Non-nullify types after inference.

Change-Id: Ie50ea84d18bc44799cadc797c76d6506539de719
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/150842
Reviewed-by: Brian Wilkerson <[email protected]>
Commit-Queue: Konstantin Shcheglov <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/dart/element/generic_inferrer.dart

@@ -14,6 +14,7 @@ import 'package:analyzer/src/dart/element/nullability_eliminator.dart';
 import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/type_algebra.dart';
 import 'package:analyzer/src/dart/element/type_constraint_gatherer.dart';
+import 'package:analyzer/src/dart/element/type_demotion.dart';
 import 'package:analyzer/src/dart/element/type_schema.dart';
 import 'package:analyzer/src/error/codes.dart' show HintCode, StrongModeCode;
 import 'package:analyzer/src/generated/type_system.dart';
@@ -257,6 +258,7 @@ class GenericInferrer {
       }
     }
 
+    _nonNullifyTypes(result);
     return result;
   }
 
@@ -461,6 +463,14 @@ class GenericInferrer {
     return t;
   }
 
+  void _nonNullifyTypes(List<DartType> types) {
+    if (_typeSystem.isNonNullableByDefault) {
+      for (var i = 0; i < types.length; i++) {
+        types[i] = nonNullifyType(_typeSystem, types[i]);
+      }
+    }
+  }
+
   /// If in a legacy library, return the legacy version of the [type].
   /// Otherwise, return the original type.
   DartType _toLegacyType(DartType type) {

pkg/analyzer/lib/src/dart/element/type_demotion.dart

@@ -8,6 +8,7 @@ import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/replacement_visitor.dart';
 import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/type_visitor.dart';
+import 'package:analyzer/src/generated/type_system.dart';
 
 /// Returns [type] in which all promoted type variables have been replace with
 /// their unpromoted equivalents, and, if [library] is non-nullable by default,
@@ -29,8 +30,8 @@ bool hasPromotedTypeVariable(DartType type) {
 
 /// Returns [type] in which all legacy types have been replaced with
 /// non-nullable types.
-DartType nonNullifyType(LibraryElement library, DartType type) {
-  if (library.isNonNullableByDefault && type != null) {
+DartType nonNullifyType(TypeSystemImpl typeSystem, DartType type) {
+  if (typeSystem.isNonNullableByDefault && type != null) {
     var visitor = const _DemotionNonNullification(demoteTypeVariables: false);
     return visitor.visit(type) ?? type;
   }

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

@@ -51,7 +51,7 @@ class FunctionExpressionResolver {
     }
 
     var contextType = InferenceContext.getContext(node);
-    contextType = nonNullifyType(_resolver.definingLibrary, contextType);
+    contextType = nonNullifyType(_typeSystem, contextType);
 
     if (contextType is FunctionType) {
       contextType = _matchFunctionTypeParameters(

pkg/analyzer/test/src/dart/element/generic_inferrer_test.dart

@@ -479,6 +479,16 @@ class GenericFunctionInferenceTest extends AbstractTypeSystemNullSafetyTest {
     _assertTypes(_inferCall(f, [], returnType: stringNone), [stringNone]);
   }
 
+  void test_returnTypeFromContext_nonNullify() {
+    // <T>() -> T
+    var T = typeParameter('T');
+    var f = functionTypeNone(
+      typeFormals: [T],
+      returnType: typeParameterTypeNone(T),
+    );
+    _assertTypes(_inferCall(f, [], returnType: intStar), [intNone]);
+  }
+
   void test_returnTypeWithBoundFromContext() {
     // <T extends num>() -> T
     var T = typeParameter('T', bound: numNone);