node: fix test-buffer-backing-arraybuffer.js (#17161)

src/bun.js/bindings/InternalForTesting.cpp

@@ -0,0 +1,19 @@
+#include "root.h"
+
+#include "ZigGlobalObject.h"
+#include "JavaScriptCore/JSCJSValue.h"
+#include "JavaScriptCore/JSCast.h"
+#include "JavaScriptCore/JSArrayBufferView.h"
+
+namespace Bun {
+
+using namespace JSC;
+
+JSC_DEFINE_HOST_FUNCTION(jsFunction_arrayBufferViewHasBuffer, (JSC::JSGlobalObject * globalObject, JSC::CallFrame* callFrame))
+{
+    auto value = callFrame->argument(0);
+    auto view = jsCast<WebCore::JSArrayBufferView*>(value);
+    return JSValue::encode(jsBoolean(view->hasArrayBuffer()));
+}
+
+}

src/bun.js/bindings/InternalForTesting.h

@@ -0,0 +1,10 @@
+#include "root.h"
+
+#include "ZigGlobalObject.h"
+#include "JavaScriptCore/JSCJSValue.h"
+
+namespace Bun {
+
+JSC_DEFINE_HOST_FUNCTION(jsFunction_arrayBufferViewHasBuffer, (JSC::JSGlobalObject * globalObject, JSC::CallFrame* callFrame));
+
+}

src/js/internal-for-testing.ts

@@ -1,3 +1,5 @@
+// Hardcoded module "bun:internal-for-testing"
+
 // If you want to test an internal API, add a binding into this file.
 //
 // Then at test time: import ... from "bun:internal-for-testing"
@@ -164,3 +166,9 @@ export const fsStreamInternals = {
     return str[require("internal/fs/streams").kWriteStreamFastPath];
   },
 };
+
+export const arrayBufferViewHasBuffer = $newCppFunction(
+  "InternalForTesting.cpp",
+  "jsFunction_arrayBufferViewHasBuffer",
+  1,
+);

test/js/node/test/parallel/test-buffer-backing-arraybuffer.js

@@ -0,0 +1,36 @@
+'use strict';
+require('../common');
+const assert = require('assert');
+// const { internalBinding } = require('internal/test/binding');
+// const { arrayBufferViewHasBuffer } = internalBinding('util');
+const { arrayBufferViewHasBuffer } = require('bun:internal-for-testing');
+
+const tests = [
+  { length: 0 },
+  { length: 48 },
+  { length: 96 },
+  { length: 1024 },
+];
+
+for (const { length, expectOnHeap } of tests) {
+  const arrays = [
+    new Uint8Array(length),
+    new Uint16Array(length / 2),
+    new Uint32Array(length / 4),
+    new Float32Array(length / 4),
+    new Float64Array(length / 8),
+    Buffer.alloc(length),
+    Buffer.allocUnsafeSlow(length),
+    // Buffer.allocUnsafe() is missing because it may use pooled allocations.
+  ];
+
+  for (const array of arrays) {
+    const isOnHeap = arrayBufferViewHasBuffer(array);
+    const expectOnHeap = false; // in JSC this will always be false until `.buffer` is first accessed.
+    assert.strictEqual(isOnHeap, expectOnHeap, `mismatch: ${isOnHeap} vs ${expectOnHeap} ` + `for ${array.constructor.name}, length = ${length}`);
+
+    // Consistency check: Accessing .buffer should create it.
+    array.buffer; // eslint-disable-line no-unused-expressions
+    assert(arrayBufferViewHasBuffer(array));
+  }
+}