How do you find the parent of a named mercurial branch?

Question

At some point in time you have a mercurial named branch, let's call it, default, and you create a named branch from default, let's call it, foo, and you make some commits on foo. That work kind of looks like this:

hg update default hg branch foo hg commit -m "created branch foo" # work, work hg commit # work work hg commit 

Meanwhile others are making commits on default. Now someone else is told to do some work on foo and they want to see if and what might need to be merged from foo's parent branch. If they knew that foo came from default they could just run:

hg merge --preview default 

but they don't know where foo came from. They could run:

hg glog 

or fire up tortoisehg and trace the line back to foo's parent, but is there a command they could run that would just tell them the parent branch of foo?

Answer 1

Thanks for the revset examples. I fiddled around and found this solution that I kind of like:

hg log -r "parents(min(branch(foo)))" 

which will print the revision that the first commit on the foo branch was based on. You can look for the branch (or lack thereof indicating the default branch) in that changeset and that is the parent branch of foo (at least the way parent branch is defined in the question).

But I have this nagging feeling...parents() could return more than one changeset. Could the first commit on a branch ever have two parents? I can't think of how that could happen.

Answer 2

You could use revsets to find this information, provided you're using Mercurial v1.6.0 or later. For example:

hg update BRANCH hg log -r "max(ancestors(BRANCH) and not branch(BRANCH))" 

this will print out a single revision, the "branch point" of your feature branch.