remote: separate the concept of push and fetch mirrors

git-remote currently has one option, "--mirror", which sets
up mirror configuration which can be used for either
fetching or pushing. It looks like this:

  [remote "mirror"]
    url = wherever
    fetch = +refs/*:refs/*
    mirror = true

However, a remote like this can be dangerous and confusing.
Specifically:

  1. If you issue the wrong command, it can be devastating.
     You are not likely to "push" when you meant to "fetch",
     but "git remote update" will try to fetch it, even if
     you intended the remote only for pushing. In either
     case, the results can be quite destructive. An
     unintended push will overwrite or delete remote refs,
     and an unintended fetch can overwrite local branches.

  2. The tracking setup code can produce confusing results.
     The fetch refspec above means that "git checkout -b new
     master" will consider refs/heads/master to come from
     the remote "mirror", even if you only ever intend to
     push to the mirror. It will set up the "new" branch to
     track mirror's refs/heads/master.

  3. The push code tries to opportunistically update
     tracking branches. If you "git push mirror foo:bar",
     it will see that we are updating mirror's
     refs/heads/bar, which corresponds to our local
     refs/heads/bar, and will update our local branch.

To solve this, we split the concept into "push mirrors" and
"fetch mirrors". Push mirrors set only remote.*.mirror,
solving (2) and (3), and making an accidental fetch write
only into FETCH_HEAD. Fetch mirrors set only the fetch
refspec, meaning an accidental push will not force-overwrite
or delete refs on the remote end.

The new syntax is "--mirror=<fetch|push>". For
compatibility, we keep "--mirror" as-is, setting up both
types simultaneously.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 13 insertions, 6 deletions

diff --git a/Documentation/git-remote.txt b/Documentation/git-remote.txt
index c258ea48d..79e38fedd 100644
--- a/Documentation/git-remote.txt
+++ b/Documentation/git-remote.txt
@@ -10,7 +10,7 @@ SYNOPSIS
 --------
 [verse]
 'git remote' [-v | --verbose]
-'git remote add' [-t <branch>] [-m <master>] [-f] [--tags|--no-tags] [--mirror] <name> <url>
+'git remote add' [-t <branch>] [-m <master>] [-f] [--tags|--no-tags] [--mirror=<fetch|push>] <name> <url>
 'git remote rename' <old> <new>
 'git remote rm' <name>
 'git remote set-head' <name> (-a | -d | <branch>)
@@ -67,11 +67,18 @@ multiple branches without grabbing all branches.
 With `-m <master>` option, `$GIT_DIR/remotes/<name>/HEAD` is set
 up to point at remote's `<master>` branch. See also the set-head command.
 +
-In mirror mode, enabled with `\--mirror`, the refs will not be stored
-in the 'refs/remotes/' namespace, but in 'refs/heads/'.  This option
-only makes sense in bare repositories.  If a remote uses mirror
-mode, furthermore, `git push` will always behave as if `\--mirror`
-was passed.
+When a fetch mirror is created with `\--mirror=fetch`, the refs will not
+be stored in the 'refs/remotes/' namespace, but rather everything in
+'refs/' on the remote will be directly mirrored into 'refs/' in the
+local repository. This option only makes sense in bare repositories,
+because a fetch would overwrite any local commits.
++
+When a push mirror is created with `\--mirror=push`, then `git push`
+will always behave as if `\--mirror` was passed.
++
+The option `\--mirror` (with no type) sets up both push and fetch
+mirror configuration. It is kept for historical purposes, and is
+probably not what you want.
 
 'rename'::