Gulp complains that a task did not finish when a parallel task fails

[MLoughry]

What were you expecting to happen?

In gulp 4, when using gulp.parallel, I expect that all tasks to complete, even if one task fails. The API documentation is ambiguous:

When the returned function is executed, the tasks or functions will be executed in parallel, all being executed at the same time. If an error occurs, all execution will complete.

I'm not sure if that means "all tasks will finish execution", or "all execution will be cut short".

Either way, if the latter is the intended behavior, gulp should not complain that a task did not signal async completion.

What actually happened?

The non-erroring task did not complete, and gulp complained that the non-erroring task did not signal async completion

PS D:\vso\gulp-parallel> gulp a
[16:37:06] Using gulpfile D:\vso\gulp-parallel\gulpfile.js
[16:37:06] Starting 'a'...
Starting work in task "a"
Finished work in task "a"
[16:37:07] Finished 'a' after 1 s

PS D:\vso\gulp-parallel> gulp ab
[16:37:10] Using gulpfile D:\vso\gulp-parallel\gulpfile.js
[16:37:10] Starting 'ab'...
[16:37:10] Starting 'a'...
[16:37:10] Starting 'b'...
Starting work in task "a"
[16:37:10] 'b' errored after 1.6 ms
[16:37:10] Error: Task "b" failed!
    at formatError (C:\Users\miclo\AppData\Local\Yarn\config\global\node_modules\gulp-cli\lib\versioned\^4.0.0\format-error.js:20:10)
    at Gulp.<anonymous> (C:\Users\miclo\AppData\Local\Yarn\config\global\node_modules\gulp-cli\lib\versioned\^4.0.0\log\events.js:31:15)
    at Gulp.emit (events.js:132:15)
    at Gulp.emit (domain.js:421:20)
    at Object.error (D:\vso\gulp-parallel\node_modules\undertaker\lib\helpers\createExtensions.js:61:10)
    at handler (D:\vso\gulp-parallel\node_modules\now-and-later\lib\map.js:46:14)
    at f (D:\vso\gulp-parallel\node_modules\once\once.js:25:25)
    at f (D:\vso\gulp-parallel\node_modules\once\once.js:25:25)
    at tryCatch (D:\vso\gulp-parallel\node_modules\async-done\index.js:24:15)
    at done (D:\vso\gulp-parallel\node_modules\async-done\index.js:40:12)
[16:37:10] 'ab' errored after 5.64 ms
[16:37:10] The following tasks did not complete: a
[16:37:10] Did you forget to signal async completion?

Please post a sample of your gulpfile (preferably reduced to just the bit that's not working)

const gulp = require('gulp');

gulp.task('a', done => {
    console.log('Starting work in task "a"');
    setTimeout(() => {
        console.log('Finished work in task "a"');
        done();
    }, 1000);
});

gulp.task('b', done => {
    done('Task "b" failed!');
});

gulp.task('ab', gulp.parallel('a', 'b'));

What version of gulp are you using?
4.0.0

What versions of npm and node are you using?

PS D:\vso\gulp-parallel> npm --version
5.6.0
PS D:\vso\gulp-parallel> node --version
v9.7.1

[phated]

The documentation for gulp 4 is not complete. Tasks aren't guaranteed to be completed unless you use the --continue command line flag and the process is forcibly exited upon error.

[MLoughry]

Ok, but can gulp not give a false positive about truncated tasks not correctly signaling async completion, at least?

[phated]

@MLoughry see above for a linked issue referenced