #t7 in #t6{core::Iterable<core::String>})
-        #t5.{core::List::add}(#t7);
-  } =>#t5;
+    final core::List<core::String> #t6 = <core::String>[];
+    final core::Iterable<core::String>? #t7 = l;
+    if(!#t7.{core::Object::==}(null))
+      for (final core::String #t8 in #t7{core::Iterable<core::String>})
+        #t6.{core::List::add}(#t8);
+  } =>#t6;
+  core::Set<core::String> a = block {
+    final core::Set<core::String> #t9 = col::LinkedHashSet::•<core::String>();
+    final core::Iterable<core::String>? #t10 = l;
+    if(!#t10.{core::Object::==}(null))
+      for (final dynamic #t11 in #t10{core::Iterable<core::String>}) {
+        final core::String #t12 = #t11 as{TypeError,ForNonNullableByDefault} core::String;
+        #t9.{core::Set::add}(#t12);
+      }
+  } =>#t9;
+  block {
+    final core::Set<core::String> #t13 = col::LinkedHashSet::•<core::String>();
+    final core::Iterable<core::String>? #t14 = l;
+    if(!#t14.{core::Object::==}(null))
+      for (final core::String #t15 in #t14{core::Iterable<core::String>})
+        #t13.{core::Set::add}(#t15);
+  } =>#t13;
+  core::Map<core::String, core::int> b = block {
+    final core::Map<core::String, core::int> #t16 = <core::String, core::int>{};
+    final core::Map<core::String, core::int>? #t17 = m;
+    if(!#t17.{core::Object::==}(null))
+      for (final core::MapEntry<core::String, core::int> #t18 in #t17{core::Map<core::String, core::int>}.{core::Map::entries})
+        #t16.{core::Map::[]=}(#t18.{core::MapEntry::key}, #t18.{core::MapEntry::value});
+  } =>#t16;
+  block {
+    final core::Map<core::String, core::int> #t19 = <core::String, core::int>{};
+    final core::Map<core::String, core::int>? #t20 = m;
+    if(!#t20.{core::Object::==}(null))
+      for (final core::MapEntry<core::String, core::int> #t21 in #t20{core::Map<core::String, core::int>}.{core::Map::entries})
+        #t19.{core::Map::[]=}(#t21.{core::MapEntry::key}, #t21.{core::MapEntry::value});
+  } =>#t19;
   s!;
+  let final core::String #t22 = s in #t22.{core::String::==}(null) ?{core::String?} null : #t22.{core::String::substring}(0, 0);
+  let final core::List<core::String> #t23 = l in #t23.{core::List::==}(null) ?{core::int?} null : #t23.{core::List::length} = 42;
+  let final core::List<core::String> #t24 = l in #t24.{core::List::==}(null) ?{core::int?} null : #t24.{core::List::length} = #t24.{core::List::length}.{core::num::+}(42);
+  let final core::List<core::String> #t25 = l in #t25.{core::List::==}(null) ?{core::int?} null : #t25.{core::List::length}.{core::num::==}(null) ?{core::int} #t25.{core::List::length} = 42 : null;
+  let final core::String #t26 = s in #t26.{core::String::==}(null) ?{core::int?} null : self::E|get#foo(#t26);
+  let final core::String #t27 = s in let final core::int #t28 = 42 in self::E|[](#t27, #t28).{core::num::==}(null) ?{core::int} self::E|[]=(#t27, #t28, 42) : null;
+  let final core::List<core::String> #t29 = l in let final core::int #t30 = 42 in #t29.{core::List::[]}(#t30).{core::String::==}(null) ?{core::String} #t29.{core::List::[]=}(#t30, "foo") : null;
+  let final core::List<core::String> #t31 = l in #t31.{core::List::length}.{core::num::==}(null) ?{core::int} #t31.{core::List::length} = 42 : null;
+  let final core::List<core::String> #t32 = l in #t32.{core::List::==}(null) ?{core::List<core::String>} null : let final void #t33 = #t32.{core::List::length} = 42 in #t32;
+  let final core::List<core::String> #t34 = l in #t34.{core::List::==}(null) ?{core::List<core::String>} null : let final void #t35 = let final core::List<core::String> #t36 = #t34 in #t36.{core::List::length}.{core::num::==}(null) ?{core::int} #t36.{core::List::length} = 42 : null in #t34;
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.strong.transformed.expect b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.strong.transformed.expect
index a35cd494b8d..a50498a66ee 100644
--- a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.strong.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.strong.transformed.expect
@@ -1,24 +1,209 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:22:10: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//     super[42] ??= "bar"; // Warning.
+//          ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:27:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.length; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:28:3: Warning: Operand of null-aware operation '?..' has type 'String' which excludes null.
+//   s?..length; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:29:3: Warning: Operand of null-aware operation '??' has type 'String' which excludes null.
+//   s ?? "foo"; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:30:3: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//   s ??= "foo"; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:31:8: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   [...?l]; // Warning.
+//        ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:32:16: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   var a = {...?l}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:33:16: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   <String>{...?l}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:34:16: Warning: Operand of null-aware operation '...?' has type 'Map<String, int>' which excludes null.
+//  - 'Map' is from 'dart:core'.
+//   var b = {...?m}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:35:21: Warning: Operand of null-aware operation '...?' has type 'Map<String, int>' which excludes null.
+//  - 'Map' is from 'dart:core'.
+//   <String, int>{...?m}; // Warning.
+//                     ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:36:3: Warning: Operand of null-aware operation '!' has type 'String' which excludes null.
+//   s!; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:37:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.substring(0, 0); // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:38:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length = 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:39:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length += 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:40:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length ??= 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:41:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.foo; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:42:7: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   E(s)[42] ??= 42; // Warning.
+//       ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:43:4: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//   l[42] ??= "foo"; // Warning.
+//    ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:44:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   l.length ??= 42; // Warning.
+//     ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:45:3: Warning: Operand of null-aware operation '?..' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?..length = 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:46:3: Warning: Operand of null-aware operation '?..' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?..length ??= 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:46:7: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   l?..length ??= 42; // Warning.
+//       ^
+//
 import self as self;
 import "dart:core" as core;
 import "dart:_internal" as _in;
+import "dart:collection" as col;
 
-static method warning(core::String s, core::List<core::String> l) → dynamic {
-  let final core::String #t1 = s in #t1.{core::String::==}(null) ?{core::int?} null : #t1.{core::String::length};
-  let final core::String #t2 = s in #t2.{core::String::==}(null) ?{core::String} null : let final void #t3 = #t2.{core::String::length} in #t2;
-  let final core::String #t4 = s in #t4.{core::String::==}(null) ?{core::String} "foo" : #t4;
+class A extends core::Object {
+  synthetic constructor •() → self::A
+    : super core::Object::•()
+    ;
+  operator [](core::int index) → core::String
+    return "foo";
+  operator []=(core::int index, core::String value) → void {}
+}
+class B extends self::A {
+  synthetic constructor •() → self::B
+    : super self::A::•()
+    ;
+  method test() → void {
+    let final core::int #t1 = 42 in super.{self::A::[]}(#t1).{core::String::==}(null) ?{core::String} super.{self::A::[]=}(#t1, "bar") : null;
+  }
+}
+extension E on core::String {
+  get foo = self::E|get#foo;
+  operator []= = self::E|[]=;
+  operator [] = self::E|[];
+}
+static method E|get#foo(final core::String #this) → core::int
+  return 42;
+static method E|[]=(final core::String #this, core::int index, core::int value) → void {}
+static method E|[](final core::String #this, core::int index) → core::int
+  return 42;
+static method warning(core::String s, core::List<core::String> l, core::Map<core::String, core::int> m) → dynamic {
+  let final core::String #t2 = s in #t2.{core::String::==}(null) ?{core::int?} null : #t2.{core::String::length};
+  let final core::String #t3 = s in #t3.{core::String::==}(null) ?{core::String} null : let final void #t4 = #t3.{core::String::length} in #t3;
+  let final core::String #t5 = s in #t5.{core::String::==}(null) ?{core::String} "foo" : #t5;
   s.{core::String::==}(null) ?{core::String} s = "foo" : null;
   block {
-    final core::List<core::String> #t5 = <core::String>[];
-    final core::Iterable<core::String>? #t6 = l;
-    if(!#t6.{core::Object::==}(null)) {
-      core::Iterator<core::String>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::String>*>(#t6{core::Iterable<core::String>}).{core::Iterable::iterator};
+    final core::List<core::String> #t6 = <core::String>[];
+    final core::Iterable<core::String>? #t7 = l;
+    if(!#t7.{core::Object::==}(null)) {
+      core::Iterator<core::String>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::String>*>(#t7{core::Iterable<core::String>}).{core::Iterable::iterator};
       for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
-        final core::String #t7 = :sync-for-iterator.{core::Iterator::current};
-        #t5.{core::List::add}(#t7);
+        final core::String #t8 = :sync-for-iterator.{core::Iterator::current};
+        #t6.{core::List::add}(#t8);
       }
     }
-  } =>#t5;
+  } =>#t6;
+  core::Set<core::String> a = block {
+    final core::Set<core::String> #t9 = col::LinkedHashSet::•<core::String>();
+    final core::Iterable<core::String>? #t10 = l;
+    if(!#t10.{core::Object::==}(null)) {
+      core::Iterator<core::String>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::String>*>(#t10{core::Iterable<core::String>}).{core::Iterable::iterator};
+      for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
+        final dynamic #t11 = :sync-for-iterator.{core::Iterator::current};
+        {
+          final core::String #t12 = #t11 as{TypeError,ForNonNullableByDefault} core::String;
+          #t9.{core::Set::add}(#t12);
+        }
+      }
+    }
+  } =>#t9;
+  block {
+    final core::Set<core::String> #t13 = col::LinkedHashSet::•<core::String>();
+    final core::Iterable<core::String>? #t14 = l;
+    if(!#t14.{core::Object::==}(null)) {
+      core::Iterator<core::String>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::String>*>(#t14{core::Iterable<core::String>}).{core::Iterable::iterator};
+      for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
+        final core::String #t15 = :sync-for-iterator.{core::Iterator::current};
+        #t13.{core::Set::add}(#t15);
+      }
+    }
+  } =>#t13;
+  core::Map<core::String, core::int> b = block {
+    final core::Map<core::String, core::int> #t16 = <core::String, core::int>{};
+    final core::Map<core::String, core::int>? #t17 = m;
+    if(!#t17.{core::Object::==}(null)) {
+      core::Iterator<core::MapEntry<core::String*, core::int*>*>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::MapEntry<core::String*, core::int*>*>*>(#t17{core::Map<core::String, core::int>}.{core::Map::entries}).{core::Iterable::iterator};
+      for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
+        final core::MapEntry<core::String, core::int> #t18 = :sync-for-iterator.{core::Iterator::current};
+        #t16.{core::Map::[]=}(#t18.{core::MapEntry::key}, #t18.{core::MapEntry::value});
+      }
+    }
+  } =>#t16;
+  block {
+    final core::Map<core::String, core::int> #t19 = <core::String, core::int>{};
+    final core::Map<core::String, core::int>? #t20 = m;
+    if(!#t20.{core::Object::==}(null)) {
+      core::Iterator<core::MapEntry<core::String*, core::int*>*>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::MapEntry<core::String*, core::int*>*>*>(#t20{core::Map<core::String, core::int>}.{core::Map::entries}).{core::Iterable::iterator};
+      for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
+        final core::MapEntry<core::String, core::int> #t21 = :sync-for-iterator.{core::Iterator::current};
+        #t19.{core::Map::[]=}(#t21.{core::MapEntry::key}, #t21.{core::MapEntry::value});
+      }
+    }
+  } =>#t19;
   s!;
+  let final core::String #t22 = s in #t22.{core::String::==}(null) ?{core::String?} null : #t22.{core::String::substring}(0, 0);
+  let final core::List<core::String> #t23 = l in #t23.{core::List::==}(null) ?{core::int?} null : #t23.{core::List::length} = 42;
+  let final core::List<core::String> #t24 = l in #t24.{core::List::==}(null) ?{core::int?} null : #t24.{core::List::length} = #t24.{core::List::length}.{core::num::+}(42);
+  let final core::List<core::String> #t25 = l in #t25.{core::List::==}(null) ?{core::int?} null : #t25.{core::List::length}.{core::num::==}(null) ?{core::int} #t25.{core::List::length} = 42 : null;
+  let final core::String #t26 = s in #t26.{core::String::==}(null) ?{core::int?} null : self::E|get#foo(#t26);
+  let final core::String #t27 = s in let final core::int #t28 = 42 in self::E|[](#t27, #t28).{core::num::==}(null) ?{core::int} self::E|[]=(#t27, #t28, 42) : null;
+  let final core::List<core::String> #t29 = l in let final core::int #t30 = 42 in #t29.{core::List::[]}(#t30).{core::String::==}(null) ?{core::String} #t29.{core::List::[]=}(#t30, "foo") : null;
+  let final core::List<core::String> #t31 = l in #t31.{core::List::length}.{core::num::==}(null) ?{core::int} #t31.{core::List::length} = 42 : null;
+  let final core::List<core::String> #t32 = l in #t32.{core::List::==}(null) ?{core::List<core::String>} null : let final void #t33 = #t32.{core::List::length} = 42 in #t32;
+  let final core::List<core::String> #t34 = l in #t34.{core::List::==}(null) ?{core::List<core::String>} null : let final void #t35 = let final core::List<core::String> #t36 = #t34 in #t36.{core::List::length}.{core::num::==}(null) ?{core::int} #t36.{core::List::length} = 42 : null in #t34;
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.weak.expect b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.weak.expect
index 19938b734a3..39835c2b657 100644
--- a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.weak.expect
+++ b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.weak.expect
@@ -1,19 +1,187 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:22:10: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//     super[42] ??= "bar"; // Warning.
+//          ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:27:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.length; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:28:3: Warning: Operand of null-aware operation '?..' has type 'String' which excludes null.
+//   s?..length; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:29:3: Warning: Operand of null-aware operation '??' has type 'String' which excludes null.
+//   s ?? "foo"; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:30:3: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//   s ??= "foo"; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:31:8: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   [...?l]; // Warning.
+//        ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:32:16: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   var a = {...?l}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:33:16: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   <String>{...?l}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:34:16: Warning: Operand of null-aware operation '...?' has type 'Map<String, int>' which excludes null.
+//  - 'Map' is from 'dart:core'.
+//   var b = {...?m}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:35:21: Warning: Operand of null-aware operation '...?' has type 'Map<String, int>' which excludes null.
+//  - 'Map' is from 'dart:core'.
+//   <String, int>{...?m}; // Warning.
+//                     ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:36:3: Warning: Operand of null-aware operation '!' has type 'String' which excludes null.
+//   s!; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:37:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.substring(0, 0); // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:38:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length = 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:39:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length += 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:40:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length ??= 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:41:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.foo; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:42:7: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   E(s)[42] ??= 42; // Warning.
+//       ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:43:4: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//   l[42] ??= "foo"; // Warning.
+//    ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:44:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   l.length ??= 42; // Warning.
+//     ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:45:3: Warning: Operand of null-aware operation '?..' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?..length = 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:46:3: Warning: Operand of null-aware operation '?..' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?..length ??= 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:46:7: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   l?..length ??= 42; // Warning.
+//       ^
+//
 import self as self;
 import "dart:core" as core;
+import "dart:collection" as col;
 
-static method warning(core::String s, core::List<core::String> l) → dynamic {
-  let final core::String #t1 = s in #t1.{core::String::==}(null) ?{core::int?} null : #t1.{core::String::length};
-  let final core::String #t2 = s in #t2.{core::String::==}(null) ?{core::String} null : let final void #t3 = #t2.{core::String::length} in #t2;
-  let final core::String #t4 = s in #t4.{core::String::==}(null) ?{core::String} "foo" : #t4;
+class A extends core::Object {
+  synthetic constructor •() → self::A
+    : super core::Object::•()
+    ;
+  operator [](core::int index) → core::String
+    return "foo";
+  operator []=(core::int index, core::String value) → void {}
+}
+class B extends self::A {
+  synthetic constructor •() → self::B
+    : super self::A::•()
+    ;
+  method test() → void {
+    let final core::int #t1 = 42 in super.{self::A::[]}(#t1).{core::String::==}(null) ?{core::String} super.{self::A::[]=}(#t1, "bar") : null;
+  }
+}
+extension E on core::String {
+  get foo = self::E|get#foo;
+  operator []= = self::E|[]=;
+  operator [] = self::E|[];
+}
+static method E|get#foo(final core::String #this) → core::int
+  return 42;
+static method E|[]=(final core::String #this, core::int index, core::int value) → void {}
+static method E|[](final core::String #this, core::int index) → core::int
+  return 42;
+static method warning(core::String s, core::List<core::String> l, core::Map<core::String, core::int> m) → dynamic {
+  let final core::String #t2 = s in #t2.{core::String::==}(null) ?{core::int?} null : #t2.{core::String::length};
+  let final core::String #t3 = s in #t3.{core::String::==}(null) ?{core::String} null : let final void #t4 = #t3.{core::String::length} in #t3;
+  let final core::String #t5 = s in #t5.{core::String::==}(null) ?{core::String} "foo" : #t5;
   s.{core::String::==}(null) ?{core::String} s = "foo" : null;
   block {
-    final core::List<core::String> #t5 = <core::String>[];
-    final core::Iterable<core::String>? #t6 = l;
-    if(!#t6.{core::Object::==}(null))
-      for (final core::String #t7 in #t6{core::Iterable<core::String>})
-        #t5.{core::List::add}(#t7);
-  } =>#t5;
+    final core::List<core::String> #t6 = <core::String>[];
+    final core::Iterable<core::String>? #t7 = l;
+    if(!#t7.{core::Object::==}(null))
+      for (final core::String #t8 in #t7{core::Iterable<core::String>})
+        #t6.{core::List::add}(#t8);
+  } =>#t6;
+  core::Set<core::String> a = block {
+    final core::Set<core::String> #t9 = col::LinkedHashSet::•<core::String>();
+    final core::Iterable<core::String>? #t10 = l;
+    if(!#t10.{core::Object::==}(null))
+      for (final dynamic #t11 in #t10{core::Iterable<core::String>}) {
+        final core::String #t12 = #t11 as{TypeError,ForNonNullableByDefault} core::String;
+        #t9.{core::Set::add}(#t12);
+      }
+  } =>#t9;
+  block {
+    final core::Set<core::String> #t13 = col::LinkedHashSet::•<core::String>();
+    final core::Iterable<core::String>? #t14 = l;
+    if(!#t14.{core::Object::==}(null))
+      for (final core::String #t15 in #t14{core::Iterable<core::String>})
+        #t13.{core::Set::add}(#t15);
+  } =>#t13;
+  core::Map<core::String, core::int> b = block {
+    final core::Map<core::String, core::int> #t16 = <core::String, core::int>{};
+    final core::Map<core::String, core::int>? #t17 = m;
+    if(!#t17.{core::Object::==}(null))
+      for (final core::MapEntry<core::String, core::int> #t18 in #t17{core::Map<core::String, core::int>}.{core::Map::entries})
+        #t16.{core::Map::[]=}(#t18.{core::MapEntry::key}, #t18.{core::MapEntry::value});
+  } =>#t16;
+  block {
+    final core::Map<core::String, core::int> #t19 = <core::String, core::int>{};
+    final core::Map<core::String, core::int>? #t20 = m;
+    if(!#t20.{core::Object::==}(null))
+      for (final core::MapEntry<core::String, core::int> #t21 in #t20{core::Map<core::String, core::int>}.{core::Map::entries})
+        #t19.{core::Map::[]=}(#t21.{core::MapEntry::key}, #t21.{core::MapEntry::value});
+  } =>#t19;
   s!;
+  let final core::String #t22 = s in #t22.{core::String::==}(null) ?{core::String?} null : #t22.{core::String::substring}(0, 0);
+  let final core::List<core::String> #t23 = l in #t23.{core::List::==}(null) ?{core::int?} null : #t23.{core::List::length} = 42;
+  let final core::List<core::String> #t24 = l in #t24.{core::List::==}(null) ?{core::int?} null : #t24.{core::List::length} = #t24.{core::List::length}.{core::num::+}(42);
+  let final core::List<core::String> #t25 = l in #t25.{core::List::==}(null) ?{core::int?} null : #t25.{core::List::length}.{core::num::==}(null) ?{core::int} #t25.{core::List::length} = 42 : null;
+  let final core::String #t26 = s in #t26.{core::String::==}(null) ?{core::int?} null : self::E|get#foo(#t26);
+  let final core::String #t27 = s in let final core::int #t28 = 42 in self::E|[](#t27, #t28).{core::num::==}(null) ?{core::int} self::E|[]=(#t27, #t28, 42) : null;
+  let final core::List<core::String> #t29 = l in let final core::int #t30 = 42 in #t29.{core::List::[]}(#t30).{core::String::==}(null) ?{core::String} #t29.{core::List::[]=}(#t30, "foo") : null;
+  let final core::List<core::String> #t31 = l in #t31.{core::List::length}.{core::num::==}(null) ?{core::int} #t31.{core::List::length} = 42 : null;
+  let final core::List<core::String> #t32 = l in #t32.{core::List::==}(null) ?{core::List<core::String>} null : let final void #t33 = #t32.{core::List::length} = 42 in #t32;
+  let final core::List<core::String> #t34 = l in #t34.{core::List::==}(null) ?{core::List<core::String>} null : let final void #t35 = let final core::List<core::String> #t36 = #t34 in #t36.{core::List::length}.{core::num::==}(null) ?{core::int} #t36.{core::List::length} = 42 : null in #t34;
 }
 static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.weak.transformed.expect b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.weak.transformed.expect
index a35cd494b8d..a50498a66ee 100644
--- a/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart.weak.transformed.expect
@@ -1,24 +1,209 @@
 library;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:22:10: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//     super[42] ??= "bar"; // Warning.
+//          ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:27:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.length; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:28:3: Warning: Operand of null-aware operation '?..' has type 'String' which excludes null.
+//   s?..length; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:29:3: Warning: Operand of null-aware operation '??' has type 'String' which excludes null.
+//   s ?? "foo"; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:30:3: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//   s ??= "foo"; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:31:8: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   [...?l]; // Warning.
+//        ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:32:16: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   var a = {...?l}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:33:16: Warning: Operand of null-aware operation '...?' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   <String>{...?l}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:34:16: Warning: Operand of null-aware operation '...?' has type 'Map<String, int>' which excludes null.
+//  - 'Map' is from 'dart:core'.
+//   var b = {...?m}; // Warning.
+//                ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:35:21: Warning: Operand of null-aware operation '...?' has type 'Map<String, int>' which excludes null.
+//  - 'Map' is from 'dart:core'.
+//   <String, int>{...?m}; // Warning.
+//                     ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:36:3: Warning: Operand of null-aware operation '!' has type 'String' which excludes null.
+//   s!; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:37:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.substring(0, 0); // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:38:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length = 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:39:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length += 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:40:3: Warning: Operand of null-aware operation '?.' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?.length ??= 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:41:3: Warning: Operand of null-aware operation '?.' has type 'String' which excludes null.
+//   s?.foo; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:42:7: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   E(s)[42] ??= 42; // Warning.
+//       ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:43:4: Warning: Operand of null-aware operation '??=' has type 'String' which excludes null.
+//   l[42] ??= "foo"; // Warning.
+//    ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:44:5: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   l.length ??= 42; // Warning.
+//     ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:45:3: Warning: Operand of null-aware operation '?..' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?..length = 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:46:3: Warning: Operand of null-aware operation '?..' has type 'List<String>' which excludes null.
+//  - 'List' is from 'dart:core'.
+//   l?..length ??= 42; // Warning.
+//   ^
+//
+// pkg/front_end/testcases/nnbd/strictly_non_nullable_warnings.dart:46:7: Warning: Operand of null-aware operation '??=' has type 'int' which excludes null.
+//   l?..length ??= 42; // Warning.
+//       ^
+//
 import self as self;
 import "dart:core" as core;
 import "dart:_internal" as _in;
+import "dart:collection" as col;
 
-static method warning(core::String s, core::List<core::String> l) → dynamic {
-  let final core::String #t1 = s in #t1.{core::String::==}(null) ?{core::int?} null : #t1.{core::String::length};
-  let final core::String #t2 = s in #t2.{core::String::==}(null) ?{core::String} null : let final void #t3 = #t2.{core::String::length} in #t2;
-  let final core::String #t4 = s in #t4.{core::String::==}(null) ?{core::String} "foo" : #t4;
+class A extends core::Object {
+  synthetic constructor •() → self::A
+    : super core::Object::•()
+    ;
+  operator [](core::int index) → core::String
+    return "foo";
+  operator []=(core::int index, core::String value) → void {}
+}
+class B extends self::A {
+  synthetic constructor •() → self::B
+    : super self::A::•()
+    ;
+  method test() → void {
+    let final core::int #t1 = 42 in super.{self::A::[]}(#t1).{core::String::==}(null) ?{core::String} super.{self::A::[]=}(#t1, "bar") : null;
+  }
+}
+extension E on core::String {
+  get foo = self::E|get#foo;
+  operator []= = self::E|[]=;
+  operator [] = self::E|[];
+}
+static method E|get#foo(final core::String #this) → core::int
+  return 42;
+static method E|[]=(final core::String #this, core::int index, core::int value) → void {}
+static method E|[](final core::String #this, core::int index) → core::int
+  return 42;
+static method warning(core::String s, core::List<core::String> l, core::Map<core::String, core::int> m) → dynamic {
+  let final core::String #t2 = s in #t2.{core::String::==}(null) ?{core::int?} null : #t2.{core::String::length};
+  let final core::String #t3 = s in #t3.{core::String::==}(null) ?{core::String} null : let final void #t4 = #t3.{core::String::length} in #t3;
+  let final core::String #t5 = s in #t5.{core::String::==}(null) ?{core::String} "foo" : #t5;
   s.{core::String::==}(null) ?{core::String} s = "foo" : null;
   block {
-    final core::List<core::String> #t5 = <core::String>[];
-    final core::Iterable<core::String>? #t6 = l;
-    if(!#t6.{core::Object::==}(null)) {
-      core::Iterator<core::String>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::String>*>(#t6{core::Iterable<core::String>}).{core::Iterable::iterator};
+    final core::List<core::String> #t6 = <core::String>[];
+    final core::Iterable<core::String>? #t7 = l;
+    if(!#t7.{core::Object::==}(null)) {
+      core::Iterator<core::String>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::String>*>(#t7{core::Iterable<core::String>}).{core::Iterable::iterator};
       for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
-        final core::String #t7 = :sync-for-iterator.{core::Iterator::current};
-        #t5.{core::List::add}(#t7);
+        final core::String #t8 = :sync-for-iterator.{core::Iterator::current};
+        #t6.{core::List::add}(#t8);
       }
     }
-  } =>#t5;
+  } =>#t6;
+  core::Set<core::String> a = block {
+    final core::Set<core::String> #t9 = col::LinkedHashSet::•<core::String>();
+    final core::Iterable<core::String>? #t10 = l;
+    if(!#t10.{core::Object::==}(null)) {
+      core::Iterator<core::String>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::String>*>(#t10{core::Iterable<core::String>}).{core::Iterable::iterator};
+      for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
+        final dynamic #t11 = :sync-for-iterator.{core::Iterator::current};
+        {
+          final core::String #t12 = #t11 as{TypeError,ForNonNullableByDefault} core::String;
+          #t9.{core::Set::add}(#t12);
+        }
+      }
+    }
+  } =>#t9;
+  block {
+    final core::Set<core::String> #t13 = col::LinkedHashSet::•<core::String>();
+    final core::Iterable<core::String>? #t14 = l;
+    if(!#t14.{core::Object::==}(null)) {
+      core::Iterator<core::String>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::String>*>(#t14{core::Iterable<core::String>}).{core::Iterable::iterator};
+      for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
+        final core::String #t15 = :sync-for-iterator.{core::Iterator::current};
+        #t13.{core::Set::add}(#t15);
+      }
+    }
+  } =>#t13;
+  core::Map<core::String, core::int> b = block {
+    final core::Map<core::String, core::int> #t16 = <core::String, core::int>{};
+    final core::Map<core::String, core::int>? #t17 = m;
+    if(!#t17.{core::Object::==}(null)) {
+      core::Iterator<core::MapEntry<core::String*, core::int*>*>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::MapEntry<core::String*, core::int*>*>*>(#t17{core::Map<core::String, core::int>}.{core::Map::entries}).{core::Iterable::iterator};
+      for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
+        final core::MapEntry<core::String, core::int> #t18 = :sync-for-iterator.{core::Iterator::current};
+        #t16.{core::Map::[]=}(#t18.{core::MapEntry::key}, #t18.{core::MapEntry::value});
+      }
+    }
+  } =>#t16;
+  block {
+    final core::Map<core::String, core::int> #t19 = <core::String, core::int>{};
+    final core::Map<core::String, core::int>? #t20 = m;
+    if(!#t20.{core::Object::==}(null)) {
+      core::Iterator<core::MapEntry<core::String*, core::int*>*>* :sync-for-iterator = _in::unsafeCast<core::Iterable<core::MapEntry<core::String*, core::int*>*>*>(#t20{core::Map<core::String, core::int>}.{core::Map::entries}).{core::Iterable::iterator};
+      for (; :sync-for-iterator.{core::Iterator::moveNext}(); ) {
+        final core::MapEntry<core::String, core::int> #t21 = :sync-for-iterator.{core::Iterator::current};
+        #t19.{core::Map::[]=}(#t21.{core::MapEntry::key}, #t21.{core::MapEntry::value});
+      }
+    }
+  } =>#t19;
   s!;
+  let final core::String #t22 = s in #t22.{core::String::==}(null) ?{core::String?} null : #t22.{core::String::substring}(0, 0);
+  let final core::List<core::String> #t23 = l in #t23.{core::List::==}(null) ?{core::int?} null : #t23.{core::List::length} = 42;
+  let final core::List<core::String> #t24 = l in #t24.{core::List::==}(null) ?{core::int?} null : #t24.{core::List::length} = #t24.{core::List::length}.{core::num::+}(42);
+  let final core::List<core::String> #t25 = l in #t25.{core::List::==}(null) ?{core::int?} null : #t25.{core::List::length}.{core::num::==}(null) ?{core::int} #t25.{core::List::length} = 42 : null;
+  let final core::String #t26 = s in #t26.{core::String::==}(null) ?{core::int?} null : self::E|get#foo(#t26);
+  let final core::String #t27 = s in let final core::int #t28 = 42 in self::E|[](#t27, #t28).{core::num::==}(null) ?{core::int} self::E|[]=(#t27, #t28, 42) : null;
+  let final core::List<core::String> #t29 = l in let final core::int #t30 = 42 in #t29.{core::List::[]}(#t30).{core::String::==}(null) ?{core::String} #t29.{core::List::[]=}(#t30, "foo") : null;
+  let final core::List<core::String> #t31 = l in #t31.{core::List::length}.{core::num::==}(null) ?{core::int} #t31.{core::List::length} = 42 : null;
+  let final core::List<core::String> #t32 = l in #t32.{core::List::==}(null) ?{core::List<core::String>} null : let final void #t33 = #t32.{core::List::length} = 42 in #t32;
+  let final core::List<core::String> #t34 = l in #t34.{core::List::==}(null) ?{core::List<core::String>} null : let final void #t35 = let final core::List<core::String> #t36 = #t34 in #t36.{core::List::length}.{core::num::==}(null) ?{core::int} #t36.{core::List::length} = 42 : null in #t34;
 }
 static method main() → dynamic {}