downgraded component: not possible to have two-way binding and change event on the same output / emitter

[FDIM]

I'm submitting a...

[ ] Regression (a behavior that used to work and stopped working in a new release)
[x] Bug report  
[x] Feature request
[ ] Documentation issue or request
[ ] Support request => Please do not submit support request here, instead see https://github.com/angular/angular/blob/master/CONTRIBUTING.md#question

Current behavior

It seems that it is not possible to have 2-way-binding and listen to the same change event when angular 5 component is downgraded.

Expected behavior

Two way binding should work and the provided expression (if any) should be evaluated.

Minimal reproduction of the problem with instructions

• open https://stackblitz.com/edit/ngupgradestatic-playground-o2xraa?file=index.html
• click the first increment button and observe that only the value from event changes even though there is two-way binding to value property
• clicking second increment button only updates counter as there is no additional binding to countChange output (all good)
• after clicking 3rd button you can see that both values update (all good)

What is the motivation / use case for changing the behavior?

To keep downgraded component behavior similar to normal usage in other angular 5 component

Environment

Angular version: 5.2.x

Browser: any

[gkalpak]

This is a valid issue. It happens, because of the if elses we have here, which only allow one form of the output binding and ignore the rest. Instead, we should collect all output bindings.

@FDIM, would you be interested in working on this?

[FDIM]

@gkalpak I am :) I'll try come up with a fix in our local copy of the library (we have it due to another issue) and I'll prepare a PR after that. So hopefully some time this week.

EDIT: I already got a fix in my fork: https://github.com/FDIM/angular/tree/bugfix/two-way-binding-and-expressions-on-same-output
I'll prepare the PR a bit later in the evening (well at least in Europe)

[gkalpak]

From a quick look, the fix looks good 👍 (Make sure to include some tests on the PR 😉)
Feel free to ping me if you get stack.

[FDIM]

After fiddling with some white space (linter is very picky!) - I think the PR is ready.

I also updated existing test case and seen it break without my changes and pass with the fix.

[gkalpak]

Thx! I'll take a look shortly.
(Pro tip: gulp format fixes linting issues 😉)

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