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GIT-REMOTE-HG(1)   GIT-REMOTE-HG(1)

NAME

git-remote-hg - bidirectional bridge between Git and Mercurial

SYNOPSIS

git clone hg::<hg repository>

DESCRIPTION

This tool allows you to transparently clone, fetch and push to and from Mercurial repositories as if they were Git ones.

To use it you simply need to use the "hg::" prefix when specifying a remote URL (e.g. when cloning).

EXAMPLE

CONFIGURATION

If you want to see Mercurial revisions as Git commit notes:

% git config core.notesRef refs/notes/hg

If you are not interested in Mercurial permanent and global branches (aka. commit labels):

% git config --global remote-hg.track-branches false

With this configuration, the branches/foo refs won’t appear.

If you want the equivalent of hg clone --insecure:

% git config --global remote-hg.insecure true

If you want git-remote-hg to be compatible with hg-git, and generate exactly the same commits:

% git config --global remote-hg.hg-git-compat true

If you would like (why?) the old behaviour (export capability) where various limitations apply:

% git config --global remote-hg.capability-push false

In the new behaviour, performing a git push will make git search for and detect file rename and copy and turn this into Mercurial commit metadata. To tweak how this detection happens, e.g. have it search even more:

% git config --global remote-hg.fast-export-options '-M -C -C'

The default otherwise is simply -M -C. See also e.g. git-log(1) manpage for more details on the options used to tweak this.

As the old refs/hg/... are actually an implementation detail, they are now maintained not so visibly. If that, however, would be preferred:

% git config --global remote-hg.show-private-refs true

Use of shared marks files is the default in a new repo, but can also be enabled for an existing repo:

% git config --global remote-hg.shared-marks true

Note that one should perform a fetch from each remote to properly complete the conversion to shared marks files.

Mercurial name(s) (of a branch or bookmark) that are not a valid git refname, can be ignored by configuring a suitable regular expression, e.g. avoiding the invalid ~

% git config --global remote-hg.ignore-name ~

NOTES

Remember to run git gc --aggressive after cloning a repository, specially if it’s a big one. Otherwise lots of space will be wasted.

The oldest version of Mercurial supported is 1.9. For the most part 1.8 works, but you might experience some issues.

Pushing branches

To push a Mercurial named branch, you need to use the "branches/" prefix:

% git checkout branches/next
# do stuff
% git push origin branches/next

All the pushed commits will receive the "next" Mercurial named branch.

Note: Make sure you don’t have remote-hg.track-branches disabled.

Cloning HTTPS

The simplest way is to specify the user and password in the URL:

You can also use the schemes extension:

[auth]
bb.prefix = https://bitbucket.org/user/
bb.username = user
bb.password = password

Finally, you can also use the keyring extension.

CAVEATS

The only major incompatibility is that Git octopus merges (a merge with more than two parents) are not supported.

Mercurial branches and bookmarks have some limitations of Git branches: you can’t have both dev/feature and dev (as Git uses files and directories to store them).

Multiple anonymous heads (which are useless anyway) are not supported; you would only see the latest head.

Closed branches are not supported; they are not shown and you can’t close or reopen. Additionally in certain rare situations a synchronization issue can occur (Bug #65).

TECHNICAL DISCUSSION

As git-remote-hg is a developer tool after all, it might be interesting to know a bit about what is going on behind the scenes, without necessarily going into all the details.

So let’s first have a look in the .git/hg directory, which typically contains a subdirectory for each remote Mercurial repo alias, as well as a .hg subdirectory. If the Mercurial repo is a local one, it will (again typically) only contain a marks-git and a marks-hg file. If the repo is a remote one, then the clone contains, well, a local clone of the remote. However, all these clones share storage through the .hg directory mentioned previously (so they do not add up separately). During a fetch/push, the local (proxy) repo is used as an intermediate stage. If you would also prefer such an intermediate stage for local repos, then setting the environment variable GIT_REMOTE_HG_TEST_REMOTE will also use a proxy repo clone for a local repo.

As for the marks files, marks-git is created and used by git-fast-export and git-fast-import and contains a mapping from mark to commit hash, where a mark is essentially a plain number. marks-hg similarly contains a (JSON) based mapping between such mark and hg revision hash. Together they provide for a (consistent) view of the synchronization state of things.

When operating with shared-marks files, the marks-git and marks-hg files are shared among all repos. As such, they are then found in the .git/hg directory (rather than a repo subdirectory). As there is really only one hg repository (the shared storage "union bag" in .git/hg/.hg), only 1 set of marks files should track the mapping between commit hash and revision hash. Each individual remote then only adds some metadata (e.g regarding heads).

Upon a fetch, the helper uses the marks-hg file to decide what is already present and what not. The required parts are then retrieved from Mercurial and turned into a git-fast-import stream as expected by import capability of gitremote-helpers(1).

Upon a push, the helper has specified the push capability in the new approach, and so git will provide a list of refspecs indicating what should go where. If the refspecs indicates a remote delete, it is performed appropriately the Mercurial way. If it is a regular push, then git-fast-export is invoked (using the existing marks-git) and the stream is processed and turned into Mercurial commits (along with bookmarks, etc). If the refspec specifies a src:dest rename, then the requested remote refname is tracked accordingly. If a dry-run is requested, no remote is touched and no (marks) state of the run is retained.

02/09/2019