refactor(mapAsyncIterable): use withCleanup to simplify (#4499)

The test changes are limited to uses of `mapAsyncIterable` that are not
actually used in the codebase, i.e. `.return()` and `.throw().

Author: yaacovCR

src/execution/__tests__/mapAsyncIterable-test.ts

@@ -91,15 +91,10 @@ describe('mapAsyncIterable', () => {
 
   it('allows returning early from mapped async generator', async () => {
     async function* source() {
-      try {
-        yield 1;
-        /* c8 ignore next 3 */
-        yield 2;
-        yield 3; // Shouldn't be reached.
-      } finally {
-        // eslint-disable-next-line no-unsafe-finally
-        return 'The End';
-      }
+      yield 1;
+      /* c8 ignore next 3 */
+      yield 2;
+      yield 3; // Shouldn't be reached.
     }
 
     const doubles = mapAsyncIterable(source(), (x) => x + x);
@@ -108,8 +103,8 @@ describe('mapAsyncIterable', () => {
     expect(await doubles.next()).to.deep.equal({ value: 4, done: false });
 
     // Early return
-    expect(await doubles.return('')).to.deep.equal({
-      value: 'The End',
+    expect(await doubles.return()).to.deep.equal({
+      value: undefined,
       done: true,
     });
 
@@ -147,23 +142,18 @@ describe('mapAsyncIterable', () => {
     expect(await doubles.next()).to.deep.equal({ value: 4, done: false });
 
     // Early return
-    expect(await doubles.return(0)).to.deep.equal({
+    expect(await doubles.return()).to.deep.equal({
       value: undefined,
       done: true,
     });
   });
 
   it('passes through early return from async values', async () => {
     async function* source() {
-      try {
-        yield 'a';
-        /* c8 ignore next 3 */
-        yield 'b';
-        yield 'c'; // Shouldn't be reached.
-      } finally {
-        yield 'Done';
-        yield 'Last';
-      }
+      yield 'a';
+      /* c8 ignore next 3 */
+      yield 'b';
+      yield 'c'; // Shouldn't be reached.
     }
 
     const doubles = mapAsyncIterable(source(), (x) => x + x);
@@ -173,14 +163,14 @@ describe('mapAsyncIterable', () => {
 
     // Early return
     expect(await doubles.return()).to.deep.equal({
-      value: 'DoneDone',
-      done: false,
+      value: undefined,
+      done: true,
     });
 
-    // Subsequent next calls may yield from finally block
+    // Subsequent next calls
     expect(await doubles.next()).to.deep.equal({
-      value: 'LastLast',
-      done: false,
+      value: undefined,
+      done: true,
     });
     expect(await doubles.next()).to.deep.equal({
       value: undefined,
@@ -260,14 +250,10 @@ describe('mapAsyncIterable', () => {
 
   it('passes through caught errors through async generators', async () => {
     async function* source() {
-      try {
-        yield 1;
-        /* c8 ignore next 2 */
-        yield 2;
-        yield 3; // Shouldn't be reached.
-      } catch (e) {
-        yield e;
-      }
+      yield 1;
+      /* c8 ignore next 2 */
+      yield 2;
+      yield 3; // Shouldn't be reached.
     }
 
     const doubles = mapAsyncIterable(source(), (x) => x + x);
@@ -276,11 +262,9 @@ describe('mapAsyncIterable', () => {
     expect(await doubles.next()).to.deep.equal({ value: 4, done: false });
 
     // Throw error
-    expect(await doubles.throw('Ouch')).to.deep.equal({
-      value: 'OuchOuch',
-      done: false,
-    });
+    await expectPromise(doubles.throw(new Error('Ouch'))).toRejectWith('Ouch');
 
+    // Subsequent next calls
     expect(await doubles.next()).to.deep.equal({
       value: undefined,
       done: true,

src/execution/mapAsyncIterable.ts

@@ -1,33 +1,18 @@
+import { isPromise } from '../jsutils/isPromise.js';
 import type { PromiseOrValue } from '../jsutils/PromiseOrValue.js';
 
+import { withCleanup } from './withCleanup.js';
+
 /**
  * Given an AsyncIterable and a callback function, return an AsyncIterator
  * which produces values mapped via calling the callback function.
  */
-export function mapAsyncIterable<T, U, R = undefined>(
-  iterable: AsyncGenerator<T, R, void> | AsyncIterable<T>,
+export function mapAsyncIterable<T, U>(
+  iterable: AsyncGenerator<T> | AsyncIterable<T>,
   callback: (value: T) => PromiseOrValue<U>,
-): AsyncGenerator<U, R, void> {
-  const iterator = iterable[Symbol.asyncIterator]();
-
-  async function mapResult(
-    promise: Promise<IteratorResult<T, R>>,
-  ): Promise<IteratorResult<U, R>> {
-    const result = await promise;
-    if (result.done) {
-      return result;
-    }
-
-    const value = result.value;
-    try {
-      return { value: await callback(value), done: false };
-    } catch (error) {
-      await returnIgnoringErrors();
-      throw error;
-    }
-  }
-
-  async function returnIgnoringErrors(): Promise<void> {
+): AsyncGenerator<U, void, void> {
+  return withCleanup(mapAsyncIterableImpl(iterable, callback), async () => {
+    const iterator = iterable[Symbol.asyncIterator]();
     if (typeof iterator.return === 'function') {
       try {
         await iterator.return(); /* c8 ignore start */
@@ -36,44 +21,19 @@ export function mapAsyncIterable<T, U, R = undefined>(
         /* ignore error */
       } /* c8 ignore stop */
     }
-  }
-
-  const asyncDispose: typeof Symbol.asyncDispose =
-    Symbol.asyncDispose /* c8 ignore start */ ??
-    Symbol.for('Symbol.asyncDispose'); /* c8 ignore stop */
-
-  return {
-    async next() {
-      return mapResult(iterator.next());
-    },
-    async return(): Promise<IteratorResult<U, R>> {
-      // If iterator.return() does not exist, then type R must be undefined.
-      return typeof iterator.return === 'function'
-        ? mapResult(iterator.return())
-        : { value: undefined as any, done: true };
-    },
-    async throw(error?: unknown) {
-      if (typeof iterator.throw === 'function') {
-        return mapResult(iterator.throw(error));
-      }
-
-      if (typeof iterator.return === 'function') {
-        await returnIgnoringErrors();
-      }
+  });
+}
 
-      throw error;
-    },
-    [Symbol.asyncIterator]() {
-      return this;
-    },
-    async [asyncDispose]() {
-      await this.return(undefined as R);
-      if (
-        typeof (iterable as AsyncGenerator<T, R, void>)[asyncDispose] ===
-        'function'
-      ) {
-        await (iterable as AsyncGenerator<T, R, void>)[asyncDispose]();
-      }
-    },
-  };
+async function* mapAsyncIterableImpl<T, U, R = undefined>(
+  iterable: AsyncGenerator<T, R, void> | AsyncIterable<T>,
+  mapFn: (value: T) => PromiseOrValue<U>,
+): AsyncGenerator<U, void, void> {
+  for await (const value of iterable) {
+    const result = mapFn(value);
+    if (isPromise(result)) {
+      yield await result;
+      continue;
+    }
+    yield result;
+  }
 }