Re: bug: git branch -d and case-insensitive file-systems

From: Jeff King <peff@peff.net>
Date: Aug 25, 2015, 05:21 UTC
Message-ID: <20150825052123.GA523@sigill.intra.peff.net>
In-Reply-To: <CAJrRhQz1UmnDi6Giejetfoh3aPX08aYcgY-neZfcKjpUav0=sA@mail.gmail.com>

On Mon, Aug 24, 2015 at 12:11:13PM -0400, Aaron Dufour wrote:

Show 20 quoted lines

> I use git (2.2.1) on OS X (10.9.5) and recently my repo got into a bad
> state.  I think this involves a mis-handling of case-insensitive file
> systems.
> 
> This reproduces the problem:
> 
>     > git init
>     Initialized empty Git repository in /Users/aarond_local/code/git-test/.git/
>     > git commit --allow-empty -m 'first commit'
>     [master (root-commit) 923d8b8] first commit
>     > git checkout -b feature
>     Switched to a new branch 'feature'
>     > git checkout -b Feature
>     fatal: A branch named 'Feature' already exists.
>     > git checkout -B Feature
>     Switched to and reset branch 'Feature'
>     > git branch -d feature
>     Deleted branch feature (was 923d8b8).
>     > git log
>     fatal: bad default revision 'HEAD'

I don't work on a case-insensitive filesystem, so my knowledge may be out of date, but as far as I know, we do not do anything special to handle ref case-sensitivity. I expect your problem would go away with this patch:

diff --git a/builtin/branch.c b/builtin/branch.c
index 58aa84f..c5545de 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -19,6 +19,7 @@
 #include "column.h"
 #include "utf8.h"
 #include "wt-status.h"
+#include "dir.h"
 
 static const char * const builtin_branch_usage[] = {
 	N_("git branch [<options>] [-r | -a] [--merged | --no-merged]"),
@@ -223,7 +224,7 @@ static int delete_branches(int argc, const char **argv, int force, int kinds,
 		int flags = 0;
 
 		strbuf_branchname(&bname, argv[i]);
-		if (kinds == REF_LOCAL_BRANCH && !strcmp(head, bname.buf)) {
+		if (kinds == REF_LOCAL_BRANCH && !strcmp_icase(head, bname.buf)) {
 			error(_("Cannot delete the branch '%s' "
 			      "which you are currently on."), bname.buf);
 			ret = 1;

but I think that is just the tip of the iceberg. E.g. (on a vfat
filesystem I just created):

  $ git init
  $ git commit -q --allow-empty -m one
  $ git branch foo
  $ git branch FOO
  fatal: A branch named 'FOO' already exists.

  $ git pack-refs --all --prune ;# usually run as part of git-gc
  $ git commit -q --allow-empty -m two
  $ git branch FOO
  $ git for-each-ref --format='%(refname) %(subject)'
  refs/heads/FOO two
  refs/heads/foo one
  refs/heads/master two

Now the patch I showed above would do the wrong thing. Running "git
checkout foo; git branch -d FOO" would be rejected, even though I really
do have two separate branches.

It would be a much more invasive change to fix this correctly. It is
probably less work overall to move to a pluggable ref system, and to
design ref storage that isn't dependent on the filesystem (this work is
already underway).

In the meantime, I think the best advice for mixed-case branch names on
a case-insensitive filesystem is: don't.

-Peff