[cfe] Class type parameters wildcards are non-binding.

Wildcard type parameters are not added to the scope of the class. They do not collide with other wildcards or other wildcard type parameters.

Bug: #55655
Change-Id: I473a5023c570623fe2a11df5c07d491082bab642
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/371943
Commit-Queue: Kallen Tu <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>
Reviewed-by: Chloe Stefantsova <[email protected]>

pkg/front_end/lib/src/fasta/builder/type_variable_builder.dart

@@ -188,6 +188,8 @@ class NominalVariableBuilder extends TypeVariableBuilderBase {
 
   final TypeParameter actualParameter;
 
+  final bool isWildcard;
+
   @override
   NominalVariableBuilder? actualOrigin;
 
@@ -196,7 +198,8 @@ class NominalVariableBuilder extends TypeVariableBuilderBase {
       {TypeBuilder? bound,
       required TypeVariableKind kind,
       Variance? variableVariance,
-      List<MetadataBuilder>? metadata})
+      List<MetadataBuilder>? metadata,
+      this.isWildcard = false})
       : actualParameter =
             new TypeParameter(name == noNameSentinel ? null : name, null)
               ..fileOffset = charOffset
@@ -220,7 +223,7 @@ class NominalVariableBuilder extends TypeVariableBuilderBase {
   ///
   ///   class A<X extends A<X>> {}
   NominalVariableBuilder.fromKernel(TypeParameter parameter,
-      {required Loader? loader})
+      {required Loader? loader, this.isWildcard = false})
       : actualParameter = parameter,
         // TODO(johnniwinther): Do we need to support synthesized type
         //  parameters from kernel?

pkg/front_end/lib/src/fasta/scope.dart

@@ -461,6 +461,7 @@ class Scope extends MutableScope {
     Scope newScope = new Scope.nested(this, "type variables",
         isModifiable: false, kind: ScopeKind.typeParameters);
     for (NominalVariableBuilder t in typeVariables) {
+      if (t.isWildcard) continue;
       (newScope._local ??= {})[t.name] = t;
     }
     return newScope;

pkg/front_end/lib/src/fasta/source/source_library_builder.dart

@@ -2583,7 +2583,10 @@ class SourceCompilationUnitImpl implements SourceCompilationUnit {
       {required TypeVariableKind kind}) {
     NominalVariableBuilder builder = new NominalVariableBuilder(
         name, _sourceLibraryBuilder, charOffset, fileUri,
-        bound: bound, metadata: metadata, kind: kind);
+        bound: bound,
+        metadata: metadata,
+        kind: kind,
+        isWildcard: libraryFeatures.wildcardVariables.isEnabled && name == '_');
 
     unboundNominalVariables.add(builder);
     return builder;
@@ -2611,6 +2614,7 @@ class SourceCompilationUnitImpl implements SourceCompilationUnit {
         <String, NominalVariableBuilder>{};
     for (NominalVariableBuilder tv in typeVariables) {
       NominalVariableBuilder? existing = typeVariablesByName[tv.name];
+      if (tv.isWildcard) continue;
       if (existing != null) {
         if (existing.kind == TypeVariableKind.extensionSynthesized) {
           // The type parameter from the extension is shadowed by the type
@@ -2673,7 +2677,9 @@ class SourceCompilationUnitImpl implements SourceCompilationUnit {
               ?.clone(newTypes, _sourceLibraryBuilder, declaration),
           kind: kind,
           variableVariance:
-              variable.parameter.isLegacyCovariant ? null : variable.variance);
+              variable.parameter.isLegacyCovariant ? null : variable.variance,
+          isWildcard: libraryFeatures.wildcardVariables.isEnabled &&
+              variable.isWildcard);
       copy.add(newVariable);
       unboundNominalVariables.add(newVariable);
     }
@@ -6219,6 +6225,7 @@ class TypeParameterScopeBuilder {
     if (typeVariables != null) {
       map = <String, NominalVariableBuilder>{};
       for (NominalVariableBuilder builder in typeVariables) {
+        if (builder.isWildcard) continue;
         map[builder.name] = builder;
       }
     }

pkg/front_end/testcases/strong.status

@@ -310,6 +310,7 @@ value_class/copy_with_call_sites: RuntimeError # Expected
 value_class/simple: RuntimeError # Expected
 value_class/value_extends_non_value: RuntimeError # Expected
 value_class/value_implements_non_value: RuntimeError # Expected
+wildcard_variables/class_type_parameters: semiFuzzFailureOnForceRebuildBodies # Expected
 wildcard_variables/local_var_no_shadowing: semiFuzzFailureOnForceRebuildBodies # Expected
 wildcard_variables/top_level_function_no_shadow: semiFuzzFailureOnForceRebuildBodies # Expected
 

pkg/front_end/testcases/wildcard_variables/class_type_parameters.dart

@@ -0,0 +1,27 @@
+// Copyright (c) 2024, the Dart project authors.  Please see the AUTHORS file
+// 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.
+
+typedef _ = BB;
+
+class AA {}
+
+class BB extends AA {}
+
+class A<T, U extends AA> {}
+
+class B<_, _ extends AA> extends A<_, _> {
+  int foo<_ extends _>([int _ = 2]) => 1;
+}
+
+class C<T, _ extends _> extends A<T, _> {
+  static const int _ = 1;
+}
+
+class D<_, _> {}
+
+class DoesNotUseTypeVariable<_> {
+  Type returnsBB() {
+    return _;
+  }
+}

pkg/front_end/testcases/wildcard_variables/class_type_parameters.dart.strong.expect

@@ -0,0 +1,52 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+typedef _ = self::BB;
+class AA extends core::Object {
+  synthetic constructor •() → self::AA
+    : super core::Object::•()
+    ;
+}
+class BB extends self::AA {
+  synthetic constructor •() → self::BB
+    : super self::AA::•()
+    ;
+}
+class A<T extends core::Object? = dynamic, U extends self::AA> extends core::Object {
+  synthetic constructor •() → self::A<self::A::T%, self::A::U>
+    : super core::Object::•()
+    ;
+}
+class B<_ extends core::Object? = dynamic, _ extends self::AA> extends self::A<self::BB, self::BB> {
+  synthetic constructor •() → self::B<self::B::_%, self::B::_>
+    : super self::A::•()
+    ;
+  method foo<_ extends self::BB>([wildcard core::int _ = #C1]) → core::int
+    return 1;
+}
+class C<T extends core::Object? = dynamic, _ extends self::BB> extends self::A<self::C::T%, self::BB> {
+  static const field core::int _ = #C2;
+  synthetic constructor •() → self::C<self::C::T%, self::C::_>
+    : super self::A::•()
+    ;
+}
+class D<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic> extends core::Object {
+  synthetic constructor •() → self::D<self::D::_%, self::D::_%>
+    : super core::Object::•()
+    ;
+}
+class DoesNotUseTypeVariable<_ extends core::Object? = dynamic> extends core::Object {
+  synthetic constructor •() → self::DoesNotUseTypeVariable<self::DoesNotUseTypeVariable::_%>
+    : super core::Object::•()
+    ;
+  method returnsBB() → core::Type {
+    return #C3;
+  }
+}
+
+constants  {
+  #C1 = 2
+  #C2 = 1
+  #C3 = TypeLiteralConstant(self::BB)
+}

pkg/front_end/testcases/wildcard_variables/class_type_parameters.dart.strong.modular.expect

@@ -0,0 +1,52 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+typedef _ = self::BB;
+class AA extends core::Object {
+  synthetic constructor •() → self::AA
+    : super core::Object::•()
+    ;
+}
+class BB extends self::AA {
+  synthetic constructor •() → self::BB
+    : super self::AA::•()
+    ;
+}
+class A<T extends core::Object? = dynamic, U extends self::AA> extends core::Object {
+  synthetic constructor •() → self::A<self::A::T%, self::A::U>
+    : super core::Object::•()
+    ;
+}
+class B<_ extends core::Object? = dynamic, _ extends self::AA> extends self::A<self::BB, self::BB> {
+  synthetic constructor •() → self::B<self::B::_%, self::B::_>
+    : super self::A::•()
+    ;
+  method foo<_ extends self::BB>([wildcard core::int _ = #C1]) → core::int
+    return 1;
+}
+class C<T extends core::Object? = dynamic, _ extends self::BB> extends self::A<self::C::T%, self::BB> {
+  static const field core::int _ = #C2;
+  synthetic constructor •() → self::C<self::C::T%, self::C::_>
+    : super self::A::•()
+    ;
+}
+class D<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic> extends core::Object {
+  synthetic constructor •() → self::D<self::D::_%, self::D::_%>
+    : super core::Object::•()
+    ;
+}
+class DoesNotUseTypeVariable<_ extends core::Object? = dynamic> extends core::Object {
+  synthetic constructor •() → self::DoesNotUseTypeVariable<self::DoesNotUseTypeVariable::_%>
+    : super core::Object::•()
+    ;
+  method returnsBB() → core::Type {
+    return #C3;
+  }
+}
+
+constants  {
+  #C1 = 2
+  #C2 = 1
+  #C3 = TypeLiteralConstant(self::BB)
+}

pkg/front_end/testcases/wildcard_variables/class_type_parameters.dart.strong.outline.expect

@@ -0,0 +1,38 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+typedef _ = self::BB;
+class AA extends core::Object {
+  synthetic constructor •() → self::AA
+    ;
+}
+class BB extends self::AA {
+  synthetic constructor •() → self::BB
+    ;
+}
+class A<T extends core::Object? = dynamic, U extends self::AA> extends core::Object {
+  synthetic constructor •() → self::A<self::A::T%, self::A::U>
+    ;
+}
+class B<_ extends core::Object? = dynamic, _ extends self::AA> extends self::A<self::BB, self::BB> {
+  synthetic constructor •() → self::B<self::B::_%, self::B::_>
+    ;
+  method foo<_ extends self::BB>([wildcard core::int _ = 2]) → core::int
+    ;
+}
+class C<T extends core::Object? = dynamic, _ extends self::BB> extends self::A<self::C::T%, self::BB> {
+  static const field core::int _ = 1;
+  synthetic constructor •() → self::C<self::C::T%, self::C::_>
+    ;
+}
+class D<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic> extends core::Object {
+  synthetic constructor •() → self::D<self::D::_%, self::D::_%>
+    ;
+}
+class DoesNotUseTypeVariable<_ extends core::Object? = dynamic> extends core::Object {
+  synthetic constructor •() → self::DoesNotUseTypeVariable<self::DoesNotUseTypeVariable::_%>
+    ;
+  method returnsBB() → core::Type
+    ;
+}

pkg/front_end/testcases/wildcard_variables/class_type_parameters.dart.strong.transformed.expect

@@ -0,0 +1,52 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+typedef _ = self::BB;
+class AA extends core::Object {
+  synthetic constructor •() → self::AA
+    : super core::Object::•()
+    ;
+}
+class BB extends self::AA {
+  synthetic constructor •() → self::BB
+    : super self::AA::•()
+    ;
+}
+class A<T extends core::Object? = dynamic, U extends self::AA> extends core::Object {
+  synthetic constructor •() → self::A<self::A::T%, self::A::U>
+    : super core::Object::•()
+    ;
+}
+class B<_ extends core::Object? = dynamic, _ extends self::AA> extends self::A<self::BB, self::BB> {
+  synthetic constructor •() → self::B<self::B::_%, self::B::_>
+    : super self::A::•()
+    ;
+  method foo<_ extends self::BB>([wildcard core::int _ = #C1]) → core::int
+    return 1;
+}
+class C<T extends core::Object? = dynamic, _ extends self::BB> extends self::A<self::C::T%, self::BB> {
+  static const field core::int _ = #C2;
+  synthetic constructor •() → self::C<self::C::T%, self::C::_>
+    : super self::A::•()
+    ;
+}
+class D<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic> extends core::Object {
+  synthetic constructor •() → self::D<self::D::_%, self::D::_%>
+    : super core::Object::•()
+    ;
+}
+class DoesNotUseTypeVariable<_ extends core::Object? = dynamic> extends core::Object {
+  synthetic constructor •() → self::DoesNotUseTypeVariable<self::DoesNotUseTypeVariable::_%>
+    : super core::Object::•()
+    ;
+  method returnsBB() → core::Type {
+    return #C3;
+  }
+}
+
+constants  {
+  #C1 = 2
+  #C2 = 1
+  #C3 = TypeLiteralConstant(self::BB)
+}

pkg/front_end/testcases/wildcard_variables/class_type_parameters.dart.textual_outline.expect

@@ -0,0 +1,21 @@
+typedef _ = BB;
+
+class AA {}
+
+class BB extends AA {}
+
+class A<T, U extends AA> {}
+
+class B<_, _ extends AA> extends A<_, _> {
+  int foo<_ extends _>([int _ = 2]) => 1;
+}
+
+class C<T, _ extends _> extends A<T, _> {
+  static const int _ = 1;
+}
+
+class D<_, _> {}
+
+class DoesNotUseTypeVariable<_> {
+  Type returnsBB() {}
+}

pkg/front_end/testcases/wildcard_variables/class_type_parameters.dart.textual_outline_modelled.expect

@@ -0,0 +1,21 @@
+class A<T, U extends AA> {}
+
+class AA {}
+
+class B<_, _ extends AA> extends A<_, _> {
+  int foo<_ extends _>([int _ = 2]) => 1;
+}
+
+class BB extends AA {}
+
+class C<T, _ extends _> extends A<T, _> {
+  static const int _ = 1;
+}
+
+class D<_, _> {}
+
+class DoesNotUseTypeVariable<_> {
+  Type returnsBB() {}
+}
+
+typedef _ = BB;