Issue 42605. Do LEGACY_ERASURE when checking inferred mixin type arguments.

Bug: #42605
Change-Id: I58d27352e770ce63fabc0da2c07920dbadb8af11
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/153482
Reviewed-by: Brian Wilkerson <[email protected]>

Author: scheglov

pkg/analyzer/lib/src/dart/analysis/driver.dart

@@ -91,7 +91,7 @@ typedef WorkToWaitAfterComputingResult = Future<void> Function(String path);
 /// TODO(scheglov) Clean up the list of implicitly analyzed files.
 class AnalysisDriver implements AnalysisDriverGeneric {
   /// The version of data format, should be incremented on every format change.
-  static const int DATA_VERSION = 104;
+  static const int DATA_VERSION = 105;
 
   /// The length of the list returned by [_computeDeclaredVariablesSignature].
   static const int _declaredVariablesSignatureLength = 4;

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

@@ -241,7 +241,16 @@ abstract class TypeSystem implements public.TypeSystem {
     var substitution = Substitution.fromPairs(typeParameters, inferredTypes);
 
     for (int i = 0; i < srcTypes.length; i++) {
-      if (substitution.substituteType(srcTypes[i]) != destTypes[i]) {
+      var srcType = substitution.substituteType(srcTypes[i]);
+      var destType = destTypes[i];
+      if (isNonNullableByDefault) {
+        // TODO(scheglov) waiting for the spec
+        // https://github.com/dart-lang/sdk/issues/42605
+      } else {
+        srcType = toLegacyType(srcType);
+        destType = toLegacyType(destType);
+      }
+      if (srcType != destType) {
         // Failed to find an appropriate substitution
         return null;
       }
@@ -345,6 +354,11 @@ abstract class TypeSystem implements public.TypeSystem {
     return type;
   }
 
+  DartType toLegacyType(DartType type) {
+    if (isNonNullableByDefault) return type;
+    return NullabilityEliminator.perform(typeProvider, type);
+  }
+
   /// Tries to promote from the first type from the second type, and returns the
   /// promoted type if it succeeds, otherwise null.
   DartType tryPromoteToType(DartType to, DartType from);
@@ -1427,11 +1441,6 @@ class TypeSystemImpl extends TypeSystem {
     return RuntimeTypeEqualityHelper(this).equal(T1, T2);
   }
 
-  DartType toLegacyType(DartType type) {
-    if (isNonNullableByDefault) return type;
-    return NullabilityEliminator.perform(typeProvider, type);
-  }
-
   /// Merges two types into a single type.
   /// Compute the canonical representation of [T].
   ///

pkg/analyzer/test/src/summary/resynthesize_ast2_test.dart

@@ -4,6 +4,7 @@
 
 import 'package:analyzer/dart/analysis/features.dart';
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/element/null_safety_understanding_flag.dart';
 import 'package:analyzer/src/context/context.dart';
 import 'package:analyzer/src/dart/analysis/session.dart';
 import 'package:analyzer/src/dart/element/class_hierarchy.dart';
@@ -108,9 +109,13 @@ class ResynthesizeAst2Test extends ResynthesizeTestStrategyTwoPhase
       LinkedBundleContext(elementFactory, sdkBundle),
     );
 
-    var linkResult = link(
-      elementFactory,
-      inputLibraries,
+    var linkResult = NullSafetyUnderstandingFlag.enableNullSafetyTypes(
+      () {
+        return link(
+          elementFactory,
+          inputLibraries,
+        );
+      },
     );
 
     elementFactory.addBundle(

pkg/analyzer/test/src/summary/resynthesize_common.dart

@@ -16,6 +16,7 @@ import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/test_utilities/mock_sdk.dart';
 import 'package:analyzer/src/test_utilities/resource_provider_mixin.dart';
 import 'package:test/test.dart';
+import 'package:test_reflective_loader/test_reflective_loader.dart';
 
 import 'element_text.dart';
 import 'test_strategies.dart';
@@ -9348,6 +9349,93 @@ mixin M on Object {
 ''');
   }
 
+  test_mixin_inference_legacy() async {
+    var library = await checkLibrary(r'''
+class A<T> {}
+mixin M<U> on A<U> {}
+class B extends A<int> with M {}
+''');
+    checkElementText(
+        library,
+        r'''
+class A<T> {
+}
+class B extends A<int*>* with M<int*>* {
+  synthetic B();
+}
+mixin M<U> on A<U*>* {
+}
+''',
+        annotateNullability: true);
+  }
+
+  test_mixin_inference_nullSafety() async {
+    featureSet = enableNnbd;
+    var library = await checkLibrary(r'''
+class A<T> {}
+mixin M<U> on A<U> {}
+class B extends A<int> with M {}
+''');
+    checkElementText(
+        library,
+        r'''
+class A<T> {
+}
+class B extends A<int> with M<int> {
+  synthetic B();
+}
+mixin M<U> on A<U> {
+}
+''',
+        annotateNullability: true);
+  }
+
+  test_mixin_inference_nullSafety_mixed_inOrder() async {
+    featureSet = enableNnbd;
+    addLibrarySource('/a.dart', r'''
+class A<T> {}
+mixin M<U> on A<U> {}
+''');
+    var library = await checkLibrary(r'''
+// @dart = 2.8
+import 'a.dart';
+class B extends A<int> with M {}
+''');
+    checkElementText(
+        library,
+        r'''
+import 'a.dart';
+class B extends A<int*>* with M<int*>* {
+  synthetic B();
+}
+''',
+        annotateNullability: true);
+  }
+
+  @FailingTest(reason: 'Out-of-order inference is not specified yet')
+  test_mixin_inference_nullSafety_mixed_outOfOrder() async {
+    featureSet = enableNnbd;
+    addLibrarySource('/a.dart', r'''
+// @dart = 2.8
+class A<T> {}
+mixin M<U> on A<U> {}
+''');
+    var library = await checkLibrary(r'''
+import 'a.dart';
+
+class B extends A<int> with M {}
+''');
+    checkElementText(
+        library,
+        r'''
+import 'a.dart';
+class B extends A<int> with M<int> {
+  synthetic B();
+}
+''',
+        annotateNullability: true);
+  }
+
   test_mixin_method_namedAsConstraint() async {
     var library = await checkLibrary(r'''
 class A {}