Issue 43144. Convert the bound of type parameter to legacy if necessary.

Bug: https://github.com/dart-lang/sdk/issues/43144
Change-Id: I2bf50c498d7919460133d1bed07ce2de861fce08
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/159646
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

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

@@ -166,14 +166,19 @@ class GenericInferrer {
     for (int i = 0; i < typeFormals.length; i++) {
       TypeParameterElement typeParam = typeFormals[i];
       var constraints = _constraints[typeParam];
-      var typeParamBound = typeParam.bound != null
-          ? Substitution.fromPairs(typeFormals, inferredTypes)
-              .substituteType(typeParam.bound)
-          : typeProvider.dynamicType;
+
+      var typeParamBound = typeParam.bound;
+      if (typeParamBound != null) {
+        typeParamBound = Substitution.fromPairs(typeFormals, inferredTypes)
+            .substituteType(typeParamBound);
+        typeParamBound = _toLegacyElementIfOptOut(typeParamBound);
+      } else {
+        typeParamBound = typeProvider.dynamicType;
+      }
 
       var inferred = inferredTypes[i];
       bool success =
-          constraints.every((c) => c.isSatisifedBy(_typeSystem, inferred));
+          constraints.every((c) => c.isSatisfiedBy(_typeSystem, inferred));
       if (success && !typeParamBound.isDynamic) {
         // If everything else succeeded, check the `extends` constraint.
         var extendsConstraint = _TypeConstraint.fromExtends(
@@ -182,7 +187,7 @@ class GenericInferrer {
           isNonNullableByDefault: isNonNullableByDefault,
         );
         constraints.add(extendsConstraint);
-        success = extendsConstraint.isSatisifedBy(_typeSystem, inferred);
+        success = extendsConstraint.isSatisfiedBy(_typeSystem, inferred);
       }
 
       if (!success) {
@@ -344,8 +349,8 @@ class GenericInferrer {
       // will fail.
       upper = _typeSystem.getGreatestLowerBound(upper, constraint.upperBound);
       lower = _typeSystem.getLeastUpperBound(lower, constraint.lowerBound);
-      upper = _toLegacyType(upper);
-      lower = _toLegacyType(lower);
+      upper = _toLegacyElementIfOptOut(upper);
+      lower = _toLegacyElementIfOptOut(lower);
     }
 
     // Prefer the known bound, if any.
@@ -405,7 +410,7 @@ class GenericInferrer {
     Iterable<_TypeConstraint> isSatisified(bool expected) => constraintsByOrigin
         .values
         .where((l) =>
-            l.every((c) => c.isSatisifedBy(_typeSystem, inferred)) == expected)
+            l.every((c) => c.isSatisfiedBy(_typeSystem, inferred)) == expected)
         .expand((i) => i);
 
     String unsatisified = _formatConstraints(isSatisified(false));
@@ -479,7 +484,7 @@ class GenericInferrer {
 
   /// If in a legacy library, return the legacy version of the [type].
   /// Otherwise, return the original type.
-  DartType _toLegacyType(DartType type) {
+  DartType _toLegacyElementIfOptOut(DartType type) {
     if (isNonNullableByDefault) return type;
     return NullabilityEliminator.perform(typeProvider, type);
   }
@@ -542,8 +547,10 @@ class _TypeConstraint extends _TypeRange {
 
   bool get isDownwards => origin is! _TypeConstraintFromArgument;
 
-  bool isSatisifedBy(TypeSystemImpl ts, DartType type) =>
-      ts.isSubtypeOf2(lowerBound, type) && ts.isSubtypeOf2(type, upperBound);
+  bool isSatisfiedBy(TypeSystemImpl ts, DartType type) {
+    return ts.isSubtypeOf2(lowerBound, type) &&
+        ts.isSubtypeOf2(type, upperBound);
+  }
 
   /// Converts this constraint to a message suitable for a type inference error.
   @override

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

@@ -192,6 +192,27 @@ class GenericFunctionInferenceTest extends AbstractTypeSystemNullSafetyTest {
     );
   }
 
+  void test_fromLegacy_nonNullableBound() {
+    typeSystem = analysisContext.typeSystemLegacy;
+
+    // void Function<T extends Object>(T)
+    var T = typeParameter('T', bound: objectNone);
+    var rawType = functionTypeNone(
+      typeFormals: [T],
+      parameters: [
+        requiredParameter(
+          type: typeParameterTypeNone(T),
+        ),
+      ],
+      returnType: voidNone,
+    );
+
+    _assertTypes(
+      _inferCall(rawType, [dynamicNone]),
+      [dynamicNone],
+    );
+  }
+
   void test_genericCastFunction() {
     // <TFrom, TTo>(TFrom) -> TTo
     var tFrom = typeParameter('TFrom');

pkg/analyzer/test/src/diagnostics/could_not_infer_test.dart

@@ -10,6 +10,7 @@ import '../dart/resolution/context_collection_resolution.dart';
 main() {
   defineReflectiveSuite(() {
     defineReflectiveTests(CouldNotInferTest);
+    defineReflectiveTests(CouldNotInferWithNullSafetyTest);
   });
 }
 
@@ -229,10 +230,10 @@ class Foo<T extends Pattern> {
   U method<U extends T>(U u) => u;
 }
 main() {
-  new Foo<String>()./*error:COULD_NOT_INFER*/method(42);
+  new Foo<String>().method(42);
 }
 ''', [
-      error(CompileTimeErrorCode.COULD_NOT_INFER, 122, 6),
+      error(CompileTimeErrorCode.COULD_NOT_INFER, 97, 6),
     ]);
   }
 
@@ -247,3 +248,24 @@ main() { new C().f(<S>(S s) => s); }
     ]);
   }
 }
+
+@reflectiveTest
+class CouldNotInferWithNullSafetyTest extends PubPackageResolutionTest
+    with WithNullSafetyMixin {
+  test_constructor_nullSafe_fromLegacy() async {
+    newFile('$testPackageLibPath/a.dart', content: '''
+class C<T extends Object> {
+  C(T t);
+}
+''');
+
+    await assertNoErrorsInCode('''
+// @dart = 2.8
+import 'a.dart';
+
+void f(dynamic a) {
+  C(a);
+}
+''');
+  }
+}