Warn if Sizzle isn't the most recent tag during a release

[dmethvin]

Or something. Our Sizzle was way out of date for the beta1 releases but there was no noise about it.

[timmywil]

Sizzle can be purposefully ahead of jQuery, and that's okay. It should not be inexorably forced upon a release. However, under no circumstances should jQuery blindly include the latest master of Sizzle. There are many reasons for this. Here are a couple:

1. In Sizzle, tags are checkmarks indicating that all tests pass (this is reason enough).
2. The latest master of Sizzle is not always releasable. We merge pull requests, uncover errors, experiment with features, expose functions and properties. Sometimes it's not ready for jQuery. Sizzle should be allowed the freedom to continue development on master without worrying about infecting jQuery or other projects that include Sizzle. That said, we _can_ adopt the convention to not create a new tag in Sizzle unless it is unequivocally primed for jQuery inclusion. This would make things simpler for jQuery releases.

[dmethvin]

I agree with your logic timmywil, and as you said in IRC the main problem is that we made ​several commits without any corresponding jQuery ticket that would have pulled them over.

If we had discovered this during a release the right procedure would have been to stop the release and pull in Sizzle, then do unit tests. I just wondered if there is anything we need to do in addition during day-to-day work to ensure we don't get out of sync again.

[timmywil]

Perhaps we should replicate relevant Sizzle issues with jQuery tickets. It's appropriate that Sizzle have its own issues, but any issue that affects jQuery should correspond to a jQuery ticket. That ticket would then be closed by an "Update Sizzle" commit.

[gibson042]

dmethvin: I didn't realize until seeing it spelled out here that we were previously talking past each other a little bit. jQuery should always be able to reference the latest Sizzle tag, not commit (and should also be free to use an older tag, but I can't remember any situation when we would have wanted to).

timmywil:

any issue that affects jQuery should correspond to a jQuery ticket. That ticket would then be closed by an "Update Sizzle" commit.

I agree. #14901 was in fact such a ticket; it was just closed prematurely because there were also changes required in the jQuery source.

[dmethvin]

I think I confused things a bit, I *was* originally thinking last commit but agree it should be last tag. Having jquery-release give a non-fatal warning about there being commits on Sizzle past the last tag would be "thing that makes you go hmmm" and worth thinking about before proceeding, but not a fatal thing.

[timmywil]

The work is ​completed, but the commit is dependent on a ​pull request on jquery-release.

[Timmy Willison]

Release: ensure Sizzle is the latest tag

Fixes #14915

Changeset: 1d931068d30b6a516b883cf7f420606de21eab68