Interest in integrating hg-git into Mercurial

[Joerg Sonnenberger]

On Thu, Aug 01, 2019 at 10:01:08AM -0700, Gregory Szorc wrote:
> Is there any interest in integrating hg-git (or hg-git functionality) into
> the Mercurial distribution as an officially supported extension?

We've been discussing this topic a bit during the Leipzig mini-sprint
now. I think there are three different cases for hg <-> git interaction
to be considered:

(1) Migrating a repository from git to hg, potentially multiple times.
(2) Migrating a repository from hg to git, potentially multiple times.
(3) Two-way synchronisation between hg and git.

The requirements in the the first two cases are quite different from the
third and it is useful to consider them standalone for that reason. Both
cases are addressed by supporting the fastimport format, either reading
or writing. I've needed a couple of changes for the hg-fastimport
extension to work well, but it is an integral part of the NetBSD
conversion chain right now. Changes are primarily dealing with non-UTF8
input (something "real" git shouldn't show) and smarter blob handling
(partially due to the way Fossil output is structured). I'm currently
looking at the fastexport (https://repo.or.cz/w/fast-export.git) tool,
but the performance looks mostly reasonable. One-way mirroring is much
simpler, because it doesn't have to try to provide stable mappings for
roundtrip consistency, the tooling just has to ensure that the mapping
is deterministic, so that rerunning the tool will result in identical
output. I believe having fastimport support in hgext would be a win,
without the need for vendoring dulwich etc.

Joerg