[PATCH v2 1/2] commit: allow editing the commit message even in shared repos

[Johannes Schindelin <johannes.schindelin@gmx.de>]

It was pointed out by Yaroslav Halchenko that the file containing the
commit message is writable only by the owner, which means that we have
to rewrite it from scratch in a shared repository.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
---
 builtin/commit.c  |  2 +-
 git-compat-util.h |  1 +
 wrapper.c         | 13 +++++++++++++
 3 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/builtin/commit.c b/builtin/commit.c
index d054f84..89bf6ad 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -761,7 +761,7 @@ static int prepare_to_commit(const char *index_file, const char *prefix,
 		hook_arg2 = "";
 	}
 
-	s->fp = fopen(git_path(commit_editmsg), "w");
+	s->fp = fopen_for_writing(git_path(commit_editmsg));
 	if (s->fp == NULL)
 		die_errno(_("could not open '%s'"), git_path(commit_editmsg));
 
diff --git a/git-compat-util.h b/git-compat-util.h
index 2da0a75..e8f2867 100644
--- a/git-compat-util.h
+++ b/git-compat-util.h
@@ -733,6 +733,7 @@ extern int xmkstemp_mode(char *template, int mode);
 extern int odb_mkstemp(char *template, size_t limit, const char *pattern);
 extern int odb_pack_keep(char *name, size_t namesz, const unsigned char *sha1);
 extern char *xgetcwd(void);
+extern FILE *fopen_for_writing(const char *path);
 
 #define REALLOC_ARRAY(x, alloc) (x) = xrealloc((x), (alloc) * sizeof(*(x)))
 
diff --git a/wrapper.c b/wrapper.c
index b43d437..29a45d2 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -391,6 +391,19 @@ FILE *xfdopen(int fd, const char *mode)
 	return stream;
 }
 
+FILE *fopen_for_writing(const char *path)
+{
+	FILE *ret = fopen(path, "w");
+
+	if (!ret && errno == EPERM) {
+		if (!unlink(path))
+			ret = fopen(path, "w");
+		else
+			errno = EPERM;
+	}
+	return ret;
+}
+
 int xmkstemp(char *template)
 {
 	int fd;
-- 
2.6.3.windows.1.300.g1c25e49