Silent failure in 4.0 branch when merging streams with distinct destinations

[epong-yu]

Hi. In the 4.0 branch, I'm having trouble merging two streams that are distinctly piped to destinations. Consider this gulpfile:

var gulp = require('gulp');
var es = require('event-stream');

function test() {
  var stream1 = gulp.src('./file1')
        .pipe(gulp.dest('./dist/foo'));
  var stream2 = gulp.src('./file2')
        .pipe(gulp.dest('./dist/bar'));

  return es.merge(stream1, stream2);
}

gulp.task('default', test);

Running gulp gets me:

[14:31:15] Using gulpfile ~/src/gulp-test/gulpfile.js
[14:31:15] Starting 'default'...

And exits. The return code is 0, and nothing seems to show up with node-inspector. The files actually get copied:

dist
├── bar
│   └── file2
└── foo
    └── file1

But the task fails, and gulp quits; if I chain another task in series, it doesn't run. If I remove the destinations and pipe the merged stream to a common destination, the task succeeds.

I think better error management is being addressed elsewhere, so this issue is just about clarifying or addressing the behavior of these merged streams.

Not sure if I've fundamentally misunderstood how these streams behave, but this recipe expresses the behavior I'm trying to achieve.

[phated]

EventStream is no longer supported because it is streams1, won't be updated and its merge method isn't a real stream. The open ticket for this is gulpjs/async-done#19

[phated]

We suggest switching to merge-stream for this use case.