From: Erik Faye-Lund <kusmabite@gmail.com>
Date: Wed, 16 Mar 2011 13:05:04 GMT
Subject: Re: [PATCH] Allow git mv FileA fILEa when core.ignorecase = true
Message-ID: <AANLkTin2s_=TVaKx6yv+nDvXB41BxebWHX4iaDYSGd-e@mail.gmail.com>
In-Reply-To: <201103042240.38969.tboegi@web.de>

2011/3/4 Torsten Bögershausen <tboegi@web.de>:
>    The typical use case is when a file "FileA" should be renamed into fILEa
>    and we are on a case insenstive file system (system core.ignorecase = true).
>    Source and destination are the same file, it can be accessed under both names.
>    This makes git think that the destination file exists.
>    Unless used with --forced, git will refuse the "git mv FileA fILEa".
>    This change will allow "git mv FileA fILEa", when core.ignorecase = true
>    and source and destination filenames only differ in case and the file length
>    is identical.
>    On Linux/Unix/Mac OS X the mv is allowed when the inode of the source and
>    destination are equal.
>    On  this allows renames of MÄRCHEN into Märchen on Mac OS X.
>    (As a side effect, a file can be renamed to a name which is already
>    hard-linked to the same inode)
>
> Signed-off-by: Torsten Bögershausen <tboegi@web.de>
> ---
>  builtin/mv.c  |   20 +++++++++++++++-----
>  t/t7001-mv.sh |   29 +++++++++++++++++++++++++++++
>  2 files changed, 44 insertions(+), 5 deletions(-)
>
> diff --git a/builtin/mv.c b/builtin/mv.c
> index 93e8995..e0aad62 100644
> --- a/builtin/mv.c
> +++ b/builtin/mv.c
> @@ -62,7 +62,7 @@ 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 st, st_dst;
>        struct string_list src_for_dst = STRING_LIST_INIT_NODUP;
>
>        git_config(git_default_config, NULL);
> @@ -164,15 +164,25 @@ 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) {
> +               else if (lstat(dst, &st_dst) == 0) {
> +                       int allow_force = force;
>                        bad = "destination exists";
> -                       if (force) {
> +                       /* Allow when src and dst have the same inode (Mac OS X) */
> +                       /* Allow when ignore_case and same file length (Windows) */

Wait, what? Same file length is sufficient to trigger overwriting
without -f? I find this to be a very dubious heuristic...

Shouldn't you be checking something like nFileIndexLow/High from
BY_HANDLE_FILE_INFORMATION instead? (ref:
http://msdn.microsoft.com/en-us/library/aa363788(v=VS.85).aspx)

Sure, we'd need some API to check that, but if we assume that this
code path is rare-ish we could do something like this (note,
untested):

diff --git a/compat/mingw.c b/compat/mingw.c
index 6750e67..fee4113 100644
--- a/compat/mingw.c
+++ b/compat/mingw.c
@@ -299,6 +299,21 @@ void mingw_mark_as_git_dir(const char *dir)
 		 "dotGitOnly" : "true"));
 }

+int is_same_file(const char *a, const char *b)
+{
+	BY_HANDLE_FILE_INFORMATION hia, hib;
+	HANDLE ha = OpenFileA(a, NULL, OF_READ),
+	       hb = OpenFileA(b, NULL, OF_READ);
+	if (!ha || !hb ||
+	    !GetFileInformationByHandle(ha) ||
+	    !GetFileInformationByHandle(hb))
+		return 0;
+
+	return hia.dwVolumeSerialNumber == hib.dwVolumeSerialNumber &&
+	    hia.nFileSizeLow == hib.nFileSizeLow &&
+	    hia.nFileSizeHigh == hib.nFileSizeHigh;
+}
+
 #undef mkdir
 int mingw_mkdir(const char *path, int mode)
 {
diff --git a/compat/mingw.h b/compat/mingw.h
index 9c00e75..43c0b5f 100644
--- a/compat/mingw.h
+++ b/compat/mingw.h
@@ -297,6 +297,9 @@ void mingw_open_html(const char *path);
 void mingw_mark_as_git_dir(const char *dir);
 #define mark_as_git_dir mingw_mark_as_git_dir

+int mingw_is_same_file(const char *a, const char *b);
+#define is_same_file mingw_is_same_file
+
 /*
  * helpers
  */
diff --git a/git-compat-util.h b/git-compat-util.h
index 2ca2fad..b95b9e2 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -558,6 +558,17 @@ int remove_or_warn(unsigned int mode, const char *path);
 #define mark_as_git_dir(x) /* noop */
 #endif

+#ifndef is_same_file
+static inline int mingw_is_same_file(const char *a, const char *b)
+{
+	struct stat sta, stb;
+	if (lstat(a, &sta) ||
+	    lstat(b, &stb))
+		return 0;
+	return sta.st_dev == stb.st_deb && sta.st_ino == stb.st_ino;
+}
+#endif
+
 #ifndef get_home_directory
 #define get_home_directory() getenv("HOME")
 #endif