[cfe] Add TypeParameterFactory

This adds a TypeParameterFactory to encapsulate the creation of type
parameters and ensure the computation of their bounds.

Change-Id: Ib9558ae3bafc7b30e67bac1fc3a098f93fbf29d0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/438080
Reviewed-by: Chloe Stefantsova <[email protected]>
Commit-Queue: Johnni Winther <[email protected]>

Author: johnniwinther

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

@@ -3,6 +3,7 @@
 // BSD-style license that can be found in the LICENSE file.
 
 import 'package:_fe_analyzer_shared/src/messages/severity.dart' show Severity;
+import 'package:_fe_analyzer_shared/src/scanner/scanner.dart' show Token;
 import 'package:kernel/ast.dart' show Annotatable, Library, Version;
 import 'package:kernel/reference_from_index.dart';
 
@@ -18,7 +19,6 @@ import '../fragment/fragment.dart';
 import '../kernel/body_builder_context.dart';
 import '../source/name_space_builder.dart';
 import '../source/offset_map.dart';
-import '../source/outline_builder.dart';
 import '../source/source_class_builder.dart';
 import '../source/source_library_builder.dart';
 import '../source/source_loader.dart';
@@ -87,7 +87,7 @@ abstract class DillCompilationUnit implements CompilationUnit {}
 
 abstract class SourceCompilationUnit
     implements CompilationUnit, LibraryFragment {
-  OutlineBuilder createOutlineBuilder();
+  void buildOutline(Token tokens);
 
   /// Creates a [SourceLibraryBuilder] for with this [SourceCompilationUnit] as
   /// the main compilation unit.
@@ -288,11 +288,7 @@ abstract class SourceCompilationUnit
   ///
   /// This is used to compute the bounds of type parameters while taking the
   /// bound dependencies, which might span multiple libraries, into account.
-  void collectUnboundTypeParameters(
-      SourceLibraryBuilder libraryBuilder,
-      Map<NominalParameterBuilder, SourceLibraryBuilder> nominalParameters,
-      Map<StructuralParameterBuilder, SourceLibraryBuilder>
-          structuralParameters);
+  List<TypeParameterBuilder> collectUnboundTypeParameters();
 
   /// Adds [prefixFragment] to library name space.
   ///

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

@@ -15,6 +15,7 @@ import '../base/scope.dart';
 import '../base/uris.dart';
 import '../codes/cfe_codes.dart';
 import '../source/source_library_builder.dart';
+import '../source/type_parameter_factory.dart';
 import '../type_inference/type_schema.dart' show UnknownType;
 import '../util/helpers.dart';
 import 'builder.dart';

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

@@ -9,6 +9,7 @@ import 'package:kernel/src/bounds_checks.dart' show VarianceCalculationValue;
 import '../base/problems.dart';
 import '../kernel/type_algorithms.dart';
 import '../source/source_loader.dart';
+import '../source/type_parameter_factory.dart';
 import 'declaration_builders.dart';
 import 'library_builder.dart';
 import 'nullability_builder.dart';
@@ -113,7 +114,7 @@ class FixedTypeBuilderImpl extends FixedTypeBuilder {
   TypeBuilder? substituteRange(
       Map<TypeParameterBuilder, TypeBuilder> upperSubstitution,
       Map<TypeParameterBuilder, TypeBuilder> lowerSubstitution,
-      List<StructuralParameterBuilder> unboundTypeParameters,
+      TypeParameterFactory typeParameterFactory,
       {Variance variance = Variance.covariant}) {
     return null;
   }

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

@@ -21,6 +21,7 @@ import '../kernel/type_algorithms.dart';
 import '../source/source_library_builder.dart';
 import '../source/source_loader.dart';
 import '../source/source_type_parameter_builder.dart';
+import '../source/type_parameter_factory.dart';
 import 'declaration_builders.dart';
 import 'formal_parameter_builder.dart';
 import 'inferable_type_builder.dart';
@@ -292,7 +293,7 @@ abstract class FunctionTypeBuilderImpl extends FunctionTypeBuilder {
   TypeBuilder? substituteRange(
       Map<TypeParameterBuilder, TypeBuilder> upperSubstitution,
       Map<TypeParameterBuilder, TypeBuilder> lowerSubstitution,
-      List<StructuralParameterBuilder> unboundTypeParameters,
+      TypeParameterFactory typeParameterFactory,
       {final Variance variance = Variance.covariant}) {
     List<StructuralParameterBuilder>? typeParameters = this.typeParameters;
     List<ParameterBuilder>? formals = this.formals;
@@ -310,16 +311,16 @@ abstract class FunctionTypeBuilderImpl extends FunctionTypeBuilder {
         TypeBuilder? bound;
         if (variable.bound != null) {
           bound = variable.bound!.substituteRange(
-              upperSubstitution, lowerSubstitution, unboundTypeParameters,
+              upperSubstitution, lowerSubstitution, typeParameterFactory,
               variance: Variance.invariant);
         }
         if (bound != null) {
           newTypeParameters ??= typeParameters.toList();
           StructuralParameterBuilder newTypeParameterBuilder =
-              newTypeParameters[i] = new SourceStructuralParameterBuilder(
-                  new SyntheticStructuralParameterDeclaration(variable))
+              newTypeParameters[i] = typeParameterFactory
+                  .createStructuralParameterBuilder(
+                      new SyntheticStructuralParameterDeclaration(variable))
                 ..bound = bound;
-          unboundTypeParameters.add(newTypeParameterBuilder);
           if (functionTypeUpperSubstitution == null) {
             functionTypeUpperSubstitution = {...upperSubstitution};
             functionTypeLowerSubstitution = {...lowerSubstitution};
@@ -340,7 +341,7 @@ abstract class FunctionTypeBuilderImpl extends FunctionTypeBuilder {
         TypeBuilder? parameterType = formal.type.substituteRange(
             functionTypeUpperSubstitution ?? upperSubstitution,
             functionTypeLowerSubstitution ?? lowerSubstitution,
-            unboundTypeParameters,
+            typeParameterFactory,
             variance: variance.combine(Variance.contravariant));
         if (parameterType != null) {
           newFormals ??= new List.of(formals);
@@ -352,7 +353,7 @@ abstract class FunctionTypeBuilderImpl extends FunctionTypeBuilder {
     newReturnType = returnType.substituteRange(
         functionTypeUpperSubstitution ?? upperSubstitution,
         functionTypeLowerSubstitution ?? lowerSubstitution,
-        unboundTypeParameters,
+        typeParameterFactory,
         variance: variance);
 
     if (newTypeParameters != null ||

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

@@ -6,6 +6,7 @@ import 'package:kernel/ast.dart';
 import 'package:kernel/class_hierarchy.dart';
 
 import '../kernel/type_algorithms.dart';
+import '../source/type_parameter_factory.dart';
 import 'declaration_builders.dart';
 import 'library_builder.dart';
 import 'nullability_builder.dart';
@@ -95,7 +96,7 @@ class InvalidTypeBuilderImpl extends InvalidTypeBuilder {
   TypeBuilder? substituteRange(
       Map<TypeParameterBuilder, TypeBuilder> upperSubstitution,
       Map<TypeParameterBuilder, TypeBuilder> lowerSubstitution,
-      List<StructuralParameterBuilder> unboundTypeParameters,
+      TypeParameterFactory typeParameterFactory,
       {Variance variance = Variance.covariant}) {
     return null;
   }

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

@@ -42,6 +42,7 @@ import '../kernel/implicit_field_type.dart';
 import '../kernel/type_algorithms.dart';
 import '../source/source_library_builder.dart';
 import '../source/source_loader.dart';
+import '../source/type_parameter_factory.dart';
 import '../util/helpers.dart';
 import 'builder.dart';
 import 'declaration_builders.dart';
@@ -494,12 +495,10 @@ abstract class NamedTypeBuilderImpl extends NamedTypeBuilder {
   @override
   TypeBuilder? unalias(
       {Set<TypeAliasBuilder>? usedTypeAliasBuilders,
-      List<TypeBuilder>? unboundTypes,
-      List<StructuralParameterBuilder>? unboundTypeParameters}) {
+      List<TypeBuilder>? unboundTypes}) {
     if (declaration is TypeAliasBuilder) {
-      return (declaration as TypeAliasBuilder).unalias(typeArguments,
-          usedTypeAliasBuilders: usedTypeAliasBuilders,
-          unboundTypeParameters: unboundTypeParameters);
+      return (declaration as TypeAliasBuilder)
+          .unalias(typeArguments, usedTypeAliasBuilders: usedTypeAliasBuilders);
     }
     return this;
   }
@@ -837,7 +836,7 @@ abstract class NamedTypeBuilderImpl extends NamedTypeBuilder {
   TypeBuilder? substituteRange(
       Map<TypeParameterBuilder, TypeBuilder> upperSubstitution,
       Map<TypeParameterBuilder, TypeBuilder> lowerSubstitution,
-      List<StructuralParameterBuilder> unboundTypeParameters,
+      TypeParameterFactory typeParameterFactory,
       {final Variance variance = Variance.covariant}) {
     TypeDeclarationBuilder declaration = this.declaration;
     List<TypeBuilder>? arguments = this.typeArguments;
@@ -870,7 +869,7 @@ abstract class NamedTypeBuilderImpl extends NamedTypeBuilder {
       case ClassBuilder():
         for (int i = 0; i < arguments.length; ++i) {
           TypeBuilder? substitutedArgument = arguments[i].substituteRange(
-              upperSubstitution, lowerSubstitution, unboundTypeParameters,
+              upperSubstitution, lowerSubstitution, typeParameterFactory,
               variance: variance);
           if (substitutedArgument != null) {
             newArguments ??= arguments.toList();
@@ -880,7 +879,7 @@ abstract class NamedTypeBuilderImpl extends NamedTypeBuilder {
       case ExtensionTypeDeclarationBuilder():
         for (int i = 0; i < arguments.length; ++i) {
           TypeBuilder? substitutedArgument = arguments[i].substituteRange(
-              upperSubstitution, lowerSubstitution, unboundTypeParameters,
+              upperSubstitution, lowerSubstitution, typeParameterFactory,
               variance: variance);
           if (substitutedArgument != null) {
             newArguments ??= arguments.toList();
@@ -891,7 +890,7 @@ abstract class NamedTypeBuilderImpl extends NamedTypeBuilder {
         for (int i = 0; i < arguments.length; ++i) {
           NominalParameterBuilder variable = declaration.typeParameters![i];
           TypeBuilder? substitutedArgument = arguments[i].substituteRange(
-              upperSubstitution, lowerSubstitution, unboundTypeParameters,
+              upperSubstitution, lowerSubstitution, typeParameterFactory,
               variance: variance.combine(variable.variance));
           if (substitutedArgument != null) {
             newArguments ??= arguments.toList();
@@ -926,15 +925,14 @@ abstract class NamedTypeBuilderImpl extends NamedTypeBuilder {
   TypeBuilder? unaliasAndErase() {
     TypeDeclarationBuilder declaration = this.declaration;
     if (declaration is TypeAliasBuilder) {
-      // We pass empty lists as [unboundTypes] and [unboundTypeParameters]
+      // We pass a fresh [TypeParameterFactory] to [TypeBuilder.unalias]
       // because new builders can be generated during unaliasing. We ignore
-      // the returned builders, however, because they will not be used in the
-      // output and are needed only for the checks.
+      // the created parameter builders, however, because they will not be used
+      // in the output and are needed only for the checks.
       //
       // We also don't instantiate-to-bound raw types because it won't affect
       // the dependency cycle analysis.
-      return declaration
-          .unalias(typeArguments, unboundTypeParameters: [])?.unaliasAndErase();
+      return declaration.unalias(typeArguments)?.unaliasAndErase();
     } else if (declaration is ExtensionTypeDeclarationBuilder) {
       TypeBuilder? representationType =
           declaration.declaredRepresentationTypeBuilder;

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

@@ -11,6 +11,7 @@ import '../kernel/implicit_field_type.dart';
 import '../kernel/type_algorithms.dart';
 import '../source/source_library_builder.dart';
 import '../source/source_loader.dart';
+import '../source/type_parameter_factory.dart';
 import 'declaration_builders.dart';
 import 'inferable_type_builder.dart';
 import 'library_builder.dart';
@@ -84,7 +85,7 @@ abstract class OmittedTypeBuilderImpl extends OmittedTypeBuilder {
   TypeBuilder? substituteRange(
       Map<TypeParameterBuilder, TypeBuilder> upperSubstitution,
       Map<TypeParameterBuilder, TypeBuilder> lowerSubstitution,
-      List<StructuralParameterBuilder> unboundTypeParameters,
+      TypeParameterFactory typeParameterFactory,
       {Variance variance = Variance.covariant}) {
     return null;
   }

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

@@ -28,6 +28,7 @@ import '../kernel/implicit_field_type.dart';
 import '../kernel/type_algorithms.dart';
 import '../source/source_library_builder.dart';
 import '../source/source_loader.dart';
+import '../source/type_parameter_factory.dart';
 import '../util/helpers.dart';
 import 'declaration_builders.dart';
 import 'inferable_type_builder.dart';
@@ -360,7 +361,7 @@ abstract class RecordTypeBuilderImpl extends RecordTypeBuilder {
   TypeBuilder? substituteRange(
       Map<TypeParameterBuilder, TypeBuilder> upperSubstitution,
       Map<TypeParameterBuilder, TypeBuilder> lowerSubstitution,
-      List<StructuralParameterBuilder> unboundTypeParameters,
+      TypeParameterFactory typeParameterFactory,
       {final Variance variance = Variance.covariant}) {
     List<RecordTypeFieldBuilder>? positionalFields = this.positionalFields;
     List<RecordTypeFieldBuilder>? namedFields = this.namedFields;
@@ -372,7 +373,7 @@ abstract class RecordTypeBuilderImpl extends RecordTypeBuilder {
         RecordTypeFieldBuilder positionalFieldBuilder = positionalFields[i];
         TypeBuilder? positionalFieldType = positionalFieldBuilder.type
             .substituteRange(
-                upperSubstitution, lowerSubstitution, unboundTypeParameters,
+                upperSubstitution, lowerSubstitution, typeParameterFactory,
                 variance: variance);
         if (positionalFieldType != null) {
           newPositionalFields ??= positionalFields.toList();
@@ -388,7 +389,7 @@ abstract class RecordTypeBuilderImpl extends RecordTypeBuilder {
       for (int i = 0; i < namedFields.length; i++) {
         RecordTypeFieldBuilder namedFieldBuilder = namedFields[i];
         TypeBuilder? namedFieldType = namedFieldBuilder.type.substituteRange(
-            upperSubstitution, lowerSubstitution, unboundTypeParameters,
+            upperSubstitution, lowerSubstitution, typeParameterFactory,
             variance: variance);
         if (namedFieldType != null) {
           newNamedFields ??= namedFields.toList();

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

@@ -12,6 +12,7 @@ import 'package:kernel/type_algebra.dart' show Substitution;
 
 import '../kernel/type_algorithms.dart';
 import '../source/source_loader.dart';
+import '../source/type_parameter_factory.dart';
 import 'declaration_builders.dart';
 import 'library_builder.dart';
 import 'nullability_builder.dart';
@@ -196,7 +197,7 @@ class SynthesizedTypeBuilder extends FixedTypeBuilder {
   TypeBuilder? substituteRange(
       Map<TypeParameterBuilder, TypeBuilder> upperSubstitution,
       Map<TypeParameterBuilder, TypeBuilder> lowerSubstitution,
-      List<StructuralParameterBuilder> unboundTypeParameters,
+      TypeParameterFactory typeParameterFactory,
       {Variance variance = Variance.covariant}) {
     Map<TypeParameterBuilder, TypeBuilder> oldUpperSubstitution = {};
     for (MapEntry<TypeParameterBuilder, TypeBuilder> entry
@@ -216,7 +217,7 @@ class SynthesizedTypeBuilder extends FixedTypeBuilder {
       }
     }
     return _applySubstitution(_typeBuilder.substituteRange(
-        oldUpperSubstitution, oldLowerSubstitution, unboundTypeParameters));
+        oldUpperSubstitution, oldLowerSubstitution, typeParameterFactory));
   }
 
   @override

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

@@ -58,8 +58,7 @@ abstract class TypeAliasBuilder implements TypeDeclarationBuilder {
   // TODO(johnniwinther): Used this instead of [unaliasDeclaration] and
   // [unaliasTypeArguments].
   TypeBuilder? unalias(List<TypeBuilder>? typeArguments,
-      {Set<TypeAliasBuilder>? usedTypeAliasBuilders,
-      List<StructuralParameterBuilder>? unboundTypeParameters});
+      {Set<TypeAliasBuilder>? usedTypeAliasBuilders});
 
   /// Returns the [TypeDeclarationBuilder] for the type aliased by `this`,
   /// based on the given [typeArguments]. It expands type aliases repeatedly
@@ -188,8 +187,7 @@ abstract class TypeAliasBuilderImpl extends TypeDeclarationBuilderImpl
         hasExplicitTypeArguments: hasExplicitTypeArguments);
   }
 
-  void _ensureUnaliasedType(
-      {required List<StructuralParameterBuilder>? unboundTypeParameters}) {
+  void _ensureUnaliasedType() {
     if (_unaliasedRhsType != null) {
       return;
     }
@@ -212,8 +210,7 @@ abstract class TypeAliasBuilderImpl extends TypeDeclarationBuilderImpl
         List<TypeBuilder>? typeArguments = type.typeArguments;
         TypeBuilder? unaliasedRhsType = rhsTypeDeclaration.unalias(
             typeArguments,
-            usedTypeAliasBuilders: usedTypeAliasBuilders,
-            unboundTypeParameters: unboundTypeParameters);
+            usedTypeAliasBuilders: usedTypeAliasBuilders);
         _unaliasedRhsType = unaliasedRhsType;
         if (typeParameters != null) {
           if (typeArguments == null ||
@@ -229,9 +226,7 @@ abstract class TypeAliasBuilderImpl extends TypeDeclarationBuilderImpl
               ?.subst(
                   new Map<NominalParameterBuilder, TypeBuilder>.fromIterables(
                       typeParameters, typeArguments))
-              .unalias(
-                  usedTypeAliasBuilders: usedTypeAliasBuilders,
-                  unboundTypeParameters: unboundTypeParameters);
+              .unalias(usedTypeAliasBuilders: usedTypeAliasBuilders);
         }
         _typeAliasesUsedInUnaliasing.addAll(usedTypeAliasBuilders);
       // Coverage-ignore(suite): Not run.
@@ -243,9 +238,8 @@ abstract class TypeAliasBuilderImpl extends TypeDeclarationBuilderImpl
 
   @override
   TypeBuilder? unalias(List<TypeBuilder>? typeArguments,
-      {Set<TypeAliasBuilder>? usedTypeAliasBuilders,
-      List<StructuralParameterBuilder>? unboundTypeParameters}) {
-    _ensureUnaliasedType(unboundTypeParameters: unboundTypeParameters);
+      {Set<TypeAliasBuilder>? usedTypeAliasBuilders}) {
+    _ensureUnaliasedType();
     if (usedTypeAliasBuilders != null) {
       usedTypeAliasBuilders.addAll(_typeAliasesUsedInUnaliasing);
     }
@@ -272,10 +266,12 @@ abstract class TypeAliasBuilderImpl extends TypeDeclarationBuilderImpl
                 typeParameter.defaultType!
             ];
           }
+          // We allow creating new type parameters during unaliasing. The type
+          // variables are short-lived and therefore don't need to be bound.
           return unaliasedRhsType!.subst(
               new Map<NominalParameterBuilder, TypeBuilder>.fromIterables(
                   typeParameters, typeArguments),
-              unboundTypeParameters: unboundTypeParameters);
+              typeParameterFactory: new TypeParameterFactory());
         }
       case ExtensionBuilder():
       case BuiltinTypeDeclarationBuilder():
@@ -569,9 +565,8 @@ abstract class TypeAliasBuilderImpl extends TypeDeclarationBuilderImpl
   Nullability computeNullabilityWithArguments(List<TypeBuilder>? typeArguments,
       {required Map<TypeParameterBuilder, TraversalState>
           typeParametersTraversalState}) {
-    return unalias(typeArguments, unboundTypeParameters: [])!
-        .computeNullability(
-            typeParametersTraversalState: typeParametersTraversalState);
+    return unalias(typeArguments)!.computeNullability(
+        typeParametersTraversalState: typeParametersTraversalState);
   }
 }