fix(shared): make await using work without a native Symbol.asyncDispose

packages/shared/src/iterator.test.ts

@@ -21,6 +21,35 @@ it('isAsyncIteratorObject', () => {
   expect(isAsyncIteratorObject(gen2())).toBe(false)
 })
 
+it('uses Symbol.for("Symbol.asyncDispose") when Symbol.asyncDispose is not native', async ({
+  onTestFinished,
+}) => {
+  onTestFinished(() => {
+    vi.unstubAllGlobals()
+    vi.resetModules()
+  })
+
+  // Symbol.asyncDispose is non-configurable, so a Proxy over Symbol itself would break the get invariant
+  const RealSymbol = Symbol
+  vi.stubGlobal(
+    'Symbol',
+    new Proxy(function () {} as any, {
+      apply: (_target, _this, args) => RealSymbol(...args),
+      get: (_target, key) => (key === 'asyncDispose' ? undefined : Reflect.get(RealSymbol, key)),
+    }),
+  )
+  vi.resetModules()
+  const { AsyncIteratorClass } = await import('./iterator')
+  vi.unstubAllGlobals()
+
+  const cleanup = vi.fn()
+  const iterator = new AsyncIteratorClass(async () => ({ done: false, value: 1 }), cleanup)
+
+  await (iterator as any)[RealSymbol.for('Symbol.asyncDispose')]()
+  expect(cleanup).toHaveBeenCalledTimes(1)
+  expect(cleanup).toHaveBeenCalledWith({ kind: 'cancelled' })
+})
+
 describe('asyncIteratorClass', () => {
   const next = vi.fn()
   const cleanup = vi.fn()

packages/shared/src/iterator.ts

@@ -18,12 +18,11 @@ export interface AsyncIteratorClassNextFn<T, TReturn> {
   (): Promise<IteratorResult<T, TReturn>>
 }
 
-const fallbackAsyncDisposeSymbol: unique symbol = Symbol.for('asyncDispose')
-/* v8 ignore start  */
+// same key as esbuild's `__using`, Babel's `usingCtx` and core-js use without a native symbol
+const fallbackAsyncDisposeSymbol: unique symbol = Symbol.for('Symbol.asyncDispose')
 const asyncDisposeSymbol: typeof Symbol extends { asyncDispose: infer T }
   ? T
   : typeof fallbackAsyncDisposeSymbol = (Symbol as any).asyncDispose ?? fallbackAsyncDisposeSymbol
-/* v8 ignore end  */
 
 export class AsyncIteratorClass<T, TReturn = unknown, TNext = unknown>
   implements AsyncIteratorObject<T, TReturn, TNext>, AsyncGenerator<T, TReturn, TNext>
@@ -99,7 +98,7 @@ export class AsyncIteratorClass<T, TReturn = unknown, TNext = unknown>
   }
 
   /**
-   * asyncDispose symbol only available in esnext, we should fallback to Symbol.for('asyncDispose')
+   * Uses the native Symbol.asyncDispose, or Symbol.for('Symbol.asyncDispose') on runtimes without it
    */
   async [asyncDisposeSymbol](): Promise<void> {
     this.isDone = true