Resolve invalid return statements in async/sync generators.

R=brianwilkerson@google.com, paulberry@google.com

Change-Id: Ic0aa6ffbffc23b10814ab369ce041bde32da1388
Reviewed-on: https://dart-review.googlesource.com/65602
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Paul Berry <paulberry@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

pkg/analyzer/test/generated/compile_time_error_code_kernel_test.dart

@@ -2432,20 +2432,6 @@ class CompileTimeErrorCodeTest_Kernel extends CompileTimeErrorCodeTest_Driver {
     await super.test_returnInGenerativeConstructor_expressionFunctionBody();
   }
 
-  @override
-  @failingTest
-  test_returnInGenerator_asyncStar() async {
-    // AnalysisException: Element mismatch in /test.dart at /test.dart
-    await super.test_returnInGenerator_asyncStar();
-  }
-
-  @override
-  @failingTest
-  test_returnInGenerator_syncStar() async {
-    // AnalysisException: Element mismatch in /test.dart at /test.dart
-    await super.test_returnInGenerator_syncStar();
-  }
-
   @override
   @failingTest
   test_superInInvalidContext_binaryExpression() async {

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

@@ -3496,6 +3496,62 @@ class C {
     assertType(thisRef, 'C');
   }
 
+  test_invalid_generator_async_return_blockBody() async {
+    addTestFile(r'''
+int a = 0;
+f() async* {
+  return a;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+
+    var aRef = findNode.simple('a;');
+    assertElement(aRef, findElement.topGet('a'));
+    assertType(aRef, 'int');
+  }
+
+  test_invalid_generator_async_return_expressionBody() async {
+    addTestFile(r'''
+int a = 0;
+f() async* => a;
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+
+    var aRef = findNode.simple('a;');
+    assertElement(aRef, findElement.topGet('a'));
+    assertType(aRef, 'int');
+  }
+
+  test_invalid_generator_sync_return_blockBody() async {
+    addTestFile(r'''
+int a = 0;
+f() sync* {
+  return a;
+}
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+
+    var aRef = findNode.simple('a;');
+    assertElement(aRef, findElement.topGet('a'));
+    assertType(aRef, 'int');
+  }
+
+  test_invalid_generator_sync_return_expressionBody() async {
+    addTestFile(r'''
+int a = 0;
+f() sync* => a;
+''');
+    await resolveTestFile();
+    expect(result.errors, isNotEmpty);
+
+    var aRef = findNode.simple('a;');
+    assertElement(aRef, findElement.topGet('a'));
+    assertType(aRef, 'int');
+  }
+
   test_invalid_instanceCreation_abstract() async {
     addTestFile(r'''
 abstract class C<T> {

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

@@ -703,6 +703,13 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
 
     _typeInferrer.inferFunctionBody(
         this, factory, _computeReturnTypeContext(member), asyncModifier, body);
+
+    // We finished the invalid body inference, desugar it into its error.
+    if (body is InvalidStatementJudgment) {
+      InvalidStatementJudgment judgment = body;
+      body = new ExpressionStatement(judgment.desugaredError);
+    }
+
     if (builder.kind == ProcedureKind.Setter) {
       bool oneParameter = formals != null &&
           formals.required.length == 1 &&
@@ -3933,7 +3940,8 @@ abstract class BodyBuilder extends ScopeListener<JumpTarget>
   @override
   void handleInvalidStatement(Token token, Message message) {
     Statement statement = pop();
-    push(wrapInCompileTimeErrorStatement(statement, message));
+    var error = buildCompileTimeError(message, statement.fileOffset, noLength);
+    push(new InvalidStatementJudgment(error, statement));
   }
 
   @override

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

@@ -93,6 +93,7 @@ export 'kernel_shadow_ast.dart'
         IndexAssignmentJudgment,
         InvalidConstructorInvocationJudgment,
         InvalidPropertyGetJudgment,
+        InvalidStatementJudgment,
         InvalidVariableWriteJudgment,
         InvalidWriteJudgment,
         ShadowInvalidFieldInitializer,

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

@@ -3101,6 +3101,31 @@ class ThrowJudgment extends Throw implements ExpressionJudgment {
   }
 }
 
+/// Synthetic judgment class representing a statement that is not allowed at
+/// the location it was found, and should be replaced with an error.
+class InvalidStatementJudgment extends ExpressionStatement
+    implements StatementJudgment {
+  final kernel.Expression desugaredError;
+  final StatementJudgment statement;
+
+  InvalidStatementJudgment(this.desugaredError, this.statement)
+      : super(new NullLiteral());
+
+  @override
+  void infer<Expression, Statement, Initializer, Type>(
+      ShadowTypeInferrer inferrer,
+      Factory<Expression, Statement, Initializer, Type> factory) {
+    inferrer.inferStatement(factory, statement);
+
+    // If this judgment is a part of a Block, replace it there.
+    // Otherwise, the parent would be a FunctionNode, but not yet.
+    if (parent is Block) {
+      parent.replaceChild(this, new ExpressionStatement(desugaredError));
+      parent = null;
+    }
+  }
+}
+
 /// Concrete shadow object representing a catch clause.
 class CatchJudgment extends Catch {
   final Token onKeyword;