[cfe] Build a lowered name for wildcard variables.

Each wildcard variable will have a unique name meaning that each local, formal, and type parameter named `_` will be named something similar to `_#wc<index>#<type>`.

This will allow the DDC tests to pass.

Change-Id: Ic5362e46142c4a51cd461280ca33a8a5ba5b910f
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/373621
Reviewed-by: Chloe Stefantsova <[email protected]>
Commit-Queue: Kallen Tu <[email protected]>

Author: kallentu

pkg/front_end/lib/src/api_prototype/lowering_predicates.dart

@@ -12,6 +12,7 @@ export '../kernel/constructor_tearoff_lowering.dart'
         isConstructorTearOffLowering,
         isTearOffLowering,
         isTypedefTearOffLowering;
+export '../kernel/wildcard_lowering.dart';
 
 // Coverage-ignore(suite): Not run.
 /// Returns `true` if [node] is the field holding the value of a lowered late

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

@@ -344,13 +344,7 @@ class TypeParameterScope with LookupScopeMixin {
     if (typeVariableBuilders == null) return parent;
     Map<String, Builder> map = {};
     for (TypeVariableBuilderBase typeVariableBuilder in typeVariableBuilders) {
-      // TODO(johnniwinther,kallentu): Why are structural variables treated
-      // differently from nominal variable here but not for instance in
-      // `BodyBuilder.enterStructuralVariablesScope`?
-      if (typeVariableBuilder is NominalVariableBuilder &&
-          typeVariableBuilder.isWildcard) {
-        continue;
-      }
+      if (typeVariableBuilder.isWildcard) continue;
       map[typeVariableBuilder.name] = typeVariableBuilder;
     }
     return new TypeParameterScope(parent, map);

pkg/front_end/lib/src/builder/formal_parameter_builder.dart

@@ -17,6 +17,7 @@ import '../base/scope.dart' show LookupScope;
 import '../kernel/body_builder.dart' show BodyBuilder;
 import '../kernel/body_builder_context.dart';
 import '../kernel/internal_ast.dart' show VariableDeclarationImpl;
+import '../kernel/wildcard_lowering.dart';
 import '../source/constructor_declaration.dart';
 import '../source/builder_factory.dart';
 import '../source/source_factory_builder.dart';
@@ -197,8 +198,10 @@ class FormalParameterBuilder extends ModifierBuilderImpl
   }
 
   FormalParameterBuilder forPrimaryConstructor(BuilderFactory builderFactory) {
+    // Primary constructors should not have a lowered wildcard name.
+    String formalName = isWildcardLoweredFormalParameter(name) ? '_' : name;
     return new FormalParameterBuilder(kind, modifiers | initializingFormalMask,
-        builderFactory.addInferableType(), name, null, charOffset,
+        builderFactory.addInferableType(), formalName, null, charOffset,
         fileUri: fileUri,
         isExtensionThis: isExtensionThis,
         hasImmediatelyDeclaredInitializer: hasImmediatelyDeclaredInitializer)

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

@@ -32,6 +32,8 @@ sealed class TypeVariableBuilderBase extends TypeDeclarationBuilderImpl
 
   final TypeVariableKind kind;
 
+  final bool isWildcard;
+
   @override
   final Uri? fileUri;
 
@@ -41,7 +43,8 @@ sealed class TypeVariableBuilderBase extends TypeDeclarationBuilderImpl
       this.defaultType,
       required this.kind,
       Variance? variableVariance,
-      List<MetadataBuilder>? metadata})
+      List<MetadataBuilder>? metadata,
+      this.isWildcard = false})
       : super(metadata, 0, name, compilationUnit, charOffset);
 
   @override
@@ -191,8 +194,6 @@ class NominalVariableBuilder extends TypeVariableBuilderBase {
 
   final TypeParameter actualParameter;
 
-  final bool isWildcard;
-
   @override
   NominalVariableBuilder? actualOrigin;
 
@@ -202,7 +203,7 @@ class NominalVariableBuilder extends TypeVariableBuilderBase {
       required TypeVariableKind kind,
       Variance? variableVariance,
       List<MetadataBuilder>? metadata,
-      this.isWildcard = false})
+      super.isWildcard = false})
       : actualParameter =
             new TypeParameter(name == noNameSentinel ? null : name, null)
               ..fileOffset = charOffset
@@ -226,7 +227,7 @@ class NominalVariableBuilder extends TypeVariableBuilderBase {
   ///
   ///   class A<X extends A<X>> {}
   NominalVariableBuilder.fromKernel(TypeParameter parameter,
-      {required Loader? loader, this.isWildcard = false})
+      {required Loader? loader, super.isWildcard = false})
       : actualParameter = parameter,
         // TODO(johnniwinther): Do we need to support synthesized type
         //  parameters from kernel?
@@ -587,8 +588,6 @@ class StructuralVariableBuilder extends TypeVariableBuilderBase {
 
   final StructuralParameter actualParameter;
 
-  final bool isWildcard;
-
   @override
   StructuralVariableBuilder? actualOrigin;
 
@@ -597,7 +596,7 @@ class StructuralVariableBuilder extends TypeVariableBuilderBase {
       {TypeBuilder? bound,
       Variance? variableVariance,
       List<MetadataBuilder>? metadata,
-      this.isWildcard = false})
+      super.isWildcard = false})
       : actualParameter =
             new StructuralParameter(name == noNameSentinel ? null : name, null)
               ..fileOffset = charOffset
@@ -609,7 +608,7 @@ class StructuralVariableBuilder extends TypeVariableBuilderBase {
             metadata: metadata);
 
   StructuralVariableBuilder.fromKernel(StructuralParameter parameter,
-      {this.isWildcard = false})
+      {super.isWildcard = false})
       : actualParameter = parameter,
         // TODO(johnniwinther): Do we need to support synthesized type
         //  parameters from kernel?

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

@@ -44,6 +44,7 @@ import 'package:kernel/type_algebra.dart';
 import 'package:kernel/type_environment.dart';
 
 import '../api_prototype/experimental_flags.dart';
+import '../api_prototype/lowering_predicates.dart';
 import '../base/constant_context.dart' show ConstantContext;
 import '../base/identifiers.dart'
     show
@@ -105,7 +106,6 @@ import 'benchmarker.dart' show Benchmarker;
 import 'body_builder_context.dart';
 import 'collections.dart';
 import 'constness.dart' show Constness;
-import 'constructor_tearoff_lowering.dart';
 import 'expression_generator.dart';
 import 'expression_generator_helper.dart';
 import 'forest.dart' show Forest;
@@ -430,6 +430,9 @@ class BodyBuilder extends StackListenerImpl
 
   JumpTarget? continueTarget;
 
+  /// Index for building unique lowered names for wildcard variables.
+  int wildcardVariableIndex = 0;
+
   BodyBuilder(
       {required this.libraryBuilder,
       required BodyBuilderContext context,
@@ -1924,17 +1927,24 @@ class BodyBuilder extends StackListenerImpl
             : new List<FormalParameterBuilder>.generate(
                 parameters.positionalParameters.length, (int i) {
                 VariableDeclaration formal = parameters.positionalParameters[i];
+                String formalName = formal.name!;
+                bool isWildcard = libraryFeatures.wildcardVariables.isEnabled &&
+                    formalName == '_';
+                if (isWildcard) {
+                  formalName =
+                      createWildcardFormalParameterName(wildcardVariableIndex);
+                  wildcardVariableIndex++;
+                }
                 return new FormalParameterBuilder(
                     FormalParameterKind.requiredPositional,
                     /* modifiers = */ 0,
                     const ImplicitTypeBuilder(),
-                    formal.name!,
+                    formalName,
                     libraryBuilder,
                     formal.fileOffset,
                     fileUri: uri,
                     hasImmediatelyDeclaredInitializer: false,
-                    isWildcard: libraryFeatures.wildcardVariables.isEnabled &&
-                        formal.name! == '_')
+                    isWildcard: isWildcard)
                   ..variable = formal;
               }, growable: false);
     enterLocalScope(new FormalParameters(formals, fileOffset, noLength, uri)
@@ -3950,7 +3960,14 @@ class BodyBuilder extends StackListenerImpl
     bool isLate = (currentLocalVariableModifiers & lateMask) != 0;
     bool isRequired = (currentLocalVariableModifiers & requiredMask) != 0;
     assert(isConst == (constantContext == ConstantContext.inferred));
-    VariableDeclaration variable = new VariableDeclarationImpl(identifier.name,
+    String name = identifier.name;
+    bool isWildcard =
+        libraryFeatures.wildcardVariables.isEnabled && name == '_';
+    if (isWildcard) {
+      name = createWildcardVariableName(wildcardVariableIndex);
+      wildcardVariableIndex++;
+    }
+    VariableDeclaration variable = new VariableDeclarationImpl(name,
         forSyntheticToken: identifier.token.isSynthetic,
         initializer: initializer,
         type: currentLocalVariableType,
@@ -3960,8 +3977,7 @@ class BodyBuilder extends StackListenerImpl
         isRequired: isRequired,
         hasDeclaredInitializer: initializer != null,
         isStaticLate: isFinal && initializer == null,
-        isWildcard: identifier.name == '_' &&
-            libraryFeatures.wildcardVariables.isEnabled)
+        isWildcard: isWildcard)
       ..fileOffset = identifier.nameOffset
       ..fileEqualsOffset = offsetForToken(equalsToken);
     typeInferrer.assignedVariables.declare(variable);
@@ -5647,6 +5663,13 @@ class BodyBuilder extends StackListenerImpl
       }
     } else {
       String parameterName = name?.name ?? '';
+      bool isWildcard =
+          libraryFeatures.wildcardVariables.isEnabled && parameterName == '_';
+      if (isWildcard) {
+        parameterName =
+            createWildcardFormalParameterName(wildcardVariableIndex);
+        wildcardVariableIndex++;
+      }
       parameter = new FormalParameterBuilder(
           kind,
           modifiers,
@@ -7427,12 +7450,18 @@ class BodyBuilder extends StackListenerImpl
     debugEvent("FunctionName");
     Identifier name = pop() as Identifier;
     Token nameToken = name.token;
-    VariableDeclaration variable = new VariableDeclarationImpl(name.name,
+    String identifierName = name.name;
+    bool isWildcard =
+        libraryFeatures.wildcardVariables.isEnabled && identifierName == '_';
+    if (isWildcard) {
+      identifierName = createWildcardVariableName(wildcardVariableIndex);
+      wildcardVariableIndex++;
+    }
+    VariableDeclaration variable = new VariableDeclarationImpl(identifierName,
         forSyntheticToken: nameToken.isSynthetic,
         isFinal: true,
         isLocalFunction: true,
-        isWildcard:
-            libraryFeatures.wildcardVariables.isEnabled && name.name == '_')
+        isWildcard: isWildcard)
       ..fileOffset = name.nameOffset;
     // TODO(ahe): Why are we looking up in local scope, but declaring in parent
     // scope?
@@ -9013,16 +9042,19 @@ class BodyBuilder extends StackListenerImpl
       unhandled("${name.runtimeType}", "beginTypeVariable.name",
           token.charOffset, uri);
     }
+    bool isWildcard =
+        libraryFeatures.wildcardVariables.isEnabled && typeVariableName == '_';
+    if (isWildcard) {
+      typeVariableName = createWildcardTypeVariableName(wildcardVariableIndex);
+      wildcardVariableIndex++;
+    }
     TypeVariableBuilderBase variable = inFunctionType
         ? new StructuralVariableBuilder(
             typeVariableName, libraryBuilder, typeVariableCharOffset, uri,
-            isWildcard: libraryFeatures.wildcardVariables.isEnabled &&
-                typeVariableName == '_')
+            isWildcard: isWildcard)
         : new NominalVariableBuilder(
             typeVariableName, libraryBuilder, typeVariableCharOffset, uri,
-            kind: TypeVariableKind.function,
-            isWildcard: libraryFeatures.wildcardVariables.isEnabled &&
-                typeVariableName == '_');
+            kind: TypeVariableKind.function, isWildcard: isWildcard);
     if (annotations != null) {
       switch (variable) {
         case StructuralVariableBuilder():
@@ -9244,6 +9276,9 @@ class BodyBuilder extends StackListenerImpl
   List<Initializer> buildFieldInitializer(String name, int fieldNameOffset,
       int assignmentOffset, Expression expression,
       {FormalParameterBuilder? formal}) {
+    if (isWildcardLoweredFormalParameter(name)) {
+      name = '_';
+    }
     Builder? builder = _context.lookupLocalMember(name);
     if (builder?.next != null) {
       // Duplicated name, already reported.

pkg/front_end/lib/src/kernel/wildcard_lowering.dart

@@ -0,0 +1,40 @@
+// 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.
+
+const String wildcardPrefix = '_#wc';
+const String wildcardFormalSuffix = '#formal';
+const String wildcardTypeVariableSuffix = '#type';
+const String wildcardVariableSuffix = '#var';
+
+/// Returns the named used for a wildcard formal parameter using [index].
+String createWildcardFormalParameterName(int index) {
+  return '$wildcardPrefix$index$wildcardFormalSuffix';
+}
+
+/// Returns the named used for a wildcard type variable using [index].
+String createWildcardTypeVariableName(int index) {
+  return '$wildcardPrefix$index$wildcardTypeVariableSuffix';
+}
+
+/// Returns the named used for a wildcard variable using [index].
+String createWildcardVariableName(int index) {
+  return '$wildcardPrefix$index$wildcardVariableSuffix';
+}
+
+/// Whether the given [name] is a wildcard formal parameter.
+bool isWildcardLoweredFormalParameter(String name) {
+  return name.startsWith(wildcardPrefix) && name.endsWith(wildcardFormalSuffix);
+}
+
+/// Whether the given [name] is a wildcard type variable.
+bool isWildcardLoweredTypeVariable(String name) {
+  return name.startsWith(wildcardPrefix) &&
+      name.endsWith(wildcardTypeVariableSuffix);
+}
+
+/// Whether the given [name] is a wildcard variable.
+bool isWildcardLoweredVariable(String name) {
+  return name.startsWith(wildcardPrefix) &&
+      name.endsWith(wildcardVariableSuffix);
+}

pkg/front_end/lib/src/source/outline_builder.dart

@@ -1724,14 +1724,17 @@ class OutlineBuilder extends StackListenerImpl {
         if (formal.isNamed) {
           firstNamedParameterOffset = formal.charOffset;
         }
+        // Primary constructors should not have a lowered wildcard name.
+        String formalName =
+            isWildcardLoweredFormalParameter(formal.name) ? '_' : formal.name;
         _builderFactory.addPrimaryConstructorField(
             // TODO(johnniwinther): Support annotations on annotations on fields
             // defined through a primary constructor. This is not needed for
             // extension types where the field is not part of the AST but will
             // be needed when primary constructors are generally supported.
             metadata: null,
             type: formal.type,
-            name: formal.name,
+            name: formalName,
             charOffset: formal.charOffset);
         formals[i] = formal.forPrimaryConstructor(_builderFactory);
       }