[PATCH] fix misuse of prefix_path()

[Junio C Hamano <gitster@pobox.com>]

When DEFAULT_GIT_TEMPLATE_DIR is specified as a relative path,
init-db made it relative to exec_path using prefix_path(), which
is wrong.  prefix_path() is about a file inside the work tree.
There was a similar misuse in config.c that takes relative
ETC_GITCONFIG path.

A convenience function prefix_filename() can concatenate two paths
to form a path that points at somewhere outside the work tree.
Use it in these codepaths instead.

Signed-off-by: Junio C Hamano <gitster@pobox.com>
---

 * This is probably an oversight in commits leading to
   7f0e39fa and I think if this patch breaks, MinGW port would
   be affected, hence I CC'ed j6t.

   There are similar misuse in builtin-mv.c that needs to be
   fixed.  But git-mv is more broken, independent from this
   prefix_path() issue.  For example, it does not check if src
   and dst are inside work tree, so (do not try this in a
   repository you care about) "git mv compat /tmp/outer-space"
   would throw tracked files in a work tree to outer space and
   then fail without touching the index.  It needs a serious
   overhaul, but because I do not use it myself, the level of
   motivation to fix it myself is very low.  A low hanging
   fruit, that is, for any git hacker wannabes...

 builtin-init-db.c |    3 +--
 config.c          |    5 +++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/builtin-init-db.c b/builtin-init-db.c
index e1393b8..e51d447 100644
--- a/builtin-init-db.c
+++ b/builtin-init-db.c
@@ -142,8 +142,7 @@ static void copy_templates(const char *git_dir, int len, const char *template_di
 		template_dir = DEFAULT_GIT_TEMPLATE_DIR;
 		if (!is_absolute_path(template_dir)) {
 			const char *exec_path = git_exec_path();
-			template_dir = prefix_path(exec_path, strlen(exec_path),
-						   template_dir);
+			template_dir = prefix_filename(exec_path, strlen(exec_path), template_dir);
 		}
 	}
 	strcpy(template_path, template_dir);
diff --git a/config.c b/config.c
index 526a3f4..0b0c9bd 100644
--- a/config.c
+++ b/config.c
@@ -485,8 +485,9 @@ const char *git_etc_gitconfig(void)
 		if (!is_absolute_path(system_wide)) {
 			/* interpret path relative to exec-dir */
 			const char *exec_path = git_exec_path();
-			system_wide = prefix_path(exec_path, strlen(exec_path),
-						system_wide);
+			system_wide = strdup(prefix_filename(exec_path,
+							     strlen(exec_path),
+							     system_wide));
 		}
 	}
 	return system_wide;
-- 
1.5.4.18.gd0b8