How to handle merges with hgsubversion?

Question

I am trying to contribute to a project that uses Subversion. I used Mercurial and its hgsubversion extension to clone the repo. My work takes place on a feature branch.

How do I keep the feature branch up to date with stuff that happens on the default branch (hg speak) aka the trunk (svn speak)?

So I used hg up feature to update to the feature branch, then hg pull which gave me changesets on the default branch. So I did hg merge default, the committed the merge, then tried hg push to send my changesets to Subversion. And Mercurial said: "Sorry, can't find svn parent of a merge revision."

Answer 1

I have finally figured out how to get my repository un-wedged after an event like that described in the question, so that I can continue work without having to re-clone the parent repository (which is, obviously, a quite slow operation when you are pulling from Subversion!). If the "tip" of Subversion outruns you so that you cannot push any more, just make sure that you have the built-in "rebase" extension activated in your Mercurial through a $HOME/.hgrc line like this:

[extensions]
rebase =

And then you should be able to run this command when your repository gets wedged:

$ hg rebase --svn

If I understand this correctly, it dissolves your current branch that has taken you away from Subversion HEAD, and rebuilds it atop the branch "tip" in Mercurial that corresponds to the HEAD in Subversion. From there, you can keep working and successfully do pushes again. It has always worked for me so far; let me know if you run into any problems!

Answer 2

Mercurial as a few different branching modes: http://stevelosh.com/blog/2009/08/a-guide-to-branching-in-mercurial/

The one you're describing is 'named branches', which is the most popular when you're working with a repo that's accessed only via mercurial (or hg-git).

However, when you're using hg-subversion so that you're pushing changes to/from subversion, which only nominally has branches, you're better off keeping all of your mercurial changes in the 'default' named branch, and using the 'clones and branches' pattern (which I prefer anyway).

Specifically, that message Sorry, can't find svn parent of a merge revision. isn't a descendant of a revision that has a direct match in subversion.

Were I you, I'd reclone from svn, and then move my work into that repo's 'default' branch with the 'transplant' command (packaged extension). If you want multiple features in parallel w/ hg-subversion use separate clones (they're so cheap), as it's more in line with how subversion thinks about branches.