Allow values to be returned from implicitly typed setters

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

Index: pkg/analyzer/lib/src/generated/error_verifier.dart
diff --git a/pkg/analyzer/lib/src/generated/error_verifier.dart b/pkg/analyzer/lib/src/generated/error_verifier.dart
index 4a3e4fdf2307b30a436be998072b8438e4bf7ef1..7824d87777cdfdea2e5b3b5f073fe73a326ec7c9 100644
--- a/pkg/analyzer/lib/src/generated/error_verifier.dart
+++ b/pkg/analyzer/lib/src/generated/error_verifier.dart
@@ -642,7 +642,13 @@ class ErrorVerifier extends RecursiveAstVisitor<Object> {
       DartType expectedReturnType = functionType == null
           ? DynamicTypeImpl.instance
           : functionType.returnType;
-      _checkForReturnOfInvalidType(node.expression, expectedReturnType);
+      bool isSetterWithImplicitReturn =
+          _enclosingFunction.hasImplicitReturnType &&
+          _enclosingFunction is PropertyAccessorElement &&
+          (_enclosingFunction as PropertyAccessorElement).isSetter;
+      if (!isSetterWithImplicitReturn) {
+        _checkForReturnOfInvalidType(node.expression, expectedReturnType);
+      }
       return super.visitExpressionFunctionBody(node);
     } finally {
       _inAsync = wasInAsync;