diff --git a/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart b/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart
index 73122407f78..54a1efcf8a3 100644
--- a/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart
+++ b/pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart
@@ -7010,6 +7010,34 @@ const MessageCode messageLoadLibraryTakesNoArguments = const MessageCode(
     analyzerCodes: <String>["LOAD_LIBRARY_TAKES_NO_ARGUMENTS"],
     problemMessage: r"""'loadLibrary' takes no arguments.""");
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Template<
+    Message Function(
+        String
+            name)> templateMacroClassNotDeclaredMacro = const Template<
+        Message Function(String name)>(
+    problemMessageTemplate:
+        r"""Non-abstract class '#name' implements 'Macro' but isn't declared as a macro class.""",
+    correctionMessageTemplate: r"""Try adding the 'macro' class modifier.""",
+    withArguments: _withArgumentsMacroClassNotDeclaredMacro);
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Message Function(String name)> codeMacroClassNotDeclaredMacro =
+    const Code<Message Function(String name)>(
+  "MacroClassNotDeclaredMacro",
+);
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+Message _withArgumentsMacroClassNotDeclaredMacro(String name) {
+  if (name.isEmpty) throw 'No name provided';
+  name = demangleMixinApplicationName(name);
+  return new Message(codeMacroClassNotDeclaredMacro,
+      problemMessage:
+          """Non-abstract class '${name}' implements 'Macro' but isn't declared as a macro class.""",
+      correctionMessage: """Try adding the 'macro' class modifier.""",
+      arguments: {'name': name});
+}
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Code<Null> codeMainNotFunctionDeclaration =
     messageMainNotFunctionDeclaration;
diff --git a/pkg/front_end/lib/src/fasta/incremental_compiler.dart b/pkg/front_end/lib/src/fasta/incremental_compiler.dart
index 3e10ccd295a..74902b33bdb 100644
--- a/pkg/front_end/lib/src/fasta/incremental_compiler.dart
+++ b/pkg/front_end/lib/src/fasta/incremental_compiler.dart
@@ -1749,6 +1749,7 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
         loader: lastGoodKernelTarget.loader,
         nameOrigin: libraryBuilder,
         isUnsupported: libraryBuilder.isUnsupported,
+        isAugmentation: false,
       );
       libraryBuilder.scope.forEachLocalMember((name, member) {
         debugLibrary.scope.addLocalMember(name, member, setter: false);
@@ -1803,6 +1804,7 @@ class IncrementalCompiler implements IncrementalKernelGenerator {
         scope: debugLibrary.scope.createNestedScope("expression"),
         nameOrigin: libraryBuilder,
         isUnsupported: libraryBuilder.isUnsupported,
+        isAugmentation: false,
       );
 
       HybridFileSystem hfs =
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 755208cb3d1..55f7c9a2197 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_target.dart
@@ -427,12 +427,25 @@ class KernelTarget extends TargetImplementation {
   Future<void> _buildForPhase1(
       Iterable<SourceLibraryBuilder> augmentationLibraries) async {
     await loader.buildOutlines();
+    // Normally patch libraries are applied in [SourceLoader.resolveParts].
+    // For augmentation libraries we instead apply them directly here.
+    for (SourceLibraryBuilder augmentationLibrary in augmentationLibraries) {
+      augmentationLibrary.applyPatches();
+    }
     loader.computeLibraryScopes(augmentationLibraries);
     // TODO(johnniwinther): Support computation of macro applications in
     // augmentation libraries?
     loader.resolveTypes(augmentationLibraries);
   }
 
+  /// Builds [augmentationLibrary] to the state expected after applying phase
+  /// 2 macros.
+  void _buildForPhase2(SourceLibraryBuilder augmentationLibrary) {
+    augmentationLibrary.finishTypeVariables(objectClassBuilder, dynamicType);
+    augmentationLibrary.build(loader.coreLibrary, modifyTarget: false);
+    augmentationLibrary.resolveConstructors();
+  }
+
   Future<BuildResult> buildOutlines({CanonicalName? nameRoot}) async {
     if (loader.first == null) return new BuildResult();
     return withCrashReporting<BuildResult>(() async {
@@ -483,7 +496,8 @@ class KernelTarget extends TargetImplementation {
           loader.checkSemantics(objectClassBuilder);
 
       benchmarker?.enterPhase(BenchmarkPhases.outline_finishTypeVariables);
-      loader.finishTypeVariables(objectClassBuilder, dynamicType);
+      loader.finishTypeVariables(
+          loader.sourceLibraryBuilders, objectClassBuilder, dynamicType);
 
       benchmarker
           ?.enterPhase(BenchmarkPhases.outline_createTypeInferenceEngine);
@@ -500,7 +514,7 @@ class KernelTarget extends TargetImplementation {
       installSyntheticConstructors(sourceClassBuilders);
 
       benchmarker?.enterPhase(BenchmarkPhases.outline_resolveConstructors);
-      loader.resolveConstructors();
+      loader.resolveConstructors(loader.sourceLibraryBuilders);
 
       benchmarker?.enterPhase(BenchmarkPhases.outline_link);
       component =
@@ -517,8 +531,11 @@ class KernelTarget extends TargetImplementation {
 
       if (macroApplications != null) {
         benchmarker?.enterPhase(BenchmarkPhases.outline_applyDeclarationMacros);
-        await macroApplications
-            .applyDeclarationsMacros(loader.hierarchyBuilder);
+        await macroApplications.applyDeclarationsMacros(loader.hierarchyBuilder,
+            (SourceLibraryBuilder augmentationLibrary) async {
+          await _buildForPhase1([augmentationLibrary]);
+          _buildForPhase2(augmentationLibrary);
+        });
       }
 
       benchmarker
diff --git a/pkg/front_end/lib/src/fasta/kernel/macro.dart b/pkg/front_end/lib/src/fasta/kernel/macro.dart
index c4a34b36798..c81a969b94c 100644
--- a/pkg/front_end/lib/src/fasta/kernel/macro.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/macro.dart
@@ -116,6 +116,7 @@ class MacroApplications {
   final macro.MacroExecutor _macroExecutor;
   final Map<SourceLibraryBuilder, LibraryMacroApplicationData> libraryData;
   final MacroApplicationDataForTesting? dataForTesting;
+  List<_ApplicationData>? _applicationDataCache;
 
   MacroApplications(
       this._macroExecutor, this.libraryData, this.dataForTesting) {
@@ -272,60 +273,57 @@ class MacroApplications {
     }
   }
 
-  Future<Map<SourceLibraryBuilder, List<macro.MacroExecutionResult>>>
-      _applyMacros(
-          Future<List<macro.MacroExecutionResult>> Function(
-                  Builder, macro.Declaration, List<MacroApplication>)
-              applyMacros) async {
-    Map<SourceLibraryBuilder, List<macro.MacroExecutionResult>> libraryResults =
-        {};
-    for (MapEntry<SourceLibraryBuilder,
-        LibraryMacroApplicationData> libraryEntry in libraryData.entries) {
-      SourceLibraryBuilder libraryBuilder = libraryEntry.key;
-      List<macro.MacroExecutionResult> results = [];
-      LibraryMacroApplicationData libraryMacroApplicationData =
-          libraryEntry.value;
-      for (MapEntry<MemberBuilder, List<MacroApplication>> memberEntry
-          in libraryMacroApplicationData.memberApplications.entries) {
-        MemberBuilder memberBuilder = memberEntry.key;
-        macro.Declaration? declaration = _getMemberDeclaration(memberBuilder);
-        if (declaration != null) {
-          results.addAll(
-              await applyMacros(memberBuilder, declaration, memberEntry.value));
-        }
-      }
-      for (MapEntry<SourceClassBuilder, ClassMacroApplicationData> classEntry
-          in libraryMacroApplicationData.classData.entries) {
-        SourceClassBuilder classBuilder = classEntry.key;
-        ClassMacroApplicationData classData = classEntry.value;
-        List<MacroApplication>? classApplications = classData.classApplications;
-        if (classApplications != null) {
-          macro.ClassDeclaration classDeclaration =
-              _getClassDeclaration(classBuilder);
-          results.addAll(await applyMacros(
-              classBuilder, classDeclaration, classApplications));
-        }
+  Iterable<_ApplicationData> get _applicationData {
+    if (_applicationDataCache == null) {
+      List<_ApplicationData> data = _applicationDataCache = [];
+      for (MapEntry<SourceLibraryBuilder,
+          LibraryMacroApplicationData> libraryEntry in libraryData.entries) {
+        SourceLibraryBuilder libraryBuilder = libraryEntry.key;
+        LibraryMacroApplicationData libraryMacroApplicationData =
+            libraryEntry.value;
         for (MapEntry<MemberBuilder, List<MacroApplication>> memberEntry
-            in classData.memberApplications.entries) {
+            in libraryMacroApplicationData.memberApplications.entries) {
           MemberBuilder memberBuilder = memberEntry.key;
           macro.Declaration? declaration = _getMemberDeclaration(memberBuilder);
           if (declaration != null) {
-            results.addAll(await applyMacros(
-                memberBuilder, declaration, memberEntry.value));
+            data.add(new _ApplicationData(
+                libraryBuilder, memberBuilder, declaration, memberEntry.value));
+          }
+        }
+        for (MapEntry<SourceClassBuilder, ClassMacroApplicationData> classEntry
+            in libraryMacroApplicationData.classData.entries) {
+          SourceClassBuilder classBuilder = classEntry.key;
+          ClassMacroApplicationData classData = classEntry.value;
+          List<MacroApplication>? classApplications =
+              classData.classApplications;
+          if (classApplications != null) {
+            macro.ClassDeclaration classDeclaration =
+                _getClassDeclaration(classBuilder);
+            data.add(new _ApplicationData(libraryBuilder, classBuilder,
+                classDeclaration, classApplications));
+          }
+          for (MapEntry<MemberBuilder, List<MacroApplication>> memberEntry
+              in classData.memberApplications.entries) {
+            MemberBuilder memberBuilder = memberEntry.key;
+            macro.Declaration? declaration =
+                _getMemberDeclaration(memberBuilder);
+            if (declaration != null) {
+              data.add(new _ApplicationData(libraryBuilder, memberBuilder,
+                  declaration, memberEntry.value));
+            }
           }
         }
       }
-      libraryResults[libraryBuilder] = results;
     }
-    return libraryResults;
+    return _applicationDataCache!;
   }
 
   Future<List<macro.MacroExecutionResult>> _applyTypeMacros(
-      Builder builder,
-      macro.Declaration declaration,
-      List<MacroApplication> macroApplications) async {
+      _ApplicationData applicationData) async {
+    macro.Declaration declaration = applicationData.declaration;
     List<macro.MacroExecutionResult> results = [];
-    for (MacroApplication macroApplication in macroApplications) {
+    for (MacroApplication macroApplication
+        in applicationData.macroApplications) {
       if (macroApplication.instanceIdentifier
           .shouldExecute(_declarationKind(declaration), macro.Phase.types)) {
         macro.MacroExecutionResult result =
@@ -336,6 +334,7 @@ class MacroApplications {
     }
 
     if (retainDataForTesting) {
+      Builder builder = applicationData.builder;
       if (builder is SourceClassBuilder) {
         dataForTesting?.classTypesResults[builder] = results;
       } else {
@@ -347,8 +346,13 @@ class MacroApplications {
 
   Future<List<SourceLibraryBuilder>> applyTypeMacros() async {
     List<SourceLibraryBuilder> augmentationLibraries = [];
-    Map<SourceLibraryBuilder, List<macro.MacroExecutionResult>> results =
-        await _applyMacros(_applyTypeMacros);
+    Map<SourceLibraryBuilder, List<macro.MacroExecutionResult>> results = {};
+    for (_ApplicationData macroApplication in _applicationData) {
+      List<macro.MacroExecutionResult> executionResults =
+          await _applyTypeMacros(macroApplication);
+      (results[macroApplication.libraryBuilder] ??= [])
+          .addAll(executionResults);
+    }
     for (MapEntry<SourceLibraryBuilder, List<macro.MacroExecutionResult>> entry
         in results.entries) {
       SourceLibraryBuilder sourceLibraryBuilder = entry.key;
@@ -363,12 +367,12 @@ class MacroApplications {
     return augmentationLibraries;
   }
 
-  Future<List<macro.MacroExecutionResult>> _applyDeclarationsMacros(
-      Builder builder,
-      macro.Declaration declaration,
-      List<MacroApplication> macroApplications) async {
+  Future<void> _applyDeclarationsMacros(_ApplicationData applicationData,
+      Future<void> Function(SourceLibraryBuilder) onAugmentationLibrary) async {
     List<macro.MacroExecutionResult> results = [];
-    for (MacroApplication macroApplication in macroApplications) {
+    macro.Declaration declaration = applicationData.declaration;
+    for (MacroApplication macroApplication
+        in applicationData.macroApplications) {
       if (macroApplication.instanceIdentifier.shouldExecute(
           _declarationKind(declaration), macro.Phase.declarations)) {
         macro.MacroExecutionResult result =
@@ -377,10 +381,19 @@ class MacroApplications {
                 declaration,
                 typeResolver,
                 classIntrospector);
-        results.add(result);
+        String source = _macroExecutor
+            .buildAugmentationLibrary([result], _resolveIdentifier);
+        SourceLibraryBuilder augmentationLibrary = await applicationData
+            .libraryBuilder
+            .createAugmentationLibrary(source);
+        await onAugmentationLibrary(augmentationLibrary);
+        if (retainDataForTesting) {
+          results.add(result);
+        }
       }
     }
     if (retainDataForTesting) {
+      Builder builder = applicationData.builder;
       if (builder is SourceClassBuilder) {
         dataForTesting?.classDeclarationsResults[builder] = results;
       } else {
@@ -388,27 +401,28 @@ class MacroApplications {
             results;
       }
     }
-    return results;
   }
 
   late Types types;
   late macro.TypeResolver typeResolver;
   late macro.ClassIntrospector classIntrospector;
 
-  Future<void> applyDeclarationsMacros(
-      ClassHierarchyBase classHierarchy) async {
+  Future<void> applyDeclarationsMacros(ClassHierarchyBase classHierarchy,
+      Future<void> Function(SourceLibraryBuilder) onAugmentationLibrary) async {
     types = new Types(classHierarchy);
     typeResolver = new _TypeResolver(this);
     classIntrospector = new _ClassIntrospector(this);
-    await _applyMacros(_applyDeclarationsMacros);
+    for (_ApplicationData macroApplication in _applicationData) {
+      await _applyDeclarationsMacros(macroApplication, onAugmentationLibrary);
+    }
   }
 
   Future<List<macro.MacroExecutionResult>> _applyDefinitionMacros(
-      Builder builder,
-      macro.Declaration declaration,
-      List<MacroApplication> macroApplications) async {
+      _ApplicationData applicationData) async {
     List<macro.MacroExecutionResult> results = [];
-    for (MacroApplication macroApplication in macroApplications) {
+    macro.Declaration declaration = applicationData.declaration;
+    for (MacroApplication macroApplication
+        in applicationData.macroApplications) {
       if (macroApplication.instanceIdentifier.shouldExecute(
           _declarationKind(declaration), macro.Phase.definitions)) {
         macro.MacroExecutionResult result =
@@ -422,6 +436,7 @@ class MacroApplications {
       }
     }
     if (retainDataForTesting) {
+      Builder builder = applicationData.builder;
       if (builder is SourceClassBuilder) {
         dataForTesting?.classDefinitionsResults[builder] = results;
       } else {
@@ -436,13 +451,16 @@ class MacroApplications {
 
   Future<void> applyDefinitionMacros() async {
     typeDeclarationResolver = new _TypeDeclarationResolver();
-    await _applyMacros(_applyDefinitionMacros);
+    for (_ApplicationData macroApplication in _applicationData) {
+      await _applyDefinitionMacros(macroApplication);
+    }
   }
 
   void close() {
     _macroExecutor.close();
     _staticTypeCache.clear();
     _typeAnnotationCache.clear();
+    _applicationDataCache?.clear();
   }
 
   macro.ClassDeclaration _createClassDeclaration(SourceClassBuilder builder) {
@@ -951,3 +969,14 @@ macro.DeclarationKind _declarationKind(macro.Declaration declaration) {
   throw new UnsupportedError(
       "Unexpected declaration ${declaration} (${declaration.runtimeType})");
 }
+
+/// Data needed to apply a list of macro applications to a class or member.
+class _ApplicationData {
+  final SourceLibraryBuilder libraryBuilder;
+  final Builder builder;
+  final macro.Declaration declaration;
+  final List<MacroApplication> macroApplications;
+
+  _ApplicationData(this.libraryBuilder, this.builder, this.declaration,
+      this.macroApplications);
+}
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 128d00fd92f..d26b6a20f02 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
@@ -618,8 +618,11 @@ class SourceClassBuilder extends ClassBuilderImpl
     }
   }
 
-  void checkSupertypes(CoreTypes coreTypes,
-      ClassHierarchyBuilder hierarchyBuilder, Class enumClass) {
+  void checkSupertypes(
+      CoreTypes coreTypes,
+      ClassHierarchyBuilder hierarchyBuilder,
+      Class enumClass,
+      Class? macroClass) {
     // This method determines whether the class (that's being built) its super
     // class appears both in 'extends' and 'implements' clauses and whether any
     // interface appears multiple times in the 'implements' clause.
@@ -679,6 +682,27 @@ class SourceClassBuilder extends ClassBuilderImpl
         }
       }
     }
+    if (macroClass != null && !cls.isMacro && !cls.isAbstract) {
+      // TODO(johnniwinther): Merge this check with the loop above.
+      bool isMacroFound = false;
+      List<Supertype> interfaces =
+          hierarchyBuilder.getNodeFromClass(cls).superclasses;
+      for (int i = 0; !isMacroFound && i < interfaces.length; i++) {
+        if (interfaces[i].classNode == macroClass) {
+          isMacroFound = true;
+        }
+      }
+      interfaces = hierarchyBuilder.getNodeFromClass(cls).interfaces;
+      for (int i = 0; !isMacroFound && i < interfaces.length; i++) {
+        if (interfaces[i].classNode == macroClass) {
+          isMacroFound = true;
+        }
+      }
+      if (isMacroFound) {
+        addProblem(templateMacroClassNotDeclaredMacro.withArguments(name),
+            charOffset, noLength);
+      }
+    }
 
     void fail(NamedTypeBuilder target, Message message,
         TypeAliasBuilder? aliasBuilder) {
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 878536f8e17..37de8c94cf5 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
@@ -243,6 +243,9 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
 
   List<SourceLibraryBuilder>? _patchLibraries;
 
+  /// `true` if this is an augmentation library.
+  final bool isAugmentation;
+
   SourceLibraryBuilder.internal(
       SourceLoader loader,
       Uri fileUri,
@@ -253,8 +256,9 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
       Library library,
       LibraryBuilder? nameOrigin,
       Library? referencesFrom,
-      bool? referenceIsPartOwner,
-      bool isUnsupported)
+      {bool? referenceIsPartOwner,
+      required bool isUnsupported,
+      required bool isAugmentation})
       : this.fromScopes(
             loader,
             fileUri,
@@ -266,7 +270,8 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
             library,
             nameOrigin,
             referencesFrom,
-            isUnsupported);
+            isUnsupported: isUnsupported,
+            isAugmentation: isAugmentation);
 
   SourceLibraryBuilder.fromScopes(
       this.loader,
@@ -279,7 +284,8 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
       this.library,
       this._nameOrigin,
       this.referencesFrom,
-      this.isUnsupported)
+      {required this.isUnsupported,
+      required this.isAugmentation})
       : _languageVersion = packageLanguageVersion,
         currentTypeParameterScopeBuilder = _libraryTypeParameterScopeBuilder,
         referencesFromIndexed =
@@ -469,7 +475,8 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
       LibraryBuilder? nameOrigin,
       Library? referencesFrom,
       bool? referenceIsPartOwner,
-      required bool isUnsupported})
+      required bool isUnsupported,
+      required bool isAugmentation})
       : this.internal(
             loader,
             fileUri,
@@ -487,8 +494,9 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
                   ..setLanguageVersion(packageLanguageVersion.version)),
             nameOrigin,
             referencesFrom,
-            referenceIsPartOwner,
-            isUnsupported);
+            referenceIsPartOwner: referenceIsPartOwner,
+            isUnsupported: isUnsupported,
+            isAugmentation: isAugmentation);
 
   @override
   bool get isPart => partOfName != null || partOfUri != null;
@@ -520,7 +528,8 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
         loader: loader,
         isUnsupported: false,
         target: library,
-        origin: this);
+        origin: this,
+        isAugmentation: true);
     addPatchLibrary(augmentationLibrary);
     loader.registerUnparsedLibrarySource(augmentationLibrary, source);
     return augmentationLibrary;
@@ -3896,9 +3905,11 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
       Builder member = patchDeclarations.current;
       // We need to inject all non-patch members into the origin library. This
       // should only apply to private members.
+      // For augmentation libraries, all members are injected into the origin
+      // library, regardless of privacy.
       if (member.isPatch) {
         // Ignore patches.
-      } else if (name.startsWith("_")) {
+      } else if (name.startsWith("_") || isAugmentation) {
         origin.injectMemberFromPatch(name, member);
       } else {
         origin.exportMemberFromPatch(name, member);
diff --git a/pkg/front_end/lib/src/fasta/source/source_loader.dart b/pkg/front_end/lib/src/fasta/source/source_loader.dart
index a429ef014a4..b77b5c9684f 100644
--- a/pkg/front_end/lib/src/fasta/source/source_loader.dart
+++ b/pkg/front_end/lib/src/fasta/source/source_loader.dart
@@ -328,7 +328,8 @@ class SourceLoader extends Loader {
         referenceIsPartOwner: referenceIsPartOwner,
         isUnsupported: origin?.library.isUnsupported ??
             importUri.isScheme('dart') &&
-                !target.uriTranslator.isLibrarySupported(importUri.path));
+                !target.uriTranslator.isLibrarySupported(importUri.path),
+        isAugmentation: false);
   }
 
   /// Return `"true"` if the [dottedName] is a 'dart.library.*' qualifier for a
@@ -1689,9 +1690,9 @@ severity: $severity
     ticker.logMs("Finished forwarders for $count procedures");
   }
 
-  void resolveConstructors() {
+  void resolveConstructors(List<SourceLibraryBuilder> libraryBuilders) {
     int count = 0;
-    for (SourceLibraryBuilder library in sourceLibraryBuilders) {
+    for (SourceLibraryBuilder library in libraryBuilders) {
       count += library.resolveConstructors();
     }
     ticker.logMs("Resolved $count constructors");
@@ -1705,9 +1706,10 @@ severity: $severity
     }
   }
 
-  void finishTypeVariables(ClassBuilder object, TypeBuilder dynamicType) {
+  void finishTypeVariables(Iterable<SourceLibraryBuilder> libraryBuilders,
+      ClassBuilder object, TypeBuilder dynamicType) {
     int count = 0;
-    for (SourceLibraryBuilder library in sourceLibraryBuilders) {
+    for (SourceLibraryBuilder library in libraryBuilders) {
       count += library.finishTypeVariables(object, dynamicType);
     }
     ticker.logMs("Resolved $count type-variable bounds");
@@ -2065,7 +2067,8 @@ severity: $severity
       List<SourceClassBuilder> sourceClasses, Class enumClass) {
     for (SourceClassBuilder builder in sourceClasses) {
       if (builder.library.loader == this && !builder.isPatch) {
-        builder.checkSupertypes(coreTypes, hierarchyBuilder, enumClass);
+        builder.checkSupertypes(
+            coreTypes, hierarchyBuilder, enumClass, _macroClassBuilder?.cls);
       }
     }
     ticker.logMs("Checked supertypes");
diff --git a/pkg/front_end/messages.status b/pkg/front_end/messages.status
index 0e1957f7a4a..b2e67dc1e73 100644
--- a/pkg/front_end/messages.status
+++ b/pkg/front_end/messages.status
@@ -578,6 +578,8 @@ LibraryDirectiveNotFirst/script2: Fail
 LibraryDirectiveNotFirst/script3: Fail
 ListLiteralTooManyTypeArguments/example: Fail
 LoadLibraryTakesNoArguments/example: Fail
+MacroClassNotDeclaredMacro/analyzerCode: Fail
+MacroClassNotDeclaredMacro/example: Fail
 MainNotFunctionDeclaration/analyzerCode: Fail
 MainNotFunctionDeclarationExported/analyzerCode: Fail
 MainNotFunctionDeclarationExported/part_wrapped_script: Fail
diff --git a/pkg/front_end/messages.yaml b/pkg/front_end/messages.yaml
index 043a64d4958..72c975af48c 100644
--- a/pkg/front_end/messages.yaml
+++ b/pkg/front_end/messages.yaml
@@ -5479,3 +5479,7 @@ EnumContainsValuesDeclaration:
 
 EnumImplementerContainsValuesDeclaration:
   problemMessage: "'#name' has 'Enum' as a superinterface and can't contain non-static member with name 'values'."
+
+MacroClassNotDeclaredMacro:
+  problemMessage: "Non-abstract class '#name' implements 'Macro' but isn't declared as a macro class."
+  correctionMessage: "Try adding the 'macro' class modifier."
diff --git a/pkg/front_end/test/fasta/generator_to_string_test.dart b/pkg/front_end/test/fasta/generator_to_string_test.dart
index 787ad86e8c0..9db87a411ff 100644
--- a/pkg/front_end/test/fasta/generator_to_string_test.dart
+++ b/pkg/front_end/test/fasta/generator_to_string_test.dart
@@ -95,7 +95,8 @@ Future<void> main() async {
                     new NoneTarget(new TargetFlags())),
                 uriTranslator)
             .loader,
-        isUnsupported: false);
+        isUnsupported: false,
+        isAugmentation: false);
     libraryBuilder.markLanguageVersionFinal();
     LoadLibraryBuilder loadLibraryBuilder =
         new LoadLibraryBuilder(libraryBuilder, dummyLibraryDependency, -1);
diff --git a/pkg/front_end/test/macro_application/data/pkgs/macro/lib/macro.dart b/pkg/front_end/test/macro_application/data/pkgs/macro/lib/macro.dart
index 5f4db94a541..15d9fb7cb9c 100644
--- a/pkg/front_end/test/macro_application/data/pkgs/macro/lib/macro.dart
+++ b/pkg/front_end/test/macro_application/data/pkgs/macro/lib/macro.dart
@@ -51,7 +51,8 @@ class FunctionTypesMacro1 implements FunctionTypesMacro {
         name, new DeclarationCode.fromParts(['''
 class $name {
   external ''', function.returnType.code, ''' method();
-}''']));
+}'''
+    ]));
   }
 }
 
@@ -129,8 +130,14 @@ class MethodDeclarationsMacro1 implements MethodDeclarationsMacro {
     if (method.isSetter) {
       sb.write('s');
     }
+    String name;
+    if (method.isOperator) {
+      name = 'operator';
+    } else {
+      name = method.identifier.name;
+    }
     builder.declareInLibrary(new DeclarationCode.fromString('''
-void ${method.definingClass.name}_${method.identifier.name}GeneratedMethod_${sb}() {}
+void ${method.definingClass.name}_${name}GeneratedMethod_${sb}() {}
 '''));
   }
 }
@@ -288,3 +295,31 @@ void ${constructor.definingClass.name}_${constructor.identifier
 '''));
   }
 }
+
+macro
+
+class ToStringMacro implements ClassDeclarationsMacro {
+  const ToStringMacro();
+
+  FutureOr<void> buildDeclarationsForClass(ClassDeclaration clazz,
+      ClassMemberDeclarationBuilder builder) async {
+    Iterable<MethodDeclaration> methods = await builder.methodsOf(clazz);
+    if (!methods.any((m) => m.identifier.name == 'toString')) {
+      Iterable<FieldDeclaration> fields = await builder.fieldsOf(clazz);
+      List<Object> parts = ['''
+  toString() {
+    return "${clazz.identifier.name}('''];
+      String comma = '';
+      for (FieldDeclaration field in fields) {
+        parts.add(comma);
+        parts.add('${field.identifier.name}=\${');
+        parts.add(field.identifier.name);
+        parts.add('}');
+        comma = ',';
+    }
+    parts.add(''')";
+  }''');
+      builder.declareInClass(new DeclarationCode.fromParts(parts));
+    }
+  }
+}
\ No newline at end of file
diff --git a/pkg/front_end/test/macro_application/data/tests/declarations.dart b/pkg/front_end/test/macro_application/data/tests/declarations.dart
index dfed26d4704..7a69a25c066 100644
--- a/pkg/front_end/test/macro_application/data/tests/declarations.dart
+++ b/pkg/front_end/test/macro_application/data/tests/declarations.dart
@@ -112,7 +112,7 @@ void Class1_instanceSetter1GeneratedMethod_s() {}
   void set instanceSetter1(int? value) {}
 
   /*member: Class1.[]:
-void Class1_[]GeneratedMethod_o() {}
+void Class1_operatorGeneratedMethod_o() {}
 */
   @MethodDeclarationsMacro1()
   int operator [](int i) => i;
diff --git a/pkg/front_end/test/macro_application/data/tests/declarations.dart.expect b/pkg/front_end/test/macro_application/data/tests/declarations.dart.expect
index 786028fbd98..dfe99d0d90e 100644
--- a/pkg/front_end/test/macro_application/data/tests/declarations.dart.expect
+++ b/pkg/front_end/test/macro_application/data/tests/declarations.dart.expect
@@ -19,6 +19,9 @@ class Class1 extends core::Object {
   constructor •() → self::Class1
     : super core::Object::•()
     ;
+  method /* from org-dartlang-augmentation:/a/b/c/main.dart-18 */ Class1_GeneratedMethod_() → void {}
+  method /* from org-dartlang-augmentation:/a/b/c/main.dart-19 */ Class1_redirectGeneratedMethod_f() → void {}
+  method /* from org-dartlang-augmentation:/a/b/c/main.dart-20 */ Class1_factGeneratedMethod_f() → void {}
   @#C5
   static factory redirect() → self::Class1
     return new self::Class1::•();
@@ -68,6 +71,35 @@ static get topLevelGetter1() → core::int?
   return null;
 @#C8
 static set topLevelSetter1(core::int? value) → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-1 */ topLevelFunction1GeneratedMethod_() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-2 */ topLevelFunction2GeneratedMethod_e() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-3 */ topLevelField1GeneratedMethod_() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-4 */ topLevelField2GeneratedMethod_e() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-5 */ topLevelField3GeneratedMethod_f() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-6 */ topLevelField4GeneratedMethod_l() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-7 */ topLevelGetter1GeneratedMethod_g() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-8 */ topLevelSetter1GeneratedMethod_s() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-9 */ Class1GeneratedMethod_() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-10 */ Class1Introspection() → void {
+  core::print("constructors=''");
+  core::print("fields='instanceField1','instanceField2','instanceField3'");
+  core::print("methods='instanceMethod1','instanceGetter1','[]','instanceSetter1'");
+}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-11 */ Class1_instanceMethod1GeneratedMethod_() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-12 */ Class1_instanceGetter1GeneratedMethod_g() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-13 */ Class1_operatorGeneratedMethod_o() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-14 */ Class1_instanceField1GeneratedMethod_() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-15 */ Class1_instanceField2GeneratedMethod_f() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-16 */ Class1_instanceField3GeneratedMethod_fl() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-17 */ Class1_instanceSetter1GeneratedMethod_s() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-21 */ Class2GeneratedMethod_a() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-22 */ Class2Introspection() → void {
+  core::print("constructors=");
+  core::print("fields='instanceField1'");
+  core::print("methods='instanceMethod1'");
+}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-23 */ Class2_instanceMethod1GeneratedMethod_a() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-24 */ Class2_instanceField1GeneratedMethod_() → void {}
 
 constants  {
   #C1 = mac::ClassDeclarationsMacro1 {}
diff --git a/pkg/front_end/test/macro_application/data/tests/subtypes.dart.expect b/pkg/front_end/test/macro_application/data/tests/subtypes.dart.expect
index d4281835b79..07374b2a74b 100644
--- a/pkg/front_end/test/macro_application/data/tests/subtypes.dart.expect
+++ b/pkg/front_end/test/macro_application/data/tests/subtypes.dart.expect
@@ -52,6 +52,10 @@ external static method topLevelFunction3(self::C1 a) → self::C2;
 @#C1
 @#C2
 external static method topLevelFunction4(self::D1 a) → self::D2;
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-1 */ topLevelFunction1GeneratedMethod_es() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-2 */ topLevelFunction2GeneratedMethod_s() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-3 */ topLevelFunction3GeneratedMethod_() → void {}
+static method /* from org-dartlang-augmentation:/a/b/c/main.dart-4 */ topLevelFunction4GeneratedMethod_() → void {}
 
 constants  {
   #C1 = mac::FunctionDeclarationsMacro2 {}
diff --git a/pkg/front_end/test/macro_application/data/tests/to_string.dart b/pkg/front_end/test/macro_application/data/tests/to_string.dart
new file mode 100644
index 00000000000..b5327e537a8
--- /dev/null
+++ b/pkg/front_end/test/macro_application/data/tests/to_string.dart
@@ -0,0 +1,47 @@
+// Copyright (c) 2022, 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.
+
+/*library: 
+
+
+*/
+
+import 'package:macro/macro.dart';
+
+@ToStringMacro()
+/*class: A:
+augment class A {
+  toString() {
+    return "A(a=${a},b=${b})";
+  }
+}*/
+class A {
+  var a;
+  var b;
+}
+
+@ToStringMacro()
+/*class: B:
+augment class B {
+  toString() {
+    return "B(c=${c},d=${d},e=${e})";
+  }
+}*/
+class B {
+  var c, d;
+  var e;
+}
+
+@ToStringMacro()
+class C {
+  var f;
+
+  @override
+  String toString() => 'C()';
+}
+
+class D {
+  var g;
+  var h;
+}
diff --git a/pkg/front_end/test/macro_application/data/tests/to_string.dart.expect b/pkg/front_end/test/macro_application/data/tests/to_string.dart.expect
new file mode 100644
index 00000000000..431c8a2589f
--- /dev/null
+++ b/pkg/front_end/test/macro_application/data/tests/to_string.dart.expect
@@ -0,0 +1,52 @@
+library /*isNonNullableByDefault*/;
+import self as self;
+import "package:macro/macro.dart" as mac;
+import "dart:core" as core;
+
+import "package:macro/macro.dart";
+
+@#C1
+class A extends core::Object {
+  field dynamic a = null;
+  field dynamic b = null;
+  synthetic constructor •() → self::A
+    : super core::Object::•()
+    ;
+  method /* from org-dartlang-augmentation:/a/b/c/main.dart-1 */ toString() → dynamic {
+    return "A(a=${this.{self::A::a}{dynamic}},b=${this.{self::A::b}{dynamic}})";
+  }
+}
+@#C1
+class B extends core::Object {
+  field dynamic c = null;
+  field dynamic d = null;
+  field dynamic e = null;
+  synthetic constructor •() → self::B
+    : super core::Object::•()
+    ;
+  method /* from org-dartlang-augmentation:/a/b/c/main.dart-2 */ toString() → dynamic {
+    return "B(c=${this.{self::B::c}{dynamic}},d=${this.{self::B::d}{dynamic}},e=${this.{self::B::e}{dynamic}})";
+  }
+}
+@#C1
+class C extends core::Object {
+  field dynamic f = null;
+  synthetic constructor •() → self::C
+    : super core::Object::•()
+    ;
+  @#C2
+  method toString() → core::String
+    return "C()";
+}
+class D extends core::Object {
+  field dynamic g = null;
+  field dynamic h = null;
+  synthetic constructor •() → self::D
+    : super core::Object::•()
+    ;
+}
+
+constants  {
+  #C1 = mac::ToStringMacro {}
+  #C2 = core::_Override {}
+}
diff --git a/pkg/front_end/test/macro_application/macro_application_test.dart b/pkg/front_end/test/macro_application/macro_application_test.dart
index fd317c75e29..647c544ea6c 100644
--- a/pkg/front_end/test/macro_application/macro_application_test.dart
+++ b/pkg/front_end/test/macro_application/macro_application_test.dart
@@ -184,7 +184,9 @@ class MacroDataComputer extends DataComputer<String> {
         in macroApplicationData.classTypesResults.entries) {
       if (entry.key.cls == cls) {
         for (MacroExecutionResult result in entry.value) {
-          sb.write('\n${codeToString(result.augmentations.first)}');
+          if (result.augmentations.isNotEmpty) {
+            sb.write('\n${codeToString(result.augmentations.first)}');
+          }
         }
       }
     }
@@ -192,7 +194,9 @@ class MacroDataComputer extends DataComputer<String> {
         in macroApplicationData.classDeclarationsResults.entries) {
       if (entry.key.cls == cls) {
         for (MacroExecutionResult result in entry.value) {
-          sb.write('\n${codeToString(result.augmentations.first)}');
+          if (result.augmentations.isNotEmpty) {
+            sb.write('\n${codeToString(result.augmentations.first)}');
+          }
         }
       }
     }
@@ -200,7 +204,9 @@ class MacroDataComputer extends DataComputer<String> {
         in macroApplicationData.classDefinitionsResults.entries) {
       if (entry.key.cls == cls) {
         for (MacroExecutionResult result in entry.value) {
-          sb.write('\n${codeToString(result.augmentations.first)}');
+          if (result.augmentations.isNotEmpty) {
+            sb.write('\n${codeToString(result.augmentations.first)}');
+          }
         }
       }
     }
diff --git a/pkg/front_end/test/macros/data/tests/macro_declarations.dart b/pkg/front_end/test/macros/data/tests/macro_declarations.dart
index c780d613c87..1ddcfd501df 100644
--- a/pkg/front_end/test/macros/data/tests/macro_declarations.dart
+++ b/pkg/front_end/test/macros/data/tests/macro_declarations.dart
@@ -38,20 +38,20 @@ macro class ImplementsAlias implements Alias {}
 
 macro class MixinAlias with Alias {}
 
-class ExtendsNoKeyword extends Macro {}
+class /*error: error=MacroClassNotDeclaredMacro*/ExtendsNoKeyword extends Macro {}
 
-class ImplementsNoKeyword implements Macro {}
+class /*error: error=MacroClassNotDeclaredMacro*/ImplementsNoKeyword implements Macro {}
 
-class MixinNoKeyword with Macro {}
+class /*error: error=MacroClassNotDeclaredMacro*/MixinNoKeyword with Macro {}
 
-class ExtendsAliasNoKeyword extends Alias {}
+class /*error: error=MacroClassNotDeclaredMacro*/ExtendsAliasNoKeyword extends Alias {}
 
-class ImplementsAliasNoKeyword implements Alias {}
+class /*error: error=MacroClassNotDeclaredMacro*/ImplementsAliasNoKeyword implements Alias {}
 
-class MixinAliasNoKeyword with Alias {}
+class /*error: error=MacroClassNotDeclaredMacro*/MixinAliasNoKeyword with Alias {}
 
-class NamedMixin1NoKeyword = Macro with _Mixin;
+class /*error: error=MacroClassNotDeclaredMacro*/NamedMixin1NoKeyword = Macro with _Mixin;
 
-class NamedMixin2NoKeyword = Object with Macro;
+class /*error: error=MacroClassNotDeclaredMacro*/NamedMixin2NoKeyword = Object with Macro;
 
 void main() {}
diff --git a/pkg/front_end/test/macros/macro_test.dart b/pkg/front_end/test/macros/macro_test.dart
index e583b6be846..a20eaf24e1c 100644
--- a/pkg/front_end/test/macros/macro_test.dart
+++ b/pkg/front_end/test/macros/macro_test.dart
@@ -17,6 +17,7 @@ import 'package:front_end/src/fasta/builder/library_builder.dart';
 import 'package:front_end/src/fasta/builder/member_builder.dart';
 import 'package:front_end/src/fasta/kernel/macro.dart';
 import 'package:front_end/src/testing/id_testing_helper.dart';
+import 'package:front_end/src/testing/id_testing_utils.dart';
 import 'package:kernel/ast.dart' hide Arguments;
 
 Future<void> main(List<String> args) async {
@@ -77,6 +78,17 @@ class MacroDataComputer extends DataComputer<Features> {
         .computeForLibrary(library);
   }
 
+  @override
+  bool get supportsErrors => true;
+
+  @override
+  Features? computeErrorData(
+      TestResultData testResultData, Id id, List<FormattedMessage> errors) {
+    Features features = new Features();
+    features[Tags.error] = errorsToText(errors, useCodes: true);
+    return features;
+  }
+
   @override
   DataInterpreter<Features> get dataValidator =>
       const FeaturesDataInterpreter();
@@ -91,6 +103,7 @@ class Tags {
   static const String appliedMacros = 'appliedMacros';
   static const String macroClassIds = 'macroClassIds';
   static const String macroInstanceIds = 'macroInstanceIds';
+  static const String error = 'error';
 }
 
 String constructorNameToString(String constructorName) {
diff --git a/pkg/front_end/test/spell_checking_list_messages.txt b/pkg/front_end/test/spell_checking_list_messages.txt
index 3230d251102..e6964cdc50e 100644
--- a/pkg/front_end/test/spell_checking_list_messages.txt
+++ b/pkg/front_end/test/spell_checking_list_messages.txt
@@ -45,6 +45,7 @@ js_util
 libraries.json
 list.filled
 loadlibrary
+macro
 migrate
 name.#name
 name.stack
diff --git a/pkg/front_end/tool/dart_doctest_impl.dart b/pkg/front_end/tool/dart_doctest_impl.dart
index 6481a4c22f6..09a9e7f6149 100644
--- a/pkg/front_end/tool/dart_doctest_impl.dart
+++ b/pkg/front_end/tool/dart_doctest_impl.dart
@@ -834,6 +834,7 @@ class DocTestIncrementalCompiler extends IncrementalCompiler {
       scope: libraryBuilder.scope.createNestedScope("dartdoctest"),
       nameOrigin: libraryBuilder,
       isUnsupported: false,
+      isAugmentation: false,
     );
 
     if (libraryBuilder is DillLibraryBuilder) {