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git-svn: Document branches with at-sign(@).

git svn sometimes creates branches with an at-sign in the name
(branchname@revision). These branches confuse many users and it is a FAQ
why they are created. Document when git svn creates them.

Signed-off-by: Sebastian Leske <sebastian.leske@sleske.name>
Acked-by: Eric Wong <normalperson@yhbt.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
This commit is contained in:
Sebastian Leske 2012-11-30 08:16:30 +01:00 committed by Junio C Hamano
parent c2999adcd5
commit d658835c19

@ -823,6 +823,52 @@ inside git back upstream to SVN users. Therefore it is advised that
users keep history as linear as possible inside git to ease
compatibility with SVN (see the CAVEATS section below).
HANDLING OF SVN BRANCHES
------------------------
If 'git svn' is configured to fetch branches (and --follow-branches
is in effect), it sometimes creates multiple git branches for one
SVN branch, where the addtional branches have names of the form
'branchname@nnn' (with nnn an SVN revision number). These additional
branches are created if 'git svn' cannot find a parent commit for the
first commit in an SVN branch, to connect the branch to the history of
the other branches.
Normally, the first commit in an SVN branch consists
of a copy operation. 'git svn' will read this commit to get the SVN
revision the branch was created from. It will then try to find the
git commit that corresponds to this SVN revision, and use that as the
parent of the branch. However, it is possible that there is no suitable
git commit to serve as parent. This will happen, among other reasons,
if the SVN branch is a copy of a revision that was not fetched by 'git
svn' (e.g. because it is an old revision that was skipped with
'--revision'), or if in SVN a directory was copied that is not tracked
by 'git svn' (such as a branch that is not tracked at all, or a
subdirectory of a tracked branch). In these cases, 'git svn' will still
create a git branch, but instead of using an existing git commit as the
parent of the branch, it will read the SVN history of the directory the
branch was copied from and create appropriate git commits. This is
indicated by the message "Initializing parent: <branchname>".
Additionally, it will create a special branch named
'<branchname>@<SVN-Revision>', where <SVN-Revision> is the SVN revision
number the branch was copied from. This branch will point to the newly
created parent commit of the branch. If in SVN the branch was deleted
and later recreated from a different version, there will be multiple
such branches with an '@'.
Note that this may mean that multiple git commits are created for a
single SVN revision.
An example: in an SVN repository with a standard
trunk/tags/branches layout, a directory trunk/sub is created in r.100.
In r.200, trunk/sub is branched by copying it to branches/. 'git svn
clone -s' will then create a branch 'sub'. It will also create new git
commits for r.100 through r.199 and use these as the history of branch
'sub'. Thus there will be two git commits for each revision from r.100
to r.199 (one containing trunk/, one containing trunk/sub/). Finally,
it will create a branch 'sub@200' pointing to the new parent commit of
branch 'sub' (i.e. the commit for r.200 and trunk/sub/).
CAVEATS
-------