[cfe] Add initial version of support for nonfunction-type-aliases

Change-Id: I9ff3f0c18a31bd1e0d16ba8b6ccd0cc261250c11
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/127005
Commit-Queue: Erik Ernst <[email protected]>
Reviewed-by: Johnni Winther <[email protected]>

Author: eernstg

pkg/_fe_analyzer_shared/lib/src/messages/codes_generated.dart

@@ -2934,6 +2934,27 @@ Message _withArgumentsExtendingRestricted(String name) {
       arguments: {'name': name});
 }
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeExtendsFutureOr = messageExtendsFutureOr;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageExtendsFutureOr = const MessageCode("ExtendsFutureOr",
+    message: r"""The type 'FutureOr' can't be used in an 'extends' clause.""");
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeExtendsNever = messageExtendsNever;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageExtendsNever = const MessageCode("ExtendsNever",
+    message: r"""The type 'Never' can't be used in an 'extends' clause.""");
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeExtendsVoid = messageExtendsVoid;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageExtendsVoid = const MessageCode("ExtendsVoid",
+    message: r"""The type 'void' can't be used in an 'extends' clause.""");
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Code<Null> codeExtensionDeclaresAbstractMember =
     messageExtensionDeclaresAbstractMember;
@@ -3904,7 +3925,15 @@ const Code<Null> codeImplementsFutureOr = messageImplementsFutureOr;
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const MessageCode messageImplementsFutureOr = const MessageCode(
     "ImplementsFutureOr",
-    message: r"""'FutureOr' can't be used in an 'implements' clause.""");
+    message:
+        r"""The type 'FutureOr' can't be used in an 'implements' clause.""");
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeImplementsNever = messageImplementsNever;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageImplementsNever = const MessageCode("ImplementsNever",
+    message: r"""The type 'Never' can't be used in an 'implements' clause.""");
 
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Template<Message Function(String name, int count)>
@@ -3959,6 +3988,13 @@ Message _withArgumentsImplementsSuperClass(String name) {
       arguments: {'name': name});
 }
 
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const Code<Null> codeImplementsVoid = messageImplementsVoid;
+
+// DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
+const MessageCode messageImplementsVoid = const MessageCode("ImplementsVoid",
+    message: r"""The type 'void' can't be used in an 'implements' clause.""");
+
 // DO NOT EDIT. THIS FILE IS GENERATED. SEE TOP OF FILE.
 const Template<
     Message Function(

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

@@ -63,8 +63,13 @@ import '../fasta_codes.dart'
     show
         LocatedMessage,
         Message,
+        messageExtendsFutureOr,
+        messageExtendsNever,
+        messageExtendsVoid,
         messageGenericFunctionTypeUsedAsActualTypeArgument,
         messageImplementsFutureOr,
+        messageImplementsNever,
+        messageImplementsVoid,
         messagePatchClassOrigin,
         messagePatchClassTypeVariablesMismatch,
         messagePatchDeclarationMismatch,
@@ -122,10 +127,14 @@ import 'library_builder.dart';
 import 'member_builder.dart';
 import 'metadata_builder.dart';
 import 'named_type_builder.dart';
+import 'never_type_builder.dart';
 import 'nullability_builder.dart';
 import 'procedure_builder.dart';
+import 'type_alias_builder.dart';
 import 'type_builder.dart';
+import 'type_declaration_builder.dart';
 import 'type_variable_builder.dart';
+import 'void_type_builder.dart';
 
 abstract class ClassBuilder implements DeclarationBuilder {
   /// The type variables declared on a class, extension or mixin declaration.
@@ -635,17 +644,43 @@ abstract class ClassBuilderImpl extends DeclarationBuilderImpl
     // This method determines whether the class (that's being built) its super
     // class appears both in 'extends' and 'implements' clauses and whether any
     // interface appears multiple times in the 'implements' clause.
-    if (interfaces == null) return;
+    // Moreover, it checks that `FutureOr` and `void` are not among the
+    // supertypes.
+
+    void fail(NamedTypeBuilder target, Message message) {
+      int nameOffset = target.nameOffset;
+      int nameLength = target.nameLength;
+      // TODO(eernst): nameOffset not fully implemented; use backup.
+      if (nameOffset == -1) {
+        nameOffset = this.charOffset;
+        nameLength = noLength;
+      }
+      addProblem(message, nameOffset, nameLength);
+    }
 
-    // Extract super class (if it exists).
+    // Extract and check superclass (if it exists).
     ClassBuilder superClass;
     TypeBuilder superClassType = supertype;
     if (superClassType is NamedTypeBuilder) {
-      Builder decl = superClassType.declaration;
-      if (decl is ClassBuilder) {
+      TypeDeclarationBuilder decl = superClassType.declaration;
+      if (decl is TypeAliasBuilder) {
+        TypeAliasBuilder aliasBuilder = decl;
+        decl = aliasBuilder.unaliasDeclaration;
+      }
+      // TODO(eernst): Should gather 'restricted supertype' checks in one place,
+      // e.g., dynamic/int/String/Null and more are checked elsewhere.
+      if (decl is VoidTypeBuilder) {
+        fail(superClassType, messageExtendsVoid);
+      } else if (decl is NeverTypeBuilder) {
+        fail(superClassType, messageExtendsNever);
+      } else if (decl is ClassBuilder) {
+        if (decl.cls == coreTypes.futureOrClass) {
+          fail(superClassType, messageExtendsFutureOr);
+        }
         superClass = decl;
       }
     }
+    if (interfaces == null) return;
 
     // Validate interfaces.
     Map<ClassBuilder, int> problems;
@@ -654,29 +689,38 @@ abstract class ClassBuilderImpl extends DeclarationBuilderImpl
     for (TypeBuilder type in interfaces) {
       if (type is NamedTypeBuilder) {
         int charOffset = -1; // TODO(ahe): Get offset from type.
-        Builder decl = type.declaration;
+        TypeDeclarationBuilder typeDeclaration = type.declaration;
+        TypeDeclarationBuilder decl = typeDeclaration is TypeAliasBuilder
+            ? typeDeclaration.unaliasDeclaration
+            : typeDeclaration;
         if (decl is ClassBuilder) {
           ClassBuilder interface = decl;
           if (superClass == interface) {
             addProblem(
                 templateImplementsSuperClass.withArguments(interface.name),
-                charOffset,
+                this.charOffset,
                 noLength);
           } else if (implemented.contains(interface)) {
             // Aggregate repetitions.
             problems ??= new Map<ClassBuilder, int>();
             problems[interface] ??= 0;
             problems[interface] += 1;
-
             problemsOffsets ??= new Map<ClassBuilder, int>();
             problemsOffsets[interface] ??= charOffset;
           } else if (interface.cls == coreTypes.futureOrClass) {
-            addProblem(messageImplementsFutureOr, charOffset,
-                interface.cls.name.length);
+            fail(type, messageImplementsFutureOr);
           } else {
             implemented.add(interface);
           }
         }
+        if (decl != superClass) {
+          // TODO(eernst): Have all 'restricted supertype' checks in one place.
+          if (decl is VoidTypeBuilder) {
+            fail(type, messageImplementsVoid);
+          } else if (decl is NeverTypeBuilder) {
+            fail(type, messageImplementsNever);
+          }
+        }
       }
     }
     if (problems != null) {
@@ -1862,6 +1906,11 @@ abstract class ClassBuilderImpl extends DeclarationBuilderImpl
         if (supertype is NamedTypeBuilder) {
           Object builder = supertype.declaration;
           if (builder is ClassBuilder) return builder;
+          if (builder is TypeAliasBuilder) {
+            TypeDeclarationBuilder declarationBuilder =
+                builder.unaliasDeclaration;
+            if (declarationBuilder is ClassBuilder) return declarationBuilder;
+          }
         }
         return null;
       }

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

@@ -14,6 +14,7 @@ import 'builder.dart';
 import 'class_builder.dart';
 import 'library_builder.dart';
 import 'prefix_builder.dart';
+import 'type_alias_builder.dart';
 import 'type_builder.dart';
 
 class ConstructorReferenceBuilder {
@@ -46,6 +47,10 @@ class ConstructorReferenceBuilder {
       String prefix = name.qualifier;
       String middle = name.name;
       declaration = scope.lookup(prefix, charOffset, fileUri);
+      if (declaration is TypeAliasBuilder) {
+        TypeAliasBuilder aliasBuilder = declaration;
+        declaration = aliasBuilder.unaliasDeclaration;
+      }
       if (declaration is PrefixBuilder) {
         PrefixBuilder prefix = declaration;
         declaration = prefix.lookup(middle, name.charOffset, fileUri);

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

@@ -35,6 +35,7 @@ import 'modifier_builder.dart';
 import 'name_iterator.dart';
 import 'nullability_builder.dart';
 import 'prefix_builder.dart';
+import 'type_alias_builder.dart';
 import 'type_builder.dart';
 
 abstract class LibraryBuilder implements ModifierBuilder {
@@ -332,6 +333,10 @@ abstract class LibraryBuilderImpl extends ModifierBuilderImpl
     }
     Builder cls = (bypassLibraryPrivacy ? scope : exportScope)
         .lookup(className, -1, null);
+    if (cls is TypeAliasBuilder) {
+      TypeAliasBuilder aliasBuilder = cls;
+      cls = aliasBuilder.unaliasDeclaration;
+    }
     if (cls is ClassBuilder) {
       // TODO(ahe): This code is similar to code in `endNewExpression` in
       // `body_builder.dart`, try to share it.

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

@@ -37,6 +37,7 @@ import 'invalid_type_declaration_builder.dart';
 import 'library_builder.dart';
 import 'nullability_builder.dart';
 import 'prefix_builder.dart';
+import 'type_alias_builder.dart';
 import 'type_builder.dart';
 import 'type_declaration_builder.dart';
 import 'type_variable_builder.dart';
@@ -63,6 +64,26 @@ class NamedTypeBuilder extends TypeBuilder {
     this.declaration = declaration?.origin;
   }
 
+  int get nameOffset {
+    if (name is Identifier) {
+      Identifier identifier = name;
+      return identifier.charOffset;
+    }
+    return -1; // TODO(eernst): make it possible to get offset.
+  }
+
+  int get nameLength {
+    if (name is Identifier) {
+      Identifier identifier = name;
+      return identifier.name.length;
+    } else if (name is String) {
+      String nameString = name;
+      return nameString.length;
+    } else {
+      return noLength;
+    }
+  }
+
   @override
   void resolveIn(
       Scope scope, int charOffset, Uri fileUri, LibraryBuilder library) {
@@ -215,6 +236,12 @@ class NamedTypeBuilder extends TypeBuilder {
     TypeDeclarationBuilder declaration = this.declaration;
     if (declaration is ClassBuilder) {
       return declaration.buildSupertype(library, arguments);
+    } else if (declaration is TypeAliasBuilder) {
+      TypeDeclarationBuilder declarationBuilder =
+          declaration.unaliasDeclaration;
+      if (declarationBuilder is ClassBuilder) {
+        return declarationBuilder.buildSupertype(library, arguments);
+      }
     } else if (declaration is InvalidTypeDeclarationBuilder) {
       library.addProblem(
           declaration.message.messageObject,
@@ -223,14 +250,17 @@ class NamedTypeBuilder extends TypeBuilder {
           declaration.message.uri,
           severity: Severity.error);
       return null;
-    } else {
-      return handleInvalidSupertype(library, charOffset, fileUri);
     }
+    return handleInvalidSupertype(library, charOffset, fileUri);
   }
 
   Supertype buildMixedInType(
       LibraryBuilder library, int charOffset, Uri fileUri) {
     TypeDeclarationBuilder declaration = this.declaration;
+    if (declaration is TypeAliasBuilder) {
+      TypeAliasBuilder aliasBuilder = declaration;
+      declaration = aliasBuilder.unaliasDeclaration;
+    }
     if (declaration is ClassBuilder) {
       return declaration.buildMixedInType(library, arguments);
     } else if (declaration is InvalidTypeDeclarationBuilder) {

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

@@ -28,6 +28,7 @@ import '../problems.dart' show unhandled;
 
 import '../source/source_library_builder.dart' show SourceLibraryBuilder;
 
+import 'class_builder.dart';
 import 'formal_parameter_builder.dart';
 import 'function_type_builder.dart';
 import 'library_builder.dart';
@@ -218,20 +219,50 @@ class TypeAliasBuilder extends TypeDeclarationBuilderImpl {
   @override
   int get typeVariablesCount => typeVariables?.length ?? 0;
 
+  /// Returns `true` if this typedef is an alias of the `Null` type.
+  bool get isNullAlias {
+    TypeDeclarationBuilder typeDeclarationBuilder = type.declaration;
+    return typeDeclarationBuilder is ClassBuilder &&
+        typeDeclarationBuilder.isNullClass;
+  }
+
   @override
   DartType buildType(LibraryBuilder library,
       NullabilityBuilder nullabilityBuilder, List<TypeBuilder> arguments) {
     DartType thisType = buildThisType(library);
     if (thisType is InvalidType) return thisType;
     if (typedef.typeParameters.isEmpty && arguments == null) {
-      return thisType.withNullability(nullabilityBuilder.build(library));
+      Nullability nullability = isNullAlias
+          ? Nullability.nullable
+          : nullabilityBuilder.build(library);
+      return thisType.withNullability(nullability);
     }
     // Otherwise, substitute.
     return buildTypesWithBuiltArguments(
         library,
         nullabilityBuilder.build(library),
         buildTypeArguments(library, arguments));
   }
+
+  /// Returns the [TypeDeclarationBuilder] for the aliased type.
+  ///
+  /// That is, it recursively looks up `type.declaration` and returns the first
+  /// one which is not a `TypeAliasBuilder`, or the last one if none exist.
+  TypeDeclarationBuilder get unaliasDeclaration {
+    Set<TypeDeclarationBuilder> builders = {this};
+    TypeDeclarationBuilder current = this;
+    while (current is TypeAliasBuilder) {
+      TypeAliasBuilder currentAliasBuilder = current;
+      TypeDeclarationBuilder next = currentAliasBuilder.type?.declaration;
+      if (next != null) {
+        current = next;
+      } else {
+        return this;
+      }
+      if (builders.contains(current)) return this;
+    }
+    return current;
+  }
 }
 
 final InvalidType cyclicTypeAliasMarker = new InvalidType();

pkg/front_end/lib/src/fasta/dill/dill_type_alias_builder.dart

@@ -4,7 +4,7 @@
 
 library fasta.dill_typedef_builder;
 
-import 'package:kernel/ast.dart' show DartType, Typedef;
+import 'package:kernel/ast.dart' show DartType, Typedef, InterfaceType;
 
 import '../builder/function_type_builder.dart';
 import '../builder/library_builder.dart';
@@ -62,4 +62,16 @@ class DillTypeAliasBuilder extends TypeAliasBuilder {
     }
     return result;
   }
+
+  @override
+  bool get isNullAlias {
+    DartType dartType = typedef.type;
+    if (dartType is InterfaceType) {
+      Uri importUri = dartType.classNode.enclosingLibrary.importUri;
+      return dartType.classNode.name == "Null" &&
+          importUri.scheme == "dart" &&
+          importUri.path == "core";
+    }
+    return false;
+  }
 }