[Webkit-unassigned] [Bug 160857] New: Promise API does not fully process microtask checkpoint: spec violation

[bugzilla-daemon at webkit.org]

https://bugs.webkit.org/show_bug.cgi?id=160857

            Bug ID: 160857
           Summary: Promise API does not fully process microtask
                    checkpoint: spec violation
    Classification: Unclassified
           Product: WebKit
           Version: WebKit Nightly Build
          Hardware: Unspecified
                OS: Unspecified
            Status: NEW
          Severity: Normal
          Priority: P2
         Component: JavaScriptCore
          Assignee: webkit-unassigned at lists.webkit.org
          Reporter: a at totic.org

Created attachment 286076
  --> https://bugs.webkit.org/attachment.cgi?id=286076&action=review
This file will demonstrate the bug

Promises microtask queue does not fully process microtasks queued while microtask is running.
According to spec, microtask queue should loop until it is empty.

Why is this bug important?
Promises are often used by developers for scheduling. When they are,
developers assume Promise.resolve() means "execute this function right 
after this script returns". This bug violates this promise.

FF/Edge/Chrome get this right. It'd be great if all browsers worked the same.

Example:

Promise.resolved()
 .then(() => {
   console.log("Promise 1");
   return Promise.resolve();
 })
 .then(() => {
   console.log("Promise 2");
 }
window.setTimeout(function() {
  console.log('timeout');
}, 0);

Might also be related to Bug #140043. I've attached a test case.

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