Create a common generator class to handle non-lvalues.

This allows all non-lvalue cases to be integrated with the analyzer
using a common code path.

Change-Id: I15cd2bc07a2d3609e78886609f3e29ee6aa807fc
Reviewed-on: https://dart-review.googlesource.com/66402
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Paul Berry <paulberry@google.com>

pkg/analyzer/lib/src/fasta/resolution_applier.dart

@@ -116,9 +116,11 @@ class ResolutionApplier extends GeneralizingAstVisitor {
     node.rightHandSide.accept(this);
 
     SyntacticEntity entity = _getAssignmentEntity(node.leftHandSide);
-    var data = _get(entity);
-    node.staticElement = _translateAuxiliaryReference(data.combiner);
-    node.staticType = _translateType(data.inferredType);
+    if (entity != null) {
+      var data = _get(entity);
+      node.staticElement = _translateAuxiliaryReference(data.combiner);
+      node.staticType = _translateType(data.inferredType);
+    }
   }
 
   @override
@@ -541,9 +543,11 @@ class ResolutionApplier extends GeneralizingAstVisitor {
   void visitPostfixExpression(PostfixExpression node) {
     node.operand.accept(this);
     SyntacticEntity entity = _getAssignmentEntity(node.operand);
-    var data = _get(entity);
-    node.staticElement = _translateAuxiliaryReference(data.combiner);
-    node.staticType = _translateType(data.inferredType);
+    if (entity != null) {
+      var data = _get(entity);
+      node.staticElement = _translateAuxiliaryReference(data.combiner);
+      node.staticType = _translateType(data.inferredType);
+    }
   }
 
   @override
@@ -561,9 +565,11 @@ class ResolutionApplier extends GeneralizingAstVisitor {
       // ++v;
       // This is an assignment, it is associated with the operand.
       SyntacticEntity entity = _getAssignmentEntity(node.operand);
-      var data = _get(entity);
-      node.staticElement = _translateAuxiliaryReference(data.combiner);
-      node.staticType = _translateType(data.inferredType);
+      if (entity != null) {
+        var data = _get(entity);
+        node.staticElement = _translateAuxiliaryReference(data.combiner);
+        node.staticType = _translateType(data.inferredType);
+      }
     } else if (tokenType == TokenType.BANG) {
       // !boolExpression;
       node.staticType = _translateType(_get(node).inferredType);
@@ -732,8 +738,7 @@ class ResolutionApplier extends GeneralizingAstVisitor {
     } else if (leftHandSide is ParenthesizedExpression) {
       return leftHandSide.rightParenthesis;
     } else {
-      throw new StateError(
-          'Unexpected LHS (${leftHandSide.runtimeType}) $leftHandSide');
+      return null;
     }
   }
 

pkg/analyzer/test/generated/compile_time_error_code_test.dart

@@ -6368,7 +6368,13 @@ class C {
 ''');
     await computeAnalysisResult(source);
     assertErrors(
-        source, [CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT]);
+        source,
+        useCFE
+            ? [
+                CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT,
+                CompileTimeErrorCode.NOT_AN_LVALUE
+              ]
+            : [CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT]);
     verify([source]);
   }
 
@@ -6382,7 +6388,13 @@ f() {
 ''');
     await computeAnalysisResult(source);
     assertErrors(
-        source, [CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT]);
+        source,
+        useCFE
+            ? [
+                CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT,
+                CompileTimeErrorCode.NOT_AN_LVALUE
+              ]
+            : [CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT]);
     verify([source]);
   }
 
@@ -6398,7 +6410,13 @@ class C {
 ''');
     await computeAnalysisResult(source);
     assertErrors(
-        source, [CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT]);
+        source,
+        useCFE
+            ? [
+                CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT,
+                CompileTimeErrorCode.NOT_AN_LVALUE
+              ]
+            : [CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT]);
     verify([source]);
   }
 
@@ -6412,7 +6430,13 @@ f() {
 ''');
     await computeAnalysisResult(source);
     assertErrors(
-        source, [CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT]);
+        source,
+        useCFE
+            ? [
+                CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT,
+                CompileTimeErrorCode.NOT_AN_LVALUE
+              ]
+            : [CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT]);
     verify([source]);
   }
 
@@ -6625,7 +6649,13 @@ f() {
 ''');
     await computeAnalysisResult(source);
     assertErrors(
-        source, [CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT]);
+        source,
+        useCFE
+            ? [
+                CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT,
+                CompileTimeErrorCode.NOT_AN_LVALUE
+              ]
+            : [CompileTimeErrorCode.PREFIX_IDENTIFIER_NOT_FOLLOWED_BY_DOT]);
     verify([source]);
   }
 

pkg/analyzer/test/src/dart/analysis/driver_resolution_test.dart

@@ -837,6 +837,32 @@ void main() {
     }
   }
 
+  test_assignment_of_postfix_increment() async {
+    addTestFile('''
+f(int x, int y) {
+  x++ = y;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+    var xElement = findElement.parameter('x');
+    assertElement(findNode.simple('x++'), xElement);
+    var yElement = findElement.parameter('y');
+    assertElement(findNode.simple('y;'), yElement);
+  }
+
+  test_assignment_of_unresolved_name() async {
+    addTestFile('''
+f(int y) {
+  x = y;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+    var yElement = findElement.parameter('y');
+    assertElement(findNode.simple('y;'), yElement);
+  }
+
   test_assignment_to_final_parameter() async {
     addTestFile('''
 f(final int x) {
@@ -963,6 +989,21 @@ main() {
     expect(xReference.staticType.toString(), useCFE ? 'dynamic' : 'int');
   }
 
+  test_assignment_to_non_generator() async {
+    addTestFile('''
+f() {}
+g(x) {
+  f() = x;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+    var fElement = findElement.function('f');
+    assertElement(findNode.simple('f() ='), fElement);
+    var xElement = findElement.parameter('x');
+    assertElement(findNode.simple('x;'), xElement);
+  }
+
   test_assignment_to_prefix() async {
     var a = _p('/test/lib/a.dart');
     provider.newFile(a, '''
@@ -2039,6 +2080,32 @@ var v = (() => 42)();
     expect(closureElement.enclosingElement, same(variableInitializer));
   }
 
+  test_compound_assignment_of_postfix_increment() async {
+    addTestFile('''
+f(int x, int y) {
+  x++ += y;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+    var xElement = findElement.parameter('x');
+    assertElement(findNode.simple('x++'), xElement);
+    var yElement = findElement.parameter('y');
+    assertElement(findNode.simple('y;'), yElement);
+  }
+
+  test_compound_assignment_of_unresolved_name() async {
+    addTestFile('''
+f(int y) {
+  x += y;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+    var yElement = findElement.parameter('y');
+    assertElement(findNode.simple('y;'), yElement);
+  }
+
   test_conditionalExpression() async {
     String content = r'''
 void main() {
@@ -2474,6 +2541,18 @@ main() async {
     }
   }
 
+  test_dual_increment() async {
+    addTestFile('''
+f(int x) {
+  ++x++;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+    var xElement = findElement.parameter('x');
+    assertElement(findNode.simple('x++'), xElement);
+  }
+
   test_enum_toString() async {
     addTestFile(r'''
 enum MyEnum { A, B, C }
@@ -6303,6 +6382,43 @@ void f<T, U>(T a, U b) {}
     }
   }
 
+  test_null_aware_assignment_of_postfix_increment() async {
+    addTestFile('''
+f(int x, int y) {
+  x++ ??= y;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+    var xElement = findElement.parameter('x');
+    assertElement(findNode.simple('x++'), xElement);
+    var yElement = findElement.parameter('y');
+    assertElement(findNode.simple('y;'), yElement);
+  }
+
+  test_postfix_increment_of_non_generator() async {
+    addTestFile('''
+f() {}
+g() {
+  f()++;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+    var fElement = findElement.function('f');
+    assertElement(findNode.simple('f()++;'), fElement);
+  }
+
+  test_postfix_increment_of_unresolved_name() async {
+    addTestFile('''
+f() {
+  x++;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+  }
+
   test_postfixExpression_local() async {
     String content = r'''
 main() {
@@ -6377,6 +6493,31 @@ class C {
     }
   }
 
+  test_prefix_increment_of_non_generator() async {
+    addTestFile('''
+f() {}
+g() {
+  ++f();
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+    var fReference = findNode.simple('f();');
+    expect(fReference.parent, const TypeMatcher<MethodInvocation>());
+    var fElement = findElement.function('f');
+    assertElement(fReference, fElement);
+  }
+
+  test_prefix_increment_of_unresolved_name() async {
+    addTestFile('''
+f() {
+  ++x;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+  }
+
   test_prefixedIdentifier_classInstance_instanceField() async {
     String content = r'''
 main() {
@@ -9431,6 +9572,24 @@ class FindElement {
     fail('Not found class method: $name');
   }
 
+  ParameterElement parameter(String name) {
+    ParameterElement parameterElement;
+    for (var function in unitElement.functions) {
+      for (var parameter in function.parameters) {
+        if (parameter.name == name) {
+          if (parameterElement != null) {
+            throw new StateError('Parameter name $name is not unique.');
+          }
+          parameterElement = parameter;
+        }
+      }
+    }
+    if (parameterElement != null) {
+      return parameterElement;
+    }
+    fail('No parameter found with name $name');
+  }
+
   PrefixElement prefix(String name) {
     for (var import_ in unitElement.library.imports) {
       var prefix = import_.prefix;

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -6,6 +6,8 @@ library fasta.body_builder;
 
 import 'dart:core' hide MapEntry;
 
+import 'package:front_end/src/fasta/kernel/kernel_expression_generator.dart';
+
 import '../constant_context.dart' show ConstantContext;
 
 import '../fasta_codes.dart' as fasta;
@@ -81,6 +83,7 @@ import 'expression_generator.dart'
         IndexedAccessGenerator,
         LargeIntAccessGenerator,
         LoadLibraryGenerator,
+        NonLvalueGenerator,
         ParenthesizedExpressionGenerator,
         PrefixUseGenerator,
         ReadOnlyAccessGenerator,
@@ -1932,20 +1935,27 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     pop(); // block
   }
 
+  Generator popForLvalue(Token token) {
+    Object value = pop();
+    if (value is Generator) {
+      return value.asLvalue();
+    } else {
+      return new NonLvalueGenerator(
+          this,
+          token,
+          buildCompileTimeError(fasta.messageNotAnLvalue, offsetForToken(token),
+              lengthForToken(token)),
+          toValue(value));
+    }
+  }
+
   @override
   void handleAssignmentExpression(Token token) {
     debugEvent("AssignmentExpression");
     Expression value = popForValue();
-    Object generator = pop();
-    if (generator is! Generator) {
-      push(new SyntheticExpressionJudgment(buildCompileTimeError(
-          fasta.messageNotAnLvalue,
-          offsetForToken(token),
-          lengthForToken(token))));
-    } else {
-      push(new DelayedAssignment(
-          this, token, generator, value, token.stringValue));
-    }
+    var generator = popForLvalue(token);
+    push(new DelayedAssignment(
+        this, token, generator, value, token.stringValue));
   }
 
   @override
@@ -2648,27 +2658,17 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
   @override
   void handleUnaryPrefixAssignmentExpression(Token token) {
     debugEvent("UnaryPrefixAssignmentExpression");
-    Object generator = pop();
-    if (generator is Generator) {
-      push(generator.buildPrefixIncrement(incrementOperator(token),
-          offset: token.charOffset));
-    } else {
-      push(
-          wrapInCompileTimeError(toValue(generator), fasta.messageNotAnLvalue));
-    }
+    var generator = popForLvalue(token);
+    push(generator.buildPrefixIncrement(incrementOperator(token),
+        offset: token.charOffset));
   }
 
   @override
   void handleUnaryPostfixAssignmentExpression(Token token) {
     debugEvent("UnaryPostfixAssignmentExpression");
-    Object generator = pop();
-    if (generator is Generator) {
-      push(new DelayedPostfixIncrement(
-          this, token, generator, incrementOperator(token), null));
-    } else {
-      push(
-          wrapInCompileTimeError(toValue(generator), fasta.messageNotAnLvalue));
-    }
+    var generator = popForLvalue(token);
+    push(new DelayedPostfixIncrement(
+        this, token, generator, incrementOperator(token), null));
   }
 
   @override
@@ -3372,7 +3372,7 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
       TypePromotionFact fact =
           typePromoter.getFactForAccess(variable, functionNestingLevel);
       TypePromotionScope scope = typePromoter.currentScope;
-      syntheticAssignment = lvalue.buildAssignment(
+      syntheticAssignment = lvalue.asLvalue().buildAssignment(
           new VariableGetJudgment(variable, fact, scope)
             ..fileOffset = inKeyword.offset,
           voidContext: true);

pkg/front_end/lib/src/fasta/kernel/expression_generator.dart

@@ -17,6 +17,7 @@ import '../fasta_codes.dart'
         messageCantUsePrefixWithNullAware,
         messageInvalidInitializer,
         messageNotAConstantExpression,
+        messageNotAnLvalue,
         templateCantUseDeferredPrefixAsConstant,
         templateDeferredTypeAnnotation,
         templateIntegerLiteralIsOutOfRange,
@@ -66,6 +67,8 @@ import 'kernel_ast_api.dart'
         DartType,
         DynamicType,
         Expression,
+        ExpressionJudgment,
+        IllegalAssignmentJudgment,
         Initializer,
         InvalidConstructorInvocationJudgment,
         InvalidType,
@@ -107,6 +110,96 @@ export 'kernel_expression_generator.dart'
         ThisAccessGenerator,
         buildIsNull;
 
+class NonLvalueGenerator extends Generator {
+  final Expression errorExpression;
+
+  final ExpressionJudgment judgment;
+
+  final assignmentOffset;
+
+  NonLvalueGenerator(ExpressionGeneratorHelper helper, Token token,
+      this.errorExpression, this.judgment,
+      {this.assignmentOffset = -1})
+      : super(helper, token);
+
+  @override
+  Generator asLvalue() => this;
+
+  @override
+  Expression buildAssignment(Expression value, {bool voidContext}) {
+    return makeJudgment(value);
+  }
+
+  @override
+  Expression buildCompoundAssignment(Name binaryOperator, Expression value,
+      {int offset,
+      bool voidContext,
+      Procedure interfaceTarget,
+      bool isPreIncDec}) {
+    return makeJudgment(value);
+  }
+
+  @override
+  Expression buildNullAwareAssignment(
+      Expression value, DartType type, int offset,
+      {bool voidContext}) {
+    return makeJudgment(value);
+  }
+
+  @override
+  Expression buildPostfixIncrement(Name binaryOperator,
+      {int offset, bool voidContext, Procedure interfaceTarget}) {
+    return makeJudgment(null);
+  }
+
+  @override
+  Expression buildPrefixIncrement(Name binaryOperator,
+      {int offset, bool voidContext, Procedure interfaceTarget}) {
+    return makeJudgment(null);
+  }
+
+  @override
+  Expression buildSimpleRead() {
+    return makeJudgment(null);
+  }
+
+  @override
+  Expression makeInvalidRead() {
+    return makeJudgment(null);
+  }
+
+  @override
+  Expression makeInvalidWrite(Expression value) {
+    return makeJudgment(value);
+  }
+
+  @override
+  String get debugName {
+    return unhandled('debugName', 'NonLvalueGenerator', token.offset, uri);
+  }
+
+  @override
+  doInvocation(int offset, Arguments arguments) {
+    return unhandled('doInvocation', 'NonLvalueGenerator', token.offset, uri);
+  }
+
+  Expression makeJudgment(ExpressionJudgment rhs) {
+    return new IllegalAssignmentJudgment(errorExpression, judgment, rhs,
+        assignmentOffset: assignmentOffset);
+  }
+
+  @override
+  String get plainNameForRead {
+    return unhandled(
+        'plainNameForRead', 'NonLvalueGenerator', token.offset, uri);
+  }
+
+  @override
+  void printOn(StringSink sink) {
+    return unhandled('printOn', 'NonLvalueGenerator', token.offset, uri);
+  }
+}
+
 abstract class ExpressionGenerator {
   /// Builds a [Expression] representing a read from the generator.
   Expression buildSimpleRead();
@@ -189,6 +282,8 @@ abstract class Generator implements ExpressionGenerator {
 
   bool get isInitializer => false;
 
+  Generator asLvalue();
+
   Expression buildForEffect() => buildSimpleRead();
 
   Initializer buildFieldInitializer(Map<String, int> initializedFields) {
@@ -233,6 +328,15 @@ abstract class Generator implements ExpressionGenerator {
     return new UnexpectedQualifiedUseGenerator(helper, name, this, false);
   }
 
+  Generator makeNonLValueGenerator() {
+    return new NonLvalueGenerator(
+        helper,
+        token,
+        helper.buildCompileTimeError(
+            messageNotAnLvalue, offsetForToken(token), lengthForToken(token)),
+        buildSimpleRead());
+  }
+
   Expression invokeConstructor(List<DartType> typeArguments, String name,
       Arguments arguments, Token nameToken, Constness constness) {
     if (typeArguments != null) {
@@ -277,6 +381,9 @@ abstract class VariableUseGenerator implements Generator {
         .variableUseGenerator(helper, token, variable, promotedType);
   }
 
+  @override
+  Generator asLvalue() => this;
+
   @override
   String get debugName => "VariableUseGenerator";
 }
@@ -312,6 +419,9 @@ abstract class PropertyAccessGenerator implements Generator {
     }
   }
 
+  @override
+  Generator asLvalue() => this;
+
   @override
   String get debugName => "PropertyAccessGenerator";
 
@@ -328,6 +438,9 @@ abstract class ThisPropertyAccessGenerator implements Generator {
         .thisPropertyAccessGenerator(helper, token, name, getter, setter);
   }
 
+  @override
+  Generator asLvalue() => this;
+
   @override
   String get debugName => "ThisPropertyAccessGenerator";
 
@@ -348,6 +461,9 @@ abstract class NullAwarePropertyAccessGenerator implements Generator {
         helper, token, receiverExpression, name, getter, setter, type);
   }
 
+  @override
+  Generator asLvalue() => this;
+
   @override
   String get debugName => "NullAwarePropertyAccessGenerator";
 }
@@ -359,6 +475,9 @@ abstract class SuperPropertyAccessGenerator implements Generator {
         .superPropertyAccessGenerator(helper, token, name, getter, setter);
   }
 
+  @override
+  Generator asLvalue() => this;
+
   @override
   String get debugName => "SuperPropertyAccessGenerator";
 }
@@ -391,6 +510,9 @@ abstract class IndexedAccessGenerator implements Generator {
     }
   }
 
+  @override
+  Generator asLvalue() => this;
+
   @override
   String get plainNameForRead => "[]";
 
@@ -410,6 +532,9 @@ abstract class ThisIndexedAccessGenerator implements Generator {
         .thisIndexedAccessGenerator(helper, token, index, getter, setter);
   }
 
+  @override
+  Generator asLvalue() => this;
+
   @override
   String get plainNameForRead => "[]";
 
@@ -427,6 +552,9 @@ abstract class SuperIndexedAccessGenerator implements Generator {
         .superIndexedAccessGenerator(helper, token, index, getter, setter);
   }
 
+  @override
+  Generator asLvalue() => this;
+
   String get plainNameForRead => "[]";
 
   String get plainNameForWrite => "[]=";
@@ -466,6 +594,9 @@ abstract class StaticAccessGenerator implements Generator {
     return new StaticAccessGenerator(helper, token, getter, setter);
   }
 
+  @override
+  Generator asLvalue() => this;
+
   Member get readTarget;
 
   @override
@@ -478,6 +609,9 @@ abstract class LoadLibraryGenerator implements Generator {
     return helper.forest.loadLibraryGenerator(helper, token, builder);
   }
 
+  @override
+  Generator asLvalue() => makeNonLValueGenerator();
+
   @override
   String get plainNameForRead => 'loadLibrary';
 
@@ -496,6 +630,9 @@ abstract class DeferredAccessGenerator implements Generator {
 
   Generator get suffixGenerator;
 
+  @override
+  Generator asLvalue() => this;
+
   @override
   buildPropertyAccess(
       IncompleteSendGenerator send, int operatorOffset, bool isNullAware) {
@@ -572,6 +709,9 @@ abstract class TypeUseGenerator implements Generator {
   @override
   String get debugName => "TypeUseGenerator";
 
+  @override
+  Generator asLvalue() => makeNonLValueGenerator();
+
   @override
   DartType buildTypeWithBuiltArguments(List<DartType> arguments,
       {bool nonInstanceAccessIsError: false, TypeInferrer typeInferrer}) {
@@ -674,6 +814,9 @@ abstract class ReadOnlyAccessGenerator implements Generator {
 
   @override
   String get debugName => "ReadOnlyAccessGenerator";
+
+  @override
+  Generator asLvalue() => makeNonLValueGenerator();
 }
 
 abstract class LargeIntAccessGenerator implements Generator {
@@ -689,6 +832,9 @@ abstract class LargeIntAccessGenerator implements Generator {
   @override
   String get debugName => "LargeIntAccessGenerator";
 
+  @override
+  Generator asLvalue() => makeNonLValueGenerator();
+
   Expression buildError() {
     return helper.buildCompileTimeError(
         templateIntegerLiteralIsOutOfRange.withArguments(token),
@@ -722,6 +868,9 @@ abstract class ErroneousExpressionGenerator implements Generator {
 
   withReceiver(Object receiver, int operatorOffset, {bool isNullAware}) => this;
 
+  @override
+  Generator asLvalue() => this;
+
   @override
   Initializer buildFieldInitializer(Map<String, int> initializedFields) {
     return helper.buildInvalidInitializer(new SyntheticExpressionJudgment(
@@ -842,7 +991,7 @@ abstract class UnresolvedNameGenerator implements ErroneousExpressionGenerator {
     offset ??= offsetForToken(this.token);
     return helper.throwNoSuchMethodError(
         forest.literalNull(null)..fileOffset = offset,
-        plainNameForRead,
+        plainNameForRead ?? '',
         arguments,
         offset,
         isGetter: isGetter,
@@ -870,6 +1019,9 @@ abstract class UnlinkedGenerator implements Generator {
   @override
   String get debugName => "UnlinkedGenerator";
 
+  @override
+  Generator asLvalue() => this;
+
   @override
   void printOn(StringSink sink) {
     sink.write(", name: ");
@@ -950,6 +1102,9 @@ abstract class DelayedAssignment implements ContextAwareGenerator {
   @override
   String get debugName => "DelayedAssignment";
 
+  @override
+  Generator asLvalue() => makeNonLValueGenerator();
+
   @override
   Expression buildSimpleRead() {
     return handleAssignment(false);
@@ -1035,6 +1190,9 @@ abstract class DelayedPostfixIncrement implements ContextAwareGenerator {
   @override
   String get debugName => "DelayedPostfixIncrement";
 
+  @override
+  Generator asLvalue() => makeNonLValueGenerator();
+
   @override
   Expression buildSimpleRead() {
     return generator.buildPostfixIncrement(binaryOperator,
@@ -1074,6 +1232,9 @@ abstract class PrefixUseGenerator implements Generator {
   @override
   String get debugName => "PrefixUseGenerator";
 
+  @override
+  Generator asLvalue() => makeNonLValueGenerator();
+
   @override
   Expression buildSimpleRead() => makeInvalidRead();
 
@@ -1144,9 +1305,6 @@ abstract class PrefixUseGenerator implements Generator {
         lengthForToken(token)));
   }
 
-  @override
-  Expression makeInvalidWrite(Expression value) => makeInvalidRead();
-
   @override
   void printOn(StringSink sink) {
     sink.write(", prefix: ");
@@ -1175,6 +1333,9 @@ abstract class UnexpectedQualifiedUseGenerator implements Generator {
   @override
   String get debugName => "UnexpectedQualifiedUseGenerator";
 
+  @override
+  Generator asLvalue() => makeNonLValueGenerator();
+
   @override
   Expression buildSimpleRead() => makeInvalidRead();
 

pkg/front_end/lib/src/fasta/kernel/kernel_ast_api.dart

@@ -96,7 +96,6 @@ export 'kernel_shadow_ast.dart'
         InvalidStatementJudgment,
         InvalidSuperInitializerJudgment,
         InvalidVariableWriteJudgment,
-        InvalidWriteJudgment,
         ShadowInvalidFieldInitializer,
         ShadowInvalidInitializer,
         LabeledStatementJudgment,

pkg/front_end/lib/src/fasta/kernel/kernel_expression_generator.dart

@@ -47,6 +47,7 @@ import 'expression_generator.dart'
         IndexedAccessGenerator,
         LargeIntAccessGenerator,
         LoadLibraryGenerator,
+        NonLvalueGenerator,
         NullAwarePropertyAccessGenerator,
         PrefixUseGenerator,
         PropertyAccessGenerator,
@@ -77,13 +78,11 @@ import 'kernel_ast_api.dart'
         Constructor,
         DartType,
         Field,
-        IllegalAssignmentJudgment,
         IndexAssignmentJudgment,
         Initializer,
         InvalidPropertyGetJudgment,
         InvalidType,
         InvalidVariableWriteJudgment,
-        InvalidWriteJudgment,
         Let,
         LoadLibraryTearOffJudgment,
         Member,
@@ -247,7 +246,7 @@ abstract class KernelExpressionGenerator implements ExpressionGenerator {
   Expression makeInvalidWrite(Expression value) {
     return buildInvalidWriteJudgment(helper.throwNoSuchMethodError(
         forest.literalNull(token),
-        plainNameForRead,
+        plainNameForRead ?? '',
         forest.arguments(<Expression>[value], noLocation),
         offsetForToken(token),
         isSetter: true));
@@ -289,8 +288,13 @@ abstract class KernelExpressionGenerator implements ExpressionGenerator {
 
   /// Creates a data structure for tracking the desugaring of a complex
   /// assignment expression whose right hand side is [rhs].
-  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) =>
-      new IllegalAssignmentJudgment(rhs);
+  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) {
+    // This code should never be reached; clients should always use .asLvalue()
+    // prior to starting a complex assignment, and generators returned by
+    // .asLvalue() should always override this method.
+    return unhandled(
+        'startComplexAssignment', '$runtimeType', token.offset, null);
+  }
 }
 
 abstract class KernelGenerator = Generator with KernelExpressionGenerator;

pkg/front_end/lib/src/fasta/kernel/kernel_expression_generator_impl.dart

@@ -32,6 +32,9 @@ class ThisAccessGenerator extends KernelGenerator {
 
   String get debugName => "ThisAccessGenerator";
 
+  @override
+  Generator asLvalue() => makeNonLValueGenerator();
+
   Expression buildSimpleRead() {
     if (!isSuper) {
       return forest.thisExpression(token);
@@ -129,46 +132,6 @@ class ThisAccessGenerator extends KernelGenerator {
     }
   }
 
-  Expression buildAssignment(Expression value, {bool voidContext: false}) {
-    return buildAssignmentError();
-  }
-
-  Expression buildNullAwareAssignment(
-      Expression value, DartType type, int offset,
-      {bool voidContext: false}) {
-    return buildAssignmentError();
-  }
-
-  Expression buildCompoundAssignment(Name binaryOperator, Expression value,
-      {int offset: TreeNode.noOffset,
-      bool voidContext: false,
-      Procedure interfaceTarget,
-      bool isPreIncDec: false,
-      bool isPostIncDec: false}) {
-    return buildAssignmentError();
-  }
-
-  Expression buildPrefixIncrement(Name binaryOperator,
-      {int offset: TreeNode.noOffset,
-      bool voidContext: false,
-      Procedure interfaceTarget}) {
-    return buildAssignmentError();
-  }
-
-  Expression buildPostfixIncrement(Name binaryOperator,
-      {int offset: TreeNode.noOffset,
-      bool voidContext: false,
-      Procedure interfaceTarget}) {
-    return buildAssignmentError();
-  }
-
-  Expression buildAssignmentError() {
-    String message =
-        isSuper ? "Can't assign to 'super'." : "Can't assign to 'this'.";
-    return helper.deprecated_buildCompileTimeError(
-        message, offsetForToken(token));
-  }
-
   @override
   void printOn(StringSink sink) {
     sink.write(", isInitializer: ");
@@ -189,6 +152,9 @@ abstract class IncompleteSendGenerator extends KernelGenerator {
 
   Arguments get arguments => null;
 
+  @override
+  Generator asLvalue() => makeNonLValueGenerator();
+
   @override
   void printOn(StringSink sink) {
     sink.write(", name: ");
@@ -378,16 +344,15 @@ class ParenthesizedExpressionGenerator extends KernelReadOnlyAccessGenerator {
   String get debugName => "ParenthesizedExpressionGenerator";
 
   @override
-  ComplexAssignmentJudgment startComplexAssignment(Expression rhs) {
-    return new IllegalAssignmentJudgment(rhs,
+  Generator asLvalue() {
+    return new NonLvalueGenerator(
+        helper,
+        token,
+        helper.buildCompileTimeError(
+            messageCannotAssignToParenthesizedExpression,
+            offsetForToken(token),
+            lengthForToken(token)),
+        buildSimpleRead(),
         assignmentOffset: offsetForToken(token));
   }
-
-  Expression makeInvalidWrite(Expression value) {
-    var error = helper.buildCompileTimeError(
-        messageCannotAssignToParenthesizedExpression,
-        offsetForToken(token),
-        lengthForToken(token));
-    return new InvalidWriteJudgment(error, expression);
-  }
 }

pkg/front_end/lib/src/fasta/kernel/kernel_shadow_ast.dart

@@ -1574,35 +1574,44 @@ class IfJudgment extends IfStatement implements StatementJudgment {
   }
 }
 
-/// Concrete shadow object representing an assignment to a target for which
-/// assignment is not allowed.
-class IllegalAssignmentJudgment extends ComplexAssignmentJudgment {
+class IllegalAssignmentJudgment extends SyntheticExpressionJudgment {
   /// The offset at which the invalid assignment should be stored.
   /// If `-1`, then there is no separate location for invalid assignment.
   final int assignmentOffset;
 
-  IllegalAssignmentJudgment(ExpressionJudgment rhs, {this.assignmentOffset: -1})
-      : super(rhs) {
-    rhs.parent = this;
+  IllegalAssignmentJudgment(kernel.Expression desugared, this.lhs, this.rhs,
+      {this.assignmentOffset: -1})
+      : super(desugared) {
+    // lhs and rhs may not be hooked up to the expression tree because they're
+    // not meant to be part of the compiled output; they only exist to allow
+    // resolution information to be reported to the analyzer.  But type
+    // inference currently requires expressions to have a parent (so that it can
+    // replace them with their desugared equivalents), so create placeholder
+    // parents if needed.
+    if (lhs.parent == null) {
+      new ExpressionStatement(lhs);
+    }
+    if (rhs != null && rhs.parent == null) {
+      new ExpressionStatement(rhs);
+    }
   }
 
-  @override
-  DartType _getWriteType(ShadowTypeInferrer inferrer) {
-    return const UnknownType();
-  }
+  final ExpressionJudgment lhs;
+
+  final ExpressionJudgment rhs;
 
   @override
   Expression infer<Expression, Statement, Initializer, Type>(
       ShadowTypeInferrer inferrer,
       Factory<Expression, Statement, Initializer, Type> factory,
       DartType typeContext) {
-    if (write != null) {
-      inferrer.inferExpression(factory, write, const UnknownType(), false);
-    }
+    inferrer.inferExpression(factory, lhs, const UnknownType(), false);
     if (assignmentOffset != -1) {
       inferrer.listener.invalidAssignment(this, assignmentOffset);
     }
-    inferrer.inferExpression(factory, rhs, const UnknownType(), false);
+    if (rhs != null) {
+      inferrer.inferExpression(factory, rhs, const UnknownType(), false);
+    }
     _replaceWithDesugared();
     inferredType = const DynamicType();
     return null;
@@ -2975,29 +2984,6 @@ class InvalidVariableWriteJudgment extends SyntheticExpressionJudgment {
   }
 }
 
-/// Synthetic judgment class representing an attempt to assign to the
-/// [expression] which is not assignable.
-class InvalidWriteJudgment extends SyntheticExpressionJudgment {
-  final ExpressionJudgment expression;
-
-  InvalidWriteJudgment(kernel.Expression desugared, this.expression)
-      : super(desugared);
-
-  @override
-  Expression infer<Expression, Statement, Initializer, Type>(
-      ShadowTypeInferrer inferrer,
-      Factory<Expression, Statement, Initializer, Type> factory,
-      DartType typeContext) {
-    // When a compound assignment, the expression is already wrapping in
-    // VariableDeclaration in _makeRead(). Otherwise, temporary associate
-    // the expression with this node.
-    expression.parent ??= this;
-
-    inferrer.inferExpression(factory, expression, const UnknownType(), false);
-    return super.infer(inferrer, factory, typeContext);
-  }
-}
-
 /// Synthetic judgment class representing an attempt reference a member
 /// that is not allowed at this location.
 class InvalidPropertyGetJudgment extends SyntheticExpressionJudgment {

pkg/front_end/messages.status

@@ -34,6 +34,7 @@ CantInferPackagesFromPackageUri/example: Fail
 CantInferTypeDueToCircularity/dart2jsCode: Fail
 CantInferTypeDueToCircularity/example: Fail
 CantInferTypeDueToInconsistentOverrides/example: Fail
+CantUsePrefixAsExpression/script: Fail
 CantUseSuperBoundedTypeForInstanceCreation/analyzerCode: Fail
 CantUseSuperBoundedTypeForInstanceCreation/example: Fail
 ColonInPlaceOfIn/example: Fail

pkg/front_end/testcases/compile.status

@@ -96,7 +96,7 @@ rasta/type_with_parse_error: Fail
 rasta/typedef: Fail
 rasta/unresolved: Fail
 rasta/unresolved_constructor: Fail
-rasta/unresolved_for_in: RuntimeError # Test contains a compile-time error, signaled at run time in the JIT VM
+rasta/unresolved_for_in: RuntimeError # Test has an intentional error
 rasta/unresolved_recovery: Fail
 
 regress/issue_29975: Fail # Issue 29975.

pkg/front_end/testcases/rasta/unresolved_for_in.dart.direct.expect

@@ -23,11 +23,13 @@ class Fisk extends core::Object {
       core::print(this.key);
     }
     for (final dynamic #t2 in x) {
-      let dynamic _ = null in throw new core::NoSuchMethodError::withInvocation(null, new core::_InvocationMirror::_withType(#Fisk, 34, const <core::Type>[], core::List::unmodifiable<dynamic>(<dynamic>[#t2]), core::Map::unmodifiable<core::Symbol, dynamic>(const <core::Symbol, dynamic>{})));
+      invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:14:10: Error: Can't assign to this.
+    for (Fisk in x) {
+         ^^^^";
       core::print(self::Fisk);
     }
     for (final dynamic #t3 in x) {
-      let dynamic _ = null in invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:17:10: Error: A prefix can't be used as an expression.
+      invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:17:10: Error: Can't assign to this.
     for (collection in x) {
          ^^^^^^^^^^";
       core::print(invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:18:13: Error: A prefix can't be used as an expression.
@@ -35,7 +37,9 @@ class Fisk extends core::Object {
             ^^^^^^^^^^");
     }
     for (final dynamic #t4 in x) {
-      let dynamic _ = null in throw new core::NoSuchMethodError::withInvocation(null, new core::_InvocationMirror::_withType(#VoidFunction, 34, const <core::Type>[], core::List::unmodifiable<dynamic>(<dynamic>[#t4]), core::Map::unmodifiable<core::Symbol, dynamic>(const <core::Symbol, dynamic>{})));
+      invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:20:10: Error: Can't assign to this.
+    for (VoidFunction in x) {
+         ^^^^^^^^^^^^";
       core::print(() → void);
     }
     for (final dynamic #t5 = let dynamic _ = null in invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:23:10: Error: Can't assign to this, so it can't be used in a for-in loop.
@@ -52,11 +56,13 @@ static method main(dynamic arguments) → dynamic {
     core::print(throw new core::NoSuchMethodError::withInvocation(null, new core::_InvocationMirror::_withType(#key, 33, const <core::Type>[], const <dynamic>[], core::Map::unmodifiable<core::Symbol, dynamic>(const <core::Symbol, dynamic>{}))));
   }
   for (final dynamic #t7 in arguments) {
-    let dynamic _ = null in throw new core::NoSuchMethodError::withInvocation(null, new core::_InvocationMirror::_withType(#Fisk, 34, const <core::Type>[], core::List::unmodifiable<dynamic>(<dynamic>[#t7]), core::Map::unmodifiable<core::Symbol, dynamic>(const <core::Symbol, dynamic>{})));
+    invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:34:8: Error: Can't assign to this.
+  for (Fisk in arguments) {
+       ^^^^";
     core::print(self::Fisk);
   }
   for (final dynamic #t8 in arguments) {
-    let dynamic _ = null in invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:37:8: Error: A prefix can't be used as an expression.
+    invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:37:8: Error: Can't assign to this.
   for (collection in arguments) {
        ^^^^^^^^^^";
     core::print(invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:38:11: Error: A prefix can't be used as an expression.
@@ -64,7 +70,9 @@ static method main(dynamic arguments) → dynamic {
           ^^^^^^^^^^");
   }
   for (final dynamic #t9 in arguments) {
-    let dynamic _ = null in throw new core::NoSuchMethodError::withInvocation(null, new core::_InvocationMirror::_withType(#VoidFunction, 34, const <core::Type>[], core::List::unmodifiable<dynamic>(<dynamic>[#t9]), core::Map::unmodifiable<core::Symbol, dynamic>(const <core::Symbol, dynamic>{})));
+    invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:40:8: Error: Can't assign to this.
+  for (VoidFunction in arguments) {
+       ^^^^^^^^^^^^";
     core::print(() → void);
   }
   for (final dynamic #t10 = let dynamic _ = null in invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:43:8: Error: Can't assign to this, so it can't be used in a for-in loop.

pkg/front_end/testcases/rasta/unresolved_for_in.dart.direct.transformed.expect

@@ -23,11 +23,13 @@ class Fisk extends core::Object {
       core::print(this.key);
     }
     for (final dynamic #t2 in x) {
-      let dynamic _ = null in throw new core::NoSuchMethodError::withInvocation(null, new core::_InvocationMirror::_withType(#Fisk, 34, const <core::Type>[], core::List::unmodifiable<dynamic>(<dynamic>[#t2]), core::Map::unmodifiable<core::Symbol, dynamic>(const <core::Symbol, dynamic>{})));
+      invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:14:10: Error: Can't assign to this.
+    for (Fisk in x) {
+         ^^^^";
       core::print(self::Fisk);
     }
     for (final dynamic #t3 in x) {
-      let dynamic _ = null in invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:17:10: Error: A prefix can't be used as an expression.
+      invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:17:10: Error: Can't assign to this.
     for (collection in x) {
          ^^^^^^^^^^";
       core::print(invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:18:13: Error: A prefix can't be used as an expression.
@@ -35,7 +37,9 @@ class Fisk extends core::Object {
             ^^^^^^^^^^");
     }
     for (final dynamic #t4 in x) {
-      let dynamic _ = null in throw new core::NoSuchMethodError::withInvocation(null, new core::_InvocationMirror::_withType(#VoidFunction, 34, const <core::Type>[], core::List::unmodifiable<dynamic>(<dynamic>[#t4]), core::Map::unmodifiable<core::Symbol, dynamic>(const <core::Symbol, dynamic>{})));
+      invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:20:10: Error: Can't assign to this.
+    for (VoidFunction in x) {
+         ^^^^^^^^^^^^";
       core::print(() → void);
     }
     for (final dynamic #t5 = let dynamic _ = null in invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:23:10: Error: Can't assign to this, so it can't be used in a for-in loop.
@@ -52,11 +56,13 @@ static method main(dynamic arguments) → dynamic {
     core::print(throw new core::NoSuchMethodError::withInvocation(null, new core::_InvocationMirror::_withType(#key, 33, const <core::Type>[], const <dynamic>[], core::Map::unmodifiable<core::Symbol, dynamic>(const <core::Symbol, dynamic>{}))));
   }
   for (final dynamic #t7 in arguments) {
-    let dynamic _ = null in throw new core::NoSuchMethodError::withInvocation(null, new core::_InvocationMirror::_withType(#Fisk, 34, const <core::Type>[], core::List::unmodifiable<dynamic>(<dynamic>[#t7]), core::Map::unmodifiable<core::Symbol, dynamic>(const <core::Symbol, dynamic>{})));
+    invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:34:8: Error: Can't assign to this.
+  for (Fisk in arguments) {
+       ^^^^";
     core::print(self::Fisk);
   }
   for (final dynamic #t8 in arguments) {
-    let dynamic _ = null in invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:37:8: Error: A prefix can't be used as an expression.
+    invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:37:8: Error: Can't assign to this.
   for (collection in arguments) {
        ^^^^^^^^^^";
     core::print(invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:38:11: Error: A prefix can't be used as an expression.
@@ -64,7 +70,9 @@ static method main(dynamic arguments) → dynamic {
           ^^^^^^^^^^");
   }
   for (final dynamic #t9 in arguments) {
-    let dynamic _ = null in throw new core::NoSuchMethodError::withInvocation(null, new core::_InvocationMirror::_withType(#VoidFunction, 34, const <core::Type>[], core::List::unmodifiable<dynamic>(<dynamic>[#t9]), core::Map::unmodifiable<core::Symbol, dynamic>(const <core::Symbol, dynamic>{})));
+    invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:40:8: Error: Can't assign to this.
+  for (VoidFunction in arguments) {
+       ^^^^^^^^^^^^";
     core::print(() → void);
   }
   for (final dynamic #t10 = let dynamic _ = null in invalid-expression "pkg/front_end/testcases/rasta/unresolved_for_in.dart:43:8: Error: Can't assign to this, so it can't be used in a for-in loop.

pkg/front_end/testcases/regress/issue_31185.dart.direct.expect

@@ -18,9 +18,9 @@ static method test1() → core::int {
   self::i;
 }
 static method test2() → core::int {
-  return let final dynamic #t3 = self::i in let final dynamic #t4 = #t3 in let final dynamic #t5 = invalid-expression "pkg/front_end/testcases/regress/issue_31185.dart:12:12: Error: Can't assign to a parenthesized expression.
+  return invalid-expression "pkg/front_end/testcases/regress/issue_31185.dart:12:12: Error: Can't assign to a parenthesized expression.
   return (i) ++ (i);
-           ^" in #t4;
+           ^";
   self::i;
 }
 static method main() → dynamic {

pkg/front_end/testcases/regress/issue_31185.dart.direct.transformed.expect

@@ -18,9 +18,9 @@ static method test1() → core::int {
   self::i;
 }
 static method test2() → core::int {
-  return let final dynamic #t3 = self::i in let final dynamic #t4 = #t3 in let final dynamic #t5 = invalid-expression "pkg/front_end/testcases/regress/issue_31185.dart:12:12: Error: Can't assign to a parenthesized expression.
+  return invalid-expression "pkg/front_end/testcases/regress/issue_31185.dart:12:12: Error: Can't assign to a parenthesized expression.
   return (i) ++ (i);
-           ^" in #t4;
+           ^";
   self::i;
 }
 static method main() → dynamic {

pkg/front_end/testcases/regress/issue_31185.dart.strong.expect

@@ -18,9 +18,9 @@ static method test1() → core::int {
   self::i;
 }
 static method test2() → core::int {
-  return (let final dynamic #t3 = self::i in let final dynamic #t4 = #t3 in let final dynamic #t5 = invalid-expression "pkg/front_end/testcases/regress/issue_31185.dart:12:12: Error: Can't assign to a parenthesized expression.
+  return invalid-expression "pkg/front_end/testcases/regress/issue_31185.dart:12:12: Error: Can't assign to a parenthesized expression.
   return (i) ++ (i);
-           ^" in #t4) as{TypeError} core::int;
+           ^" as{TypeError} core::int;
   self::i;
 }
 static method main() → dynamic {

pkg/front_end/testcases/regress/issue_31185.dart.strong.transformed.expect

@@ -18,9 +18,9 @@ static method test1() → core::int {
   self::i;
 }
 static method test2() → core::int {
-  return (let final core::int #t3 = self::i in let final core::int #t4 = #t3 in let final dynamic #t5 = invalid-expression "pkg/front_end/testcases/regress/issue_31185.dart:12:12: Error: Can't assign to a parenthesized expression.
+  return invalid-expression "pkg/front_end/testcases/regress/issue_31185.dart:12:12: Error: Can't assign to a parenthesized expression.
   return (i) ++ (i);
-           ^" in #t4) as{TypeError} core::int;
+           ^" as{TypeError} core::int;
   self::i;
 }
 static method main() → dynamic {

runtime/vm/dart_api_impl_test.cc

@@ -6662,7 +6662,7 @@ TEST_CASE(DartAPI_ImportLibrary3) {
     if (TestCase::UsingStrongMode()) {
       EXPECT_ERROR(lib,
                    "Compilation failed file:///test-lib:4:10:"
-                   " Error: Setter not found: 'foo'");
+                   " Error: Can't assign to this.");
       return;
     }
     EXPECT_VALID(lib);