Git 2.0: git svn: Set default --prefix='origin/' if --prefix is not given

git-svn by default puts its Subversion-tracking refs directly in
refs/remotes/*. This runs counter to Git's convention of using
refs/remotes/$remote/* for storing remote-tracking branches.

Furthermore, combining git-svn with regular git remotes run the risk of
clobbering refs under refs/remotes (e.g. if you have a git remote
called "tags" with a "v1" branch, it will overlap with the git-svn's
tracking branch for the "v1" tag from Subversion.

Even though the git-svn refs stored in refs/remotes/* are not "proper"
remote-tracking branches (since they are not covered by a proper git
remote's refspec), they clearly represent a similar concept, and would
benefit from following the same convention.

For example, if git-svn tracks Subversion branch "foo" at
refs/remotes/foo, and you create a local branch refs/heads/foo to add
some commits to be pushed back to Subversion (using "git svn dcommit),
then it is clearly unhelpful of Git to throw

  warning: refname 'foo' is ambiguous.

every time you checkout, rebase, or otherwise interact with the branch.

The existing workaround for this is to supply the --prefix=quux/ to
git svn init/clone, so that git-svn's tracking branches end up in
refs/remotes/quux/* instead of refs/remotes/*. However, encouraging
users to specify --prefix to work around a design flaw in git-svn is
suboptimal, and not a long term solution to the problem. Instead,
git-svn should default to use a non-empty prefix that saves
unsuspecting users from the inconveniences described above.

This patch will only affect newly created git-svn setups, as the
--prefix option only applies to git svn init (and git svn clone).
Existing git-svn setups will continue with their existing (lack of)
prefix. Also, if anyone somehow prefers git-svn's old layout, they
can recreate that by explicitly passing an empty prefix (--prefix "")
on the git svn init/clone command line.

The patch changes the default value for --prefix from "" to "origin/",
updates the git-svn manual page, and fixes the fallout in the git-svn
testcases.

(Note that this patch might be easier to review using the --word-diff
and --word-diff-regex=. diff options.)

[ew: squashed description of <= 1.9 behavior into manpage]

Suggested-by: Thomas Ferris Nicolaisen <tfnico@gmail.com>
Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Eric Wong <normalperson@yhbt.net>

Documentation/git-svn.txt

@@ -86,13 +86,11 @@ COMMANDS
 	(refs/remotes/$remote/*). Setting a prefix is also useful
 	if you wish to track multiple projects that share a common
 	repository.
+	By default, the prefix is set to 'origin/'.
 +
-NOTE: In Git v2.0, the default prefix will CHANGE from "" (no prefix)
-to "origin/". This is done to put SVN-tracking refs at
-"refs/remotes/origin/*" instead of "refs/remotes/*", and make them
-more compatible with how Git's own remote-tracking refs are organized
-(i.e. refs/remotes/$remote/*). You can enjoy the same benefits today,
-by using the --prefix option.
+NOTE: Before Git v2.0, the default prefix was "" (no prefix). This
+meant that SVN-tracking refs were put at "refs/remotes/*", which is
+incompatible with how Git's own remote-tracking refs are organized.
 
 --ignore-paths=<regex>;;
 	When passed to 'init' or 'clone' this regular expression will
@@ -994,16 +992,6 @@ without giving any repository layout options.  If the full history with
 branches and tags is required, the options '--trunk' / '--branches' /
 '--tags' must be used.
 
-When using the options for describing the repository layout (--trunk,
---tags, --branches, --stdlayout), please also specify the --prefix
-option (e.g. '--prefix=origin/') to cause your SVN-tracking refs to be
-placed at refs/remotes/origin/* rather than the default refs/remotes/*.
-The former is more compatible with the layout of Git's "regular"
-remote-tracking refs (refs/remotes/$remote/*), and may potentially
-prevent similarly named SVN branches and Git remotes from clobbering
-each other. In Git v2.0 the default prefix used (i.e. when no --prefix
-is given) will change from "" (no prefix) to "origin/".
-
 When using multiple --branches or --tags, 'git svn' does not automatically
 handle name collisions (for example, if two branches from different paths have
 the same name, or if a branch and a tag have the same name).  In these cases,