Allowing `e` of any type in `void f(...) => e`

pkg/analyzer/lib/src/generated/error_verifier.dart

 // Copyright (c) 2014, 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 analyzer.src.generated.error_verifier;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 642 matching lines @@
       _inGenerator = node.isGenerator;
       FunctionType functionType = _enclosingFunction?.type;
       DartType expectedReturnType = functionType == null
           ? DynamicTypeImpl.instance
           : functionType.returnType;
       ExecutableElement function = _enclosingFunction;
       bool isSetterWithImplicitReturn = function.hasImplicitReturnType &&
           function is PropertyAccessorElement &&
           function.isSetter;
       if (!isSetterWithImplicitReturn) {
-        _checkForReturnOfInvalidType(node.expression, expectedReturnType);
+        _checkForReturnOfInvalidType(node.expression, expectedReturnType,
+            isArrowFunction: true);
       }
       return super.visitExpressionFunctionBody(node);
     } finally {
       _inAsync = wasInAsync;
       _inGenerator = wasInGenerator;
     }
   }
 
   @override
   Object visitFieldDeclaration(FieldDeclaration node) {
@@ skipping 4917 matching lines @@
   /**
    * Check that a type mis-match between the type of the [returnExpression] and
    * the [expectedReturnType] by the enclosing method or function.
    *
    * This method is called both by [_checkForAllReturnStatementErrorCodes]
    * and [visitExpressionFunctionBody].
    *
    * See [StaticTypeWarningCode.RETURN_OF_INVALID_TYPE].
    */
   void _checkForReturnOfInvalidType(
-      Expression returnExpression, DartType expectedReturnType) {
+      Expression returnExpression, DartType expectedReturnType,
+      {bool isArrowFunction = false}) {
     if (_enclosingFunction == null) {
       return;
     }
     if (_inGenerator) {
       // "return expression;" is disallowed in generators, but this is checked
       // elsewhere.  Bare "return" is always allowed in generators regardless
       // of the return type.  So no need to do any further checking.
       return;
     }
     DartType staticReturnType = _computeReturnTypeForMethod(returnExpression);
     if (expectedReturnType.isVoid) {
+      if (isArrowFunction) {
+        // "void f(..) => e" admits all types for "e".
+        return;
+      }
       if (staticReturnType.isVoid ||
           staticReturnType.isDynamic ||
           staticReturnType.isBottom ||
           staticReturnType.isDartCoreNull) {
         return;
       }
       _errorReporter.reportTypeErrorForNode(
           StaticTypeWarningCode.RETURN_OF_INVALID_TYPE, returnExpression, [
         staticReturnType,
         expectedReturnType,
@@ skipping 1507 matching lines @@
 class _InvocationCollector extends RecursiveAstVisitor {
   final List<String> superCalls = <String>[];
 
   @override
   visitMethodInvocation(MethodInvocation node) {
     if (node.target is SuperExpression) {
       superCalls.add(node.methodName.name);
     }
   }
 }