Use ParameterMember when substituting function types.

This ensures that the parameters from the function type still point to
the original function declaration (previously, they were synthetic
parameters).  This should lead to a better user experience in editor
integration, by ensuring that the editor can still find the parameter
declarations associated with parameters in generic function
invocations.

Fixes #48500.

Change-Id: I10a0dd54e7c70e1d0d05dced37565c35bcaabfd0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/243524
Reviewed-by: Konstantin Shcheglov <[email protected]>
Commit-Queue: Paul Berry <[email protected]>

Author: stereotype441

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

@@ -24,7 +24,7 @@ class ConstructorMember extends ExecutableMember
   /// Initialize a newly created element to represent a constructor, based on
   /// the [declaration], and applied [substitution].
   ConstructorMember(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     ConstructorElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -138,7 +138,7 @@ abstract class ExecutableMember extends Member implements ExecutableElement {
   /// their bounds.  The [substitution] includes replacing [declaration] type
   /// parameters with the provided fresh [typeParameters].
   ExecutableMember(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     ExecutableElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -178,6 +178,12 @@ abstract class ExecutableMember extends Member implements ExecutableElement {
   @override
   bool get isSynchronous => declaration.isSynchronous;
 
+  @override
+  LibraryElement get library => _declaration.library!;
+
+  @override
+  Source get librarySource => _declaration.librarySource!;
+
   @override
   List<ParameterElement> get parameters {
     return declaration.parameters.map<ParameterElement>((p) {
@@ -220,7 +226,7 @@ abstract class ExecutableMember extends Member implements ExecutableElement {
     ExecutableElement element,
     MapSubstitution substitution,
   ) {
-    TypeProviderImpl typeProvider;
+    TypeProviderImpl? typeProvider;
     var isLegacy = false;
     var combined = substitution;
     if (element is ExecutableMember) {
@@ -261,7 +267,7 @@ abstract class ExecutableMember extends Member implements ExecutableElement {
 class FieldFormalParameterMember extends ParameterMember
     implements FieldFormalParameterElement {
   factory FieldFormalParameterMember(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     FieldFormalParameterElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -280,7 +286,7 @@ class FieldFormalParameterMember extends ParameterMember
   }
 
   FieldFormalParameterMember._(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     FieldFormalParameterElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -320,7 +326,7 @@ class FieldMember extends VariableMember implements FieldElement {
   /// Initialize a newly created element to represent a field, based on the
   /// [declaration], with applied [substitution].
   FieldMember(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     FieldElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -360,6 +366,9 @@ class FieldMember extends VariableMember implements FieldElement {
   @override
   bool get isExternal => declaration.isExternal;
 
+  @override
+  LibraryElement get library => _declaration.library!;
+
   @override
   String get name => declaration.name;
 
@@ -406,8 +415,8 @@ class FieldMember extends VariableMember implements FieldElement {
 }
 
 class FunctionMember extends ExecutableMember implements FunctionElement {
-  FunctionMember(
-      TypeProviderImpl typeProvider, FunctionElement declaration, bool isLegacy)
+  FunctionMember(TypeProviderImpl? typeProvider, FunctionElement declaration,
+      bool isLegacy)
       : super(
           typeProvider,
           declaration,
@@ -441,7 +450,7 @@ class FunctionMember extends ExecutableMember implements FunctionElement {
 /// parameters are known.
 abstract class Member implements Element {
   /// A type provider (might be legacy, might be null-safe).
-  final TypeProviderImpl _typeProvider;
+  final TypeProviderImpl? _typeProvider;
 
   /// The element on which the parameterized element was created.
   final Element _declaration;
@@ -459,6 +468,10 @@ abstract class Member implements Element {
     if (_declaration is Member) {
       throw StateError('Members must be created from a declarations.');
     }
+    if (_typeProvider == null && isLegacy) {
+      throw StateError(
+          'A type provider must be supplied for legacy conversion');
+    }
   }
 
   @override
@@ -552,10 +565,10 @@ abstract class Member implements Element {
   ElementKind get kind => _declaration.kind;
 
   @override
-  LibraryElement get library => _declaration.library!;
+  LibraryElement? get library => _declaration.library;
 
   @override
-  Source get librarySource => _declaration.librarySource!;
+  Source? get librarySource => _declaration.librarySource;
 
   @override
   ElementLocation get location => _declaration.location!;
@@ -642,7 +655,7 @@ abstract class Member implements Element {
   /// Otherwise, return the type unchanged.
   DartType _toLegacyType(DartType type) {
     if (isLegacy) {
-      return NullabilityEliminator.perform(_typeProvider, type);
+      return NullabilityEliminator.perform(_typeProvider!, type);
     } else {
       return type;
     }
@@ -720,7 +733,7 @@ abstract class Member implements Element {
 /// type parameters are known.
 class MethodMember extends ExecutableMember implements MethodElement {
   factory MethodMember(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     MethodElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -739,7 +752,7 @@ class MethodMember extends ExecutableMember implements MethodElement {
   }
 
   MethodMember._(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     MethodElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -799,7 +812,7 @@ class ParameterMember extends VariableMember
   final List<TypeParameterElement> typeParameters;
 
   factory ParameterMember(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     ParameterElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -820,7 +833,7 @@ class ParameterMember extends VariableMember
   /// Initialize a newly created element to represent a parameter, based on the
   /// [declaration], with applied [substitution].
   ParameterMember._(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     ParameterElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -887,14 +900,41 @@ class ParameterMember extends VariableMember
     super.visitChildren(visitor);
     safelyVisitChildren(parameters, visitor);
   }
+
+  static ParameterElement from(
+      ParameterElement element, MapSubstitution substitution) {
+    TypeProviderImpl? typeProvider;
+    var isLegacy = false;
+    var combined = substitution;
+    if (element is ParameterMember) {
+      var member = element;
+      element = member.declaration;
+      typeProvider = member._typeProvider;
+
+      isLegacy = member.isLegacy;
+
+      var map = <TypeParameterElement, DartType>{};
+      for (var entry in member._substitution.map.entries) {
+        map[entry.key] = substitution.substituteType(entry.value);
+      }
+      map.addAll(substitution.map);
+      combined = Substitution.fromMap(map);
+    }
+
+    if (!isLegacy && combined.map.isEmpty) {
+      return element;
+    }
+
+    return ParameterMember(typeProvider, element, combined, isLegacy);
+  }
 }
 
 /// A property accessor element defined in a parameterized type where the values
 /// of the type parameters are known.
 class PropertyAccessorMember extends ExecutableMember
     implements PropertyAccessorElement {
   factory PropertyAccessorMember(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     PropertyAccessorElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -913,7 +953,7 @@ class PropertyAccessorMember extends ExecutableMember
   }
 
   PropertyAccessorMember._(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     PropertyAccessorElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -1005,7 +1045,7 @@ class PropertyAccessorMember extends ExecutableMember
 class SuperFormalParameterMember extends ParameterMember
     implements SuperFormalParameterElement {
   factory SuperFormalParameterMember(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     SuperFormalParameterElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -1024,7 +1064,7 @@ class SuperFormalParameterMember extends ParameterMember
   }
 
   SuperFormalParameterMember._(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     SuperFormalParameterElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -1063,7 +1103,7 @@ class SuperFormalParameterMember extends ParameterMember
 class TopLevelVariableMember extends VariableMember
     implements TopLevelVariableElement {
   TopLevelVariableMember(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     VariableElement declaration,
     MapSubstitution substitution,
     bool isLegacy,
@@ -1092,6 +1132,9 @@ class TopLevelVariableMember extends VariableMember
   @override
   bool get isExternal => declaration.isExternal;
 
+  @override
+  LibraryElement get library => _declaration.library!;
+
   @override
   String get name => declaration.name;
 
@@ -1119,7 +1162,7 @@ abstract class VariableMember extends Member implements VariableElement {
   /// Initialize a newly created element to represent a variable, based on the
   /// [declaration], with applied [substitution].
   VariableMember(
-    TypeProviderImpl typeProvider,
+    TypeProviderImpl? typeProvider,
     VariableElement declaration,
     MapSubstitution substitution,
     bool isLegacy,

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

@@ -10,7 +10,6 @@ import 'package:analyzer/dart/element/type_visitor.dart';
 import 'package:analyzer/src/dart/analysis/session.dart';
 import 'package:analyzer/src/dart/element/display_string_builder.dart';
 import 'package:analyzer/src/dart/element/element.dart';
-import 'package:analyzer/src/dart/element/extensions.dart';
 import 'package:analyzer/src/dart/element/inheritance_manager3.dart';
 import 'package:analyzer/src/dart/element/member.dart';
 import 'package:analyzer/src/dart/element/type_algebra.dart';
@@ -224,9 +223,8 @@ class FunctionTypeImpl extends TypeImpl implements FunctionType {
     return FunctionTypeImpl(
       returnType: substitution.substituteType(returnType),
       typeFormals: const [],
-      parameters: parameters
-          .map((p) => p.copyWith(type: substitution.substituteType(p.type)))
-          .toList(),
+      parameters:
+          parameters.map((p) => ParameterMember.from(p, substitution)).toList(),
       nullabilitySuffix: nullabilitySuffix,
     );
   }

pkg/analyzer/lib/src/test_utilities/mock_sdk.dart

@@ -591,6 +591,9 @@ abstract class Set<E> implements Iterable<E> {
   void addAll(Iterable<E> elements);
   bool remove(Object? value);
   E? lookup(Object? object);
+
+  static Set<T> castFrom<S, T>(Set<S> source, {Set<R> Function<R>()? newSet}) =>
+      throw '';
 }
 
 class StackTrace {}

pkg/analyzer/test/generated/non_error_resolver_test.dart

@@ -1458,10 +1458,8 @@ test(C c) => c.method<bool>(arg: true);
 ''');
     var x = findNode.namedExpression('arg: true');
     var y = x.staticParameterElement!;
-    // Note: the staticParameterElement is synthetic; see
-    // https://github.com/dart-lang/sdk/issues/48500
-    expect(y, isNot(TypeMatcher<ParameterMember>()));
-    expect(y.enclosingElement, isNull);
+    expect(y.enclosingElement, isNotNull);
+    expect(y.declaration, findElement.parameter('arg'));
   }
 
   test_generic_staticParameterElement_methodCall_implicitTypeArg() async {
@@ -1473,10 +1471,8 @@ bool test(C c) => c.method<bool>(arg: true);
 ''');
     var x = findNode.namedExpression('arg: true');
     var y = x.staticParameterElement!;
-    // Note: the staticParameterElement is synthetic; see
-    // https://github.com/dart-lang/sdk/issues/48500
-    expect(y, isNot(TypeMatcher<ParameterMember>()));
-    expect(y.enclosingElement, isNull);
+    expect(y.enclosingElement, isNotNull);
+    expect(y.declaration, findElement.parameter('arg'));
   }
 
   test_genericTypeAlias_castsAndTypeChecks_hasTypeParameters() async {
@@ -2258,6 +2254,21 @@ int f(v) {
 ''');
   }
 
+  test_librarySource_of_type_substituted_synthetic_parameter() async {
+    await assertErrorsInCode('''
+Map<int, T> f<T>(T t) => throw '';
+Map<double, T> g<T>(T t) => throw '';
+h(bool b) {
+  Map<num, String> m = (b ? f : g)('x');
+}
+''', [
+      error(HintCode.UNUSED_LOCAL_VARIABLE, 104, 1),
+    ]);
+    var parameter = findNode.stringLiteral("'x'").staticParameterElement;
+    expect(parameter!.library, isNull);
+    expect(parameter.librarySource, isNull);
+  }
+
   test_loadLibraryDefined() async {
     newFile('$testPackageLibPath/lib.dart', r'''
 library lib;
@@ -3310,6 +3321,24 @@ core.dynamic dynamicVariable;
 @reflectiveTest
 class NonErrorResolverWithoutNullSafetyTest extends PubPackageResolutionTest
     with WithoutNullSafetyMixin, NonErrorResolverTestCases {
+  test_castFrom() async {
+    // This test exercises a corner case of legacy erasure: due to the type
+    // substitution in the `newSet` parameter of `Set.castFrom`, we wind up with
+    // a synthetic `ParameterMember` that belongs to no library.  We need to
+    // make sure this doesn't lead to a crash.
+    await assertErrorsInCode('''
+class C {}
+
+void testNewSet(Set<C> setEls) {
+  var customNewSet;
+  Set.castFrom<C, Object>(setEls,
+      newSet: <T>() => customNewSet = new Set<T>());
+}
+''', [
+      error(HintCode.UNUSED_LOCAL_VARIABLE, 51, 12),
+    ]);
+  }
+
   test_conflictingStaticGetterAndInstanceSetter_thisClass() async {
     await assertNoErrorsInCode(r'''
 class A {

pkg/analyzer/test/src/dart/resolution/constructor_reference_test.dart

@@ -242,6 +242,21 @@ ConstructorReference
 ''');
   }
 
+  test_alias_generic_with_inferred_type_parameter() async {
+    await assertErrorsInCode('''
+class C<T> {
+  final T x;
+  C(this.x);
+}
+typedef Direct<T> = C<T>;
+void main() {
+  var x = const <C<int> Function(int)>[Direct.new];
+}
+''', [
+      error(HintCode.UNUSED_LOCAL_VARIABLE, 87, 1),
+    ]);
+  }
+
   test_alias_genericWithBound_unnamed() async {
     await assertNoErrorsInCode('''
 class A<T> {