diff --git a/build/dart/dart_action.gni b/build/dart/dart_action.gni
index c357aad..334a09a 100644
--- a/build/dart/dart_action.gni
+++ b/build/dart/dart_action.gni
@@ -51,6 +51,10 @@
       testonly = invoker.testonly
     }
 
+    if (defined(invoker.pool)) {
+      pool = invoker.pool
+    }
+
     script = "$_dart_root/build/gn_run_binary.py"
 
     if (defined(invoker.inputs)) {
@@ -109,6 +113,7 @@
                              "depfile",
                              "deps",
                              "outputs",
+                             "pool",
                              "testonly",
                              "visibility",
                            ])
@@ -256,6 +261,7 @@
                              "deps",
                              "inputs",
                              "outputs",
+                             "pool",
                              "tool",
                              "testonly",
                              "visibility",
@@ -321,6 +327,7 @@
                                "inputs",
                                "outputs",
                                "packages",
+                               "pool",
                                "script",
                                "testonly",
                                "tool",
@@ -380,6 +387,7 @@
                                "inputs",
                                "outputs",
                                "packages",
+                               "pool",
                                "testonly",
                                "tool",
                                "visibility",
diff --git a/pkg/front_end/lib/src/fasta/builder/fixed_type_builder.dart b/pkg/front_end/lib/src/fasta/builder/fixed_type_builder.dart
index d9894e4..14f3d3d 100644
--- a/pkg/front_end/lib/src/fasta/builder/fixed_type_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/fixed_type_builder.dart
@@ -12,8 +12,8 @@
 
 class FixedTypeBuilder extends TypeBuilder {
   final DartType type;
-  final Uri fileUri;
-  final int charOffset;
+  final Uri? fileUri;
+  final int? charOffset;
 
   const FixedTypeBuilder(this.type, this.fileUri, this.charOffset);
 
diff --git a/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart b/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart
index b1bd488..cf242da 100644
--- a/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart
+++ b/pkg/front_end/lib/src/fasta/builder/formal_parameter_builder.dart
@@ -51,6 +51,8 @@
 /// constructor.
 class FormalParameterBuilder extends ModifierBuilderImpl
     implements VariableBuilder {
+  static const String noNameSentinel = 'no name sentinel';
+
   /// List of metadata builders for the metadata declared on this parameter.
   final List<MetadataBuilder>? metadata;
 
@@ -130,7 +132,8 @@
       if (!library.isNonNullableByDefault && builtType != null) {
         builtType = legacyErasure(builtType);
       }
-      variable = new VariableDeclarationImpl(name, functionNestingLevel,
+      variable = new VariableDeclarationImpl(
+          name == noNameSentinel ? null : name, functionNestingLevel,
           type: builtType,
           isFinal: isFinal,
           isConst: isConst,
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 ef545f2..264bbc2 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -1256,12 +1256,16 @@
       } else {
         Substitution substitution = Substitution.fromPairs(
             initialTarget.function.typeParameters, arguments.types);
-        arguments.types.clear();
-        arguments.types.length = redirectionTarget!.typeArguments.length;
-        for (int i = 0; i < arguments.types.length; i++) {
-          arguments.types[i] =
+        for (int i = 0; i < redirectionTarget!.typeArguments.length; i++) {
+          DartType typeArgument =
               substitution.substituteType(redirectionTarget.typeArguments[i]);
+          if (i < arguments.types.length) {
+            arguments.types[i] = typeArgument;
+          } else {
+            arguments.types.add(typeArgument);
+          }
         }
+        arguments.types.length = redirectionTarget.typeArguments.length;
 
         replacementNode = buildStaticInvocation(
             resolvedTarget,
@@ -1686,7 +1690,10 @@
   @override
   void handleSend(Token beginToken, Token endToken) {
     assert(checkState(beginToken, [
-      ValueKinds.ArgumentsOrNull,
+      unionOfKinds([
+        ValueKinds.ArgumentsOrNull,
+        ValueKinds.ParserRecovery,
+      ]),
       ValueKinds.TypeArgumentsOrNull,
       unionOfKinds([
         ValueKinds.Expression,
@@ -1697,12 +1704,12 @@
       ])
     ]));
     debugEvent("Send");
-    Arguments? arguments = pop() as Arguments?;
+    Object? arguments = pop();
     List<UnresolvedType>? typeArguments = pop() as List<UnresolvedType>?;
     Object receiver = pop()!;
     // Delay adding [typeArguments] to [forest] for type aliases: They
     // must be unaliased to the type arguments of the denoted type.
-    bool isInForest = arguments != null &&
+    bool isInForest = arguments is Arguments &&
         typeArguments != null &&
         (receiver is! TypeUseGenerator ||
             (receiver is TypeUseGenerator &&
@@ -1716,22 +1723,23 @@
           (receiver is TypeUseGenerator &&
               receiver.declaration is TypeAliasBuilder));
     }
-    if (receiver is Identifier) {
+    if (receiver is ParserRecovery || arguments is ParserRecovery) {
+      push(new ParserErrorGenerator(
+          this, beginToken, fasta.messageSyntheticToken));
+    } else if (receiver is Identifier) {
       Name name = new Name(receiver.name, libraryBuilder.nameOrigin);
       if (arguments == null) {
         push(new IncompletePropertyAccessGenerator(this, beginToken, name));
       } else {
         push(new SendAccessGenerator(
-            this, beginToken, name, typeArguments, arguments,
+            this, beginToken, name, typeArguments, arguments as Arguments,
             isTypeArgumentsInForest: isInForest));
       }
-    } else if (receiver is ParserRecovery) {
-      push(new ParserErrorGenerator(
-          this, beginToken, fasta.messageSyntheticToken));
     } else if (arguments == null) {
       push(receiver);
     } else {
-      push(finishSend(receiver, typeArguments, arguments, beginToken.charOffset,
+      push(finishSend(receiver, typeArguments, arguments as Arguments,
+          beginToken.charOffset,
           isTypeArgumentsInForest: isInForest));
     }
     assert(checkState(beginToken, [
@@ -2679,7 +2687,7 @@
     if (!libraryBuilder.isNonNullableByDefault) {
       reportNonNullableModifierError(lateToken);
     }
-    UnresolvedType type = pop() as UnresolvedType;
+    UnresolvedType? type = pop() as UnresolvedType?;
     int modifiers = (lateToken != null ? lateMask : 0) |
         Modifier.validateVarFinalOrConst(varFinalOrConst?.lexeme);
     _enterLocalState(inLateLocalInitializer: lateToken != null);
@@ -4954,7 +4962,8 @@
   @override
   void endTypeArguments(int count, Token beginToken, Token endToken) {
     debugEvent("TypeArguments");
-    push(const FixedNullableList<UnresolvedType>().pop(stack, count) ??
+    push(const FixedNullableList<UnresolvedType>()
+            .popNonNullable(stack, count, dummyUnresolvedType) ??
         NullValue.TypeArguments);
   }
 
@@ -5001,10 +5010,28 @@
   @override
   void handleNamedArgument(Token colon) {
     debugEvent("NamedArgument");
+    assert(checkState(colon, [
+      unionOfKinds([
+        ValueKinds.Expression,
+        ValueKinds.Generator,
+      ]),
+      unionOfKinds([
+        ValueKinds.Identifier,
+        ValueKinds.ParserRecovery,
+      ])
+    ]));
     Expression value = popForValue();
-    Identifier identifier = pop() as Identifier;
-    push(new NamedExpression(identifier.name, value)
-      ..fileOffset = identifier.charOffset);
+    Object? identifier = pop();
+    if (identifier is Identifier) {
+      push(new NamedExpression(identifier.name, value)
+        ..fileOffset = identifier.charOffset);
+    } else {
+      assert(
+          identifier is ParserRecovery,
+          "Unexpected argument name: "
+          "${identifier} (${identifier.runtimeType})");
+      push(identifier);
+    }
   }
 
   @override
diff --git a/pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart b/pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart
index 653af5c..211d929 100644
--- a/pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart
@@ -943,7 +943,7 @@
       : numberSemantics = backend.numberSemantics,
         coreTypes = typeEnvironment.coreTypes,
         canonicalizationCache = <Constant, Constant>{},
-        nodeCache = <Node, Constant>{},
+        nodeCache = <Node, Constant?>{},
         env = new EvaluationEnvironment() {
     if (environmentDefines == null && !backend.supportsUnevaluatedConstants) {
       throw new ArgumentError(
diff --git a/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart b/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart
index e08aaf2..e11111a 100644
--- a/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/inference_visitor.dart
@@ -2078,7 +2078,7 @@
       DartType inferredKeyType,
       DartType inferredValueType,
       DartType spreadContext,
-      List<DartType?> actualTypes,
+      List<DartType> actualTypes,
       List<DartType> actualTypesForSet,
       Map<TreeNode, DartType> inferredSpreadTypes,
       Map<Expression, DartType> inferredConditionTypes,
@@ -2096,8 +2096,8 @@
       DartType spreadType = spreadResult.inferredType;
       inferredSpreadTypes[entry.expression] = spreadType;
       int length = actualTypes.length;
-      actualTypes.add(null);
-      actualTypes.add(null);
+      actualTypes.add(noInferredType);
+      actualTypes.add(noInferredType);
       storeSpreadMapEntryElementTypes(
           spreadType, entry.isNullAware, actualTypes, length);
       DartType? actualKeyType = actualTypes[length];
@@ -2108,7 +2108,7 @@
 
       MapLiteralEntry replacement = entry;
       if (typeChecksNeeded) {
-        if (actualKeyType == null) {
+        if (actualKeyType == noInferredType) {
           if (inferrer.coreTypes.isNull(spreadTypeBound) &&
               !entry.isNullAware) {
             replacement = new MapLiteralEntry(
@@ -2204,7 +2204,7 @@
                   1);
             }
           }
-          if (!inferrer.isAssignable(inferredValueType, actualValueType!)) {
+          if (!inferrer.isAssignable(inferredValueType, actualValueType)) {
             if (inferrer.isNonNullableByDefault) {
               IsSubtypeOf subtypeCheckResult = inferrer.typeSchemaEnvironment
                   .performNullabilityAwareSubtypeCheck(
@@ -2273,7 +2273,7 @@
       }
 
       // Use 'dynamic' for error recovery.
-      if (actualKeyType == null) {
+      if (actualKeyType == noInferredType) {
         actualKeyType = actualTypes[length] = const DynamicType();
         actualValueType = actualTypes[length + 1] = const DynamicType();
       }
@@ -2287,7 +2287,7 @@
       entry.entryType = new InterfaceType(
           mapEntryClass!,
           inferrer.library.nonNullable,
-          <DartType>[actualKeyType, actualValueType!]);
+          <DartType>[actualKeyType, actualValueType]);
 
       bool isMap = inferrer.typeSchemaEnvironment.isSubtypeOf(
           spreadType,
@@ -2354,10 +2354,10 @@
             typeChecksNeeded);
         int length = actualTypes.length;
         actualTypes[length - 2] = inferrer.typeSchemaEnvironment
-            .getStandardUpperBound(actualKeyType!, actualTypes[length - 2]!,
+            .getStandardUpperBound(actualKeyType, actualTypes[length - 2],
                 inferrer.library.library);
         actualTypes[length - 1] = inferrer.typeSchemaEnvironment
-            .getStandardUpperBound(actualValueType!, actualTypes[length - 1]!,
+            .getStandardUpperBound(actualValueType, actualTypes[length - 1],
                 inferrer.library.library);
         int lengthForSet = actualTypesForSet.length;
         actualTypesForSet[lengthForSet - 1] = inferrer.typeSchemaEnvironment
@@ -2622,7 +2622,7 @@
       inferredConditionTypes = new Map<Expression, DartType>.identity();
     }
     if (inferenceNeeded) {
-      inferredTypes = [const UnknownType(), const UnknownType()];
+      inferredTypes = [noInferredType, noInferredType];
       inferrer.typeSchemaEnvironment.inferGenericFunctionOrType(
           mapType,
           mapClass.typeParameters,
@@ -2701,7 +2701,7 @@
           formalTypesForSet.add(setType.typeArguments[0]);
         }
 
-        List<DartType> inferredTypesForSet = <DartType>[const UnknownType()];
+        List<DartType> inferredTypesForSet = <DartType>[noInferredType];
         inferrer.typeSchemaEnvironment.inferGenericFunctionOrType(
             setType,
             inferrer.coreTypes.setClass.typeParameters,
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
index 098e1aa..fb00d81 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
@@ -716,7 +716,9 @@
       Constructor? referenceFrom) {
     VariableDeclaration copyFormal(VariableDeclaration formal) {
       VariableDeclaration copy = new VariableDeclaration(formal.name,
-          isFinal: formal.isFinal, isConst: formal.isConst);
+          isFinal: formal.isFinal,
+          isConst: formal.isConst,
+          type: const UnknownType());
       if (formal.type is! UnknownType) {
         copy.type = substitute(formal.type, substitutionMap);
       } else {
@@ -1424,7 +1426,7 @@
 
   void updateType() {
     // ignore: unnecessary_null_comparison
-    assert(source.type != null, "No type computed for $source.");
+    assert(source.type is! UnknownType, "No type computed for $source.");
     target.type = substitute(source.type, substitutionMap);
   }
 }
diff --git a/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart b/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart
index 265cee2..4f63d8b 100644
--- a/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/redirecting_factory_body.dart
@@ -179,12 +179,11 @@
 }
 
 RedirectionTarget? getRedirectionTarget(Procedure member, EnsureLoaded helper) {
-  List<DartType> typeArguments = <DartType>[]..length =
-      member.function.typeParameters.length;
-  for (int i = 0; i < typeArguments.length; i++) {
-    typeArguments[i] = new TypeParameterType.withDefaultNullabilityForLibrary(
+  List<DartType> typeArguments = new List<DartType>.generate(
+      member.function.typeParameters.length, (int i) {
+    return new TypeParameterType.withDefaultNullabilityForLibrary(
         member.function.typeParameters[i], member.enclosingLibrary);
-  }
+  }, growable: true);
 
   // We use the [tortoise and hare algorithm]
   // (https://en.wikipedia.org/wiki/Cycle_detection#Tortoise_and_hare) to
@@ -201,15 +200,15 @@
     Member nextTortoise = tortoiseBody!.target!;
     helper.ensureLoaded(nextTortoise);
     List<DartType>? nextTypeArguments = tortoiseBody.typeArguments;
-    if (nextTypeArguments == null) {
-      nextTypeArguments = <DartType>[];
-    }
-
-    Substitution sub = Substitution.fromPairs(
-        tortoise.function!.typeParameters, typeArguments);
-    typeArguments = <DartType>[]..length = nextTypeArguments.length;
-    for (int i = 0; i < typeArguments.length; i++) {
-      typeArguments[i] = sub.substituteType(nextTypeArguments[i]);
+    if (nextTypeArguments != null) {
+      Substitution sub = Substitution.fromPairs(
+          tortoise.function!.typeParameters, typeArguments);
+      typeArguments =
+          new List<DartType>.generate(nextTypeArguments.length, (int i) {
+        return sub.substituteType(nextTypeArguments[i]);
+      }, growable: true);
+    } else {
+      typeArguments = <DartType>[];
     }
 
     tortoise = nextTortoise;
diff --git a/pkg/front_end/lib/src/fasta/kernel/type_builder_computer.dart b/pkg/front_end/lib/src/fasta/kernel/type_builder_computer.dart
index b5828a4..7f6631d 100644
--- a/pkg/front_end/lib/src/fasta/kernel/type_builder_computer.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/type_builder_computer.dart
@@ -11,6 +11,7 @@
 
 import '../builder/class_builder.dart';
 import '../builder/dynamic_type_declaration_builder.dart';
+import '../builder/fixed_type_builder.dart';
 import '../builder/formal_parameter_builder.dart';
 import '../builder/function_type_builder.dart';
 import '../builder/future_or_type_declaration_builder.dart';
@@ -39,7 +40,10 @@
 
   @override
   TypeBuilder visitInvalidType(InvalidType node) {
-    throw "Not implemented";
+    return new FixedTypeBuilder(
+        node,
+        /* fileUri = */ null,
+        /* charOffset = */ null);
   }
 
   @override
diff --git a/pkg/front_end/lib/src/fasta/kernel/utils.dart b/pkg/front_end/lib/src/fasta/kernel/utils.dart
index b24667f..a077ad7 100644
--- a/pkg/front_end/lib/src/fasta/kernel/utils.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/utils.dart
@@ -32,9 +32,12 @@
 
 import '../builder/fixed_type_builder.dart';
 import '../builder/formal_parameter_builder.dart';
+import '../builder/metadata_builder.dart';
 import '../builder/type_builder.dart';
 import '../builder/type_variable_builder.dart';
+import '../builder/unresolved_type.dart';
 import '../combinator.dart';
+import '../configuration.dart';
 import '../identifiers.dart';
 import '../source/source_library_builder.dart';
 import 'body_builder.dart';
@@ -159,6 +162,7 @@
 final Token dummyToken = new SyntheticToken(TokenType.AT, -1);
 final Identifier dummyIdentifier = new Identifier(dummyToken);
 final Combinator dummyCombinator = new Combinator(false, {}, -1, dummyUri);
+final MetadataBuilder dummyMetadataBuilder = new MetadataBuilder(dummyToken);
 final TypeBuilder dummyTypeBuilder =
     new FixedTypeBuilder(dummyDartType, dummyUri, -1);
 final FormalParameterBuilder dummyFormalParameterBuilder =
@@ -167,3 +171,6 @@
     new TypeVariableBuilder(TypeVariableBuilder.noNameSentinel, null, -1, null);
 final Label dummyLabel = new Label('', -1);
 final FieldInfo dummyFieldInfo = new FieldInfo('', -1, null, dummyToken, -1);
+final Configuration dummyConfiguration = new Configuration(-1, '', '', '');
+final UnresolvedType dummyUnresolvedType =
+    new UnresolvedType(dummyTypeBuilder, -1, dummyUri);
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 37348d5..331d16b 100644
--- a/pkg/front_end/lib/src/fasta/source/diet_listener.dart
+++ b/pkg/front_end/lib/src/fasta/source/diet_listener.dart
@@ -339,7 +339,7 @@
     debugEvent("TopLevelMethod");
     Token bodyToken = pop() as Token;
     Object? name = pop();
-    Token metadata = pop() as Token;
+    Token? metadata = pop() as Token?;
     checkEmpty(beginToken.charOffset);
     if (name is ParserRecovery) return;
 
@@ -509,7 +509,7 @@
     debugEvent("Import");
     Object? name = pop(NullValue.Prefix);
 
-    Token metadata = pop() as Token;
+    Token? metadata = pop() as Token?;
     checkEmpty(importKeyword.charOffset);
     if (name is ParserRecovery) return;
 
@@ -535,7 +535,7 @@
   void endExport(Token exportKeyword, Token semicolon) {
     debugEvent("Export");
 
-    Token metadata = pop() as Token;
+    Token? metadata = pop() as Token?;
     Library libraryNode = libraryBuilder.library;
     LibraryDependency dependency =
         libraryNode.dependencies[importExportDirectiveIndex++];
@@ -546,7 +546,7 @@
   void endPart(Token partKeyword, Token semicolon) {
     debugEvent("Part");
 
-    Token metadata = pop() as Token;
+    Token? metadata = pop() as Token?;
     Library libraryNode = libraryBuilder.library;
     if (libraryNode.parts.length > partDirectiveIndex) {
       // If partDirectiveIndex >= libraryNode.parts.length we are in a case of
@@ -588,7 +588,7 @@
     debugEvent("ClassFactoryMethod");
     Token bodyToken = pop() as Token;
     Object? name = pop();
-    Token metadata = pop() as Token;
+    Token? metadata = pop() as Token?;
     checkEmpty(beginToken.charOffset);
     if (name is ParserRecovery || currentClassIsParserRecovery) return;
 
@@ -699,7 +699,7 @@
     // in handleNoFormalParameters rather than the supplied token.
     pop(); // bodyToken
     Object? name = pop();
-    Token metadata = pop() as Token;
+    Token? metadata = pop() as Token?;
     checkEmpty(beginToken.charOffset);
     if (name is ParserRecovery || currentClassIsParserRecovery) return;
     FunctionBuilderImpl builder;
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 a4c8a0e..1cbd3d7 100644
--- a/pkg/front_end/lib/src/fasta/source/outline_builder.dart
+++ b/pkg/front_end/lib/src/fasta/source/outline_builder.dart
@@ -162,7 +162,8 @@
   @override
   void endMetadataStar(int count) {
     debugEvent("MetadataStar");
-    push(const FixedNullableList<MetadataBuilder>().pop(stack, count) ??
+    push(const FixedNullableList<MetadataBuilder>()
+            .popNonNullable(stack, count, dummyMetadataBuilder) ??
         NullValue.Metadata);
   }
 
@@ -259,7 +260,8 @@
   @override
   void endConditionalUris(int count) {
     debugEvent("EndConditionalUris");
-    push(const FixedNullableList<Configuration>().pop(stack, count) ??
+    push(const FixedNullableList<Configuration>()
+            .popNonNullable(stack, count, dummyConfiguration) ??
         NullValue.ConditionalUris);
   }
 
@@ -1369,7 +1371,8 @@
   @override
   void endTypeArguments(int count, Token beginToken, Token endToken) {
     debugEvent("TypeArguments");
-    push(const FixedNullableList<TypeBuilder>().pop(stack, count) ??
+    push(const FixedNullableList<TypeBuilder>()
+            .popNonNullable(stack, count, dummyTypeBuilder) ??
         NullValue.TypeArguments);
   }
 
@@ -1468,8 +1471,14 @@
     if (name is ParserRecovery) {
       push(name);
     } else {
-      push(libraryBuilder.addFormalParameter(metadata, modifiers, type,
-          name as String, thisKeyword != null, charOffset, initializerStart));
+      push(libraryBuilder.addFormalParameter(
+          metadata,
+          modifiers,
+          type,
+          name == null ? FormalParameterBuilder.noNameSentinel : name as String,
+          thisKeyword != null,
+          charOffset,
+          initializerStart));
     }
   }
 
@@ -1557,8 +1566,8 @@
       assert(formals.isNotEmpty);
       if (formals.length == 2) {
         // The name may be null for generalized function types.
-        // ignore: unnecessary_null_comparison
-        if (formals[0].name != null && formals[0].name == formals[1].name) {
+        if (formals[0].name != FormalParameterBuilder.noNameSentinel &&
+            formals[0].name == formals[1].name) {
           addProblem(
               templateDuplicatedParameterName.withArguments(formals[1].name),
               formals[1].charOffset,
@@ -1574,8 +1583,7 @@
         Map<String, FormalParameterBuilder> seenNames =
             <String, FormalParameterBuilder>{};
         for (FormalParameterBuilder formal in formals) {
-          // ignore: unnecessary_null_comparison
-          if (formal.name == null) continue;
+          if (formal.name == FormalParameterBuilder.noNameSentinel) continue;
           if (seenNames.containsKey(formal.name)) {
             addProblem(
                 templateDuplicatedParameterName.withArguments(formal.name),
@@ -1877,7 +1885,7 @@
     bool isParserRecovery = false;
     for (int i = count - 1; i != -1; i--) {
       int charEndOffset = popCharOffset();
-      Token beforeLast = pop() as Token;
+      Token? beforeLast = pop() as Token?;
       Token? initializerTokenForInference = pop() as Token?;
       int charOffset = popCharOffset();
       Object? name = pop(NullValue.Identifier);
@@ -1909,7 +1917,8 @@
   void handleTypeVariablesDefined(Token token, int count) {
     debugEvent("TypeVariablesDefined");
     assert(count > 0);
-    push(const FixedNullableList<TypeVariableBuilder>().pop(stack, count) ??
+    push(const FixedNullableList<TypeVariableBuilder>()
+            .popNonNullable(stack, count, dummyTypeVariableBuilder) ??
         NullValue.TypeVariables);
   }
 
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 cead87b..324a721 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
@@ -803,7 +803,7 @@
       if (startToken != null) {
         // Extract only the tokens for the initializer expression from the
         // token stream.
-        Token endToken = info.beforeLast;
+        Token endToken = info.beforeLast!;
         endToken.setNext(new Token.eof(endToken.next!.offset));
         new Token.eof(startToken.previous!.offset).setNext(startToken);
       }
@@ -4241,12 +4241,11 @@
       Builder? declaration = iterator.current;
       while (declaration != null) {
         if (declaration is SourceTypeAliasBuilder) {
-          declaration.buildTypedefTearOffs(this,
-              (Procedure procedure) {
-                procedure.isStatic = true;
-              if (!declaration!.isPatch && !declaration.isDuplicate) {
-                library.addProcedure(procedure);
-              }
+          declaration.buildTypedefTearOffs(this, (Procedure procedure) {
+            procedure.isStatic = true;
+            if (!declaration!.isPatch && !declaration.isDuplicate) {
+              library.addProcedure(procedure);
+            }
           });
         }
         declaration = declaration.next;
@@ -4523,7 +4522,7 @@
   final String name;
   final int charOffset;
   final Token? initializerToken;
-  final Token beforeLast;
+  final Token? beforeLast;
   final int charEndOffset;
 
   const FieldInfo(this.name, this.charOffset, this.initializerToken,
diff --git a/pkg/front_end/test/spell_checking_list_tests.txt b/pkg/front_end/test/spell_checking_list_tests.txt
index d6f2f0c..269a892 100644
--- a/pkg/front_end/test/spell_checking_list_tests.txt
+++ b/pkg/front_end/test/spell_checking_list_tests.txt
@@ -245,6 +245,7 @@
 dash
 dashes
 day
+days
 db
 ddart
 dds
diff --git a/pkg/front_end/testcases/general/crashes/crash_04/main.dart.weak.expect b/pkg/front_end/testcases/general/crashes/crash_04/main.dart.weak.expect
new file mode 100644
index 0000000..9b02f5d
--- /dev/null
+++ b/pkg/front_end/testcases/general/crashes/crash_04/main.dart.weak.expect
@@ -0,0 +1,32 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/crashes/crash_04/main.dart:1:19: Error: Type 'C' not found.
+// mixin A<T extends C> on D {}
+//                   ^
+//
+// pkg/front_end/testcases/general/crashes/crash_04/main.dart:1:25: Error: Type 'D' not found.
+// mixin A<T extends C> on D {}
+//                         ^
+//
+// pkg/front_end/testcases/general/crashes/crash_04/main.dart:3:17: Error: Type 'D' not found.
+// class B extends D with A {}
+//                 ^
+//
+import self as self;
+import "dart:core" as core;
+
+abstract class A<T extends invalid-type> extends core::Object /*isMixinDeclaration*/  {
+}
+abstract class _B&D&A = core::Object with self::A<invalid-type> /*isAnonymousMixin*/  {
+  synthetic constructor •() → self::_B&D&A
+    : super core::Object::•()
+    ;
+}
+class B extends self::_B&D&A {
+  synthetic constructor •() → self::B
+    : super self::_B&D&A::•()
+    ;
+}
+static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/general/crashes/crash_04/main.dart.weak.outline.expect b/pkg/front_end/testcases/general/crashes/crash_04/main.dart.weak.outline.expect
new file mode 100644
index 0000000..e9d2a26
--- /dev/null
+++ b/pkg/front_end/testcases/general/crashes/crash_04/main.dart.weak.outline.expect
@@ -0,0 +1,31 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/crashes/crash_04/main.dart:1:19: Error: Type 'C' not found.
+// mixin A<T extends C> on D {}
+//                   ^
+//
+// pkg/front_end/testcases/general/crashes/crash_04/main.dart:1:25: Error: Type 'D' not found.
+// mixin A<T extends C> on D {}
+//                         ^
+//
+// pkg/front_end/testcases/general/crashes/crash_04/main.dart:3:17: Error: Type 'D' not found.
+// class B extends D with A {}
+//                 ^
+//
+import self as self;
+import "dart:core" as core;
+
+abstract class A<T extends invalid-type> extends core::Object /*isMixinDeclaration*/  {
+}
+abstract class _B&D&A = core::Object with self::A<invalid-type> /*isAnonymousMixin*/  {
+  synthetic constructor •() → self::_B&D&A
+    ;
+}
+class B extends self::_B&D&A {
+  synthetic constructor •() → self::B
+    ;
+}
+static method main() → dynamic
+  ;
diff --git a/pkg/front_end/testcases/general/crashes/crash_04/main.dart.weak.transformed.expect b/pkg/front_end/testcases/general/crashes/crash_04/main.dart.weak.transformed.expect
new file mode 100644
index 0000000..8b03fd8a
--- /dev/null
+++ b/pkg/front_end/testcases/general/crashes/crash_04/main.dart.weak.transformed.expect
@@ -0,0 +1,32 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/crashes/crash_04/main.dart:1:19: Error: Type 'C' not found.
+// mixin A<T extends C> on D {}
+//                   ^
+//
+// pkg/front_end/testcases/general/crashes/crash_04/main.dart:1:25: Error: Type 'D' not found.
+// mixin A<T extends C> on D {}
+//                         ^
+//
+// pkg/front_end/testcases/general/crashes/crash_04/main.dart:3:17: Error: Type 'D' not found.
+// class B extends D with A {}
+//                 ^
+//
+import self as self;
+import "dart:core" as core;
+
+abstract class A<T extends invalid-type> extends core::Object /*isMixinDeclaration*/  {
+}
+abstract class _B&D&A extends core::Object implements self::A<invalid-type> /*isAnonymousMixin,isEliminatedMixin*/  {
+  synthetic constructor •() → self::_B&D&A
+    : super core::Object::•()
+    ;
+}
+class B extends self::_B&D&A {
+  synthetic constructor •() → self::B
+    : super self::_B&D&A::•()
+    ;
+}
+static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/general/issue44007.dart b/pkg/front_end/testcases/general/issue44007.dart
new file mode 100644
index 0000000..9e5ebd9
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44007.dart
@@ -0,0 +1,19 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+void test() {
+  var list = [
+    DateTime.now().add(Duration(days: 3)),
+    DateTime.now().add(Duration(days: 2)),
+    DateTime.now(),
+    DateTime.now().subtract(Duration(days: 1))
+  ];
+
+  list.sort((a, b) => a.compareTo(b));
+  print(list);
+
+  print(DateTime.parse(2019-01-17 00:00:00.000));
+}
+
+main() {}
\ No newline at end of file
diff --git a/pkg/front_end/testcases/general/issue44007.dart.textual_outline.expect b/pkg/front_end/testcases/general/issue44007.dart.textual_outline.expect
new file mode 100644
index 0000000..31c91a2
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44007.dart.textual_outline.expect
@@ -0,0 +1,2 @@
+void test() {}
+main() {}
diff --git a/pkg/front_end/testcases/general/issue44007.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/general/issue44007.dart.textual_outline_modelled.expect
new file mode 100644
index 0000000..4742c78
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44007.dart.textual_outline_modelled.expect
@@ -0,0 +1,2 @@
+main() {}
+void test() {}
diff --git a/pkg/front_end/testcases/general/issue44007.dart.weak.expect b/pkg/front_end/testcases/general/issue44007.dart.weak.expect
new file mode 100644
index 0000000..efd3a92
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44007.dart.weak.expect
@@ -0,0 +1,35 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue44007.dart:16:35: Error: Expected ',' before this.
+//   print(DateTime.parse(2019-01-17 00:00:00.000));
+//                                   ^^
+//
+// pkg/front_end/testcases/general/issue44007.dart:16:35: Error: Expected an identifier, but got '00'.
+// Try inserting an identifier before '00'.
+//   print(DateTime.parse(2019-01-17 00:00:00.000));
+//                                   ^^
+//
+// pkg/front_end/testcases/general/issue44007.dart:16:40: Error: Expected ')' before this.
+//   print(DateTime.parse(2019-01-17 00:00:00.000));
+//                                        ^
+//
+// pkg/front_end/testcases/general/issue44007.dart:16:18: Error: Expected an identifier, but got 'parse'.
+// Try inserting an identifier before 'parse'.
+//   print(DateTime.parse(2019-01-17 00:00:00.000));
+//                  ^^^^^
+//
+import self as self;
+import "dart:core" as core;
+
+static method test() → void {
+  core::List<core::DateTime> list = <core::DateTime>[new core::DateTime::now().{core::DateTime::add}(new core::Duration::•(days: 3)){(core::Duration) → core::DateTime}, new core::DateTime::now().{core::DateTime::add}(new core::Duration::•(days: 2)){(core::Duration) → core::DateTime}, new core::DateTime::now(), new core::DateTime::now().{core::DateTime::subtract}(new core::Duration::•(days: 1)){(core::Duration) → core::DateTime}];
+  list.{core::List::sort}((core::DateTime a, core::DateTime b) → core::int => a.{core::DateTime::compareTo}(b){(core::DateTime) → core::int}){([(core::DateTime, core::DateTime) →? core::int]) → void};
+  core::print(list);
+  core::print(invalid-expression "pkg/front_end/testcases/general/issue44007.dart:16:18: Error: Expected an identifier, but got 'parse'.
+Try inserting an identifier before 'parse'.
+  print(DateTime.parse(2019-01-17 00:00:00.000));
+                 ^^^^^");
+}
+static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/general/issue44007.dart.weak.outline.expect b/pkg/front_end/testcases/general/issue44007.dart.weak.outline.expect
new file mode 100644
index 0000000..d7d3d2f
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44007.dart.weak.outline.expect
@@ -0,0 +1,7 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+
+static method test() → void
+  ;
+static method main() → dynamic
+  ;
diff --git a/pkg/front_end/testcases/general/issue44007.dart.weak.transformed.expect b/pkg/front_end/testcases/general/issue44007.dart.weak.transformed.expect
new file mode 100644
index 0000000..244d264
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44007.dart.weak.transformed.expect
@@ -0,0 +1,35 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue44007.dart:16:35: Error: Expected ',' before this.
+//   print(DateTime.parse(2019-01-17 00:00:00.000));
+//                                   ^^
+//
+// pkg/front_end/testcases/general/issue44007.dart:16:35: Error: Expected an identifier, but got '00'.
+// Try inserting an identifier before '00'.
+//   print(DateTime.parse(2019-01-17 00:00:00.000));
+//                                   ^^
+//
+// pkg/front_end/testcases/general/issue44007.dart:16:40: Error: Expected ')' before this.
+//   print(DateTime.parse(2019-01-17 00:00:00.000));
+//                                        ^
+//
+// pkg/front_end/testcases/general/issue44007.dart:16:18: Error: Expected an identifier, but got 'parse'.
+// Try inserting an identifier before 'parse'.
+//   print(DateTime.parse(2019-01-17 00:00:00.000));
+//                  ^^^^^
+//
+import self as self;
+import "dart:core" as core;
+
+static method test() → void {
+  core::List<core::DateTime> list = core::_GrowableList::_literal4<core::DateTime>(new core::DateTime::now().{core::DateTime::add}(new core::Duration::•(days: 3)){(core::Duration) → core::DateTime}, new core::DateTime::now().{core::DateTime::add}(new core::Duration::•(days: 2)){(core::Duration) → core::DateTime}, new core::DateTime::now(), new core::DateTime::now().{core::DateTime::subtract}(new core::Duration::•(days: 1)){(core::Duration) → core::DateTime});
+  list.{core::List::sort}((core::DateTime a, core::DateTime b) → core::int => a.{core::DateTime::compareTo}(b){(core::DateTime) → core::int}){([(core::DateTime, core::DateTime) →? core::int]) → void};
+  core::print(list);
+  core::print(invalid-expression "pkg/front_end/testcases/general/issue44007.dart:16:18: Error: Expected an identifier, but got 'parse'.
+Try inserting an identifier before 'parse'.
+  print(DateTime.parse(2019-01-17 00:00:00.000));
+                 ^^^^^");
+}
+static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/general/issue44347.dart b/pkg/front_end/testcases/general/issue44347.dart
index 2d9a01e..074b4e5 100644
--- a/pkg/front_end/testcases/general/issue44347.dart
+++ b/pkg/front_end/testcases/general/issue44347.dart
@@ -1,7 +1,9 @@
 // Copyright (c) 2020, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
+
 // @dart=2.9
+
 test() {
   Set<int>.();
 }
diff --git a/pkg/front_end/testcases/general/issue44347.dart.weak.expect b/pkg/front_end/testcases/general/issue44347.dart.weak.expect
index 23f91b5..fc179e1 100644
--- a/pkg/front_end/testcases/general/issue44347.dart.weak.expect
+++ b/pkg/front_end/testcases/general/issue44347.dart.weak.expect
@@ -2,17 +2,17 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/general/issue44347.dart:6:6: Error: This requires the 'constructor-tearoffs' language feature to be enabled.
+// pkg/front_end/testcases/general/issue44347.dart:8:6: Error: This requires the 'constructor-tearoffs' language feature to be enabled.
 // Try updating your pubspec.yaml to set the minimum SDK constraint to 2.14 or higher, and running 'pub get'.
 //   Set<int>.();
 //      ^
 //
-// pkg/front_end/testcases/general/issue44347.dart:6:13: Error: Expected an identifier, but got ')'.
+// pkg/front_end/testcases/general/issue44347.dart:8:13: Error: Expected an identifier, but got ')'.
 // Try inserting an identifier before ')'.
 //   Set<int>.();
 //             ^
 //
-// pkg/front_end/testcases/general/issue44347.dart:6:12: Error: Expected an identifier, but got '('.
+// pkg/front_end/testcases/general/issue44347.dart:8:12: Error: Expected an identifier, but got '('.
 // Try inserting an identifier before '('.
 //   Set<int>.();
 //            ^
@@ -20,7 +20,7 @@
 import self as self;
 
 static method test() → dynamic {
-  invalid-expression "pkg/front_end/testcases/general/issue44347.dart:6:12: Error: Expected an identifier, but got '('.
+  invalid-expression "pkg/front_end/testcases/general/issue44347.dart:8:12: Error: Expected an identifier, but got '('.
 Try inserting an identifier before '('.
   Set<int>.();
            ^";
diff --git a/pkg/front_end/testcases/general/issue44347.dart.weak.transformed.expect b/pkg/front_end/testcases/general/issue44347.dart.weak.transformed.expect
index 23f91b5..fc179e1 100644
--- a/pkg/front_end/testcases/general/issue44347.dart.weak.transformed.expect
+++ b/pkg/front_end/testcases/general/issue44347.dart.weak.transformed.expect
@@ -2,17 +2,17 @@
 //
 // Problems in library:
 //
-// pkg/front_end/testcases/general/issue44347.dart:6:6: Error: This requires the 'constructor-tearoffs' language feature to be enabled.
+// pkg/front_end/testcases/general/issue44347.dart:8:6: Error: This requires the 'constructor-tearoffs' language feature to be enabled.
 // Try updating your pubspec.yaml to set the minimum SDK constraint to 2.14 or higher, and running 'pub get'.
 //   Set<int>.();
 //      ^
 //
-// pkg/front_end/testcases/general/issue44347.dart:6:13: Error: Expected an identifier, but got ')'.
+// pkg/front_end/testcases/general/issue44347.dart:8:13: Error: Expected an identifier, but got ')'.
 // Try inserting an identifier before ')'.
 //   Set<int>.();
 //             ^
 //
-// pkg/front_end/testcases/general/issue44347.dart:6:12: Error: Expected an identifier, but got '('.
+// pkg/front_end/testcases/general/issue44347.dart:8:12: Error: Expected an identifier, but got '('.
 // Try inserting an identifier before '('.
 //   Set<int>.();
 //            ^
@@ -20,7 +20,7 @@
 import self as self;
 
 static method test() → dynamic {
-  invalid-expression "pkg/front_end/testcases/general/issue44347.dart:6:12: Error: Expected an identifier, but got '('.
+  invalid-expression "pkg/front_end/testcases/general/issue44347.dart:8:12: Error: Expected an identifier, but got '('.
 Try inserting an identifier before '('.
   Set<int>.();
            ^";
diff --git a/pkg/front_end/testcases/general/issue44733.dart b/pkg/front_end/testcases/general/issue44733.dart
new file mode 100644
index 0000000..92227d1
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44733.dart
@@ -0,0 +1,25 @@
+// Copyright (c) 2021, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+abstract class B extends A with C {}
+
+mixin C on D {}
+
+B get x => super.x;
+void f() {
+  switch (x.y.z) {
+  }
+}
+
+abstract class E {}
+
+abstract class D {
+  E get y {}
+}
+
+abstract class A {
+  F get y => super.y as F;
+}
+
+main() {}
\ No newline at end of file
diff --git a/pkg/front_end/testcases/general/issue44733.dart.textual_outline.expect b/pkg/front_end/testcases/general/issue44733.dart.textual_outline.expect
new file mode 100644
index 0000000..7fafd11
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44733.dart.textual_outline.expect
@@ -0,0 +1,17 @@
+abstract class B extends A with C {}
+
+mixin C on D {}
+B get x => super.x;
+void f() {}
+
+abstract class E {}
+
+abstract class D {
+  E get y {}
+}
+
+abstract class A {
+  F get y => super.y as F;
+}
+
+main() {}
diff --git a/pkg/front_end/testcases/general/issue44733.dart.textual_outline_modelled.expect b/pkg/front_end/testcases/general/issue44733.dart.textual_outline_modelled.expect
new file mode 100644
index 0000000..ba7e44d
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44733.dart.textual_outline_modelled.expect
@@ -0,0 +1,17 @@
+B get x => super.x;
+
+abstract class A {
+  F get y => super.y as F;
+}
+
+abstract class B extends A with C {}
+
+abstract class D {
+  E get y {}
+}
+
+abstract class E {}
+
+main() {}
+mixin C on D {}
+void f() {}
diff --git a/pkg/front_end/testcases/general/issue44733.dart.weak.expect b/pkg/front_end/testcases/general/issue44733.dart.weak.expect
new file mode 100644
index 0000000..186db3f
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44733.dart.weak.expect
@@ -0,0 +1,79 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue44733.dart:22:3: Error: Type 'F' not found.
+//   F get y => super.y as F;
+//   ^
+//
+// pkg/front_end/testcases/general/issue44733.dart:5:16: Error: 'A' doesn't implement 'D' so it can't be used with 'C'.
+//  - 'A' is from 'pkg/front_end/testcases/general/issue44733.dart'.
+//  - 'D' is from 'pkg/front_end/testcases/general/issue44733.dart'.
+//  - 'C' is from 'pkg/front_end/testcases/general/issue44733.dart'.
+// abstract class B extends A with C {}
+//                ^
+//
+// pkg/front_end/testcases/general/issue44733.dart:9:12: Error: Expected identifier, but got 'super'.
+// B get x => super.x;
+//            ^^^^^
+//
+// pkg/front_end/testcases/general/issue44733.dart:18:9: Error: A non-null value must be returned since the return type 'E' doesn't allow null.
+//  - 'E' is from 'pkg/front_end/testcases/general/issue44733.dart'.
+//   E get y {}
+//         ^
+//
+// pkg/front_end/testcases/general/issue44733.dart:22:25: Error: 'F' isn't a type.
+//   F get y => super.y as F;
+//                         ^
+//
+// pkg/front_end/testcases/general/issue44733.dart:22:20: Error: Superclass has no getter named 'y'.
+//   F get y => super.y as F;
+//                    ^
+//
+import self as self;
+import "dart:core" as core;
+
+abstract class _B&A&C = self::A with self::C /*isAnonymousMixin*/  {
+  synthetic constructor •() → self::_B&A&C
+    : super self::A::•()
+    ;
+}
+abstract class B extends self::_B&A&C {
+  synthetic constructor •() → self::B
+    : super self::_B&A&C::•()
+    ;
+}
+abstract class C extends self::D /*isMixinDeclaration*/  {
+}
+abstract class E extends core::Object {
+  synthetic constructor •() → self::E
+    : super core::Object::•()
+    ;
+}
+abstract class D extends core::Object {
+  synthetic constructor •() → self::D
+    : super core::Object::•()
+    ;
+  get y() → self::E {
+    return let final Never #t1 = invalid-expression "pkg/front_end/testcases/general/issue44733.dart:18:9: Error: A non-null value must be returned since the return type 'E' doesn't allow null.
+ - 'E' is from 'pkg/front_end/testcases/general/issue44733.dart'.
+  E get y {}
+        ^" in null;
+  }
+}
+abstract class A extends core::Object {
+  synthetic constructor •() → self::A
+    : super core::Object::•()
+    ;
+  get y() → invalid-type
+    return super.y as{ForNonNullableByDefault} invalid-type;
+}
+static get x() → self::B
+  return invalid-expression "pkg/front_end/testcases/general/issue44733.dart:9:12: Error: Expected identifier, but got 'super'.
+B get x => super.x;
+           ^^^^^"{dynamic}.x as{TypeError,ForDynamic,ForNonNullableByDefault} self::B;
+static method f() → void {
+  switch(self::x.{self::A::y}{invalid-type}{<invalid>}.z) {
+  }
+}
+static method main() → dynamic {}
diff --git a/pkg/front_end/testcases/general/issue44733.dart.weak.outline.expect b/pkg/front_end/testcases/general/issue44733.dart.weak.outline.expect
new file mode 100644
index 0000000..b1f8519
--- /dev/null
+++ b/pkg/front_end/testcases/general/issue44733.dart.weak.outline.expect
@@ -0,0 +1,51 @@
+library /*isNonNullableByDefault*/;
+//
+// Problems in library:
+//
+// pkg/front_end/testcases/general/issue44733.dart:22:3: Error: Type 'F' not found.
+//   F get y => super.y as F;
+//   ^
+//
+// pkg/front_end/testcases/general/issue44733.dart:5:16: Error: 'A' doesn't implement 'D' so it can't be used with 'C'.
+//  - 'A' is from 'pkg/front_end/testcases/general/issue44733.dart'.
+//  - 'D' is from 'pkg/front_end/testcases/general/issue44733.dart'.
+//  - 'C' is from 'pkg/front_end/testcases/general/issue44733.dart'.
+// abstract class B extends A with C {}
+//                ^
+//
+import self as self;
+import "dart:core" as core;
+
+abstract class _B&A&C = self::A with self::C /*isAnonymousMixin*/  {
+  synthetic constructor •() → self::_B&A&C
+    : super self::A::•()
+    ;
+}
+abstract class B extends self::_B&A&C {
+  synthetic constructor •() → self::B
+    ;
+}
+abstract class C extends self::D /*isMixinDeclaration*/  {
+}
+abstract class E extends core::Object {
+  synthetic constructor •() → self::E
+    ;
+}
+abstract class D extends core::Object {
+  synthetic constructor •() → self::D
+    ;
+  get y() → self::E
+    ;
+}
+abstract class A extends core::Object {
+  synthetic constructor •() → self::A
+    ;
+  get y() → invalid-type
+    ;
+}
+static get x() → self::B
+  ;
+static method f() → void
+  ;
+static method main() → dynamic
+  ;
diff --git a/pkg/front_end/testcases/incremental.status b/pkg/front_end/testcases/incremental.status
index 7edb02b..afed71c 100644
--- a/pkg/front_end/testcases/incremental.status
+++ b/pkg/front_end/testcases/incremental.status
@@ -6,5 +6,3 @@
 
 # http://dartbug.com/41812#issuecomment-684825703
 strongmode_mixins_2: Crash
-
-crash_07: Crash
\ No newline at end of file
diff --git a/pkg/front_end/testcases/incremental/type_change_on_recompile.yaml.world.1.expect b/pkg/front_end/testcases/incremental/type_change_on_recompile.yaml.world.1.expect
index 5938335..38493c4 100644
--- a/pkg/front_end/testcases/incremental/type_change_on_recompile.yaml.world.1.expect
+++ b/pkg/front_end/testcases/incremental/type_change_on_recompile.yaml.world.1.expect
@@ -43,7 +43,7 @@
       ;
   }
   abstract class _A&B&C&D extends main::_A&B&C implements main::D /*isAnonymousMixin,isEliminatedMixin*/  {
-    synthetic constructor named(dynamic _field) → main::_A&B&C&D*
+    synthetic constructor named(lib::E* _field) → main::_A&B&C&D*
       : super main::_A&B&C::named(_field)
       ;
   }
diff --git a/pkg/front_end/testcases/outline.status b/pkg/front_end/testcases/outline.status
index b866349..4f83215 100644
--- a/pkg/front_end/testcases/outline.status
+++ b/pkg/front_end/testcases/outline.status
@@ -13,7 +13,6 @@
 general/bug30695: TypeCheckError
 general/covariant_field: TypeCheckError
 general/crashes/crash_02/main: Crash
-general/crashes/crash_04/main: Crash
 general/crashes/crash_06/main: Crash
 general/getter_vs_setter_type: TypeCheckError
 general/infer_field_from_multiple: TypeCheckError
diff --git a/pkg/front_end/testcases/text_serialization.status b/pkg/front_end/testcases/text_serialization.status
index 29295ce..6aacb2f 100644
--- a/pkg/front_end/testcases/text_serialization.status
+++ b/pkg/front_end/testcases/text_serialization.status
@@ -35,7 +35,6 @@
 general/covariant_field: TypeCheckError
 general/covariant_generic: RuntimeError
 general/crashes/crash_02/main: Crash
-general/crashes/crash_04/main: Crash
 general/crashes/crash_06/main: Crash
 general/duplicated_declarations: TypeCheckError
 general/duplicated_field_initializer: RuntimeError
@@ -86,6 +85,7 @@
 general/issue41210a: TypeCheckError
 general/issue41210b/issue41210.no_link: TypeCheckError
 general/issue41210b/issue41210: TypeCheckError
+general/issue44733: TypeCheckError
 general/issue45204: TypeCheckError
 general/micro: RuntimeError
 general/mixin_application_override: TypeCheckError
diff --git a/pkg/front_end/testcases/weak.status b/pkg/front_end/testcases/weak.status
index 569aa45..d88eb7b16 100644
--- a/pkg/front_end/testcases/weak.status
+++ b/pkg/front_end/testcases/weak.status
@@ -40,7 +40,6 @@
 general/covariant_field: TypeCheckError
 general/covariant_generic: RuntimeError
 general/crashes/crash_02/main: Crash
-general/crashes/crash_04/main: Crash
 general/crashes/crash_06/main: Crash
 general/duplicated_declarations: TypeCheckError
 general/duplicated_field_initializer: RuntimeError
@@ -91,6 +90,7 @@
 general/issue41210a: TypeCheckError
 general/issue41210b/issue41210.no_link: TypeCheckError
 general/issue41210b/issue41210: TypeCheckError
+general/issue44733: TypeCheckError
 general/issue45204: TypeCheckError
 general/micro: RuntimeError
 general/mixin_application_override: ExpectationFileMismatch # Too many errors.
diff --git a/pkg/kernel/lib/binary/ast_to_binary.dart b/pkg/kernel/lib/binary/ast_to_binary.dart
index babe0c6..1d243d9 100644
--- a/pkg/kernel/lib/binary/ast_to_binary.dart
+++ b/pkg/kernel/lib/binary/ast_to_binary.dart
@@ -25,8 +25,8 @@
   final ConstantIndexer _constantIndexer;
   final UriIndexer _sourceUriIndexer = new UriIndexer();
   bool _currentlyInNonimplementation = false;
-  final List<bool> _sourcesFromRealImplementation = <bool>[];
-  final List<bool> _sourcesUsedInLibrary = <bool>[];
+  final List<bool?> _sourcesFromRealImplementation = <bool?>[];
+  final List<bool?> _sourcesUsedInLibrary = <bool?>[];
   Map<LibraryDependency, int> _libraryDependencyIndex =
       <LibraryDependency, int>{};
   NonNullableByDefaultCompiledMode? compilationMode;
diff --git a/pkg/kernel/lib/class_hierarchy.dart b/pkg/kernel/lib/class_hierarchy.dart
index f66182a..7a61ee2 100644
--- a/pkg/kernel/lib/class_hierarchy.dart
+++ b/pkg/kernel/lib/class_hierarchy.dart
@@ -1722,6 +1722,8 @@
 /// are removed first; in the case of ties, classes with lower topological sort
 /// index are removed first.
 class _LubHeap extends Heap<_ClassInfo> {
+  _LubHeap() : super(_dummyClassInfo);
+
   @override
   bool sortsBefore(_ClassInfo a, _ClassInfo b) => sortsBeforeStatic(a, b);
 
@@ -1731,3 +1733,5 @@
     return a.topologicalIndex < b.topologicalIndex;
   }
 }
+
+final _ClassInfo _dummyClassInfo = new _ClassInfo(dummyClass);
diff --git a/pkg/kernel/lib/src/heap.dart b/pkg/kernel/lib/src/heap.dart
index ecb3f0a..f70098b 100644
--- a/pkg/kernel/lib/src/heap.dart
+++ b/pkg/kernel/lib/src/heap.dart
@@ -5,6 +5,9 @@
 /// Basic implementation of a heap, with O(log n) insertion and removal.
 abstract class Heap<T> {
   final _items = <T>[];
+  final T _dummyValue;
+
+  Heap(this._dummyValue);
 
   bool get isEmpty => _items.isEmpty;
 
@@ -12,7 +15,7 @@
 
   void add(T item) {
     int index = _items.length;
-    _items.length += 1;
+    _items.add(_dummyValue);
     while (index > 0) {
       T parent = _items[_parentIndex(index)];
       if (sortsBefore(parent, item)) break;
diff --git a/pkg/kernel/test/heap_test.dart b/pkg/kernel/test/heap_test.dart
index 95071ef..07f5245 100644
--- a/pkg/kernel/test/heap_test.dart
+++ b/pkg/kernel/test/heap_test.dart
@@ -36,5 +36,7 @@
 }
 
 class _intHeap extends Heap<int> {
+  _intHeap() : super(0);
+
   bool sortsBefore(int a, int b) => a < b;
 }
diff --git a/runtime/vm/object.cc b/runtime/vm/object.cc
index 1903854..c52f156 100644
--- a/runtime/vm/object.cc
+++ b/runtime/vm/object.cc
@@ -18961,9 +18961,9 @@
   if (Symbol::IsSymbolCid(GetClassId())) {
     hash = Symbol::CanonicalizeHash(*this);
   } else {
-    const intptr_t instance_size = SizeFromClass();
-    ASSERT(instance_size != 0);
-    hash = instance_size / kCompressedWordSize;
+    const intptr_t class_id = cls.id();
+    ASSERT(class_id != 0);
+    hash = class_id;
     uword this_addr = reinterpret_cast<uword>(this->untag());
     Object& obj = Object::Handle(zone);
     Instance& instance = Instance::Handle(zone);
diff --git a/runtime/vm/object_test.cc b/runtime/vm/object_test.cc
index dae798f..93cfc12 100644
--- a/runtime/vm/object_test.cc
+++ b/runtime/vm/object_test.cc
@@ -5029,6 +5029,64 @@
                                         /*check_identity=*/false));
 }
 
+// Because we want to reuse CanonicalizeHash for hashCode, we should not have
+// collisions.
+TEST_CASE(CanonicalizeHash_Const_Instances) {
+  const char* kScript =
+      "class A {\n"
+      "  final int n;\n"
+      "  \n"
+      "  const A(this.n);\n"
+      "}\n"
+      "\n"
+      "class B {\n"
+      "  final int n;\n"
+      "  \n"
+      "  const B(this.n);\n"
+      "}\n"
+      "\n"
+      "valueA() {\n"
+      "  return const A(5);\n"
+      "}\n"
+      "\n"
+      "valueB() {\n"
+      "  return const B(5);\n"
+      "}\n";
+
+  Dart_Handle lib = TestCase::LoadTestScript(kScript, nullptr);
+  EXPECT_VALID(lib);
+
+  Dart_Handle value_a_result =
+      Dart_Invoke(lib, NewString("valueA"), 0, nullptr);
+  EXPECT_VALID(value_a_result);
+  Dart_Handle value_b_result =
+      Dart_Invoke(lib, NewString("valueB"), 0, nullptr);
+  EXPECT_VALID(value_b_result);
+
+  TransitionNativeToVM transition(Thread::Current());
+
+  const auto& value_a_dart = Instance::CheckedHandle(
+      Thread::Current()->zone(), Api::UnwrapHandle(value_a_result));
+  const auto& value_b_dart = Instance::CheckedHandle(
+      Thread::Current()->zone(), Api::UnwrapHandle(value_b_result));
+
+  const uint32_t canonicalize_hash_a = value_a_dart.CanonicalizeHash();
+  const uint32_t canonicalize_hash_b = value_b_dart.CanonicalizeHash();
+
+  bool success = canonicalize_hash_a != canonicalize_hash_b;
+
+  if (!success) {
+    LogBlock lb;
+    THR_Print("Hash collision between %s and %s\n", value_a_dart.ToCString(),
+              value_b_dart.ToCString());
+    THR_Print("VM CanonicalizeHash a %" Px32 " %" Pd32 "\n",
+              canonicalize_hash_a, canonicalize_hash_a);
+    THR_Print("VM CanonicalizeHash b %" Px32 " %" Pd32 "\n",
+              canonicalize_hash_b, canonicalize_hash_b);
+  }
+  EXPECT(success);
+}
+
 TEST_CASE(LinkedHashMap_iteration) {
   const char* kScript =
       "makeMap() {\n"
diff --git a/tools/VERSION b/tools/VERSION
index ce0eb0e..b155add 100644
--- a/tools/VERSION
+++ b/tools/VERSION
@@ -27,5 +27,5 @@
 MAJOR 2
 MINOR 14
 PATCH 0
-PRERELEASE 353
+PRERELEASE 354
 PRERELEASE_PATCH 0
\ No newline at end of file
diff --git a/utils/application_snapshot.gni b/utils/application_snapshot.gni
index 317153a..6a2efbb 100644
--- a/utils/application_snapshot.gni
+++ b/utils/application_snapshot.gni
@@ -82,6 +82,9 @@
   # Build the kernel file using the prebuilt VM to speed up the debug and
   # simulator builds.
   prebuilt_dart_action(target_name + "_dill") {
+    if (defined(invoker.pool)) {
+      pool = invoker.pool
+    }
     deps = extra_deps + [
              "$_dart_root/runtime/vm:kernel_platform_files($host_toolchain)",
              "$_dart_root/runtime/vm:vm_platform",
@@ -131,6 +134,9 @@
 
   # Create a snapshot from kernel built above.
   dart_action(target_name) {
+    if (defined(invoker.pool)) {
+      pool = invoker.pool
+    }
     deps = extra_deps + [ ":${target_name}_dill" ]
     depfile = "$output.d"
 
diff --git a/utils/compile_platform.gni b/utils/compile_platform.gni
index 447ed64..37c3407 100644
--- a/utils/compile_platform.gni
+++ b/utils/compile_platform.gni
@@ -41,6 +41,9 @@
   }
 
   prebuilt_dart_action(target_name) {
+    if (defined(invoker.pool)) {
+      pool = invoker.pool
+    }
     script = "$_dart_root/pkg/front_end/tool/_fasta/compile_platform.dart"
 
     packages = "$_dart_root/.packages"