diff --git a/pkg/analyzer/lib/src/generated/resolver.dart b/pkg/analyzer/lib/src/generated/resolver.dart
index 0382710..91657b9 100644
--- a/pkg/analyzer/lib/src/generated/resolver.dart
+++ b/pkg/analyzer/lib/src/generated/resolver.dart
@@ -473,6 +473,14 @@
   }
 
   @override
+  void visitFunctionExpression(FunctionExpression node) {
+    if (node.parent is! FunctionDeclaration) {
+      _checkForMissingReturn(null, node.body, node.element, node);
+    }
+    super.visitFunctionExpression(node);
+  }
+
+  @override
   void visitImportDirective(ImportDirective node) {
     _checkForDeprecatedMemberUse(node.uriElement, node);
     ImportElement importElement = node.element;
@@ -1034,7 +1042,27 @@
       var flattenedType =
           body.isAsynchronous ? _typeSystem.flatten(returnType) : returnType;
 
-      // dynamic/Null/void are allowed to omit a return.
+      // Function expressions without a return will have their return type set
+      // to `Null` regardless of their context type. So we need to figure out
+      // if a return type was expected from the original downwards context.
+      //
+      // This helps detect hint cases like `int Function() f = () {}`.
+      // See https://github.com/dart-lang/sdk/issues/28233 for context.
+      if (flattenedType.isDartCoreNull && functionNode is FunctionExpression) {
+        var contextType = InferenceContext.getContext(functionNode);
+        if (contextType is FunctionType) {
+          returnType = contextType.returnType;
+          flattenedType = body.isAsynchronous
+              ? returnType.flattenFutures(_typeSystem)
+              : returnType;
+        }
+      }
+
+      // dynamic, Null, void, and FutureOr<T> where T is (dynamic, Null, void)
+      // are allowed to omit a return.
+      if (flattenedType.isDartAsyncFutureOr) {
+        flattenedType = (flattenedType as InterfaceType).typeArguments[0];
+      }
       if (flattenedType.isDynamic ||
           flattenedType.isDartCoreNull ||
           flattenedType.isVoid) {
diff --git a/pkg/analyzer/test/src/diagnostics/missing_return_test.dart b/pkg/analyzer/test/src/diagnostics/missing_return_test.dart
index 41042fb..902c4f3 100644
--- a/pkg/analyzer/test/src/diagnostics/missing_return_test.dart
+++ b/pkg/analyzer/test/src/diagnostics/missing_return_test.dart
@@ -79,11 +79,96 @@
 ''', [HintCode.MISSING_RETURN]);
   }
 
+  test_functionExpression_declared() async {
+    await assertNoErrorsInCode(r'''
+main() {
+  f() {} // no hint
+}
+''');
+  }
+
+  test_functionExpression_expression() async {
+    await assertNoErrorsInCode(r'''
+main() {
+  int Function() f = () => null; // no hint
+}
+''');
+  }
+
+  test_functionExpression_futureOrDynamic() async {
+    await assertNoErrorsInCode(r'''
+import 'dart:async';
+main() {
+  FutureOr<dynamic> Function() f = () { print(42); };
+}
+''');
+  }
+
+  test_functionExpression_futureOrInt() async {
+    await assertErrorCodesInCode(r'''
+import 'dart:async';
+main() {
+  FutureOr<int> Function() f = () { print(42); };
+}
+''', [HintCode.MISSING_RETURN]);
+  }
+
+  test_functionExpression_inferred() async {
+    await assertErrorCodesInCode(r'''
+main() {
+  int Function() f = () { print(42); };
+}
+''', [HintCode.MISSING_RETURN]);
+  }
+
+  test_functionExpression_inferred_dynamic() async {
+    await assertNoErrorsInCode(r'''
+main() {
+  Function() f = () { print(42); }; // no hint
+}
+''');
+  }
+
+  test_functionExpressionAsync_inferred() async {
+    await assertErrorCodesInCode(r'''
+main() {
+  Future<int> Function() f = () async { print(42); }; 
+}
+''', [HintCode.MISSING_RETURN]);
+  }
+
+  test_functionExpressionAsync_inferred_dynamic() async {
+    await assertNoErrorsInCode(r'''
+main() {
+  Future Function() f = () async { print(42); }; // no hint
+}
+''');
+  }
+
   test_method() async {
     await assertErrorCodesInCode(r'''
 class A {
   int m() {}
-}''', [HintCode.MISSING_RETURN]);
+}
+''', [HintCode.MISSING_RETURN]);
+  }
+
+  test_method_futureOrDynamic() async {
+    await assertNoErrorsInCode(r'''
+import 'dart:async';
+class A {
+  FutureOr<dynamic> m() {}
+}
+''');
+  }
+
+  test_method_futureOrInt() async {
+    await assertErrorCodesInCode(r'''
+import 'dart:async';
+class A {
+  FutureOr<int> m() {}
+}
+''', [HintCode.MISSING_RETURN]);
   }
 
   test_method_inferred() async {
diff --git a/pkg/compiler/lib/src/js/rewrite_async.dart b/pkg/compiler/lib/src/js/rewrite_async.dart
index b3768c4..01cad9d 100644
--- a/pkg/compiler/lib/src/js/rewrite_async.dart
+++ b/pkg/compiler/lib/src/js/rewrite_async.dart
@@ -1385,8 +1385,9 @@
           if (clause is js.Case) {
             return new js.Case(
                 clause.expression, translateToBlock(clause.body));
-          } else if (clause is js.Default) {
-            return new js.Default(translateToBlock(clause.body));
+          } else {
+            return new js.Default(
+                translateToBlock((clause as js.Default).body));
           }
         }).toList();
         addStatement(new js.Switch(key, cases));
diff --git a/pkg/compiler/lib/src/js_backend/interceptor_data.dart b/pkg/compiler/lib/src/js_backend/interceptor_data.dart
index cc38bab..ee38c00 100644
--- a/pkg/compiler/lib/src/js_backend/interceptor_data.dart
+++ b/pkg/compiler/lib/src/js_backend/interceptor_data.dart
@@ -12,6 +12,7 @@
 import '../inferrer/abstract_value_domain.dart';
 import '../js/js.dart' as jsAst;
 import '../serialization/serialization.dart';
+import '../universe/class_set.dart';
 import '../universe/selector.dart';
 import '../world.dart' show JClosedWorld;
 import 'namer.dart' show ModularNamer, suffixForGetInterceptor;
@@ -252,6 +253,7 @@
           if (result == null) result = new Set<ClassEntity>();
           result.add(subclass);
         }
+        return IterationStep.CONTINUE;
       });
     }
     return result;
diff --git a/pkg/compiler/lib/src/js_backend/runtime_types.dart b/pkg/compiler/lib/src/js_backend/runtime_types.dart
index 3dd3633..fa7a7d1 100644
--- a/pkg/compiler/lib/src/js_backend/runtime_types.dart
+++ b/pkg/compiler/lib/src/js_backend/runtime_types.dart
@@ -22,6 +22,7 @@
 import '../options.dart';
 import '../serialization/serialization.dart';
 import '../universe/class_hierarchy.dart';
+import '../universe/class_set.dart';
 import '../universe/codegen_world_builder.dart';
 import '../universe/feature.dart';
 import '../universe/selector.dart';
@@ -1525,6 +1526,7 @@
         closedWorld.classHierarchy.forEachStrictSubtypeOf(cls,
             (ClassEntity sub) {
           potentiallyNeedTypeArguments(sub);
+          return IterationStep.CONTINUE;
         });
       } else if (entity is FunctionEntity) {
         methodsNeedingTypeArguments.add(entity);
diff --git a/pkg/compiler/lib/src/js_model/js_world_builder.dart b/pkg/compiler/lib/src/js_model/js_world_builder.dart
index fa4c4d9..3785a41 100644
--- a/pkg/compiler/lib/src/js_model/js_world_builder.dart
+++ b/pkg/compiler/lib/src/js_model/js_world_builder.dart
@@ -108,6 +108,7 @@
         .getClassHierarchyNode(closedWorld.commonElements.objectClass)
         .forEachSubclass((ClassEntity cls) {
       convertClassSet(closedWorld.classHierarchy.getClassSet(cls));
+      return IterationStep.CONTINUE;
     }, ClassHierarchyNode.ALL);
 
     Set<MemberEntity> liveInstanceMembers =
diff --git a/pkg/compiler/lib/src/old_to_new_api.dart b/pkg/compiler/lib/src/old_to_new_api.dart
index 808e242..a5d7c45 100644
--- a/pkg/compiler/lib/src/old_to_new_api.dart
+++ b/pkg/compiler/lib/src/old_to_new_api.dart
@@ -23,6 +23,8 @@
 
   @override
   Future<Input> readFromUri(Uri uri, {InputKind inputKind: InputKind.UTF8}) {
+    // The switch handles all enum values, but not null.
+    // ignore: missing_return
     return _inputProvider(uri).then((/*String|List<int>*/ data) {
       switch (inputKind) {
         case InputKind.UTF8:
diff --git a/pkg/compiler/lib/src/universe/class_hierarchy.dart b/pkg/compiler/lib/src/universe/class_hierarchy.dart
index 776b4f1..49a899e 100644
--- a/pkg/compiler/lib/src/universe/class_hierarchy.dart
+++ b/pkg/compiler/lib/src/universe/class_hierarchy.dart
@@ -195,10 +195,12 @@
         getClassHierarchyNode(_commonElements.objectClass);
     node.forEachSubclass((ClassEntity cls) {
       getClassHierarchyNode(cls).writeToDataSink(sink);
+      return null;
     }, ClassHierarchyNode.ALL);
     ClassSet set = getClassSet(_commonElements.objectClass);
     set.forEachSubclass((ClassEntity cls) {
       getClassSet(cls).writeToDataSink(sink);
+      return null;
     }, ClassHierarchyNode.ALL);
     sink.end(tag);
   }
@@ -836,6 +838,7 @@
         if (builder._isSubtypeOf(z, y)) {
           classes.add(z);
         }
+        return null;
       }, ClassHierarchyNode.ALL, strict: strict);
     }
 
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 51d5070..b97c08b 100644
--- a/pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/constant_evaluator.dart
@@ -1591,6 +1591,7 @@
       } else {
         reportInvalid(
             node, 'No support for ${target.runtimeType} in a static-get.');
+        return null;
       }
     });
   }
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 6987266..7f59d4b 100644
--- a/pkg/front_end/test/fasta/generator_to_string_test.dart
+++ b/pkg/front_end/test/fasta/generator_to_string_test.dart
@@ -241,5 +241,6 @@
         "offset: 4, prefixGenerator: , isInitializer: false, isSuper: false)",
         new KernelUnexpectedQualifiedUseGenerator(
             helper, token, generator, false));
+    return Future<void>.value();
   });
 }
diff --git a/pkg/front_end/test/fasta/unlinked_scope_test.dart b/pkg/front_end/test/fasta/unlinked_scope_test.dart
index e58294c..fb933f8 100644
--- a/pkg/front_end/test/fasta/unlinked_scope_test.dart
+++ b/pkg/front_end/test/fasta/unlinked_scope_test.dart
@@ -108,5 +108,6 @@
     testExpression("unresolved");
     testExpression("a + b", "a.+(b)");
     testExpression("a = b");
+    return Future<void>.value();
   });
 }
diff --git a/pkg/front_end/test/src/base/processed_options_test.dart b/pkg/front_end/test/src/base/processed_options_test.dart
index 605b5ac..0abc4cb 100644
--- a/pkg/front_end/test/src/base/processed_options_test.dart
+++ b/pkg/front_end/test/src/base/processed_options_test.dart
@@ -22,6 +22,7 @@
     defineReflectiveSuite(() {
       defineReflectiveTests(ProcessedOptionsTest);
     });
+    return Future<void>.value();
   });
 }
 
diff --git a/pkg/front_end/tool/_fasta/entry_points.dart b/pkg/front_end/tool/_fasta/entry_points.dart
index a3cd069..18b7445 100644
--- a/pkg/front_end/tool/_fasta/entry_points.dart
+++ b/pkg/front_end/tool/_fasta/entry_points.dart
@@ -192,6 +192,7 @@
     // TODO(ahe): Extend this entry point so it can replace
     // batchEntryPoint.
     new IncrementalCompiler(c);
+    return Future<void>.value();
   });
 }
 
diff --git a/pkg/vm/test/frontend_server_test.dart b/pkg/vm/test/frontend_server_test.dart
index 5310517..a56d500 100644
--- a/pkg/vm/test/frontend_server_test.dart
+++ b/pkg/vm/test/frontend_server_test.dart
@@ -83,11 +83,12 @@
           new StreamController<List<int>>();
       final ReceivePort compileCalled = new ReceivePort();
       when(compiler.compile(any, any, generator: anyNamed('generator')))
-          .thenAnswer((Invocation invocation) {
+          .thenAnswer((Invocation invocation) async {
         expect(invocation.positionalArguments[0], equals('server.dart'));
         expect(
             invocation.positionalArguments[1]['sdk-root'], equals('sdkroot'));
         compileCalled.sendPort.send(true);
+        return true;
       });
 
       Future<int> result = starter(
@@ -116,11 +117,12 @@
           new StreamController<List<int>>();
       final ReceivePort compileCalled = new ReceivePort();
       when(compiler.compile(any, any, generator: anyNamed('generator')))
-          .thenAnswer((Invocation invocation) {
+          .thenAnswer((Invocation invocation) async {
         expect(invocation.positionalArguments[0], equals('server.dart'));
         expect(
             invocation.positionalArguments[1]['sdk-root'], equals('sdkroot'));
         compileCalled.sendPort.send(true);
+        return true;
       });
 
       Future<int> result = starter(
@@ -141,12 +143,13 @@
       final ReceivePort compileCalled = new ReceivePort();
       int counter = 1;
       when(compiler.compile(any, any, generator: anyNamed('generator')))
-          .thenAnswer((Invocation invocation) {
+          .thenAnswer((Invocation invocation) async {
         expect(invocation.positionalArguments[0],
             equals('server${counter++}.dart'));
         expect(
             invocation.positionalArguments[1]['sdk-root'], equals('sdkroot'));
         compileCalled.sendPort.send(true);
+        return true;
       });
 
       Future<int> result = starter(
@@ -180,7 +183,7 @@
       final ReceivePort recompileCalled = new ReceivePort();
 
       when(compiler.recompileDelta(entryPoint: null))
-          .thenAnswer((Invocation invocation) {
+          .thenAnswer((Invocation invocation) async {
         recompileCalled.sendPort.send(true);
       });
       Future<int> result = starter(
@@ -208,7 +211,7 @@
       final ReceivePort recompileCalled = new ReceivePort();
 
       when(compiler.recompileDelta(entryPoint: 'file2.dart'))
-          .thenAnswer((Invocation invocation) {
+          .thenAnswer((Invocation invocation) async {
         recompileCalled.sendPort.send(true);
       });
       Future<int> result = starter(
@@ -275,7 +278,7 @@
       final ReceivePort recompileCalled = new ReceivePort();
 
       when(compiler.recompileDelta(entryPoint: null))
-          .thenAnswer((Invocation invocation) {
+          .thenAnswer((Invocation invocation) async {
         recompileCalled.sendPort.send(true);
       });
       Future<int> result = starter(
diff --git a/tests/compiler/dart2js/model/class_set_test.dart b/tests/compiler/dart2js/model/class_set_test.dart
index 5ceb1e8..ea78222 100644
--- a/tests/compiler/dart2js/model/class_set_test.dart
+++ b/tests/compiler/dart2js/model/class_set_test.dart
@@ -344,6 +344,7 @@
     List<ClassEntity> visited = <ClassEntity>[];
     classSet.forEachSubclass((cls) {
       visited.add(cls);
+      return IterationStep.CONTINUE;
     }, ClassHierarchyNode.ALL);
 
     Expect.listEquals(
@@ -381,6 +382,7 @@
     List<ClassEntity> visited = <ClassEntity>[];
     classSet.forEachSubtype((cls) {
       visited.add(cls);
+      return IterationStep.CONTINUE;
     }, ClassHierarchyNode.ALL);
 
     Expect.listEquals(
diff --git a/tests/compiler/dart2js/model/receiver_type_test.dart b/tests/compiler/dart2js/model/receiver_type_test.dart
index 663c6e3..3ad5042 100644
--- a/tests/compiler/dart2js/model/receiver_type_test.dart
+++ b/tests/compiler/dart2js/model/receiver_type_test.dart
@@ -6,6 +6,7 @@
 import 'package:async_helper/async_helper.dart';
 import 'package:compiler/src/elements/entities.dart';
 import 'package:compiler/src/inferrer/typemasks/masks.dart';
+import 'package:compiler/src/universe/class_set.dart';
 import 'package:compiler/src/universe/selector.dart';
 import 'package:compiler/src/world.dart';
 import 'package:expect/expect.dart';
@@ -49,7 +50,8 @@
   Selector callSelector = new Selector.callClosure(0);
   closedWorld.classHierarchy.forEachStrictSubclassOf(
       closedWorld.commonElements.objectClass, (ClassEntity cls) {
-    if (cls.library.canonicalUri.scheme != 'memory') return;
+    if (cls.library.canonicalUri.scheme != 'memory')
+      return IterationStep.CONTINUE;
 
     TypeMask mask = new TypeMask.nonNullSubclass(cls, closedWorld);
     TypeMask receiverType = closedWorld.computeReceiverType(callSelector, mask);
@@ -65,6 +67,7 @@
       Expect.equals(expected, '$receiverType',
           "Unexpected receiver type for $callSelector on $mask");
     }
+    return IterationStep.CONTINUE;
   });
 
   Expect.equals(2, closureCount);
diff --git a/tests/compiler/dart2js/model/world_test.dart b/tests/compiler/dart2js/model/world_test.dart
index c49ff3d..b2106a8 100644
--- a/tests/compiler/dart2js/model/world_test.dart
+++ b/tests/compiler/dart2js/model/world_test.dart
@@ -99,6 +99,7 @@
       List<ClassEntity> visited = <ClassEntity>[];
       forEach(cls, (ClassEntity c) {
         visited.add(c);
+        return IterationStep.CONTINUE;
       });
       checkClasses('forEach($property)', cls, visited, expectedClasses,
           exact: exact);
@@ -424,6 +425,7 @@
       if (allClasses.contains(other)) {
         strictSubclasses.add(other);
       }
+      return IterationStep.CONTINUE;
     });
     Expect.setEquals(subclasses, strictSubclasses,
         "Unexpected strict subclasses of $cls: ${strictSubclasses}.");
@@ -433,6 +435,7 @@
       if (allClasses.contains(other)) {
         strictSubtypes.add(other);
       }
+      return IterationStep.CONTINUE;
     });
     Expect.setEquals(subtypes, strictSubtypes,
         "Unexpected strict subtypes of $cls: $strictSubtypes.");
diff --git a/tests/compiler/dart2js/sourcemaps/helpers/sourcemap_helper.dart b/tests/compiler/dart2js/sourcemaps/helpers/sourcemap_helper.dart
index f38c7a6..9e4273d 100644
--- a/tests/compiler/dart2js/sourcemaps/helpers/sourcemap_helper.dart
+++ b/tests/compiler/dart2js/sourcemaps/helpers/sourcemap_helper.dart
@@ -262,6 +262,7 @@
         }
         return null;
       }
+      return null;
     });
   }
 }