[PATCH] Extend "checkout --track" DWIM to support more cases

[Alex Riesen <raa.lkml@gmail.com>]

The code handles additionally "refs/remotes/<something>/name",
"remotes/<something>/name", and "refs/<namespace>/name".

Signed-off-by: Alex Riesen <raa.lkml@gmail.com>
---
Junio C Hamano, Thu, Aug 21, 2008 00:22:21 +0200:
> Alex Riesen <raa.lkml@gmail.com> writes:
> > Johannes Schindelin, Wed, Aug 20, 2008 22:16:19 +0200:
> >> > No. It strips refs/ OR remotes/ (because of prefixcmp with argv[0]).
> >> > And I still wanted refs/<namespace>/something...
> >> 
> >> Yes, you are correct.  However, to fix my thinko, I deem this preferable:
> >> 
> >
> > Yes, I agree (and its shorter). The git-checkout manpage can be
> > improved, too (no DWIM is obvious, except may be for the implementor).
> 
> I think that makes sense.  Care to send an appliable patch with
> documentation updates, please?

I just have another quiet evening, so I did that. Johannes, I changed
your fix a bit: I see that argv[0] is used later (or if I'm blind and
it actually isn't, it may be used in future: I have a feeling that
builtint-checkout.c will be popular place).

 Documentation/git-checkout.txt |   18 +++++++++++++++---
 builtin-checkout.c             |   13 ++++++++-----
 t/t7201-co.sh                  |   23 ++++++++++++++++++++++-
 3 files changed, 45 insertions(+), 9 deletions(-)

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 43d4502..d93a18f 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -64,9 +64,21 @@ OPTIONS
 	given. Set it to `always` if you want this behavior when the
 	start-point is either a local or remote branch.
 +
-If no '-b' option was given, a name will be made up for you, by stripping
-the part up to the first slash of the tracked branch.  For example, if you
-called 'git checkout --track origin/next', the branch name will be 'next'.
+If no '-b' option was given, the name of the new branch will be
+derived from the remote branch, by attempting to guess the name of the
+branch on remote system and use it. The algorithm will remove a
+prefixed refs/ and the part after refs/ up to a slash (that part
+usually being a branch namespace, which makes it confusing to use for
+branch names). If the part after refs/ was remotes/, than a part past
+it is stripped too (it is expected to be the name of remote system).
+Otherwise, the part up to the first slash is removed.
+The algorithm aborts either if the given name has no slashes in it or
+if the part left after stripping the prefixes is empty. In this case,
+the name should be provided with '-b'.
++
+For example, if you called 'git checkout --track origin/next', the
+branch name will be 'next', as it will for 'git checkout --track
+remotes/origin/next'.
 
 --no-track::
 	Ignore the branch.autosetupmerge configuration variable.
diff --git a/builtin-checkout.c b/builtin-checkout.c
index e95eab9..214b0b2 100644
--- a/builtin-checkout.c
+++ b/builtin-checkout.c
@@ -445,12 +445,15 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	/* --track without -b should DWIM */
 	if (opts.track && opts.track != -1 && !opts.new_branch) {
 		char *slash;
-		if (!argc || !strcmp(argv[0], "--"))
+		char *argv0 = argv[0];
+		if (!argc || !strcmp(argv0, "--"))
 			die ("--track needs a branch name");
-		slash = strchr(argv[0], '/');
-		if (slash && !prefixcmp(argv[0], "refs/"))
-			slash = strchr(slash + 1, '/');
-		if (slash && !prefixcmp(argv[0], "remotes/"))
+		slash = strchr(argv0, '/');
+		if (slash && !prefixcmp(argv0, "refs/")) {
+			argv0 = slash + 1;
+			slash = strchr(argv0, '/');
+		}
+		if (slash && !prefixcmp(argv0, "remotes/"))
 			slash = strchr(slash + 1, '/');
 		if (!slash || !slash[1])
 			die ("Missing branch name; try -b");
diff --git a/t/t7201-co.sh b/t/t7201-co.sh
index 943dd57..1dff84d 100755
--- a/t/t7201-co.sh
+++ b/t/t7201-co.sh
@@ -340,9 +340,30 @@ test_expect_success \
 test_expect_success \
     'checkout with --track fakes a sensible -b <name>' '
     git update-ref refs/remotes/origin/koala/bear renamer &&
+    git update-ref refs/new/koala/bear renamer &&
+
     git checkout --track origin/koala/bear &&
     test "refs/heads/koala/bear" = "$(git symbolic-ref HEAD)" &&
-    test "$(git rev-parse HEAD)" = "$(git rev-parse renamer)"'
+    test "$(git rev-parse HEAD)" = "$(git rev-parse renamer)" &&
+
+    git checkout master && git branch -D koala/bear &&
+
+    git checkout --track refs/remotes/origin/koala/bear &&
+    test "refs/heads/koala/bear" = "$(git symbolic-ref HEAD)" &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse renamer)" &&
+
+    git checkout master && git branch -D koala/bear &&
+
+    git checkout --track remotes/origin/koala/bear &&
+    test "refs/heads/koala/bear" = "$(git symbolic-ref HEAD)" &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse renamer)" &&
+
+    git checkout master && git branch -D koala/bear &&
+
+    git checkout --track refs/new/koala/bear &&
+    test "refs/heads/koala/bear" = "$(git symbolic-ref HEAD)" &&
+    test "$(git rev-parse HEAD)" = "$(git rev-parse renamer)"
+'
 
 test_expect_success \
     'checkout with --track, but without -b, fails with too short tracked name' '
-- 
1.6.0.59.g8ae62