Issue 42278. Null-nullify types after function expression inference, not the context type.

Bug: #42278
Change-Id: I40abcb6e7e97ef4f3993da65a21dffbdbc1f483a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/151000
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/dart/resolver/body_inference_context.dart

@@ -7,6 +7,7 @@ import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/dart/element/type_provider.dart';
 import 'package:analyzer/src/dart/element/type.dart';
+import 'package:analyzer/src/dart/element/type_demotion.dart';
 import 'package:analyzer/src/generated/resolver.dart';
 import 'package:analyzer/src/generated/type_system.dart';
 import 'package:meta/meta.dart';
@@ -97,7 +98,7 @@ class BodyInferenceContext {
         _typeSystem.isSubtypeOf2(actualReturnedType, contextType)) {
       clampedReturnedType = actualReturnedType;
     } else {
-      clampedReturnedType = contextType;
+      clampedReturnedType = nonNullifyType(_typeSystem, contextType);
     }
 
     if (_isGenerator) {

pkg/analyzer/lib/src/dart/resolver/function_expression_resolver.dart

@@ -51,8 +51,6 @@ class FunctionExpressionResolver {
     }
 
     var contextType = InferenceContext.getContext(node);
-    contextType = nonNullifyType(_typeSystem, contextType);
-
     if (contextType is FunctionType) {
       contextType = _matchFunctionTypeParameters(
         node.typeParameters,
@@ -110,6 +108,8 @@ class FunctionExpressionResolver {
           if (_migrationResolutionHooks != null) {
             inferredType = _migrationResolutionHooks
                 .modifyInferredParameterType(p, inferredType);
+          } else {
+            inferredType = nonNullifyType(_typeSystem, inferredType);
           }
           if (!inferredType.isDynamic) {
             p.type = inferredType;

pkg/analyzer/test/src/dart/resolution/type_inference/function_expression_test.dart

@@ -429,6 +429,38 @@ void f() {
     _assertReturnType('(a) {', 'int');
   }
 
+  test_contextFunctionType_nonNullify_returnType_takeActual() async {
+    newFile('/test/lib/a.dart', content: r'''
+// @dart = 2.7
+
+void foo(int Function() x) {}
+''');
+    await assertNoErrorsInCode('''
+import 'a.dart';
+
+void test(int? a) {
+  foo(() => a);
+}
+''');
+    _assertReturnType('() => a', 'int?');
+  }
+
+  test_contextFunctionType_nonNullify_returnType_takeContext() async {
+    newFile('/test/lib/a.dart', content: r'''
+// @dart = 2.7
+
+void foo(int Function() x) {}
+''');
+    await assertNoErrorsInCode('''
+import 'a.dart';
+
+void test(dynamic a) {
+  foo(() => a);
+}
+''');
+    _assertReturnType('() => a', 'int');
+  }
+
   test_contextFunctionType_returnType_async_blockBody_objectQ() async {
     await assertNoErrorsInCode('''
 T foo<T>() => throw 0;