Fix setup_git_directory_gently() with relative GIT_DIR & GIT_WORK_TREE

There are a few programs, such as config and diff, which allow running
without a git repository.  Therefore, they have to call
setup_git_directory_gently().

However, when GIT_DIR and GIT_WORK_TREE were set, and the current
directory was a subdirectory of the work tree,
setup_git_directory_gently() would return a bogus NULL prefix.

This patch fixes that.

Noticed by REPLeffect on IRC.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Shawn O. Pearce <spearce@spearce.org>

1 files changed, 12 insertions, 1 deletions

diff --git a/setup.c b/setup.c
index 06004f1587..145eca50f4 100644
--- a/setup.c
+++ b/setup.c
@@ -227,9 +227,20 @@ const char *setup_git_directory_gently(int *nongit_ok)
 		if (PATH_MAX - 40 < strlen(gitdirenv))
 			die("'$%s' too big", GIT_DIR_ENVIRONMENT);
 		if (is_git_directory(gitdirenv)) {
+			static char buffer[1024 + 1];
+			const char *retval;
+
 			if (!work_tree_env)
 				return set_work_tree(gitdirenv);
-			return NULL;
+			retval = get_relative_cwd(buffer, sizeof(buffer) - 1,
+					get_git_work_tree());
+			if (!retval || !*retval)
+				return NULL;
+			set_git_dir(make_absolute_path(gitdirenv));
+			if (chdir(work_tree_env) < 0)
+				die ("Could not chdir to %s", work_tree_env);
+			strcat(buffer, "/");
+			return retval;
 		}
 		if (nongit_ok) {
 			*nongit_ok = 1;