[regression] dojo/_base/Deferred.when (via dojo/when) coerces to promise when an errback but no callback is passed

[Kenneth G. Franqueiro]

In Dojo 1.8, dojo/when has a feature (shared with other implementations) where simply passing an immediate value to it will yield a promise resolving to that value.

Unfortunately, due to how this feature is implemented, it leads to a bug, and a regression in dojo/_base/Deferred.when which now relies on dojo/when. Previously in 1.7, you could call Deferred.when(something, null, errback) to pass only an error handler for handling; if the value isn't a promise and no callback is provided, it would return the value straight through. If you do this in 1.8, however, it ends up wrapping the value in a promise, because of the code at ​https://github.com/dojo/dojo/blob/1.8.3/when.js#L39-43.

If we go about fixing this, also be wary of ​https://github.com/dojo/dojo/blob/1.8.3/when.js#L50 which currently assumes that if any of the 3 callbacks are defined, then we have a promise (which wouldn't necessarily be the case).

[Kenneth G. Franqueiro]

Proposed patch against 1.8 branch

[Kenneth G. Franqueiro]

I've attached a patch which I think resolves the issue without any side-effects. All when tests pass (including one I added to test this issue). Would like Mark to look at it if he gets a chance... it'd certainly be good to get this fixed for 1.9 as well.

[Mark Wubben]

Patch looks good. Please merge it, I have no clue how to deal with SVN anymore.

[Kenneth G. Franqueiro]

Thanks Mark, I'll work on merging this into 1.8 branch and trunk later today.

[Kenneth G. Franqueiro]

In [30605]:

Revise conditions under which dojo/when creates a promise; fixes #16667 in trunk !strict

[Kenneth G. Franqueiro]

In [30606]:

Revise conditions under which dojo/when creates a promise; fixes #16667 in 1.8 branch !strict