[vm/ffi] Add Opaque type

Issue: https://github.com/dart-lang/sdk/issues/44622
Issue: https://github.com/dart-lang/sdk/issues/43974

TEST=samples/ffi/sqlite/lib/src/bindings/types.dart
TEST=tests/ffi/vmspecific_static_checks_test.dart

Change-Id: Ib9e72df6a07b1bc2b72a7db66f945652814baf51
Cq-Include-Trybots: luci.dart.try:vm-precomp-ffi-qemu-linux-release-arm-try,analyzer-analysis-server-linux-try,analyzer-linux-release-try,analyzer-nnbd-linux-release-try,front-end-linux-release-x64-try,front-end-nnbd-linux-release-x64-try,benchmark-linux-try,dart-sdk-linux-try,pkg-linux-release-try,vm-ffi-android-release-arm-try,vm-ffi-android-release-arm64-try,vm-kernel-nnbd-win-debug-x64-try,vm-kernel-win-debug-x64-try
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/178984
Commit-Queue: Daco Harkes <dacoharkes@google.com>
Reviewed-by: Clement Skau <cskau@google.com>

pkg/analyzer/lib/src/generated/ffi_verifier.dart

@@ -18,6 +18,7 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
   static const _allocateExtensionMethodName = 'call';
   static const _allocatorExtensionName = 'AllocatorAlloc';
   static const _dartFfiLibraryName = 'dart.ffi';
+  static const _opaqueClassName = 'Opaque';
 
   static const List<String> _primitiveIntegerNativeTypes = [
     'Int8',
@@ -54,7 +55,7 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
   @override
   void visitClassDeclaration(ClassDeclaration node) {
     inStruct = false;
-    // Only the Struct class may be extended.
+    // Only the Allocator, Opaque and Struct class may be extended.
     ExtendsClause extendsClause = node.extendsClause;
     if (extendsClause != null) {
       final TypeName superclass = extendsClause.superclass;
@@ -62,7 +63,8 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
         final className = superclass.name.staticElement.name;
         if (className == _structClassName) {
           inStruct = true;
-        } else if (className != _allocatorClassName) {
+        } else if (className != _allocatorClassName &&
+            className != _opaqueClassName) {
           _errorReporter.reportErrorForNode(
               FfiCode.SUBTYPE_OF_FFI_CLASS_IN_EXTENDS,
               superclass.name,
@@ -245,6 +247,21 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
     return false;
   }
 
+  /// Returns `true` iff [nativeType] is a opaque type, i.e. a subtype of `Opaque`.
+  bool _isOpaqueClass(DartType nativeType) {
+    if (nativeType is InterfaceType) {
+      final superType = nativeType.element.supertype;
+      if (superType == null) {
+        return false;
+      }
+      final superClassElement = superType.element;
+      if (superClassElement.library.name == _dartFfiLibraryName) {
+        return superClassElement.name == _opaqueClassName;
+      }
+    }
+    return false;
+  }
+
   /// Return `true` if the given [element] represents the class `Pointer`.
   bool _isPointer(Element element) =>
       element.name == 'Pointer' && element.library.name == _dartFfiLibraryName;
@@ -345,6 +362,9 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
         }
         return true;
       }
+      if (_isOpaqueClass(nativeType)) {
+        return true;
+      }
     } else if (nativeType is FunctionType) {
       return _isValidFfiNativeFunctionType(nativeType);
     }

pkg/front_end/testcases/general_nnbd_opt_out/ffi_sample.dart.weak.expect

@@ -41,4 +41,4 @@ constants  {
 
 Constructor coverage from constants:
 org-dartlang-testcase:///ffi_sample.dart:
-- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:116:9)
+- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:122:9)

pkg/front_end/testcases/general_nnbd_opt_out/ffi_sample.dart.weak.transformed.expect

@@ -72,4 +72,4 @@ constants  {
 
 Constructor coverage from constants:
 org-dartlang-testcase:///ffi_sample.dart:
-- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:116:9)
+- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:122:9)

pkg/front_end/testcases/nnbd/ffi_sample.dart.strong.expect

@@ -35,4 +35,4 @@ constants  {
 
 Constructor coverage from constants:
 org-dartlang-testcase:///ffi_sample.dart:
-- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:116:9)
+- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:122:9)

pkg/front_end/testcases/nnbd/ffi_sample.dart.strong.transformed.expect

@@ -66,4 +66,4 @@ constants  {
 
 Constructor coverage from constants:
 org-dartlang-testcase:///ffi_sample.dart:
-- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:116:9)
+- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:122:9)

pkg/front_end/testcases/nnbd/ffi_sample.dart.weak.expect

@@ -35,4 +35,4 @@ constants  {
 
 Constructor coverage from constants:
 org-dartlang-testcase:///ffi_sample.dart:
-- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:116:9)
+- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:122:9)

pkg/front_end/testcases/nnbd/ffi_sample.dart.weak.transformed.expect

@@ -66,4 +66,4 @@ constants  {
 
 Constructor coverage from constants:
 org-dartlang-testcase:///ffi_sample.dart:
-- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:116:9)
+- Double. (from org-dartlang-sdk:///sdk/lib/ffi/native_type.dart:122:9)

pkg/vm/lib/transformations/ffi.dart

@@ -34,6 +34,7 @@ enum NativeType {
   kFloat,
   kDouble,
   kVoid,
+  kOpaque,
   kStruct,
   kHandle,
 }
@@ -60,6 +61,7 @@ const List<String> nativeTypeClassNames = [
   'Float',
   'Double',
   'Void',
+  'Opaque',
   'Struct',
   'Handle'
 ];
@@ -86,6 +88,7 @@ const List<int> nativeTypeSizes = [
   4, // Float
   8, // Double
   UNKNOWN, // Void
+  UNKNOWN, // Opaque
   UNKNOWN, // Struct
   WORD_SIZE, // Handle
 ];
@@ -207,6 +210,7 @@ class FfiTransformer extends Transformer {
   final Library ffiLibrary;
   final Class allocatorClass;
   final Class nativeFunctionClass;
+  final Class opaqueClass;
   final Class pointerClass;
   final Class structClass;
   final Procedure allocateMethod;
@@ -263,6 +267,7 @@ class FfiTransformer extends Transformer {
         ffiLibrary = index.getLibrary('dart:ffi'),
         allocatorClass = index.getClass('dart:ffi', 'Allocator'),
         nativeFunctionClass = index.getClass('dart:ffi', 'NativeFunction'),
+        opaqueClass = index.getClass('dart:ffi', 'Opaque'),
         pointerClass = index.getClass('dart:ffi', 'Pointer'),
         structClass = index.getClass('dart:ffi', 'Struct'),
         allocateMethod = index.getMember('dart:ffi', 'AllocatorAlloc', 'call'),

pkg/vm/lib/transformations/ffi_use_sites.dart

@@ -488,10 +488,15 @@ class _FfiUseSiteTransformer extends FfiTransformer {
   Class _extendsOrImplementsSealedClass(Class klass) {
     final Class superClass = klass.supertype?.classNode;
 
-    // The Struct class can be extended, but subclasses of Struct cannot be (nor
-    // implemented).
-    if (klass != structClass && hierarchy.isSubtypeOf(klass, structClass)) {
-      return superClass != structClass ? superClass : null;
+    // The Opaque and Struct classes can be extended, but subclasses
+    // cannot be (nor implemented).
+    if (klass != opaqueClass &&
+        klass != structClass &&
+        (hierarchy.isSubtypeOf(klass, opaqueClass) ||
+            hierarchy.isSubtypeOf(klass, structClass))) {
+      return superClass != opaqueClass && superClass != structClass
+          ? superClass
+          : null;
     }
 
     if (!nativeTypesClasses.contains(klass)) {

samples/ffi/async/sample_async_callback.dart

@@ -105,7 +105,7 @@ final stopWorkSimulator =
 final executeCallback = dl.lookupFunction<Void Function(Pointer<Work>),
     void Function(Pointer<Work>)>('ExecuteCallback');
 
-class Work extends Struct {}
+class Work extends Opaque {}
 
 Future asyncSleep(int ms) {
   return new Future.delayed(Duration(milliseconds: ms));

samples/ffi/resource_management/pool_isolate_shutdown_sample.dart

@@ -86,4 +86,4 @@ final releaseResource = ffiTestDynamicLibrary.lookupFunction<
     void Function(Pointer<SomeResource>)>("ReleaseResource");
 
 /// Represents some opaque resource being managed by a library.
-class SomeResource extends Struct {}
+class SomeResource extends Opaque {}

samples/ffi/resource_management/pool_sample.dart

@@ -110,4 +110,4 @@ main() {
 }
 
 /// Represents some opaque resource being managed by a library.
-class SomeResource extends Struct {}
+class SomeResource extends Opaque {}

samples/ffi/resource_management/pool_zoned_sample.dart

@@ -111,4 +111,4 @@ main() {
 }
 
 /// Represents some opaque resource being managed by a library.
-class SomeResource extends Struct {}
+class SomeResource extends Opaque {}

samples/ffi/sqlite/lib/src/bindings/types.dart

@@ -13,7 +13,7 @@ import "dart:ffi";
 /// is its destructor.  There are many other interfaces (such as
 /// [sqlite3_prepare_v2()], [sqlite3_create_function()], and
 /// [sqlite3_busy_timeout()] to name but three) that are methods on an
-class Database extends Struct {}
+class Database extends Opaque {}
 
 /// SQL Statement Object
 ///
@@ -36,7 +36,7 @@ class Database extends Struct {}
 ///
 /// Refer to documentation on individual methods above for additional
 /// information.
-class Statement extends Struct {}
+class Statement extends Opaque {}
 
 /// Dynamically Typed Value Object
 ///
@@ -72,4 +72,4 @@ class Statement extends Struct {}
 /// [sqlite3_result_value()] and [sqlite3_bind_value()].
 /// The [sqlite3_value_blob | sqlite3_value_type()] family of
 /// interfaces require protected sqlite3_value objects.
-class Value extends Struct {}
+class Value extends Opaque {}

samples_2/ffi/async/sample_async_callback.dart

@@ -107,7 +107,7 @@ final stopWorkSimulator =
 final executeCallback = dl.lookupFunction<Void Function(Pointer<Work>),
     void Function(Pointer<Work>)>('ExecuteCallback');
 
-class Work extends Struct {}
+class Work extends Opaque {}
 
 Future asyncSleep(int ms) {
   return new Future.delayed(Duration(milliseconds: ms));

samples_2/ffi/resource_management/pool_isolate_shutdown_sample.dart

@@ -88,4 +88,4 @@ final releaseResource = ffiTestDynamicLibrary.lookupFunction<
     void Function(Pointer<SomeResource>)>("ReleaseResource");
 
 /// Represents some opaque resource being managed by a library.
-class SomeResource extends Struct {}
+class SomeResource extends Opaque {}

samples_2/ffi/resource_management/pool_sample.dart

@@ -112,4 +112,4 @@ main() {
 }
 
 /// Represents some opaque resource being managed by a library.
-class SomeResource extends Struct {}
+class SomeResource extends Opaque {}

samples_2/ffi/resource_management/pool_zoned_sample.dart

@@ -113,4 +113,4 @@ main() {
 }
 
 /// Represents some opaque resource being managed by a library.
-class SomeResource extends Struct {}
+class SomeResource extends Opaque {}

samples_2/ffi/sqlite/lib/src/bindings/types.dart

@@ -15,7 +15,7 @@ import "dart:ffi";
 /// is its destructor.  There are many other interfaces (such as
 /// [sqlite3_prepare_v2()], [sqlite3_create_function()], and
 /// [sqlite3_busy_timeout()] to name but three) that are methods on an
-class Database extends Struct {}
+class Database extends Opaque {}
 
 /// SQL Statement Object
 ///
@@ -38,7 +38,7 @@ class Database extends Struct {}
 ///
 /// Refer to documentation on individual methods above for additional
 /// information.
-class Statement extends Struct {}
+class Statement extends Opaque {}
 
 /// Dynamically Typed Value Object
 ///
@@ -74,4 +74,4 @@ class Statement extends Struct {}
 /// [sqlite3_result_value()] and [sqlite3_bind_value()].
 /// The [sqlite3_value_blob | sqlite3_value_type()] family of
 /// interfaces require protected sqlite3_value objects.
-class Value extends Struct {}
+class Value extends Opaque {}

sdk/lib/ffi/ffi.dart

@@ -559,7 +559,7 @@ extension NativePort on SendPort {
 }
 
 /// Opaque, not exposing it's members.
-class Dart_CObject extends Struct {}
+class Dart_CObject extends Opaque {}
 
 typedef Dart_NativeMessageHandler = Void Function(Int64, Pointer<Dart_CObject>);
 

sdk/lib/ffi/native_type.dart

@@ -12,6 +12,12 @@ abstract class NativeType {
   const NativeType();
 }
 
+/// [Opaque]'s subtypes represent opaque types in C.
+///
+/// [Opaque]'s subtypes are not constructible in the Dart code and serve purely
+/// as markers in type signatures.
+abstract class Opaque extends NativeType {}
+
 /// [_NativeInteger]'s subtypes represent a native integer in C.
 ///
 /// [_NativeInteger]'s subtypes are not constructible in the Dart code and serve

tests/ffi/vmspecific_static_checks_test.dart

@@ -477,6 +477,8 @@ class IPointer implements Pointer {} //# 814: compile-time error
 
 class IStruct implements Struct {} //# 815: compile-time error
 
+class IOpaque implements Opaque {} //# 816: compile-time error
+
 class MyClass {
   int x;
   MyClass(this.x);

tests/ffi_2/vmspecific_static_checks_test.dart

@@ -477,6 +477,8 @@ class IPointer implements Pointer {} //# 814: compile-time error
 
 class IStruct implements Struct {} //# 815: compile-time error
 
+class IOpaque implements Opaque {} //# 816: compile-time error
+
 class MyClass {
   int x;
   MyClass(this.x);