[PATCH] handle rename of case only, for windows

Hi folks,

I've never contributed to git before so be gentle :-)

Would someone have the time to help me get this patch into mailine git?

I tripped over a failure to rename files on windows when only the case
has changed. I've created a patch which fixes it for me and doesn't seem
to break on linux or windows. I also created a test to demonstrate the
issue (part of this patch). This test passes on linux and fails on
windows before my patch for mv.c is applied, and passes on both windows
and linux for me after my patch is applied.

The problem with changing the case of a file happens because git mv
checks if the destination filename exists before performing a
move/rename, and on windows lstat reports that the destination file
*does* already exist because it ignores case for this check and
semi-erroneously finds the source file.

The way I've attempted to fix it in my patch is by checking if the inode
of the source and destination are the same before deciding to fail with
a "destination exists" error.

When using "git mv" it is possible to work around the error by using
--force.

I've also seen a problem with windows users pulling from remotes where a
case only rename has been performed which is more problematic as you
have to tell every user how to handle the issue. I'm not sure if I've
managed to fix that case or not.

The fault exists in both the current cygwin git and the current msysgit,
so I figured it would be good to get a patch to upstream (you) so that
it could work everywhere. 

I found an email from Linus relating to this issue here:
http://marc.info/?l=git&m=120612172706823 so it's a known problem.

Thanks

Tim Abell

---
 builtin/mv.c  |   33 ++++++++++++++++++++++-----------
 t/t7001-mv.sh |    9 +++++++++
 2 files changed, 31 insertions(+), 11 deletions(-)

diff --git a/builtin/mv.c b/builtin/mv.c
index 93e8995..6bb262e 100644
--- a/builtin/mv.c
+++ b/builtin/mv.c

@@ -63,6 +63,7 @@ int cmd_mv(int argc, const char **argv, const char

*prefix)
 	const char **source, **destination, **dest_path;
 	enum update_mode { BOTH = 0, WORKING_DIRECTORY, INDEX } *modes;
 	struct stat st;
+       struct stat src_st;
 	struct string_list src_for_dst = STRING_LIST_INIT_NODUP;
 
 	git_config(git_default_config, NULL);

@@ -165,17 +166,27 @@ int cmd_mv(int argc, const char **argv, const char

*prefix)
 		} else if (cache_name_pos(src, length) < 0)
 			bad = "not under version control";
 		else if (lstat(dst, &st) == 0) {
-                       bad = "destination exists";
-                       if (force) {
-                               /*
-                                * only files can overwrite each other:
-                                * check both source and destination
-                                */
-                               if (S_ISREG(st.st_mode) ||
S_ISLNK(st.st_mode)) {
-                                       warning("%s; will overwrite!",
bad);
-                                       bad = NULL;
-                               } else
-                                       bad = "Cannot overwrite";
+                       /* If we are on a case insensitive files= system
(windows) http://is.gd/kyxgg
+                        * and we are only changing the case of the file
then lstat for the
+                        * destination will return != 0 because it sees
the source file.
+                        * To prevent this causing failure, lstat is
used to get the inode of the src
+                        * and see if it's actually the same file.
+                        */
+                       lstat(src, &src_st); //get file serial number
(inode) for source
+                       #warning("src inode: %s, dst inode: %s",
src_st.st_ino, st.st_ino);
+                       if (src_st.st_ino != st.st_ino) {
+                               bad = "destination exists";
+                               if (force) {
+                                       /*
+                                        * only files can overwrite each
other:
+                                        * check both source and
destination
+                                        */
+                                       if (S_ISREG(st.st_mode) ||
S_ISLNK(st.st_mode)) {
+                                               warning("%s; will
overwrite!", bad);
+                                               bad = NULL;
+                                       } else
+                                               bad = "Cannot
overwrite";
+                               }
 			}
 		} else if (string_list_has_string(&src_for_dst, dst))
 			bad = "multiple sources for the same target";

diff --git a/t/t7001-mv.sh b/t/t7001-mv.sh
index a845b15..95146bf 100755
--- a/t/t7001-mv.sh
+++ b/t/t7001-mv.sh

@@ -255,4 +255,13 @@ test_expect_success SYMLINKS 'git mv should

overwrite file with a symlink' '
 
 rm -f moved symlink
 
+test_expect_success 'git mv should not fail when only changing case' '
+
+       rm -fr .git &&
+       git init &&
+       >foo.txt &&
+       git add foo.txt &&
+       git mv foo.txt Foo.txt
+'
+
 test_done
-- 
1.5.6.5

On Fri, Jan 14, 2011 at 2:41 PM, Tim Abell [off-list ref] wrote:

Hi folks,

I've never contributed to git before so be gentle :-)

Would someone have the time to help me get this patch into mailine git?

First of all, welcome!

There are some problems with your patch that aren't directly related
to the code:
- It's become white-space damaged, most likely from when you e-mailed
it. Perhaps you could try again with git-send-email?
- There's no real commit-message. This e-mail description isn't really
suited as a commit message as it is, IMO. It might just be a matter of
snipping away some stuff, though.
- The patch lacks a sign-off
- Since this is a Windows-issue, it would be nice if you CC'ed
msysgit@googlegroups.com as well. I've done that for now.

I suggest you read through Documentation/SubmittingPatches to get to
know the process.

I tripped over a failure to rename files on windows when only the case
has changed. I've created a patch which fixes it for me and doesn't seem
to break on linux or windows. I also created a test to demonstrate the
issue (part of this patch). This test passes on linux and fails on
windows before my patch for mv.c is applied, and passes on both windows
and linux for me after my patch is applied.

The problem with changing the case of a file happens because git mv
checks if the destination filename exists before performing a
move/rename, and on windows lstat reports that the destination file
*does* already exist because it ignores case for this check and
semi-erroneously finds the source file.

<snip>

When using "git mv" it is possible to work around the error by using
--force.

Your reasoning seems to match what we've discussed on the msysGit
mailing list. Good work, and a clear description.

The way I've attempted to fix it in my patch is by checking if the inode
of the source and destination are the same before deciding to fail with
a "destination exists" error.

Hmm, not so good. st_ino is always 0 on Windows, so this would make
false positives, no?

The fault exists in both the current cygwin git and the current msysgit,
so I figured it would be good to get a patch to upstream (you) so that
it could work everywhere.

It also affects MacOS X, AFAIK. So yes, it'd be good for upstream.

Couldn't this be moved inside the scope around "cache_name_pos"?
That's the only scope it is valid inside anyway...

And if not, perhaps you could piggy-back on the st-definition, like this:
-       struct stat st;
+       struct stat st, src_st;

Perhaps you could use the full URL (and maybe put it in the commit
message insted)? It'd be nice if we could reach this information even
if is.gd disappears...

+                        * and we are only changing the case of the file
then lstat for the
+                        * destination will return != 0 because it sees
the source file.
+                        * To prevent this causing failure, lstat is
used to get the inode of the src
+                        * and see if it's actually the same file.
+                        */
+                       lstat(src, &src_st); //get file serial number
(inode) for source
+                       #warning("src inode: %s, dst inode: %s",
src_st.st_ino, st.st_ino);

Uhm, is this debug-leftovers? #warning is a preprocessor-construct,
and it can't understand varaibles in c. Especially not formatted as
strings. Can #warning even do varags? :P

Blah, it's too tiresome to review this white-space broken version, and
I seen now that you have re-posted a non-broken version. Thanks!