[cfe] Implement subtype relation for ExtensionType

Change-Id: I725c6abd4ad2ec7fe217e271fbe60d57af443f7a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/196933
Reviewed-by: Johnni Winther <johnniwinther@google.com>
Commit-Queue: Dmitry Stefantsov <dmitryas@google.com>

pkg/front_end/test/fasta/types/kernel_type_parser_test.dart

@@ -38,6 +38,9 @@ class ExtendedClass;
 class ExtendedGenericClass<X>;
 extension Extension on ExtendedClass;
 extension GenericExtension<Y> on ExtendedGenericClass<Y>;
+extension TopExtension on dynamic;
+extension GenericTopExtension<Z> on dynamic;
+class ExtendedSubclass extends ExtendedClass;
 """;
 
 const String expectedSdk = """
@@ -89,10 +92,16 @@ class ExtendedClass extends self::Object {
 }
 class ExtendedGenericClass<X extends self::Object? = dynamic> extends self::Object {
 }
+class ExtendedSubclass extends self::ExtendedClass {
+}
 extension Extension on self::ExtendedClass {
 }
 extension GenericExtension<Y extends self::Object? = dynamic> on self::ExtendedGenericClass<Y%> {
 }
+extension TopExtension on dynamic {
+}
+extension GenericTopExtension<Z extends self::Object? = dynamic> on dynamic {
+}
 """;
 
 Component parseSdk(Uri uri, TypeParserEnvironment environment) {

pkg/front_end/test/fasta/types/shared_type_tests.dart

@@ -1042,5 +1042,32 @@ abstract class SubtypeTest<T, E> {
     isSubtype("List<int?>?", "List<int?>?");
     isSubtype("T & int?", "T & int?", typeParameters: "T extends Object?");
     isSubtype("T? & int?", "T? & int?", typeParameters: "T extends Object");
+
+    // Tests for extension types.
+    isSubtype("Never", "Extension");
+    isSubtype("Never", "GenericExtension<Never>");
+    isSubtype("Extension", "dynamic");
+    isSubtype("Extension", "void");
+    isSubtype("Extension", "Object?");
+    isSubtype("Extension", "FutureOr<dynamic>");
+    isSubtype("GenericExtension<dynamic>", "dynamic");
+    isSubtype("GenericExtension<dynamic>", "void");
+    isSubtype("GenericExtension<dynamic>", "Object?");
+    isSubtype("GenericExtension<dynamic>", "FutureOr<dynamic>");
+    isSubtype("dynamic", "TopExtension");
+    isSubtype("void", "TopExtension");
+    isSubtype("Object?", "TopExtension");
+    isSubtype("FutureOr<dynamic>", "TopExtension");
+    isSubtype("num", "TopExtension");
+    isSubtype("dynamic", "GenericTopExtension<String>");
+    isSubtype("void", "GenericTopExtension<String>");
+    isSubtype("Object?", "GenericTopExtension<String>");
+    isSubtype("FutureOr<dynamic>", "GenericTopExtension<String>");
+    isSubtype("num", "GenericTopExtension<String>");
+    isNotSubtype("Extension", "ExtendedClass");
+    isNotSubtype("GenericExtension<num>", "ExtendedGenericClass<num>");
+    isSubtype("ExtendedClass", "Extension");
+    isSubtype("ExtendedGenericClass<num>", "GenericExtension<num>");
+    isSubtype("ExtendedSubclass", "Extension");
   }
 }

pkg/front_end/testcases/extension_types/issue45775.dart.strong.expect

@@ -1,12 +1,4 @@
 library /*isNonNullableByDefault*/;
-//
-// Problems in library:
-//
-// pkg/front_end/testcases/extension_types/issue45775.dart:10:13: Error: A value of type 'Foo' can't be assigned to a variable of type 'Bar'.
-//  - 'Foo' is from 'pkg/front_end/testcases/extension_types/issue45775.dart'.
-//   Bar bar = Foo();
-//             ^
-//
 import self as self;
 import "dart:core" as core;
 
@@ -18,8 +10,5 @@ class Foo extends core::Object {
 extension Bar on self::Foo {
 }
 static method main() → void {
-  self::Bar bar = let final Never #t1 = invalid-expression "pkg/front_end/testcases/extension_types/issue45775.dart:10:13: Error: A value of type 'Foo' can't be assigned to a variable of type 'Bar'.
- - 'Foo' is from 'pkg/front_end/testcases/extension_types/issue45775.dart'.
-  Bar bar = Foo();
-            ^" in new self::Foo::•() as{TypeError,ForNonNullableByDefault} self::Bar;
+  self::Bar bar = new self::Foo::•();
 }

pkg/front_end/testcases/extension_types/issue45775.dart.weak.expect

@@ -1,12 +1,4 @@
 library /*isNonNullableByDefault*/;
-//
-// Problems in library:
-//
-// pkg/front_end/testcases/extension_types/issue45775.dart:10:13: Error: A value of type 'Foo' can't be assigned to a variable of type 'Bar'.
-//  - 'Foo' is from 'pkg/front_end/testcases/extension_types/issue45775.dart'.
-//   Bar bar = Foo();
-//             ^
-//
 import self as self;
 import "dart:core" as core;
 
@@ -18,8 +10,5 @@ class Foo extends core::Object {
 extension Bar on self::Foo {
 }
 static method main() → void {
-  self::Bar bar = let final Never #t1 = invalid-expression "pkg/front_end/testcases/extension_types/issue45775.dart:10:13: Error: A value of type 'Foo' can't be assigned to a variable of type 'Bar'.
- - 'Foo' is from 'pkg/front_end/testcases/extension_types/issue45775.dart'.
-  Bar bar = Foo();
-            ^" in new self::Foo::•() as{TypeError,ForNonNullableByDefault} self::Bar;
+  self::Bar bar = new self::Foo::•();
 }

pkg/kernel/lib/src/types.dart

@@ -447,7 +447,6 @@ class IsInterfaceSubtypeOf extends TypeRelation<InterfaceType> {
   @override
   IsSubtypeOf isExtensionRelated(
       ExtensionType s, InterfaceType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
     return const IsSubtypeOf.never();
   }
 }
@@ -628,7 +627,6 @@ class IsFunctionSubtypeOf extends TypeRelation<FunctionType> {
 
   @override
   IsSubtypeOf isExtensionRelated(ExtensionType s, FunctionType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
     return const IsSubtypeOf.never();
   }
 }
@@ -715,7 +713,6 @@ class IsTypeParameterSubtypeOf extends TypeRelation<TypeParameterType> {
   @override
   IsSubtypeOf isExtensionRelated(
       ExtensionType s, TypeParameterType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
     return const IsSubtypeOf.never();
   }
 }
@@ -767,8 +764,7 @@ class IsTypedefSubtypeOf extends TypeRelation<TypedefType> {
 
   @override
   IsSubtypeOf isExtensionRelated(ExtensionType s, TypedefType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
-    return const IsSubtypeOf.never();
+    return types.performNullabilityAwareSubtypeCheck(s, t.unalias);
   }
 }
 
@@ -900,8 +896,9 @@ class IsFutureOrSubtypeOf extends TypeRelation<FutureOrType> {
 
   @override
   IsSubtypeOf isExtensionRelated(ExtensionType s, FutureOrType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
-    return const IsSubtypeOf.never();
+    // Rule 11.
+    return types.performNullabilityAwareSubtypeCheck(
+        s, t.typeArgument.withDeclaredNullability(t.nullability));
   }
 }
 
@@ -966,7 +963,6 @@ class IsIntersectionSubtypeOf extends TypeRelation<TypeParameterType> {
   @override
   IsSubtypeOf isExtensionRelated(
       ExtensionType s, TypeParameterType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
     return const IsSubtypeOf.never();
   }
 }
@@ -1022,7 +1018,6 @@ class IsNullTypeSubtypeOf implements TypeRelation<NullType> {
 
   @override
   IsSubtypeOf isExtensionRelated(ExtensionType s, NullType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
     return const IsSubtypeOf.never();
   }
 }
@@ -1077,7 +1072,6 @@ class IsNeverTypeSubtypeOf implements TypeRelation<NeverType> {
 
   @override
   IsSubtypeOf isExtensionRelated(ExtensionType s, NeverType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
     return const IsSubtypeOf.never();
   }
 }
@@ -1087,62 +1081,54 @@ class IsExtensionTypeSubtypeOf implements TypeRelation<ExtensionType> {
 
   @override
   IsSubtypeOf isDynamicRelated(DynamicType s, ExtensionType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
-    return const IsSubtypeOf.never();
+    return types.performNullabilityAwareSubtypeCheck(s, t.onType);
   }
 
   @override
   IsSubtypeOf isVoidRelated(VoidType s, ExtensionType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
-    return const IsSubtypeOf.never();
+    return types.performNullabilityAwareSubtypeCheck(s, t.onType);
   }
 
   @override
   IsSubtypeOf isInterfaceRelated(
       InterfaceType s, ExtensionType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
-    return const IsSubtypeOf.never();
+    return types.performNullabilityAwareSubtypeCheck(s, t.onType);
   }
 
   @override
   IsSubtypeOf isIntersectionRelated(
       TypeParameterType intersection, ExtensionType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
-    return const IsSubtypeOf.never();
+    return types.performNullabilityAwareSubtypeCheck(intersection, t.onType);
   }
 
   @override
   IsSubtypeOf isFunctionRelated(FunctionType s, ExtensionType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
-    return const IsSubtypeOf.never();
+    return types.performNullabilityAwareSubtypeCheck(s, t.onType);
   }
 
   @override
   IsSubtypeOf isFutureOrRelated(FutureOrType s, ExtensionType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
-    return const IsSubtypeOf.never();
+    return types.performNullabilityAwareSubtypeCheck(s, t.onType);
   }
 
   @override
   IsSubtypeOf isTypeParameterRelated(
       TypeParameterType s, ExtensionType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
-    return const IsSubtypeOf.never();
+    return types.performNullabilityAwareSubtypeCheck(s, t.onType);
   }
 
   @override
   IsSubtypeOf isTypedefRelated(TypedefType s, ExtensionType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
-    return const IsSubtypeOf.never();
+    return types.performNullabilityAwareSubtypeCheck(s, t.onType);
   }
 
   @override
   IsSubtypeOf isExtensionRelated(
       ExtensionType s, ExtensionType t, Types types) {
-    // TODO(dmitryas): Use with the actual subtyping rules for extension types.
     if (s.extension != t.extension) {
       return const IsSubtypeOf.never();
     }
+    // TODO(dmitryas): Check if subtyping or mutual subtyping should be used.
     return types
         .areTypeArgumentsOfSubtypeKernel(
             s.typeArguments, t.typeArguments, t.extension.typeParameters)

pkg/kernel/lib/testing/type_parser_environment.dart

@@ -327,6 +327,9 @@ class _KernelFromParsedType implements Visitor<Node, TypeParserEnvironment> {
     } else if (declaration is Typedef) {
       return new TypedefType(declaration,
           interpretParsedNullability(node.parsedNullability), kernelArguments);
+    } else if (declaration is Extension) {
+      return new ExtensionType(declaration,
+          interpretParsedNullability(node.parsedNullability), kernelArguments);
     } else {
       throw "Unhandled ${declaration.runtimeType}";
     }
@@ -380,7 +383,7 @@ class _KernelFromParsedType implements Visitor<Node, TypeParserEnvironment> {
       ..addAll(parameters);
     {
       TypeParserEnvironment environment = parameterEnvironment.environment;
-      InterfaceType onType =
+      DartType onType =
           node.onType?.accept<Node, TypeParserEnvironment>(this, environment);
       ext.onType = onType;
     }