[async-iteration] implement Async-from-Sync Iterator

test/mjsunit/harmony/async-from-sync-iterator.js

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// Flags: --harmony-async-iteration --allow-natives-syntax
+
+let testFailed = false;
+let testFailure;
+
+function assertThrowsAsync(run, errorType, message) {
+  var actual;
+  var hadValue = false;
+  var hadError = false;
+  var promise = run();
+
+  if (typeof promise !== "object" || typeof promise.then !== "function") {
+    throw new MjsUnitAssertionError(
+        "Expected " + run.toString() +
+        " to return a Promise, but it returned " + PrettyPrint(promise));
+  }
+
+  promise.then(function(value) { hadValue = true; actual = value; },
+               function(error) { hadError = true; actual = error; });
+
+  assertFalse(hadValue || hadError);
+
+  %RunMicrotasks();
+
+  if (!hadError) {
+    throw new MjsUnitAssertionError(
+        "Expected " + run + "() to throw " + errorType.name +
+        ", but did not throw.");
+  }
+  if (!(actual instanceof errorType))
+    throw new MjsUnitAssertionError(
+        "Expected " + run + "() to throw " + errorType.name +
+        ", but threw '" + actual + "'");
+  if (message !== void 0 && actual.message !== message)
+    throw new MjsUnitAssertionError(
+        "Expected " + run + "() to throw '" + message + "', but threw '" +
+        actual.message + "'");
+};
+
+function resolveLater(value) {
+  return new Promise(function(resolve) {
+    Promise.resolve().then(function() {
+      resolve(value);
+    });
+  });
+}
+
+function rejectLater(value) {
+  return new Promise(function(resolve, reject) {
+    Promise.resolve().then(function() {
+      reject(value);
+    });
+  });
+}
+
+const kNext = 1;
+const kThrow = 2;
+const kReturn = 4;
+const kNextThrows = kNext | 8;
+const kReturnThrows = kReturn | 16;
+const kThrowNormal = kThrow | 32;
+const kNextUnchanged = kNext | 64;
+const kReturnUnchanged = kReturn | 128;
+const kThrowUnchanged = kThrow | 256;
+function sync(array, features, log) {
+  let i = 0;
+
+  // Abort if `log` was not passed, otherwise TypeError may be eaten.
+  if (log === void 0) %AbortJS("`log` is undefined");

[neis, 2017/02/21 12:48:09]

Nit: move this up.

[caitp, 2017/02/21 14:36:53]

Acknowledged.

+  let methods = {
+    next(sent) {
+      let done = i >= array.length;
+      let value = array[i];
+      log.push({ method: "next", sent, value, done });
+      if ((features & kNextThrows) === kNextThrows) throw sent;
+      if ((features & kNextUnchanged) === kNextUnchanged) return sent;
+      i++;
+      return { value, done };
+    },
+    throw(sent) {
+      let done = i >= array.length;
+      log.push({ method: "throw", sent, done });
+      if ((features & kThrowNormal) === kThrowNormal)
+          return { value: sent, done };
+      if ((features & kThrowUnchanged) === kThrowUnchanged) return sent;
+      throw sent;
+    },
+    return(sent) {
+      let done = true;
+      log.push({ method: "return", sent, done });
+      if ((features & kReturnThrows) === kReturnThrows) throw sent;
+      if ((features & kReturnUnchanged) === kReturnUnchanged) return sent;
+      return { value: sent, done };
+    }
+  };
+  return {
+    [Symbol.iterator]() { return this; },
+    next: (features & kNext) ? methods.next : undefined,
+    throw: (features & kThrow) ? methods.throw : undefined,
+    return: (features & kReturn) ? methods.return : undefined
+  };
+}
+
+class MyError extends Error {};
+
+(async function AsyncFromSyncWithGenerator() {
+  function* gen() {
+    yield "sync value";
+    try {
+      yield new Promise(function(resolve) {
+        resolve("async value");
+      });
+    } catch (error) {
+      throw error;
+    }
+    assertUnreachable("generator is closed");
+  }
+  let iter = %CreateAsyncFromSyncIterator(gen());
+
+  // [Async-from-Sync Iterator] wraps sync iterator values in a Promise
+  let promise = iter.next();
+  assertInstanceof(promise, Promise);
+  let iter_result = await promise;
+  assertEquals({ value: "sync value", done: false }, iter_result);
+
+  // [Async-from-Sync Iterator] will wait for resolution of Promise values
+  promise = iter.next();
+  assertInstanceof(promise, Promise);
+  iter_result = await promise;
+  assertEquals({ value: "async value", done: false }, iter_result);
+
+  // [Async-from-Sync Iterator].throw delegates to .throw() method of sync
+  // iterator.
+  promise = iter.throw(new MyError("Error#1"));
+  assertInstanceof(promise, Promise);
+  try {
+    await promise;
+    assertUnreachable("promise should be rejected");
+  } catch (e) {
+    assertInstanceof(e, MyError);
+    assertEquals("Error#1", e.message);
+  }
+
+  promise = iter.return("generator closed");
+  assertInstanceof(promise, Promise);
+  iter_result = await promise;
+  assertEquals({ value: "generator closed", done: true }, iter_result);
+
+  // .next(), .return() and .throw() delegate to sync iterator methods, without
+  // keeping track of the state of the generator.
+  promise = iter.next("unused");
+  assertInstanceof(promise, Promise);
+  iter_result = await promise;
+  assertEquals({ value: undefined, done: true }, iter_result);
+
+  promise = iter.throw(new MyError("Error#2"));
+  assertInstanceof(promise, Promise);
+  try {
+    await promise;
+  } catch (e) {
+    assertInstanceof(e, MyError);
+    assertEquals("Error#2", e.message);
+  }
+
+  promise = iter.return("return-after-completed");
+  assertInstanceof(promise, Promise);
+  iter_result = await promise;
+  assertEquals({ value: "return-after-completed", done: true }, iter_result);
+})().catch(function(error) {
+  testFailed = true;
+  testFailure = error;
+});
+
+%RunMicrotasks();
+if (testFailed) {
+  throw testFailure;
+}
+
+
+(async function AsyncFromSyncOrderOfOperations() {
+  let log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(["sync-value"], 0, log));
+
+  try {
+    await iter.next();
+    assertUnreachable("Iterator.next() method is not optional");
+  } catch (e) {
+    assertInstanceof(e, TypeError);
+    assertEquals([], log);
+  }
+
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(["sync-value"], kNext, log));
+  assertEquals({ value: "sync-value", done: false }, await iter.next("a"));
+  assertEquals([
+    {
+      method: "next",
+      sent: "a",
+      value: "sync-value",
+      done: false
+    }
+  ], log);
+
+  log = [];
+  let asyncValue = resolveLater("async-value");
+  iter = %CreateAsyncFromSyncIterator(sync([asyncValue], kNext, log));
+  assertEquals({ value: "async-value", done: false }, await iter.next("b"));
+  assertEquals([
+    {
+      method: "next",
+      sent: "b",
+      value: asyncValue,
+      done: false
+    }
+  ], log);
+
+  // If [sync_iterator].next() produces a rejected Promise or an exception is
+  // thrown, Promise is rejected with thrown/rejected value.
+  log = [];
+  asyncValue = rejectLater("Boo!");
+  iter = %CreateAsyncFromSyncIterator(sync([asyncValue], kNext, log));
+  try {
+    await iter.next('c');
+    assertUnreachable('Expected `iter.next(\'c\') to throw, but did not throw');
+  } catch (e) {
+    assertEquals("Boo!", e);
+    assertEquals([
+      {
+        method: 'next',
+        sent: 'c',
+        value: asyncValue,
+        done: false
+      }
+    ], log);
+  }
+
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-value'], kNextThrows, log));
+  try {
+    await iter.next('Boo!');
+    assertUnreachable('Expected `iter.next(\'c\') to throw, but did not throw');
+  } catch (e) {
+    assertEquals("Boo!", e);
+    assertEquals([
+      {
+        method: 'next',
+        sent: 'Boo!',
+        value: 'sync-value',
+        done: false
+      }
+    ], log);
+  }
+
+
+  // [Async-from-Sync Iterator].next() will be rejected with a TypeError if
+  // Type([sync_iterator].next()) is not Object.
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-value'],
+                                      kNext|kNextUnchanged, log));

[neis, 2017/02/21 12:48:09]

Nit: kNextUnchanged includes kNext.

[caitp, 2017/02/21 14:36:52]

Acknowledged.

+  try {
+    await iter.next('not-a-JSReceiver');
+    assertUnreachable('Expected `iter.next(\'not-a-JSReceiver\')` to ' +
+                      'throw, but did not throw')
+  } catch (e) {
+    assertEquals(e.constructor, TypeError);
+  }
+
+  assertEquals([
+    {
+      method: 'next',
+      sent: 'not-a-JSReceiver',
+      value: 'sync-value',
+      done: false
+    }
+  ], log);
+
+  // If [sync_iterator] does not have a .return() method, return a Promise
+  // resolved with the value `{ value: <<sent value>>, done: true }`.
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-return'], kNext, log));
+  assertEquals({
+    value: 'd',
+    done: true
+  }, await iter.return('d'));
+
+  // [Async-from-Sync Iterator] merely delegates, and does not keep track of
+  // whether [sync_iterator] is completed or not.
+  assertEquals({
+    value: 'sync-return',
+    done: false
+  }, await iter.next('e'));
+
+  assertEquals([
+    {
+      method: 'next',
+      sent: 'e',
+      value: 'sync-return',
+      done: false
+    }
+  ], log);
+
+  // If [sync_iterator] does have a .return() method, return a Promise
+  // fulfilled with the iterator result of [sync_iterator].return().
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-return'],
+                                      kNext|kReturn, log));
+  assertEquals({
+    value: 'f',
+    done: true
+  }, await iter.return('f'));
+
+  // [Async-from-Sync Iterator] merely delegates, and does not keep track of
+  // whether [sync_iterator] is completed or not.
+  assertEquals({
+    value: 'sync-return',
+    done: false
+  }, await iter.next('g'));
+
+  assertEquals([
+    {
+      method: 'return',
+      sent: 'f',
+      done: true
+    },
+    {
+      method: 'next',
+      sent: 'g',
+      value: 'sync-return',
+      done: false
+    }
+  ], log);
+
+  // If [sync_iterator].return() produces a rejected Promise or an exception is
+  // thrown, Promise is rejected with thrown/rejected value.
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-value'], kNext|kReturnThrows,
+                                      log));
+  try {
+    await iter.return('Boo!!');
+    assertUnreachable('Expected `iter.return(\'Boo!!\')` to throw, but did ' +
+                      'not throw');
+  } catch (e) {
+    assertEquals("Boo!!", e);
+  }
+
+  // [Async-from-Sync Iterator] merely delegates, and does not keep track of
+  // whether [sync_iterator] is completed or not.
+  assertEquals({ value: 'sync-value', done: false }, await iter.next('h'));
+  assertEquals([
+    {
+      method: 'return',
+      sent: 'Boo!!',
+      done: true
+    },
+    {
+      method: 'next',
+      sent: 'h',
+      value: 'sync-value',
+      done: false
+    }
+  ], log);
+
+
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-value'], kNext|kReturn, log));
+
+  let rejection = Promise.reject('Boo!!');
+  try {
+    await iter.return(rejection);
+    assertUnreachable('Expected `iter.return(Promise.reject(\'Boo!!\'))` to ' +
+                      'throw, but did not throw');
+  } catch (e) {
+    assertEquals('Boo!!', e);
+  }
+
+  // [Async-from-Sync Iterator] merely delegates, and does not keep track of
+  // whether [sync_iterator] is completed or not.
+  assertEquals({ value: 'sync-value', done: false }, await iter.next('i'));
+  assertEquals([
+    {
+      method: 'return',
+      sent: rejection,
+      done: true
+    },
+    {
+      method: 'next',
+      sent: 'i',
+      value: 'sync-value',
+      done: false
+    }
+  ], log);
+
+  // [Async-from-Sync Iterator].return() will be rejected with a TypeError if
+  // Type([sync_iterator].return()) is not Object.
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-value'],
+                                      kNext|kReturnUnchanged, log));
+  try {
+    await iter.return('not-a-JSReceiver');
+    assertUnreachable('Expected `iter.return(\'not-a-JSReceiver\')` to ' +
+                      'throw, but did not throw')
+  } catch (e) {
+    assertEquals(e.constructor, TypeError);
+  }
+
+  // [Async-from-Sync Iterator] merely delegates, and does not keep track of
+  // whether [sync_iterator] is completed or not.
+  assertEquals({ value: 'sync-value', done: false }, await iter.next('j'));
+  assertEquals([
+    {
+      method: 'return',
+      sent: 'not-a-JSReceiver',
+      done: true
+    },
+    {
+      method: 'next',
+      sent: 'j',
+      value: 'sync-value',
+      done: false
+    }
+  ], log);
+
+  // If [sync_iterator] does not have a .throw method, return a Promise rejected
+  // with the sent value.
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-value'], kNext, log));
+  try {
+    await iter.throw('Boo!!');
+    assertUnreachable('Expected iter.throw(\'Boo!!\') to throw, but did not ' +
+                      'throw');
+  } catch (e) {
+    assertEquals('Boo!!', e);
+  }
+
+  // [Async-from-Sync Iterator] merely delegates, and does not keep track of
+  // whether [sync_iterator] is completed or not.
+  assertEquals({ value: 'sync-value', done: false }, await iter.next('k'));
+  assertEquals([
+    {
+      method: 'next',
+      sent: 'k',
+      value: 'sync-value',
+      done: false
+    }
+  ], log);
+
+
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-value'], kNext|kThrow, log));
+  try {
+    await iter.throw('Boo!!');
+    assertUnreachable('Expected iter.throw(\'Boo!!\') to throw, but did not ' +
+                      'throw');
+  } catch (e) {
+    assertEquals('Boo!!', e);
+  }
+
+  // [Async-from-Sync Iterator] merely delegates, and does not keep track of
+  // whether [sync_iterator] is completed or not.
+  assertEquals({ value: 'sync-value', done: false }, await iter.next('l'));
+  assertEquals([
+    {
+      method: 'throw',
+      sent: 'Boo!!',
+      done: false
+    },
+    {
+      method: 'next',
+      sent: 'l',
+      value: 'sync-value',
+      done: false
+    }
+  ], log);
+
+  // If [sync_iterator].throw() returns a resolved Promise or a Completion
+  // with [[Type]] "normal" or "return", return a resolved Promise
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-value'], kNext|kThrowNormal,
+                                      log));
+  assertEquals({
+    value: 'Boo!!',
+    done: false
+  }, await iter.throw('Boo!!'));
+
+  // [Async-from-Sync Iterator] merely delegates, and does not keep track of
+  // whether [sync_iterator] is completed or not.
+  assertEquals({ value: 'sync-value', done: false }, await iter.next('m'));
+  assertEquals([
+    {
+      method: 'throw',
+      sent: 'Boo!!',
+      done: false
+    },
+    {
+      method: 'next',
+      sent: 'm',
+      value: 'sync-value',
+      done: false
+    }
+  ], log);
+
+  // [Async-from-Sync Iterator].throw() will be rejected with a TypeError if
+  // Type([sync_iterator].throw()) is not Object.
+  log = [];
+  iter = %CreateAsyncFromSyncIterator(sync(['sync-value'],
+                                      kNext|kThrowUnchanged, log));
+  try {
+    await iter.throw('not-a-JSReceiver');
+    assertUnreachable('Expected `iter.throw(\'not-a-JSReceiver\')` to ' +
+                      'throw, but did not throw')
+  } catch (e) {
+    assertEquals(e.constructor, TypeError);
+  }
+
+  // [Async-from-Sync Iterator] merely delegates, and does not keep track of
+  // whether [sync_iterator] is completed or not.
+  assertEquals({ value: 'sync-value', done: false }, await iter.next('n'));
+  assertEquals([
+    {
+      method: 'throw',
+      sent: 'not-a-JSReceiver',
+      done: false
+    },
+    {
+      method: 'next',
+      sent: 'n',
+      value: 'sync-value',
+      done: false
+    }
+  ], log);
+
+  // Let nextValue be IteratorValue(nextResult).
+  // IfAbruptRejectPromise(nextValue, promiseCapability).)
+  iter = %CreateAsyncFromSyncIterator({
+    next() { return { get value() { throw "BadValue!" }, done: false }; }
+  });
+  try {
+    await iter.next();
+    assertUnreachable('Expected `iter.next()` to throw, but did not throw');
+  } catch (e) {
+    assertEquals('BadValue!', e);
+  }
+
+  // Let nextDone be IteratorComplete(nextResult).
+  // IfAbruptRejectPromise(nextDone, promiseCapability).
+  iter = %CreateAsyncFromSyncIterator({
+    next() { return { value: undefined, get done() { throw "BadValue!" } }; }
+  });
+  try {
+    await iter.next();
+    assertUnreachable('Expected `iter.next()` to throw, but did not throw');
+  } catch (e) {
+    assertEquals('BadValue!', e);
+  }
+
+  // IfAbruptRejectPromise(returnResult, promiseCapability).
+  // Let returnValue be IteratorValue(returnResult).
+  iter = %CreateAsyncFromSyncIterator({
+    return() { return { get value() { throw "BadValue!" }, done: false }; }
+  });
+  try {
+    await iter.return();
+    assertUnreachable('Expected `iter.return()` to throw, but did not throw');
+  } catch (e) {
+    assertEquals('BadValue!', e);
+  }
+
+  // IfAbruptRejectPromise(returnValue, promiseCapability).
+  // Let returnDone be IteratorComplete(returnResult).
+  iter = %CreateAsyncFromSyncIterator({
+    return() { return { value: undefined, get done() { throw "BadValue!" } }; }
+  });
+  try {
+    await iter.return();
+    assertUnreachable('Expected `iter.return()` to throw, but did not throw');
+  } catch (e) {
+    assertEquals('BadValue!', e);
+  }
+
+  // IfAbruptRejectPromise(throwResult, promiseCapability).
+  // Let throwValue be IteratorValue(throwResult).
+  iter = %CreateAsyncFromSyncIterator({
+    throw() { return { get value() { throw "BadValue!" }, done: false }; }
+  });
+  try {
+    await iter.throw();
+    assertUnreachable('Expected `iter.throw()` to throw, but did not throw');
+  } catch (e) {
+    assertEquals('BadValue!', e);
+  }
+
+  // IfAbruptRejectPromise(throwValue, promiseCapability).
+  // Let throwDone be IteratorComplete(throwResult).
+  iter = %CreateAsyncFromSyncIterator({
+    throw() { return { value: undefined, get done() { throw "BadValue!" } }; }
+  });
+  try {
+    await iter.throw();
+    assertUnreachable('Expected `iter.throw()` to throw, but did not throw');
+  } catch (e) {
+    assertEquals('BadValue!', e);
+  }
+})().catch(function(error) {
+  testFailed = true;
+  testFailure = error;
+});
+
+%RunMicrotasks();
+if (testFailed) {
+  throw testFailure;
+}
+
+(function ExtractedAsyncFromSyncIteratorMethods() {
+  // Async-from-Sync iterator methods can be extracted via function.caller.
+  // TODO(caitp): test extracted `throw` method using yield* in async generator.
+  let extractor = [0, 1, 2, 3, 4,5,6,7,8,9];
+  let extractedNext;
+  let extractedReturn;
+
+  extractor[Symbol.iterator] = function() {
+    let it = [][Symbol.iterator].call(extractor);
+    let origNext = it.next, origThrow = it.throw, origReturn = it.return;
+    function extractNext() {
+      extractedNext = extractNext.caller;
+      return origNext;
+    }
+    function extractReturn() {
+      extractedReturn = extractReturn.caller;
+      return origReturn;
+    }
+    Object.defineProperties(it, {
+      "next": { get: extractNext, configurable: true },
+      "return": { get: extractReturn, configurable: true }
+    });
+    return it;
+  };
+
+  async function f() {
+    let i;
+    let it = extractor[Symbol.iterator]();
+    for await (let x of it) break;
+    for await (let x of it) return "x";
+  }
+
+  // Cycle through `f` to extract iterator methods
+  f().catch(function() { assertUnreachable("No error should have occurred"); });

[neis, 2017/02/21 12:48:09]

This assertUnreachable would go unnoticed.

[caitp, 2017/02/21 14:36:52]

Good point, using %AbortJS instead.

+  %RunMicrotasks();
+
+  assertEquals(typeof extractedNext, "function");
+  assertThrowsAsync(() => extractedNext.call(undefined), TypeError);
+  assertThrowsAsync(() => extractedNext.call(1), TypeError);
+
+  assertEquals(typeof extractedReturn, "function");
+  assertThrowsAsync(() => extractedReturn.call(undefined), TypeError);
+  assertThrowsAsync(() => extractedReturn.call(1), TypeError);
+})();