[users at bb.net] Trigger build via tag on old revision?

[John W.]

I'm still figuring out my preffered workflow here, but what I currently
have in mind goes like this:

    1. I manually tag a revision as "rc1" (or somesuch)
    2. BuildBot notices this tag, and kicks off the packaging process,
       to build a release candidate for that revision.

However, I'm not sure how to express that in BuildBot's config.

My initial idea was to use a ChangeFilter, but I think that won't work
because of the following situation:

	1. I commit revision X
	2. BuildBot scheduler sees X, but skips it because it's not tagged
	3. I commit revision Y, which adds the "rc1" tag to X
	   (I'm using Mercurial so this is just editing the .hgtags file)
	4. scheduler sees Y, but Y is *also* not tagged as "rc1", so it is
	   skipped.

Basically, my worry is that by the time the tag is applied to X,
BuildBot has already decided not to build that change.

Even if I make the scheduler smart enough to notice that Y is actually
adding a tag for X, is there a way to have it trigger a build for that
other revision (X, rather than Y)? The ChangeFilter stuff only seems to
provide a yes/no response, not "build X instead."

Is that a real concern, or do I misunderstand?

Is there a better way to accomplish what I'm describing?

Thanks
-John