Add an v8::ArrayBuffer::WasDetached method to the C++ API

V8's C++ API does not give a way to tell whether an ArrayBuffer has
been detached from the `v8::ArrayBuffer` class. In fact, as far as can
be told from the C++ API without running JS code, detached
ArrayBuffers behave the same as zero-sized ArrayBuffers and there is
no way to observe the difference. However, this difference can be
observed in JS because constructing a TypedArray from a detached
ArrayBuffer will throw.

This change adds a `WasDetached` method to the `v8::ArrayBuffer` class
to give embedders access to this information without having to run JS
code.

Bug: v8:13159
Change-Id: I2bb1e380cee1cecd31f6d48ec3d9f28c03a8a673
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3810345
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/main@{#83963}

AUTHORS

@@ -60,6 +60,7 @@ Allan Sandfeld Jensen <allan.jensen@qt.io>
 Amos Lim <eui-sang.lim@samsung.com>
 Andreas Anyuru <andreas.anyuru@gmail.com>
 Andrei Kashcha <anvaka@gmail.com>
+Andreu Botella <andreu@andreubotella.com>
 Andrew Paprocki <andrew@ishiboo.com>
 Anna Henningsen <anna@addaleax.net>
 Antoine du Hamel <duhamelantoine1995@gmail.com>

include/v8-array-buffer.h

@@ -240,6 +240,11 @@ class V8_EXPORT ArrayBuffer : public Object {
    */
   bool IsDetachable() const;
 
+  /**
+   * Returns true if this ArrayBuffer has been detached.
+   */
+  bool WasDetached() const;
+
   /**
    * Detaches this ArrayBuffer and all its views (typed arrays).
    * Detaching sets the byte length of the buffer and all typed arrays to zero,
@@ -271,6 +276,9 @@ class V8_EXPORT ArrayBuffer : public Object {
    * pointer coordinates the lifetime management of the internal storage
    * with any live ArrayBuffers on the heap, even across isolates. The embedder
    * should not attempt to manage lifetime of the storage through other means.
+   *
+   * The returned shared pointer will not be empty, even if the ArrayBuffer has
+   * been detached. Use |WasDetached| to tell if it has been detached instead.
    */
   std::shared_ptr<BackingStore> GetBackingStore();
 

src/api/api.cc

@@ -8100,6 +8100,10 @@ bool v8::ArrayBuffer::IsDetachable() const {
   return Utils::OpenHandle(this)->is_detachable();
 }
 
+bool v8::ArrayBuffer::WasDetached() const {
+  return Utils::OpenHandle(this)->was_detached();
+}
+
 namespace {
 std::shared_ptr<i::BackingStore> ToInternal(
     std::shared_ptr<i::BackingStoreBase> backing_store) {

test/cctest/cctest.status

@@ -513,6 +513,7 @@
   'test-api/WasmI32AtomicWaitCallback': [SKIP],
   'test-api/WasmI64AtomicWaitCallback': [SKIP],
   'test-api/WasmSetJitCodeEventHandler': [SKIP],
+  'test-api-array-buffer/ArrayBuffer_NonDetachableWasDetached': [SKIP],
   'test-backing-store/Run_WasmModule_Buffer_Externalized_Regression_UseAfterFree': [SKIP],
   'test-c-wasm-entry/*': [SKIP],
   'test-compilation-cache/*': [SKIP],

test/cctest/test-api-array-buffer.cc

@@ -245,6 +245,37 @@ THREADED_TEST(ArrayBuffer_DetachingScript) {
   CheckDataViewIsDetached(dv);
 }
 
+THREADED_TEST(ArrayBuffer_WasDetached) {
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  v8::HandleScope handle_scope(isolate);
+
+  Local<v8::ArrayBuffer> ab = v8::ArrayBuffer::New(isolate, 0);
+  CHECK(!ab->WasDetached());
+
+  ab->Detach(v8::Local<v8::Value>()).Check();
+  CHECK(ab->WasDetached());
+}
+
+THREADED_TEST(ArrayBuffer_NonDetachableWasDetached) {
+  LocalContext env;
+  v8::Isolate* isolate = env->GetIsolate();
+  v8::HandleScope handle_scope(isolate);
+
+  CompileRun(R"JS(
+    var wasmMemory = new WebAssembly.Memory({initial: 1, maximum: 2});
+  )JS");
+
+  Local<v8::ArrayBuffer> non_detachable =
+      CompileRun("wasmMemory.buffer").As<v8::ArrayBuffer>();
+  CHECK(!non_detachable->IsDetachable());
+  CHECK(!non_detachable->WasDetached());
+
+  CompileRun("wasmMemory.grow(1)");
+  CHECK(!non_detachable->IsDetachable());
+  CHECK(non_detachable->WasDetached());
+}
+
 THREADED_TEST(ArrayBuffer_ExternalizeEmpty) {
   LocalContext env;
   v8::Isolate* isolate = env->GetIsolate();