From 4e32a356e0f2affebe612a09fa835652a7a95deb Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Peter=20von=20der=20Ahe=CC=81?= <ahe@google.com>
Date: Tue, 25 Sep 2018 14:15:23 +0000
Subject: [PATCH] Ignore synthetic elements created by the parser
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

Change-Id: I558827417c938a22075c5b5357294d27cbd6286a
Reviewed-on: https://dart-review.googlesource.com/76121
Reviewed-by: Aske Simon Christensen <askesc@google.com>
Commit-Queue: Peter von der Ahé <ahe@google.com>
---
 .../src/fasta/builder/procedure_builder.dart  |   6 +-
 .../lib/src/fasta/kernel/body_builder.dart    | 111 +++--
 .../fasta/kernel/kernel_library_builder.dart  |  14 +-
 .../kernel_mixin_application_builder.dart     |   3 +-
 .../lib/src/fasta/source/diet_listener.dart   |  77 ++--
 .../lib/src/fasta/source/outline_builder.dart | 380 ++++++++++++------
 .../lib/src/fasta/source/scope_listener.dart  |   3 +-
 .../fasta/source/source_class_builder.dart    |   9 +-
 .../fasta/source/source_library_builder.dart  |   6 +-
 .../lib/src/fasta/source/stack_listener.dart  |  31 +-
 10 files changed, 435 insertions(+), 205 deletions(-)

diff --git a/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart b/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart
index 73020a55244..aeb7fd1b3ef 100644
--- a/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/procedure_builder.dart
@@ -117,8 +117,10 @@ abstract class ProcedureBuilder<T extends TypeBuilder> extends MemberBuilder {
   }
 
   FormalParameterBuilder getFormal(String name) {
-    for (FormalParameterBuilder formal in formals) {
-      if (formal.name == name) return formal;
+    if (formals != null) {
+      for (FormalParameterBuilder formal in formals) {
+        if (formal.name == name) return formal;
+      }
     }
     return null;
   }
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index adf249b01c1..63d3ae2d674 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -31,8 +31,7 @@ import '../parser.dart'
         offsetForToken,
         optional;
 
-import '../problems.dart'
-    show internalProblem, unexpected, unhandled, unsupported;
+import '../problems.dart' show unexpected, unhandled, unsupported;
 
 import '../quote.dart'
     show
@@ -57,6 +56,7 @@ import '../source/scope_listener.dart'
         GrowableList,
         JumpTargetKind,
         NullValue,
+        ParserRecovery,
         ScopeListener;
 
 import '../type_inference/type_inferrer.dart' show TypeInferrer;
@@ -324,8 +324,10 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
   }
 
   Statement popBlock(int count, Token openBrace, Token closeBrace) {
-    return forest.block(openBrace,
-        const GrowableList<Statement>().pop(stack, count), closeBrace);
+    return forest.block(
+        openBrace,
+        const GrowableList<Statement>().pop(stack, count) ?? <Statement>[],
+        closeBrace);
   }
 
   Statement popStatementIfNotNull(Object value) {
@@ -471,7 +473,8 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     if (count == 0) {
       push(NullValue.Metadata);
     } else {
-      push(const GrowableList<Expression>().pop(stack, count));
+      push(const GrowableList<Expression>().pop(stack, count) ??
+          NullValue.Metadata /* Ignore parser recovery */);
     }
   }
 
@@ -1085,8 +1088,13 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
   @override
   void endArguments(int count, Token beginToken, Token endToken) {
     debugEvent("Arguments");
-    List<Object> arguments =
-        const FixedNullableList<Object>().pop(stack, count) ?? <Object>[];
+    List<Object> arguments = count == 0
+        ? <Object>[]
+        : const FixedNullableList<Object>().pop(stack, count);
+    if (arguments == null) {
+      push(new ParserRecovery(beginToken.charOffset));
+      return;
+    }
     int firstNamedArgumentIndex = arguments.length;
     for (int i = 0; i < arguments.length; i++) {
       Object node = arguments[i];
@@ -1728,6 +1736,10 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     } else {
       int count = 1 + interpolationCount * 2;
       List<Object> parts = const FixedNullableList<Object>().pop(stack, count);
+      if (parts == null) {
+        push(new ParserRecovery(endToken.charOffset));
+        return;
+      }
       Token first = parts.first;
       Token last = parts.last;
       Quote quote = analyzeQuote(first.lexeme);
@@ -1974,6 +1986,10 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
       currentLocalVariableType = pop();
       currentLocalVariableModifiers = pop();
       List<Expression> annotations = pop();
+      if (variables == null) {
+        push(new ParserRecovery(endToken.charOffset));
+        return;
+      }
       if (annotations != null) {
         bool isFirstVariable = true;
         for (VariableDeclarationJudgment variable in variables) {
@@ -2185,7 +2201,8 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
   void handleLiteralMap(
       int count, Token leftBrace, Token constKeyword, Token rightBrace) {
     debugEvent("LiteralMap");
-    List<MapEntry> entries = const GrowableList<MapEntry>().pop(stack, count);
+    List<MapEntry> entries =
+        const GrowableList<MapEntry>().pop(stack, count) ?? <MapEntry>[];
     List<UnresolvedType<KernelTypeBuilder>> typeArguments = pop();
     DartType keyType;
     DartType valueType;
@@ -2245,6 +2262,10 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     } else {
       List<Identifier> parts =
           const FixedNullableList<Identifier>().pop(stack, identifierCount);
+      if (parts == null) {
+        push(new ParserRecovery(hashToken.charOffset));
+        return;
+      }
       value = symbolPartToString(parts.first);
       for (int i = 1; i < parts.length; i++) {
         value += ".${symbolPartToString(parts[i])}";
@@ -2460,6 +2481,10 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
       modifiers |= finalMask;
     }
     List<Expression> annotations = pop();
+    if (nameToken.isSynthetic) {
+      push(new ParserRecovery(nameToken.charOffset));
+      return;
+    }
     KernelFormalParameterBuilder parameter;
     if (!inCatchClause &&
         functionNestingLevel == 0 &&
@@ -2467,11 +2492,8 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
       ProcedureBuilder<TypeBuilder> member = this.member;
       parameter = member.getFormal(name.name);
       if (parameter == null) {
-        internalProblem(
-            fasta.templateInternalProblemNotFoundIn
-                .withArguments(name.name, "formals"),
-            offsetForToken(nameToken),
-            uri);
+        push(new ParserRecovery(nameToken.charOffset));
+        return;
       }
     } else {
       parameter = new KernelFormalParameterBuilder(null, modifiers,
@@ -2517,10 +2539,14 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     List<KernelFormalParameterBuilder> parameters =
         const FixedNullableList<KernelFormalParameterBuilder>()
             .pop(stack, count);
-    for (KernelFormalParameterBuilder parameter in parameters) {
-      parameter.kind = kind;
+    if (parameters == null) {
+      push(new ParserRecovery(offsetForToken(beginToken)));
+    } else {
+      for (KernelFormalParameterBuilder parameter in parameters) {
+        parameter.kind = kind;
+      }
+      push(parameters);
     }
-    push(parameters);
   }
 
   @override
@@ -2595,6 +2621,7 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     if (optionals != null && parameters != null) {
       parameters.setRange(count, count + optionalsCount, optionals);
     }
+    assert(parameters?.isNotEmpty ?? true);
     FormalParameters formals = new FormalParameters(parameters,
         offsetForToken(beginToken), lengthOfSpan(beginToken, endToken), uri);
     constantContext = pop();
@@ -3238,7 +3265,8 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
   void endTypeArguments(int count, Token beginToken, Token endToken) {
     debugEvent("TypeArguments");
     push(const FixedNullableList<UnresolvedType<KernelTypeBuilder>>()
-        .pop(stack, count));
+            .pop(stack, count) ??
+        NullValue.TypeArguments);
   }
 
   @override
@@ -3564,8 +3592,10 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     enterLocalScope(null, scope.createNestedLabelScope());
     LabelTarget target =
         new LabelTarget(member, functionNestingLevel, token.charOffset);
-    for (Label label in labels) {
-      scope.declareLabel(label.name, target);
+    if (labels != null) {
+      for (Label label in labels) {
+        scope.declareLabel(label.name, target);
+      }
     }
     push(target);
   }
@@ -3690,7 +3720,7 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     int count = labelCount + expressionCount;
     List<Object> labelsAndExpressions =
         const FixedNullableList<Object>().pop(stack, count);
-    List<Label> labels = new List<Label>(labelCount);
+    List<Label> labels = labelCount == 0 ? null : new List<Label>(labelCount);
     List<Expression> expressions =
         new List<Expression>.filled(expressionCount, null, growable: true);
     int labelIndex = 0;
@@ -3705,23 +3735,26 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
       }
     }
     assert(scope == switchScope);
-    for (Label label in labels) {
-      String labelName = label.name;
-      if (scope.hasLocalLabel(labelName)) {
-        // TODO(ahe): Should validate this is a goto target.
-        if (!scope.claimLabel(labelName)) {
-          addProblem(
-              fasta.templateDuplicateLabelInSwitchStatement
-                  .withArguments(labelName),
-              label.charOffset,
-              labelName.length);
+    if (labels != null) {
+      for (Label label in labels) {
+        String labelName = label.name;
+        if (scope.hasLocalLabel(labelName)) {
+          // TODO(ahe): Should validate this is a goto target.
+          if (!scope.claimLabel(labelName)) {
+            addProblem(
+                fasta.templateDuplicateLabelInSwitchStatement
+                    .withArguments(labelName),
+                label.charOffset,
+                labelName.length);
+          }
+        } else {
+          scope.declareLabel(
+              labelName, createGotoTarget(firstToken.charOffset));
         }
-      } else {
-        scope.declareLabel(labelName, createGotoTarget(firstToken.charOffset));
       }
     }
     push(expressions);
-    push(labels);
+    push(labels ?? NullValue.Labels);
     enterLocalScope("switch case");
   }
 
@@ -3749,7 +3782,7 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     push(new SwitchCaseJudgment(expressions, expressionOffsets, block,
         isDefault: defaultKeyword != null)
       ..fileOffset = firstToken.charOffset);
-    push(labels);
+    push(labels ?? NullValue.Labels);
   }
 
   @override
@@ -3778,10 +3811,12 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
     for (int i = caseCount - 1; i >= 0; i--) {
       List<Label> labels = pop();
       SwitchCase current = cases[i] = pop();
-      for (Label label in labels) {
-        JumpTarget target = switchScope.lookupLabel(label.name);
-        if (target != null) {
-          target.resolveGotos(forest, current);
+      if (labels != null) {
+        for (Label label in labels) {
+          JumpTarget target = switchScope.lookupLabel(label.name);
+          if (target != null) {
+            target.resolveGotos(forest, current);
+          }
         }
       }
     }
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
index 1ff9f835227..af4869f589b 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_library_builder.dart
@@ -83,6 +83,7 @@ import 'kernel_builder.dart'
         ConstructorReferenceBuilder,
         Declaration,
         DynamicTypeBuilder,
+        EnumConstantInfo,
         FormalParameterBuilder,
         InvalidTypeBuilder,
         KernelClassBuilder,
@@ -700,22 +701,17 @@ class KernelLibraryBuilder
     }
   }
 
+  @override
   void addEnum(
       String documentationComment,
       List<MetadataBuilder> metadata,
       String name,
-      List<Object> constantNamesAndOffsets,
+      List<EnumConstantInfo> enumConstantInfos,
       int charOffset,
       int charEndOffset) {
     MetadataCollector metadataCollector = loader.target.metadataCollector;
-    KernelEnumBuilder builder = new KernelEnumBuilder(
-        metadataCollector,
-        metadata,
-        name,
-        constantNamesAndOffsets,
-        this,
-        charOffset,
-        charEndOffset);
+    KernelEnumBuilder builder = new KernelEnumBuilder(metadataCollector,
+        metadata, name, enumConstantInfos, this, charOffset, charEndOffset);
     addBuilder(name, builder, charOffset);
     metadataCollector?.setDocumentationComment(
         builder.target, documentationComment);
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_mixin_application_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_mixin_application_builder.dart
index 95d36340d2b..5356ee70a68 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_mixin_application_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_mixin_application_builder.dart
@@ -27,7 +27,8 @@ class KernelMixinApplicationBuilder
 
   KernelMixinApplicationBuilder(
       KernelTypeBuilder supertype, List<KernelTypeBuilder> mixins)
-      : super(supertype, mixins);
+      : assert(mixins != null),
+        super(supertype, mixins);
 
   @override
   InterfaceType build(LibraryBuilder library) {
diff --git a/pkg/front_end/lib/src/fasta/source/diet_listener.dart b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
index 03ba93b16f4..bc03d282898 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
@@ -32,8 +32,8 @@ import '../deprecated_problems.dart'
 
 import '../fasta_codes.dart'
     show
-        LocatedMessage,
         Code,
+        LocatedMessage,
         Message,
         messageExpectedBlockToSkip,
         templateInternalProblemNotFound;
@@ -56,7 +56,8 @@ import '../type_inference/type_inference_engine.dart' show TypeInferenceEngine;
 
 import 'source_library_builder.dart' show SourceLibraryBuilder;
 
-import 'stack_listener.dart' show FixedNullableList, NullValue, StackListener;
+import 'stack_listener.dart'
+    show FixedNullableList, NullValue, ParserRecovery, StackListener;
 
 import '../quote.dart' show unescapeString;
 
@@ -78,6 +79,8 @@ class DietListener extends StackListener {
 
   ClassBuilder currentClass;
 
+  bool currentClassIsParserRecovery = false;
+
   /// For top-level declarations, this is the library scope. For class members,
   /// this is the instance scope of [currentClass].
   Scope memberScope;
@@ -95,12 +98,6 @@ class DietListener extends StackListener {
         stringExpectedAfterNative =
             library.loader.target.backendTarget.nativeExtensionExpectsString;
 
-  void discard(int n) {
-    for (int i = 0; i < n; i++) {
-      pop();
-    }
-  }
-
   @override
   void endMetadataStar(int count) {
     debugEvent("MetadataStar");
@@ -235,8 +232,10 @@ class DietListener extends StackListener {
     debugEvent("FunctionTypeAlias");
 
     if (equals == null) pop(); // endToken
-    String name = pop();
+    Object name = pop();
     Token metadata = pop();
+    checkEmpty(typedefKeyword.charOffset);
+    if (name is ParserRecovery) return;
 
     Declaration typedefBuilder = lookupBuilder(typedefKeyword, null, name);
     parseMetadata(typedefBuilder, metadata, typedefBuilder.target);
@@ -292,9 +291,11 @@ class DietListener extends StackListener {
   void endTopLevelMethod(Token beginToken, Token getOrSet, Token endToken) {
     debugEvent("TopLevelMethod");
     Token bodyToken = pop();
-    String name = pop();
+    Object name = pop();
     Token metadata = pop();
     checkEmpty(beginToken.charOffset);
+    if (name is ParserRecovery) return;
+
     final StackListener listener =
         createFunctionListener(lookupBuilder(beginToken, getOrSet, name));
     buildFunctionBody(listener, bodyToken, metadata, MemberKind.TopLevelMethod);
@@ -330,10 +331,16 @@ class DietListener extends StackListener {
   @override
   void handleQualified(Token period) {
     debugEvent("handleQualified");
-    String suffix = pop();
-    var prefix = pop();
-    assert(identical(suffix, period.next.lexeme));
-    push(new QualifiedName(prefix, period.next));
+    Object suffix = pop();
+    Object prefix = pop();
+    if (prefix is ParserRecovery) {
+      push(prefix);
+    } else if (suffix is ParserRecovery) {
+      push(suffix);
+    } else {
+      assert(identical(suffix, period.next.lexeme));
+      push(new QualifiedName(prefix, period.next));
+    }
   }
 
   @override
@@ -433,9 +440,11 @@ class DietListener extends StackListener {
   @override
   void endImport(Token importKeyword, Token semicolon) {
     debugEvent("Import");
-    pop(NullValue.Prefix);
+    Object name = pop(NullValue.Prefix);
 
     Token metadata = pop();
+    checkEmpty(importKeyword.charOffset);
+    if (name is ParserRecovery) return;
 
     // Native imports must be skipped because they aren't assigned corresponding
     // LibraryDependency nodes.
@@ -507,6 +516,7 @@ class DietListener extends StackListener {
     Object name = pop();
     Token metadata = pop();
     checkEmpty(beginToken.charOffset);
+    if (name is ParserRecovery || currentClassIsParserRecovery) return;
 
     ProcedureBuilder builder = lookupConstructor(beginToken, name);
     if (bodyToken == null || optional("=", bodyToken.endGroup.next)) {
@@ -555,6 +565,7 @@ class DietListener extends StackListener {
     Object name = pop();
     Token metadata = pop();
     checkEmpty(beginToken.charOffset);
+    if (name is ParserRecovery || currentClassIsParserRecovery) return;
     ProcedureBuilder builder;
     if (name is QualifiedName ||
         (getOrSet == null && name == currentClass.name)) {
@@ -633,8 +644,11 @@ class DietListener extends StackListener {
 
   void buildFields(int count, Token token, bool isTopLevel) {
     List<String> names = const FixedNullableList<String>().pop(stack, count);
-    Declaration declaration = lookupBuilder(token, null, names.first);
     Token metadata = pop();
+    checkEmpty(token.charOffset);
+    if (names == null || currentClassIsParserRecovery) return;
+
+    Declaration declaration = lookupBuilder(token, null, names.first);
     // TODO(paulberry): don't re-parse the field if we've already parsed it
     // for type inference.
     parseFields(
@@ -642,6 +656,7 @@ class DietListener extends StackListener {
         token,
         metadata,
         isTopLevel);
+    checkEmpty(token.charOffset);
   }
 
   @override
@@ -665,11 +680,15 @@ class DietListener extends StackListener {
 
   @override
   void beginClassOrMixinBody(Token token) {
-    debugEvent("beginClassBody");
-    String name = pop();
+    debugEvent("beginClassOrMixinBody");
+    Object name = pop();
     Token metadata = pop();
     assert(currentClass == null);
     assert(memberScope == library.scope);
+    if (name is ParserRecovery) {
+      currentClassIsParserRecovery = true;
+      return;
+    }
 
     Declaration classBuilder = lookupBuilder(token, null, name);
     parseMetadata(classBuilder, metadata, classBuilder.target);
@@ -682,6 +701,7 @@ class DietListener extends StackListener {
   void endClassOrMixinBody(int memberCount, Token beginToken, Token endToken) {
     debugEvent("ClassOrMixinBody");
     currentClass = null;
+    currentClassIsParserRecovery = false;
     memberScope = library.scope;
   }
 
@@ -702,8 +722,10 @@ class DietListener extends StackListener {
     debugEvent("Enum");
     List<Object> metadataAndValues =
         const FixedNullableList<Object>().pop(stack, count * 2);
-    String name = pop();
+    Object name = pop();
     Token metadata = pop();
+    checkEmpty(enumKeyword.charOffset);
+    if (name is ParserRecovery) return;
 
     ClassBuilder enumBuilder = lookupBuilder(enumKeyword, null, name);
     parseMetadata(enumBuilder, metadata, enumBuilder.target);
@@ -726,13 +748,20 @@ class DietListener extends StackListener {
       Token equals, Token implementsKeyword, Token endToken) {
     debugEvent("NamedMixinApplication");
 
-    String name = pop();
+    Object name = pop();
     Token metadata = pop();
-
-    Declaration classBuilder = lookupBuilder(classKeyword, null, name);
-    parseMetadata(classBuilder, metadata, classBuilder.target);
-
     checkEmpty(beginToken.charOffset);
+    if (name is ParserRecovery) return;
+
+    Declaration classBuilder = library.scopeBuilder[name];
+    if (classBuilder != null) {
+      // TODO(ahe): We shouldn't have to check for null here. The problem is
+      // that we don't create a named mixin application if the mixins or
+      // supertype are missing. Could we create a class instead? The nested
+      // declarations wouldn't match up.
+      parseMetadata(classBuilder, metadata, classBuilder.target);
+      checkEmpty(beginToken.charOffset);
+    }
   }
 
   AsyncMarker getAsyncMarker(StackListener listener) => listener.pop();
diff --git a/pkg/front_end/lib/src/fasta/source/outline_builder.dart b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
index c7674c6bccb..73bb7c4a465 100644
--- a/pkg/front_end/lib/src/fasta/source/outline_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
@@ -87,7 +87,8 @@ import '../scanner.dart' show Token;
 
 import 'source_library_builder.dart' show FieldInfo, SourceLibraryBuilder;
 
-import 'stack_listener.dart' show FixedNullableList, NullValue, StackListener;
+import 'stack_listener.dart'
+    show FixedNullableList, NullValue, ParserRecovery, StackListener;
 
 enum MethodBody {
   Abstract,
@@ -120,12 +121,18 @@ class OutlineBuilder extends StackListener {
 
   List<String> popIdentifierList(int count) {
     if (count == 0) return null;
-    List<String> list = new List<String>.filled(count, null, growable: true);
+    List<String> list = new List<String>(count);
+    bool isParserRecovery = false;
     for (int i = count - 1; i >= 0; i--) {
       popCharOffset();
-      list[i] = pop();
+      Object identifier = pop();
+      if (identifier is ParserRecovery) {
+        isParserRecovery = true;
+      } else {
+        list[i] = identifier;
+      }
     }
-    return list;
+    return isParserRecovery ? null : list;
   }
 
   @override
@@ -143,12 +150,16 @@ class OutlineBuilder extends StackListener {
     } else {
       int charOffset = pop();
       Object typeName = pop();
-      push(new MetadataBuilder.fromConstructor(
-          library.addConstructorReference(
-              typeName, typeArguments, postfix, charOffset),
-          arguments,
-          library,
-          beginToken.charOffset));
+      if (typeName is ParserRecovery) {
+        push(typeName);
+      } else {
+        push(new MetadataBuilder.fromConstructor(
+            library.addConstructorReference(
+                typeName, typeArguments, postfix, charOffset),
+            arguments,
+            library,
+            beginToken.charOffset));
+      }
     }
   }
 
@@ -169,15 +180,23 @@ class OutlineBuilder extends StackListener {
   @override
   void endHide(Token hideKeyword) {
     debugEvent("Hide");
-    List<String> names = pop();
-    push(new Combinator.hide(names, hideKeyword.charOffset, library.fileUri));
+    Object names = pop();
+    if (names is ParserRecovery) {
+      push(names);
+    } else {
+      push(new Combinator.hide(names, hideKeyword.charOffset, library.fileUri));
+    }
   }
 
   @override
   void endShow(Token showKeyword) {
     debugEvent("Show");
-    List<String> names = pop();
-    push(new Combinator.show(names, showKeyword.charOffset, library.fileUri));
+    Object names = pop();
+    if (names is ParserRecovery) {
+      push(names);
+    } else {
+      push(new Combinator.show(names, showKeyword.charOffset, library.fileUri));
+    }
   }
 
   @override
@@ -218,11 +237,13 @@ class OutlineBuilder extends StackListener {
     List<Combinator> combinators = pop();
     bool isDeferred = pop();
     int prefixOffset = pop();
-    String prefix = pop(NullValue.Prefix);
+    Object prefix = pop(NullValue.Prefix);
     List<Configuration> configurations = pop();
     int uriOffset = popCharOffset();
     String uri = pop(); // For a conditional import, this is the default URI.
     List<MetadataBuilder> metadata = pop();
+    checkEmpty(importKeyword.charOffset);
+    if (prefix is ParserRecovery) return;
     library.addImport(
         metadata,
         uri,
@@ -234,7 +255,6 @@ class OutlineBuilder extends StackListener {
         prefixOffset,
         uriOffset,
         importIndex++);
-    checkEmpty(importKeyword.charOffset);
   }
 
   @override
@@ -251,14 +271,23 @@ class OutlineBuilder extends StackListener {
     String uri = pop();
     if (equalSign != null) popCharOffset();
     String condition = popIfNotNull(equalSign) ?? "true";
-    String dottedName = pop();
-    push(new Configuration(charOffset, dottedName, condition, uri));
+    Object dottedName = pop();
+    if (dottedName is ParserRecovery) {
+      push(dottedName);
+    } else {
+      push(new Configuration(charOffset, dottedName, condition, uri));
+    }
   }
 
   @override
   void handleDottedName(int count, Token firstIdentifier) {
     debugEvent("DottedName");
-    push(popIdentifierList(count).join('.'));
+    List<String> names = popIdentifierList(count);
+    if (names == null) {
+      push(new ParserRecovery(firstIdentifier.charOffset));
+    } else {
+      push(names.join('.'));
+    }
   }
 
   @override
@@ -300,8 +329,12 @@ class OutlineBuilder extends StackListener {
     if (context == IdentifierContext.enumValueDeclaration) {
       debugEvent("handleIdentifier");
       List<MetadataBuilder> metadata = pop();
-      push(new EnumConstantInfo(metadata, token.lexeme, token.charOffset,
-          getDocumentationComment(token)));
+      if (token.isSynthetic) {
+        push(new ParserRecovery(token.charOffset));
+      } else {
+        push(new EnumConstantInfo(metadata, token.lexeme, token.charOffset,
+            getDocumentationComment(token)));
+      }
     } else {
       super.handleIdentifier(token, context);
       push(token.charOffset);
@@ -347,7 +380,12 @@ class OutlineBuilder extends StackListener {
     if (hasName) {
       // Pop the native clause which in this case is a StringLiteral.
       pop(); // Char offset.
-      nativeMethodName = pop(); // String.
+      Object name = pop();
+      if (name is ParserRecovery) {
+        nativeMethodName = '';
+      } else {
+        nativeMethodName = name; // String.
+      }
     } else {
       nativeMethodName = '';
     }
@@ -369,19 +407,26 @@ class OutlineBuilder extends StackListener {
   @override
   void handleIdentifierList(int count) {
     debugEvent("endIdentifierList");
-    push(popIdentifierList(count) ?? NullValue.IdentifierList);
+    push(popIdentifierList(count) ??
+        (count == 0 ? NullValue.IdentifierList : new ParserRecovery(-1)));
   }
 
   @override
   void handleQualified(Token period) {
     debugEvent("handleQualified");
     int suffixOffset = pop();
-    String suffix = pop();
-    assert(identical(suffix, period.next.lexeme));
-    assert(suffixOffset == period.next.charOffset);
+    Object suffix = pop();
     int offset = pop();
-    var prefix = pop();
-    push(new QualifiedName(prefix, period.next));
+    Object prefix = pop();
+    if (prefix is ParserRecovery) {
+      push(prefix);
+    } else if (suffix is ParserRecovery) {
+      push(suffix);
+    } else {
+      assert(identical(suffix, period.next.lexeme));
+      assert(suffixOffset == period.next.charOffset);
+      push(new QualifiedName(prefix, period.next));
+    }
     push(offset);
   }
 
@@ -393,7 +438,9 @@ class OutlineBuilder extends StackListener {
     Object name = pop();
     List<MetadataBuilder> metadata = pop();
     library.documentationComment = documentationComment;
-    library.name = flattenName(name, offsetForToken(libraryKeyword), uri);
+    if (name is! ParserRecovery) {
+      library.name = flattenName(name, offsetForToken(libraryKeyword), uri);
+    }
     library.metadata = metadata;
   }
 
@@ -474,7 +521,7 @@ class OutlineBuilder extends StackListener {
     debugEvent("handleMixinOn");
     push(const FixedNullableList<KernelNamedTypeBuilder>()
             .pop(stack, typeCount) ??
-        NullValue.TypeList);
+        new ParserRecovery(offsetForToken(onKeyword)));
   }
 
   @override
@@ -483,15 +530,20 @@ class OutlineBuilder extends StackListener {
     String documentationComment = getDocumentationComment(beginToken);
     List<TypeBuilder> interfaces = pop(NullValue.TypeBuilderList);
     int supertypeOffset = pop();
-    TypeBuilder supertype = pop();
+    TypeBuilder supertype = nullIfParserRecovery(pop());
     int modifiers = pop();
     List<TypeVariableBuilder> typeVariables = pop();
     int charOffset = pop();
-    String name = pop();
+    Object name = pop();
     if (typeVariables != null && supertype is MixinApplicationBuilder) {
       supertype.typeVariables = typeVariables;
     }
     List<MetadataBuilder> metadata = pop();
+    checkEmpty(beginToken.charOffset);
+    if (name is ParserRecovery) {
+      library.endNestedDeclaration("<syntax-error>");
+      return;
+    }
 
     final int startCharOffset =
         metadata == null ? beginToken.charOffset : metadata.first.charOffset;
@@ -508,7 +560,10 @@ class OutlineBuilder extends StackListener {
         charOffset,
         endToken.charOffset,
         supertypeOffset);
-    checkEmpty(beginToken.charOffset);
+  }
+
+  Object nullIfParserRecovery(Object node) {
+    return node is ParserRecovery ? null : node;
   }
 
   @override
@@ -516,14 +571,18 @@ class OutlineBuilder extends StackListener {
     debugEvent("endMixinDeclaration");
     String documentationComment = getDocumentationComment(mixinToken);
     List<TypeBuilder> interfaces = pop(NullValue.TypeBuilderList);
-    List<KernelTypeBuilder> supertypeConstraints = pop();
+    List<KernelTypeBuilder> supertypeConstraints = nullIfParserRecovery(pop());
     List<TypeVariableBuilder> typeVariables = pop(NullValue.TypeVariables);
     int nameOffset = pop();
-    String name = pop();
+    Object name = pop();
     List<MetadataBuilder> metadata = pop(NullValue.Metadata);
+    checkEmpty(mixinToken.charOffset);
+    if (name is ParserRecovery) {
+      library.endNestedDeclaration("<syntax-error>");
+      return;
+    }
     int startOffset =
         metadata == null ? mixinToken.charOffset : metadata.first.charOffset;
-
     TypeBuilder supertype;
     if (supertypeConstraints != null && supertypeConstraints.isNotEmpty) {
       if (supertypeConstraints.length == 1) {
@@ -545,7 +604,6 @@ class OutlineBuilder extends StackListener {
         nameOffset,
         endToken.charOffset,
         -1);
-    checkEmpty(mixinToken.charOffset);
   }
 
   ProcedureKind computeProcedureKind(Token token) {
@@ -570,7 +628,7 @@ class OutlineBuilder extends StackListener {
     int formalsOffset = pop();
     List<TypeVariableBuilder> typeVariables = pop();
     int charOffset = pop();
-    String name = pop();
+    Object name = pop();
     TypeBuilder returnType = pop();
     bool isAbstract = kind == MethodBody.Abstract;
     if (getOrSet != null && optional("set", getOrSet)) {
@@ -585,13 +643,14 @@ class OutlineBuilder extends StackListener {
       modifiers |= abstractMask;
     }
     List<MetadataBuilder> metadata = pop();
-    String documentationComment = getDocumentationComment(beginToken);
     checkEmpty(beginToken.charOffset);
     library
         .endNestedDeclaration("#method")
         .resolveTypes(typeVariables, library);
+    if (name is ParserRecovery) return;
     final int startCharOffset =
         metadata == null ? beginToken.charOffset : metadata.first.charOffset;
+    String documentationComment = getDocumentationComment(beginToken);
     library.addProcedure(
         documentationComment,
         metadata,
@@ -655,8 +714,9 @@ class OutlineBuilder extends StackListener {
       Token varFinalOrConst, Token getOrSet, Token name) {
     inConstructor =
         name?.lexeme == library.currentDeclaration.name && getOrSet == null;
-    List<Modifier> modifiers = <Modifier>[];
+    List<Modifier> modifiers;
     if (externalToken != null) {
+      modifiers ??= <Modifier>[];
       modifiers.add(External);
     }
     if (staticToken != null) {
@@ -664,24 +724,29 @@ class OutlineBuilder extends StackListener {
         handleRecoverableError(
             messageStaticConstructor, staticToken, staticToken);
       } else {
+        modifiers ??= <Modifier>[];
         modifiers.add(Static);
       }
     }
     if (covariantToken != null) {
+      modifiers ??= <Modifier>[];
       modifiers.add(Covariant);
     }
     if (varFinalOrConst != null) {
       String lexeme = varFinalOrConst.lexeme;
       if (identical('var', lexeme)) {
+        modifiers ??= <Modifier>[];
         modifiers.add(Var);
       } else if (identical('final', lexeme)) {
+        modifiers ??= <Modifier>[];
         modifiers.add(Final);
       } else {
+        modifiers ??= <Modifier>[];
         modifiers.add(Const);
       }
     }
     push(varFinalOrConst?.charOffset ?? -1);
-    push(modifiers);
+    push(modifiers ?? NullValue.Modifiers);
     library.beginNestedDeclaration("#method", hasMembers: false);
   }
 
@@ -698,7 +763,7 @@ class OutlineBuilder extends StackListener {
     int formalsOffset = pop();
     List<TypeVariableBuilder> typeVariables = pop();
     int charOffset = pop();
-    dynamic nameOrOperator = pop();
+    Object nameOrOperator = pop();
     if (Operator.subtract == nameOrOperator && formals == null) {
       nameOrOperator = Operator.unaryMinus;
     }
@@ -767,6 +832,11 @@ class OutlineBuilder extends StackListener {
     library
         .endNestedDeclaration("#method")
         .resolveTypes(typeVariables, library);
+    if (name is ParserRecovery) {
+      nativeMethodName = null;
+      inConstructor = false;
+      return;
+    }
     String constructorName =
         kind == ProcedureKind.Getter || kind == ProcedureKind.Setter
             ? null
@@ -828,10 +898,16 @@ class OutlineBuilder extends StackListener {
   @override
   void handleNamedMixinApplicationWithClause(Token withKeyword) {
     debugEvent("NamedMixinApplicationWithClause");
-    List<TypeBuilder> mixins = pop();
-    TypeBuilder supertype = pop();
-    push(
-        library.addMixinApplication(supertype, mixins, withKeyword.charOffset));
+    Object mixins = pop();
+    Object supertype = pop();
+    if (mixins is ParserRecovery) {
+      push(mixins);
+    } else if (supertype is ParserRecovery) {
+      push(supertype);
+    } else {
+      push(library.addMixinApplication(
+          supertype, mixins, withKeyword.charOffset));
+    }
   }
 
   @override
@@ -840,15 +916,19 @@ class OutlineBuilder extends StackListener {
     debugEvent("endNamedMixinApplication");
     String documentationComment = getDocumentationComment(beginToken);
     List<TypeBuilder> interfaces = popIfNotNull(implementsKeyword);
-    TypeBuilder mixinApplication = pop();
+    Object mixinApplication = pop();
     int modifiers = pop();
     List<TypeVariableBuilder> typeVariables = pop();
     int charOffset = pop();
-    String name = pop();
+    Object name = pop();
     List<MetadataBuilder> metadata = pop();
+    checkEmpty(beginToken.charOffset);
+    if (name is ParserRecovery || mixinApplication is ParserRecovery) {
+      library.endNestedDeclaration("<syntax-error>");
+      return;
+    }
     library.addNamedMixinApplication(documentationComment, metadata, name,
         typeVariables, modifiers, mixinApplication, interfaces, charOffset);
-    checkEmpty(beginToken.charOffset);
   }
 
   @override
@@ -869,14 +949,18 @@ class OutlineBuilder extends StackListener {
     List<TypeBuilder> arguments = pop();
     int charOffset = pop();
     Object name = pop();
-    push(library.addNamedType(name, arguments, charOffset));
+    if (name is ParserRecovery) {
+      push(name);
+    } else {
+      push(library.addNamedType(name, arguments, charOffset));
+    }
   }
 
   @override
   void endTypeList(int count) {
     debugEvent("TypeList");
     push(const FixedNullableList<KernelNamedTypeBuilder>().pop(stack, count) ??
-        NullValue.TypeList);
+        new ParserRecovery(-1));
   }
 
   @override
@@ -903,12 +987,16 @@ class OutlineBuilder extends StackListener {
       Token nameToken, FormalParameterKind kind, MemberKind memberKind) {
     debugEvent("FormalParameter");
     int charOffset = pop();
-    String name = pop();
-    TypeBuilder type = pop();
+    Object name = pop();
+    TypeBuilder type = nullIfParserRecovery(pop());
     int modifiers = pop();
     List<MetadataBuilder> metadata = pop();
-    push(library.addFormalParameter(
-        metadata, modifiers, type, name, thisKeyword != null, charOffset));
+    if (name is ParserRecovery) {
+      push(name);
+    } else {
+      push(library.addFormalParameter(
+          metadata, modifiers, type, name, thisKeyword != null, charOffset));
+    }
   }
 
   @override
@@ -946,12 +1034,15 @@ class OutlineBuilder extends StackListener {
     // case, however, then [beginOptionalFormalParameters] wouldn't always be
     // matched by this method.
     List<FormalParameterBuilder> parameters =
-        const FixedNullableList<FormalParameterBuilder>().pop(stack, count) ??
-            new List<FormalParameterBuilder>(0);
-    for (FormalParameterBuilder parameter in parameters) {
-      parameter.kind = kind;
+        const FixedNullableList<FormalParameterBuilder>().pop(stack, count);
+    if (parameters == null) {
+      push(new ParserRecovery(offsetForToken(beginToken)));
+    } else {
+      for (FormalParameterBuilder parameter in parameters) {
+        parameter.kind = kind;
+      }
+      push(parameters);
     }
-    push(parameters);
   }
 
   @override
@@ -963,7 +1054,7 @@ class OutlineBuilder extends StackListener {
       Object last = pop();
       if (last is List<FormalParameterBuilder>) {
         formals = last;
-      } else {
+      } else if (last is! ParserRecovery) {
         assert(last != null);
         formals = new List<FormalParameterBuilder>(1);
         formals[0] = last;
@@ -971,7 +1062,9 @@ class OutlineBuilder extends StackListener {
     } else if (count > 1) {
       Object last = pop();
       count--;
-      if (last is List<FormalParameterBuilder>) {
+      if (last is ParserRecovery) {
+        discard(count);
+      } else if (last is List<FormalParameterBuilder>) {
         formals = const FixedNullableList<FormalParameterBuilder>()
             .popPadded(stack, count, last.length);
         if (formals != null) {
@@ -979,13 +1072,14 @@ class OutlineBuilder extends StackListener {
         }
       } else {
         formals = const FixedNullableList<FormalParameterBuilder>()
-            .popPadded(stack, count, last == null ? 0 : 1);
-        if (formals != null && last != null) {
+            .popPadded(stack, count, 1);
+        if (formals != null) {
           formals[count] = last;
         }
       }
     }
     if (formals != null) {
+      assert(formals.isNotEmpty);
       if (formals.length == 2) {
         // The name may be null for generalized function types.
         if (formals[0].name != null && formals[0].name == formals[1].name) {
@@ -1046,11 +1140,12 @@ class OutlineBuilder extends StackListener {
     List<EnumConstantInfo> enumConstantInfos =
         const FixedNullableList<EnumConstantInfo>().pop(stack, count);
     int charOffset = pop();
-    String name = pop();
+    Object name = pop();
     List<MetadataBuilder> metadata = pop();
+    checkEmpty(enumKeyword.charOffset);
+    if (name is ParserRecovery) return;
     library.addEnum(documentationComment, metadata, name, enumConstantInfos,
         charOffset, leftBrace?.endGroup?.charOffset);
-    checkEmpty(enumKeyword.charOffset);
   }
 
   @override
@@ -1098,7 +1193,7 @@ class OutlineBuilder extends StackListener {
     debugEvent("endFunctionTypeAlias");
     String documentationComment = getDocumentationComment(typedefKeyword);
     List<TypeVariableBuilder> typeVariables;
-    String name;
+    Object name;
     int charOffset;
     FunctionTypeBuilder functionType;
     if (equals == null) {
@@ -1110,6 +1205,11 @@ class OutlineBuilder extends StackListener {
       TypeBuilder returnType = pop();
       // Create a nested declaration that is ended below by
       // `library.addFunctionType`.
+      if (name is ParserRecovery) {
+        pop(); // Metadata.
+        library.endNestedDeclaration("<syntax-error>");
+        return;
+      }
       library.beginNestedDeclaration("#function_type", hasMembers: false);
       functionType =
           library.addFunctionType(returnType, null, formals, charOffset);
@@ -1118,6 +1218,11 @@ class OutlineBuilder extends StackListener {
       typeVariables = pop();
       charOffset = pop();
       name = pop();
+      if (name is ParserRecovery) {
+        pop(); // Metadata.
+        library.endNestedDeclaration("<syntax-error>");
+        return;
+      }
       if (type is FunctionTypeBuilder) {
         // TODO(ahe): We need to start a nested declaration when parsing the
         // formals and return type so we can correctly bind
@@ -1131,9 +1236,9 @@ class OutlineBuilder extends StackListener {
       }
     }
     List<MetadataBuilder> metadata = pop();
+    checkEmpty(typedefKeyword.charOffset);
     library.addFunctionTypeAlias(documentationComment, metadata, name,
         typeVariables, functionType, charOffset);
-    checkEmpty(typedefKeyword.charOffset);
   }
 
   @override
@@ -1141,15 +1246,16 @@ class OutlineBuilder extends StackListener {
       Token varFinalOrConst, int count, Token beginToken, Token endToken) {
     debugEvent("endTopLevelFields");
     List<FieldInfo> fieldInfos = popFieldInfos(count);
-    TypeBuilder type = pop();
+    TypeBuilder type = nullIfParserRecovery(pop());
     int modifiers = (staticToken != null ? staticMask : 0) |
         (covariantToken != null ? covariantMask : 0) |
         Modifier.validateVarFinalOrConst(varFinalOrConst?.lexeme);
     List<MetadataBuilder> metadata = pop();
+    checkEmpty(beginToken.charOffset);
+    if (fieldInfos == null) return;
     String documentationComment = getDocumentationComment(beginToken);
     library.addFields(
         documentationComment, metadata, modifiers, type, fieldInfos);
-    checkEmpty(beginToken.charOffset);
   }
 
   @override
@@ -1169,6 +1275,7 @@ class OutlineBuilder extends StackListener {
       modifiers &= ~constMask;
     }
     List<MetadataBuilder> metadata = pop();
+    if (fieldInfos == null) return;
     String documentationComment = getDocumentationComment(beginToken);
     library.addFields(
         documentationComment, metadata, modifiers, type, fieldInfos);
@@ -1177,44 +1284,54 @@ class OutlineBuilder extends StackListener {
   List<FieldInfo> popFieldInfos(int count) {
     if (count == 0) return null;
     List<FieldInfo> fieldInfos = new List<FieldInfo>(count);
+    bool isParserRecovery = false;
     for (int i = count - 1; i != -1; i--) {
       Token beforeLast = pop();
       Token initializerTokenForInference = pop();
       int charOffset = pop();
       Object name = pop(NullValue.Identifier);
-      fieldInfos[i] = new FieldInfo(
-          name, charOffset, initializerTokenForInference, beforeLast);
+      if (name is ParserRecovery) {
+        isParserRecovery = true;
+      } else {
+        fieldInfos[i] = new FieldInfo(
+            name, charOffset, initializerTokenForInference, beforeLast);
+      }
     }
-    return fieldInfos;
+    return isParserRecovery ? null : fieldInfos;
   }
 
   @override
   void beginTypeVariable(Token token) {
     debugEvent("beginTypeVariable");
     int charOffset = pop();
-    String name = pop();
+    Object name = pop();
     // TODO(paulberry): type variable metadata should not be ignored.  See
     // dartbug.com/28981.
     /* List<MetadataBuilder> metadata = */ pop();
-
-    push(library.addTypeVariable(name, null, charOffset));
+    if (name is ParserRecovery) {
+      push(name);
+    } else {
+      push(library.addTypeVariable(name, null, charOffset));
+    }
   }
 
   @override
   void handleTypeVariablesDefined(Token token, int count) {
     debugEvent("TypeVariablesDefined");
     assert(count > 0);
-    push(const FixedNullableList<TypeVariableBuilder>().pop(stack, count));
+    push(const FixedNullableList<TypeVariableBuilder>().pop(stack, count) ??
+        NullValue.TypeVariables);
   }
 
   @override
   void endTypeVariable(Token token, int index, Token extendsOrSuper) {
     debugEvent("endTypeVariable");
-    TypeBuilder bound = pop();
+    TypeBuilder bound = nullIfParserRecovery(pop());
     // Peek to leave type parameters on top of stack.
-    List typeParameters = peek();
-
-    typeParameters[index].bound = bound;
+    List<TypeVariableBuilder> typeParameters = peek();
+    if (typeParameters != null) {
+      typeParameters[index].bound = bound;
+    }
   }
 
   @override
@@ -1222,48 +1339,50 @@ class OutlineBuilder extends StackListener {
     debugEvent("endTypeVariables");
 
     // Peek to leave type parameters on top of stack.
-    List typeParameters = peek();
+    List<TypeVariableBuilder> typeParameters = peek();
 
     Map<String, TypeVariableBuilder> typeVariablesByName;
-    for (TypeVariableBuilder builder in typeParameters) {
-      if (builder.bound != null) {
-        if (typeVariablesByName == null) {
-          typeVariablesByName = new Map<String, TypeVariableBuilder>();
-          for (TypeVariableBuilder builder in typeParameters) {
-            typeVariablesByName[builder.name] = builder;
+    if (typeParameters != null) {
+      for (TypeVariableBuilder builder in typeParameters) {
+        if (builder.bound != null) {
+          if (typeVariablesByName == null) {
+            typeVariablesByName = new Map<String, TypeVariableBuilder>();
+            for (TypeVariableBuilder builder in typeParameters) {
+              typeVariablesByName[builder.name] = builder;
+            }
           }
-        }
 
-        // Find cycle: If there's no cycle we can at most step through all
-        // `typeParameters` (at which point the last builders bound will be
-        // null).
-        // If there is a cycle with `builder` 'inside' the steps to get back to
-        // it will also be bound by `typeParameters.length`.
-        // If there is a cycle without `builder` 'inside' we will just ignore it
-        // for now. It will be reported when processing one of the `builder`s
-        // that is in fact `inside` the cycle. This matches the cyclic class
-        // hierarchy error.
-        TypeVariableBuilder bound = builder;
-        for (int steps = 0;
-            bound.bound != null && steps < typeParameters.length;
-            ++steps) {
-          bound = typeVariablesByName[bound.bound.name];
-          if (bound == null || bound == builder) break;
-        }
-        if (bound == builder && bound.bound != null) {
-          // Write out cycle.
-          List<String> via = new List<String>();
-          bound = typeVariablesByName[builder.bound.name];
-          while (bound != builder) {
-            via.add(bound.name);
+          // Find cycle: If there's no cycle we can at most step through all
+          // `typeParameters` (at which point the last builders bound will be
+          // null).
+          // If there is a cycle with `builder` 'inside' the steps to get back to
+          // it will also be bound by `typeParameters.length`.
+          // If there is a cycle without `builder` 'inside' we will just ignore it
+          // for now. It will be reported when processing one of the `builder`s
+          // that is in fact `inside` the cycle. This matches the cyclic class
+          // hierarchy error.
+          TypeVariableBuilder bound = builder;
+          for (int steps = 0;
+              bound.bound != null && steps < typeParameters.length;
+              ++steps) {
             bound = typeVariablesByName[bound.bound.name];
+            if (bound == null || bound == builder) break;
+          }
+          if (bound == builder && bound.bound != null) {
+            // Write out cycle.
+            List<String> via = new List<String>();
+            bound = typeVariablesByName[builder.bound.name];
+            while (bound != builder) {
+              via.add(bound.name);
+              bound = typeVariablesByName[bound.bound.name];
+            }
+            String involvedString = via.join("', '");
+            addProblem(
+                templateCycleInTypeVariables.withArguments(
+                    builder.name, involvedString),
+                builder.charOffset,
+                builder.name.length);
           }
-          String involvedString = via.join("', '");
-          addProblem(
-              templateCycleInTypeVariables.withArguments(
-                  builder.name, involvedString),
-              builder.charOffset,
-              builder.name.length);
         }
       }
     }
@@ -1299,8 +1418,12 @@ class OutlineBuilder extends StackListener {
     List<TypeBuilder> typeArguments = pop();
     int charOffset = pop();
     Object name = pop();
-    push(library.addConstructorReference(
-        name, typeArguments, suffix, charOffset));
+    if (name is ParserRecovery) {
+      push(name);
+    } else {
+      push(library.addConstructorReference(
+          name, typeArguments, suffix, charOffset));
+    }
   }
 
   @override
@@ -1319,7 +1442,7 @@ class OutlineBuilder extends StackListener {
     MethodBody kind = pop();
     ConstructorReferenceBuilder redirectionTarget;
     if (kind == MethodBody.RedirectingFactoryBody) {
-      redirectionTarget = pop();
+      redirectionTarget = nullIfParserRecovery(pop());
     }
     List<FormalParameterBuilder> formals = pop();
     int formalsOffset = pop();
@@ -1328,6 +1451,10 @@ class OutlineBuilder extends StackListener {
     Object name = pop();
     int modifiers = pop();
     List<MetadataBuilder> metadata = pop();
+    if (name is ParserRecovery) {
+      library.endNestedDeclaration("<syntax-error>");
+      return;
+    }
     String documentationComment = getDocumentationComment(beginToken);
     library.addFactoryMethod(
         documentationComment,
@@ -1405,12 +1532,15 @@ class OutlineBuilder extends StackListener {
   void handleClassWithClause(Token withKeyword) {
     debugEvent("ClassWithClause");
 
-    List<TypeBuilder> mixins = pop();
+    Object mixins = pop();
     int extendsOffset = pop();
-    TypeBuilder supertype = pop();
-
-    push(
-        library.addMixinApplication(supertype, mixins, withKeyword.charOffset));
+    Object supertype = pop();
+    if (supertype is ParserRecovery || mixins is ParserRecovery) {
+      push(new ParserRecovery(withKeyword.charOffset));
+    } else {
+      push(library.addMixinApplication(
+          supertype, mixins, withKeyword.charOffset));
+    }
     push(extendsOffset);
   }
 
diff --git a/pkg/front_end/lib/src/fasta/source/scope_listener.dart b/pkg/front_end/lib/src/fasta/source/scope_listener.dart
index 02cc108b63d..c49ce0878aa 100644
--- a/pkg/front_end/lib/src/fasta/source/scope_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/scope_listener.dart
@@ -10,7 +10,8 @@ import '../scope.dart' show Scope;
 
 import 'stack_listener.dart' show NullValue, StackListener;
 
-export 'stack_listener.dart' show FixedNullableList, GrowableList, NullValue;
+export 'stack_listener.dart'
+    show FixedNullableList, GrowableList, NullValue, ParserRecovery;
 
 enum JumpTargetKind {
   Break,
diff --git a/pkg/front_end/lib/src/fasta/source/source_class_builder.dart b/pkg/front_end/lib/src/fasta/source/source_class_builder.dart
index 97430ab0fe6..e04fdd6043d 100644
--- a/pkg/front_end/lib/src/fasta/source/source_class_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_class_builder.dart
@@ -116,8 +116,13 @@ class SourceClassBuilder extends KernelClassBuilder {
     void buildBuilders(String name, Declaration declaration) {
       do {
         if (declaration.parent != this) {
-          unexpected(
-              "$fileUri", "${declaration.parent.fileUri}", charOffset, fileUri);
+          if (fileUri != declaration.parent.fileUri) {
+            unexpected("$fileUri", "${declaration.parent.fileUri}", charOffset,
+                fileUri);
+          } else {
+            unexpected(fullNameForErrors, declaration.parent?.fullNameForErrors,
+                charOffset, fileUri);
+          }
         } else if (declaration is KernelFieldBuilder) {
           // TODO(ahe): It would be nice to have a common interface for the
           // build method to avoid duplicating these two cases.
diff --git a/pkg/front_end/lib/src/fasta/source/source_library_builder.dart b/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
index 10a1746999d..cd865402c8e 100644
--- a/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_library_builder.dart
@@ -180,7 +180,8 @@ abstract class SourceLibraryBuilder<T extends TypeBuilder, R>
     assert(
         (name?.startsWith(currentDeclaration.name) ??
                 (name == currentDeclaration.name)) ||
-            currentDeclaration.name == "operator",
+            currentDeclaration.name == "operator" ||
+            identical(name, "<syntax-error>"),
         "${name} != ${currentDeclaration.name}");
     DeclarationBuilder<T> previous = currentDeclaration;
     currentDeclaration = currentDeclaration.parent;
@@ -477,6 +478,9 @@ abstract class SourceLibraryBuilder<T extends TypeBuilder, R>
     // TODO(ahe): Set the parent correctly here. Could then change the
     // implementation of MemberBuilder.isTopLevel to test explicitly for a
     // LibraryBuilder.
+    if (name == null) {
+      unhandled("null", "name", charOffset, fileUri);
+    }
     if (currentDeclaration == libraryDeclaration) {
       if (declaration is MemberBuilder) {
         declaration.parent = this;
diff --git a/pkg/front_end/lib/src/fasta/source/stack_listener.dart b/pkg/front_end/lib/src/fasta/source/stack_listener.dart
index b840a61692d..34dc2c8e0aa 100644
--- a/pkg/front_end/lib/src/fasta/source/stack_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/stack_listener.dart
@@ -54,6 +54,7 @@ enum NullValue {
   Identifier,
   IdentifierList,
   Initializers,
+  Labels,
   Metadata,
   Modifiers,
   ParameterDefaultValue,
@@ -76,6 +77,12 @@ abstract class StackListener extends Listener {
   @override
   Uri get uri;
 
+  void discard(int n) {
+    for (int i = 0; i < n; i++) {
+      pop();
+    }
+  }
+
   // TODO(ahe): This doesn't belong here. Only implemented by body_builder.dart
   // and ast_builder.dart.
   void finishFunction(covariant List<Object> annotations, covariant formals,
@@ -150,7 +157,14 @@ abstract class StackListener extends Listener {
   @override
   void handleIdentifier(Token token, IdentifierContext context) {
     debugEvent("handleIdentifier");
-    push(token.lexeme);
+    if (!token.isSynthetic) {
+      push(token.lexeme);
+    } else {
+      // This comes from a synthetic token which is inserted by the parser in
+      // an attempt to recover.  This almost always means that the parser has
+      // gotten very confused and we need to ignore the results.
+      push(new ParserRecovery(token.charOffset));
+    }
   }
 
   @override
@@ -410,6 +424,7 @@ class Stack {
     final List<Object> array = this.array;
     final int length = arrayLength;
     final int startIndex = length - count;
+    bool isParserRecovery = false;
     for (int i = 0; i < count; i++) {
       int arrayIndex = startIndex + i;
       final Object value = array[arrayIndex];
@@ -417,13 +432,18 @@ class Stack {
       if (value is NullValue && nullValue == null ||
           identical(value, nullValue)) {
         list[i] = null;
+      } else if (value is ParserRecovery) {
+        isParserRecovery = true;
       } else {
+        if (value is NullValue) {
+          print(value);
+        }
         list[i] = value;
       }
     }
     arrayLength -= count;
 
-    return list;
+    return isParserRecovery ? null : list;
   }
 
   List<Object> get values {
@@ -469,3 +489,10 @@ class GrowableList<T> {
         count, new List<T>.filled(count, null, growable: true), nullValue);
   }
 }
+
+class ParserRecovery {
+  final int charOffset;
+  ParserRecovery(this.charOffset);
+
+  String toString() => "ParserRecovery(charOffset)";
+}