[cfe] Local and top level function wildcard type parameters are non-binding.

This CL adds `isWildcard` to `StructuralVariableBuilder` and allows type variables in functions and function types. It also removes them from scope so they can't be used.

Bug: #55655
Change-Id: I26237375480318dd0c9a01cb59b3426b783ca7be
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/372240
Reviewed-by: Johnni Winther <[email protected]>
Commit-Queue: Kallen Tu <[email protected]>
Reviewed-by: Chloe Stefantsova <[email protected]>

Author: kallentu

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

@@ -578,14 +578,17 @@ class StructuralVariableBuilder extends TypeVariableBuilderBase {
 
   final StructuralParameter actualParameter;
 
+  final bool isWildcard;
+
   @override
   StructuralVariableBuilder? actualOrigin;
 
   StructuralVariableBuilder(
       String name, Builder? compilationUnit, int charOffset, Uri? fileUri,
       {TypeBuilder? bound,
       Variance? variableVariance,
-      List<MetadataBuilder>? metadata})
+      List<MetadataBuilder>? metadata,
+      this.isWildcard = false})
       : actualParameter =
             new StructuralParameter(name == noNameSentinel ? null : name, null)
               ..fileOffset = charOffset
@@ -596,7 +599,8 @@ class StructuralVariableBuilder extends TypeVariableBuilderBase {
             variableVariance: variableVariance,
             metadata: metadata);
 
-  StructuralVariableBuilder.fromKernel(StructuralParameter parameter)
+  StructuralVariableBuilder.fromKernel(StructuralParameter parameter,
+      {this.isWildcard = false})
       : actualParameter = parameter,
         // TODO(johnniwinther): Do we need to support synthesized type
         //  parameters from kernel?

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

@@ -5137,6 +5137,7 @@ class BodyBuilder extends StackListenerImpl
         kind: ScopeKind.typeParameters));
     if (nominalVariableBuilders != null) {
       for (NominalVariableBuilder builder in nominalVariableBuilders) {
+        if (builder.isWildcard) continue;
         String name = builder.name;
         NominalVariableBuilder? existing = scope.lookupLocalMember(name,
             setter: false) as NominalVariableBuilder?;
@@ -5158,6 +5159,7 @@ class BodyBuilder extends StackListenerImpl
         kind: ScopeKind.typeParameters));
     if (structuralVariableBuilders != null) {
       for (StructuralVariableBuilder builder in structuralVariableBuilders) {
+        if (builder.isWildcard) continue;
         String name = builder.name;
         StructuralVariableBuilder? existing = scope.lookupLocalMember(name,
             setter: false) as StructuralVariableBuilder?;
@@ -8798,10 +8800,14 @@ class BodyBuilder extends StackListenerImpl
     }
     TypeVariableBuilderBase variable = inFunctionType
         ? new StructuralVariableBuilder(
-            typeVariableName, libraryBuilder, typeVariableCharOffset, uri)
+            typeVariableName, libraryBuilder, typeVariableCharOffset, uri,
+            isWildcard: libraryFeatures.wildcardVariables.isEnabled &&
+                typeVariableName == '_')
         : new NominalVariableBuilder(
             typeVariableName, libraryBuilder, typeVariableCharOffset, uri,
-            kind: TypeVariableKind.function);
+            kind: TypeVariableKind.function,
+            isWildcard: libraryFeatures.wildcardVariables.isEnabled &&
+                typeVariableName == '_');
     if (annotations != null) {
       switch (variable) {
         case StructuralVariableBuilder():

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

@@ -259,6 +259,7 @@ abstract class SourceFunctionBuilderImpl extends SourceMemberBuilderImpl
     if (typeVariables == null) return parent;
     Map<String, Builder> local = <String, Builder>{};
     for (NominalVariableBuilder variable in typeVariables!) {
+      if (variable.isWildcard) continue;
       local[variable.name] = variable;
     }
     return new Scope(

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

@@ -2539,6 +2539,7 @@ class SourceCompilationUnitImpl implements SourceCompilationUnit {
     Map<String, StructuralVariableBuilder> typeVariablesByName =
         <String, StructuralVariableBuilder>{};
     for (StructuralVariableBuilder tv in typeVariables) {
+      if (tv.isWildcard) continue;
       StructuralVariableBuilder? existing = typeVariablesByName[tv.name];
       if (existing != null) {
         addProblem(messageTypeVariableDuplicatedName, tv.charOffset,
@@ -2600,7 +2601,9 @@ class SourceCompilationUnitImpl implements SourceCompilationUnit {
       Uri fileUri) {
     StructuralVariableBuilder builder = new StructuralVariableBuilder(
         name, _sourceLibraryBuilder, charOffset, fileUri,
-        bound: bound, metadata: metadata);
+        bound: bound,
+        metadata: metadata,
+        isWildcard: libraryFeatures.wildcardVariables.isEnabled && name == '_');
 
     unboundStructuralVariables.add(builder);
     return builder;
@@ -2677,8 +2680,7 @@ class SourceCompilationUnitImpl implements SourceCompilationUnit {
           kind: kind,
           variableVariance:
               variable.parameter.isLegacyCovariant ? null : variable.variance,
-          isWildcard: libraryFeatures.wildcardVariables.isEnabled &&
-              variable.isWildcard);
+          isWildcard: variable.isWildcard);
       copy.add(newVariable);
       unboundNominalVariables.add(newVariable);
     }
@@ -4453,7 +4455,8 @@ class SourceLibraryBuilder extends LibraryBuilderImpl {
           variable.name, this, variable.charOffset, variable.fileUri,
           bound: variable.bound?.clone(newTypes, this, declaration),
           variableVariance:
-              variable.parameter.isLegacyCovariant ? null : variable.variance);
+              variable.parameter.isLegacyCovariant ? null : variable.variance,
+          isWildcard: variable.isWildcard);
       copy.add(newVariable);
       unboundStructuralVariables.add(newVariable);
     }

pkg/front_end/testcases/wildcard_variables/class_type_parameters.dart

@@ -24,4 +24,8 @@ class DoesNotUseTypeVariable<_> {
   Type returnsBB() {
     return _;
   }
+
+  Type alsoReturnsBB<_, _ extends int>() {
+    return _;
+  }
 }

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

@@ -43,6 +43,9 @@ class DoesNotUseTypeVariable<_ extends core::Object? = dynamic> extends core::Ob
   method returnsBB() → core::Type {
     return #C3;
   }
+  method alsoReturnsBB<_ extends core::Object? = dynamic, _ extends core::int>() → core::Type {
+    return #C3;
+  }
 }
 
 constants  {

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

@@ -43,6 +43,9 @@ class DoesNotUseTypeVariable<_ extends core::Object? = dynamic> extends core::Ob
   method returnsBB() → core::Type {
     return #C3;
   }
+  method alsoReturnsBB<_ extends core::Object? = dynamic, _ extends core::int>() → core::Type {
+    return #C3;
+  }
 }
 
 constants  {

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

@@ -35,4 +35,6 @@ class DoesNotUseTypeVariable<_ extends core::Object? = dynamic> extends core::Ob
     ;
   method returnsBB() → core::Type
     ;
+  method alsoReturnsBB<_ extends core::Object? = dynamic, _ extends core::int>() → core::Type
+    ;
 }

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

@@ -43,6 +43,9 @@ class DoesNotUseTypeVariable<_ extends core::Object? = dynamic> extends core::Ob
   method returnsBB() → core::Type {
     return #C3;
   }
+  method alsoReturnsBB<_ extends core::Object? = dynamic, _ extends core::int>() → core::Type {
+    return #C3;
+  }
 }
 
 constants  {

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

@@ -18,4 +18,5 @@ class D<_, _> {}
 
 class DoesNotUseTypeVariable<_> {
   Type returnsBB() {}
+  Type alsoReturnsBB<_, _ extends int>() {}
 }

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

@@ -15,6 +15,7 @@ class C<T, _ extends _> extends A<T, _> {
 class D<_, _> {}
 
 class DoesNotUseTypeVariable<_> {
+  Type alsoReturnsBB<_, _ extends int>() {}
   Type returnsBB() {}
 }
 

pkg/front_end/testcases/wildcard_variables/function_type_parameters.dart

@@ -0,0 +1,14 @@
+// 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 F = void Function<_, _ extends int, _>();
+
+void fn(void Function<_, _>() x) {}
+void fn1<_, _ extends int>(void Function<_, _>() x) {}
+
+test() {
+  void foo1(void Function<_, _ extends int>() x) {}
+  void foo2<_, _ extends int>() {}
+  void foo3(F x) {}
+}

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

@@ -0,0 +1,12 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+typedef F = <_ extends core::Object? = dynamic, _ extends core::int = dynamic, _ extends core::Object? = dynamic>() → void;
+static method fn(<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic>() → void x) → void {}
+static method fn1<_ extends core::Object? = dynamic, _ extends core::int>(<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic>() → void x) → void {}
+static method test() → dynamic {
+  function foo1(<_ extends core::Object? = dynamic, _ extends core::int>() → void x) → void {}
+  function foo2<_ extends core::Object? = dynamic, _ extends core::int>() → void {}
+  function foo3(<_ extends core::Object? = dynamic, _ extends core::int = dynamic, _ extends core::Object? = dynamic>() → void x) → void {}
+}

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

@@ -0,0 +1,12 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+typedef F = <_ extends core::Object? = dynamic, _ extends core::int = dynamic, _ extends core::Object? = dynamic>() → void;
+static method fn(<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic>() → void x) → void {}
+static method fn1<_ extends core::Object? = dynamic, _ extends core::int>(<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic>() → void x) → void {}
+static method test() → dynamic {
+  function foo1(<_ extends core::Object? = dynamic, _ extends core::int>() → void x) → void {}
+  function foo2<_ extends core::Object? = dynamic, _ extends core::int>() → void {}
+  function foo3(<_ extends core::Object? = dynamic, _ extends core::int = dynamic, _ extends core::Object? = dynamic>() → void x) → void {}
+}

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

@@ -0,0 +1,11 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+typedef F = <_ extends core::Object? = dynamic, _ extends core::int = dynamic, _ extends core::Object? = dynamic>() → void;
+static method fn(<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic>() → void x) → void
+  ;
+static method fn1<_ extends core::Object? = dynamic, _ extends core::int>(<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic>() → void x) → void
+  ;
+static method test() → dynamic
+  ;

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

@@ -0,0 +1,12 @@
+library;
+import self as self;
+import "dart:core" as core;
+
+typedef F = <_ extends core::Object? = dynamic, _ extends core::int = dynamic, _ extends core::Object? = dynamic>() → void;
+static method fn(<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic>() → void x) → void {}
+static method fn1<_ extends core::Object? = dynamic, _ extends core::int>(<_ extends core::Object? = dynamic, _ extends core::Object? = dynamic>() → void x) → void {}
+static method test() → dynamic {
+  function foo1(<_ extends core::Object? = dynamic, _ extends core::int>() → void x) → void {}
+  function foo2<_ extends core::Object? = dynamic, _ extends core::int>() → void {}
+  function foo3(<_ extends core::Object? = dynamic, _ extends core::int = dynamic, _ extends core::Object? = dynamic>() → void x) → void {}
+}

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

@@ -0,0 +1,7 @@
+typedef F = void Function<_, _ extends int, _>();
+
+void fn(void Function<_, _>() x) {}
+
+void fn1<_, _ extends int>(void Function<_, _>() x) {}
+
+test() {}

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

@@ -0,0 +1,7 @@
+test() {}
+
+typedef F = void Function<_, _ extends int, _>();
+
+void fn(void Function<_, _>() x) {}
+
+void fn1<_, _ extends int>(void Function<_, _>() x) {}

tests/language/wildcard_variables/non_binding/top_level_typedef_test.dart

@@ -20,7 +20,7 @@ void main<_ extends _>() {
   _ foo<_ extends _>([_ _ = int]) => _;
   _ bar<_ extends _>([_ _ = _]) => int;
   Expect.type<Type>(foo());
-  Expect.type<int>(bar());
+  Expect.type<Type>(bar());
 }
 
 class CConst {

tests/language/wildcard_variables/non_binding/top_level_variable_test.dart

@@ -12,7 +12,8 @@ import 'package:expect/expect.dart';
 var _ = 2;
 
 void main() {
-  Clas().member();
+  Clas().member(); // Top level _ is 4 after this call.
+  _ = 2;
 
   int _ = _;
   int _ = 3;