git_handler: don't store rename source if branch info is stored Consider a Mercurial commit with hash 'h1'. Originally, if the only Mercurial field stored is the branch info (which is stored in the commit message rather than as an extra field), we'd store the rename source explicitly as a Git extra field -- let's call the original exported hash 'g1'. In Git, some operations throw all extra fields away. (One such example is a rebase.) If such an operation happens, we'll be left with a frankencommit with the branch info but without the rename source. Let's call this hash 'g2'. For a setup where Git is the source of truth, let's say that this 'g2' frankencommit is what gets pushed to the server. When 'g2' is subsequently imported into Mercurial, we'd look at the fact that it contains a Mercurial field in the commit message and believe that it was a legacy commit from the olden days when all info was stored in the commit message. In that case, in an attempt to preserve the hash, we wouldn't store any extra rename source info, resulting in 'h1'. Then, when the commit is re-exported to Git, we'd add the rename source again and produce 'g1' -- and thus break bidirectionality. Prevent this situation by not storing the rename source if we're adding branch info to the commit message. Then for 'h1' we export as 'g2' directly and never produce 'g1'. What happens if we not only need to store branch info but also other extra info, like renames? For 'h1' we'd produce 'g1', then it'd be rewritten on the Git side to 'g2' throwing away all that extra information. 'g2' being subsequently imported into Mercurial would produce a new hash, say 'h2'. That's fine because the commit did get rewritten in Git. We unfortunately wouldn't perform rename detection thinking that the commit is from Mercurial and had no renames recorded there, but when the commit is re-exported to Git we'd export it to 'g2' again. This at least preserves bidirectionality.

The short version:
 * Patches should have a good summary line for first line of commit message
 * Patches should be sent to the Google Group[0]
 * Patch needs to do exactly one thing
 * testsuite passes

The longer version:

We use a variant of Mercurial's own contribution
system. http://mercurial.selenic.com/wiki/ContributingChanges contains
their full guidelines. Key differences are (by rule number):

 1. For hg-git, I'm not strict about the "topic: a few words" format
    for the first line, but I do insist on a sensible summary as the
    first line of your commit
 2. We don't require use of issueNNN for bug fixes (we have no robot)
 3. Use the hg-git google group
 10. We use mostly pep8 style. The current codebase is a mess, but new
     code should be basically pep8.

0: Pull requests are generally not noticed more than once every few
months. If you do a pull request, I'm still going to expect you to
have a clean history, and to be willing to rework history so it's
clean before I push the "merge" button.