Replace ClassElement/FunctionTypeAliasElement.instantiateToBounds() with TypeSystem.instantiateToBounds2()

Change-Id: I2b1aacc9d72ab444176a2a0e4d6a44d13780e357
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/132804
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>

pkg/analyzer/CHANGELOG.md

@@ -1,3 +1,10 @@
+## 0.39.5-dev
+* Deprecated `ClassElement.instantiateToBounds()` and
+  `FunctionTypeAliasElement.instantiateToBounds()`. With the null-safety
+  feature, type arguments derived from type parameter bounds cannot be used as
+  is, and might require erasing nullability, when the element is instantiated
+  from a legacy library. Use `TypeSystem.instantiateToBounds2()` instead.
+
 ## 0.39.4
 * Deprecated `DartType.name`, use `element` or `getDisplayString()` instead.
 * Fixed bugs 35108 and 39996.

pkg/analyzer/lib/dart/element/element.dart

@@ -232,6 +232,7 @@ abstract class ClassElement
   /// Create the [InterfaceType] for this class with type arguments that
   /// correspond to the bounds of the type parameters, and the given
   /// [nullabilitySuffix].
+  @Deprecated('Use TypeSystem.instantiateToBounds2() instead')
   InterfaceType instantiateToBounds({
     @required NullabilitySuffix nullabilitySuffix,
   });
@@ -1191,6 +1192,7 @@ abstract class FunctionTypeAliasElement
   /// generic function, with type formals. For example, if the typedef is:
   ///     typedef F<T> = void Function<U>(T, U);
   /// then `F<int>` will produce `void Function<U>(int, U)`.
+  @Deprecated('Use TypeSystem.instantiateToBounds2() instead')
   FunctionType instantiateToBounds({
     @required NullabilitySuffix nullabilitySuffix,
   });

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

@@ -2,6 +2,8 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
+import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/dart/element/nullability_suffix.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:meta/meta.dart';
 
@@ -33,6 +35,17 @@ abstract class TypeSystem {
   /// Other type systems may define this operation differently.
   DartType flatten(DartType type);
 
+  /// Instantiate the given generic element using the type arguments that
+  /// correspond to the bounds of its type parameters.
+  ///
+  /// One and only one of [classElement] or [functionTypeAliasElement] must
+  /// be provided.
+  DartType instantiateToBounds2({
+    ClassElement classElement,
+    FunctionTypeAliasElement functionTypeAliasElement,
+    @required NullabilitySuffix nullabilitySuffix,
+  });
+
   /// Return `true` if the [leftType] is assignable to the [rightType].
   ///
   /// For the Dart 2.0 type system, the definition of this relationship is given

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

@@ -207,6 +207,7 @@ abstract class AbstractClassElementImpl extends ElementImpl
     );
   }
 
+  @Deprecated('Use TypeSystem.instantiateToBounds2() instead')
   @override
   InterfaceType instantiateToBounds({
     @required NullabilitySuffix nullabilitySuffix,
@@ -4785,6 +4786,7 @@ class GenericTypeAliasElementImpl extends ElementImpl
     );
   }
 
+  @Deprecated('Use TypeSystem.instantiateToBounds2() instead')
   @override
   FunctionType instantiateToBounds({
     @required NullabilitySuffix nullabilitySuffix,

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

@@ -358,13 +358,15 @@ class TypeNameResolver {
         return _inferRedirectedConstructor(element);
       }
 
-      return element.instantiateToBounds(
+      return typeSystem.instantiateToBounds2(
+        classElement: element,
         nullabilitySuffix: nullability,
       );
     } else if (element is DynamicElementImpl) {
       return DynamicTypeImpl.instance;
     } else if (element is FunctionTypeAliasElement) {
-      return element.instantiateToBounds(
+      return typeSystem.instantiateToBounds2(
+        functionTypeAliasElement: element,
         nullabilitySuffix: nullability,
       );
     } else if (element is NeverElementImpl) {

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

@@ -715,6 +715,31 @@ class Dart2TypeSystem extends TypeSystem {
     return instantiateType(type, arguments);
   }
 
+  @override
+  DartType instantiateToBounds2({
+    ClassElement classElement,
+    FunctionTypeAliasElement functionTypeAliasElement,
+    @required NullabilitySuffix nullabilitySuffix,
+  }) {
+    if (classElement != null) {
+      var typeParameters = classElement.typeParameters;
+      var typeArguments = _defaultTypeArguments(typeParameters);
+      return classElement.instantiate(
+        typeArguments: typeArguments,
+        nullabilitySuffix: nullabilitySuffix,
+      );
+    } else if (functionTypeAliasElement != null) {
+      var typeParameters = functionTypeAliasElement.typeParameters;
+      var typeArguments = _defaultTypeArguments(typeParameters);
+      return functionTypeAliasElement.instantiate(
+        typeArguments: typeArguments,
+        nullabilitySuffix: nullabilitySuffix,
+      );
+    } else {
+      throw ArgumentError('Missing element');
+    }
+  }
+
   /**
    * Given uninstantiated [typeFormals], instantiate them to their bounds.
    * See the issue for the algorithm description.
@@ -1761,6 +1786,17 @@ class Dart2TypeSystem extends TypeSystem {
     return null;
   }
 
+  List<DartType> _defaultTypeArguments(
+    List<TypeParameterElement> typeParameters,
+  ) {
+    return typeParameters.map((typeParameter) {
+      var typeParameterImpl = typeParameter as TypeParameterElementImpl;
+      var typeArgument = typeParameterImpl.defaultType;
+      typeArgument = _toLegacyType(typeArgument);
+      return typeArgument;
+    }).toList();
+  }
+
   /**
    * Eliminates type variables from the context [type], replacing them with
    * `Null` or `Object` as appropriate.
@@ -2255,6 +2291,11 @@ class Dart2TypeSystem extends TypeSystem {
     return false;
   }
 
+  DartType _toLegacyType(DartType type) {
+    if (isNonNullableByDefault) return type;
+    return NullabilityEliminator.perform(typeProvider, type);
+  }
+
   DartType _typeParameterResolveToObjectBounds(DartType type) {
     var element = type.element;
     type = type.resolveToBound(typeProvider.objectType);