[analyzer/ffi] Allow implementing Finalizable

This does not yet add `Finalizable` to `dart:ffi`, but already extends
the ffi_verifier to not give errors on implementing it.

Bug: #47777

Change-Id: I381d4954f39ae031d540cdbe97b112edafc25df8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/227721
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Daco Harkes <dacoharkes@google.com>

pkg/analyzer/lib/src/dart/error/ffi_code.g.dart

@@ -440,7 +440,7 @@ class FfiCode extends AnalyzerErrorCode {
   static const FfiCode SUBTYPE_OF_FFI_CLASS_IN_IMPLEMENTS = FfiCode(
     'SUBTYPE_OF_FFI_CLASS',
     "The class '{0}' can't implement '{1}'.",
-    correctionMessage: "Try extending 'Struct' or 'Union'.",
+    correctionMessage: "Try implementing 'Allocator' or 'Finalizable'.",
     uniqueName: 'SUBTYPE_OF_FFI_CLASS_IN_IMPLEMENTS',
   );
 

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

@@ -24,6 +24,7 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
   static const _allocatorExtensionName = 'AllocatorAlloc';
   static const _arrayClassName = 'Array';
   static const _dartFfiLibraryName = 'dart.ffi';
+  static const _finalizableClassName = 'Finalizable';
   static const _isLeafParamName = 'isLeaf';
   static const _opaqueClassName = 'Opaque';
   static const _ffiNativeName = 'FfiNative';
@@ -116,7 +117,8 @@ class FfiVerifier extends RecursiveAstVisitor<void> {
     void checkSupertype(NamedType typename, FfiCode subtypeOfFfiCode,
         FfiCode subtypeOfStructCode) {
       final superName = typename.name.staticElement?.name;
-      if (superName == _allocatorClassName) {
+      if (superName == _allocatorClassName ||
+          superName == _finalizableClassName) {
         return;
       }
       if (typename.ffiClass != null) {

pkg/analyzer/lib/src/test_utilities/mock_sdk.dart

@@ -833,6 +833,9 @@ class AbiSpecificIntegerMapping {
   const AbiSpecificIntegerMapping(this.mapping);
 }
 
+abstract class Finalizable {
+  factory Finalizable._() => throw UnsupportedError("");
+}
 ''',
   )
 ]);

pkg/analyzer/messages.yaml

@@ -13993,7 +13993,7 @@ FfiCode:
   SUBTYPE_OF_FFI_CLASS_IN_IMPLEMENTS:
     sharedName: SUBTYPE_OF_FFI_CLASS
     problemMessage: "The class '{0}' can't implement '{1}'."
-    correctionMessage: "Try extending 'Struct' or 'Union'."
+    correctionMessage: "Try implementing 'Allocator' or 'Finalizable'."
     comment: |-
       Parameters:
       0: the name of the subclass

pkg/analyzer/test/src/diagnostics/subtype_of_ffi_class_test.dart

@@ -27,6 +27,17 @@ class C extends Double {}
     ]);
   }
 
+  test_Finalizable() async {
+    await assertErrorsInCode(r'''
+import 'dart:ffi';
+class C extends Finalizable {}
+''', [
+      error(FfiCode.SUBTYPE_OF_FFI_CLASS_IN_EXTENDS, 35, 11),
+      error(CompileTimeErrorCode.NO_GENERATIVE_CONSTRUCTORS_IN_SUPERCLASS, 35,
+          11),
+    ]);
+  }
+
   test_Float() async {
     await assertErrorsInCode(r'''
 import 'dart:ffi';
@@ -169,6 +180,13 @@ class C implements ffi.Double {}
     ]);
   }
 
+  test_Finalizable() async {
+    await assertNoErrorsInCode(r'''
+import 'dart:ffi';
+class C implements Finalizable {}
+''');
+  }
+
   test_Float() async {
     await assertErrorsInCode(r'''
 import 'dart:ffi';