Mercurial: what's the tag containing this changeset?

In software development, you often need to know: when was this feature released? in which releases was this changeset included?

Typical example is: you're debugging a problem, you find out what's the changeset introducing it, now you want to know when that changeset was firstly released (i.e. included in a tag) - how to do that?

hg log -r "cset:: and tag()"

where cset is the changeset you're looking for.

So know I know that Sphinx new way to load searchindex.js was introduced in the this changeset, and released for the first time in 1.0b2:

$ hg log -r "423faa03c908:: and tag()"
changeset:   2261:b494009dccf1
tag:         1.0b2
user:        Georg Brandl <georg@python.org>
date:        Sun May 30 19:52:08 2010 +0200
summary:     Release preparation for 1.0b2.
...

awesome!

PS: why did I need to know that? because Matplotlib is still using the old way, but Debian needs the new one.

Mercurial: how to completely remove a named branch

I like so much the git feature branch workflow, that in the early days of development on Python with Mercurial I created some named branches; well, that is something you should not do.

In Mercurial, the changeset contains the branch name, so you cannot develop on a separated (named) branch and then merge on default and hope that branch goes away, because it will stay.

What do I do now? Python Mercurial repository is quite big (around 200Megs) so I wanted to avoid to re-check it out. Thanks to the help of the folks on #mercurial (on freenode IRC network) I found my solution: strip the branch!

Please note that strip is dangerous. Use it only as last resort, and mind you can lose data with it. That said, it's a very powerful tool :) My main aim was to remove completely those named branches, leave no traces, and lose the changes I made on them. Another important aspect is that I didn't merged those branches on default.

So, how to get rid of a named branch:

$ hg strip "branch(${BRANCHNAME})"

and re-iterate for all the branches you have, that's it. Now, to be completely sure they were removed and no spurious changes are in the repository, you can:

$ hg pull -u
$ hg outgoing

and if it says "no changes found" you're sure that those branches are really gone.