[PATCH] rev-parse: fix --git-common-dir when executed from subpath of main tree

[Michael Rappazzo <rappazzo@gmail.com>]

Executing `git-rev-parse --git-common-dir` from the root of the main
worktree results in '.git', which is the relative path to the git dir.
When executed from a subpath of the main tree it returned somthing like:
'sub/path/.git'.  Change this to return the proper relative path to the
git directory (similar to `--show-cdup`).

Add as test to t1500-rev-parse.sh for this case and adjust another test
in t2027-worktree-list.sh to use this expectation.

Signed-off-by: Michael Rappazzo <rappazzo@gmail.com>
---
 builtin/rev-parse.c      | 14 ++++++++++++--
 t/t1500-rev-parse.sh     | 10 ++++++++++
 t/t2027-worktree-list.sh |  2 +-
 3 files changed, 23 insertions(+), 3 deletions(-)

diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index c961b74..c2918e1 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -787,8 +787,18 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				continue;
 			}
 			if (!strcmp(arg, "--git-common-dir")) {
-				const char *pfx = prefix ? prefix : "";
-				puts(prefix_filename(pfx, strlen(pfx), get_git_common_dir()));
+				const char *git_common_dir = get_git_common_dir();
+				if (prefix && !is_absolute_path(git_common_dir)) {
+					const char *pfx = prefix;
+					while (pfx) {
+						pfx = strchr(pfx, '/');
+						if (pfx) {
+							pfx++;
+							printf("../");
+						}
+					}
+				}
+				printf("%s\n", git_common_dir);
 				continue;
 			}
 			if (!strcmp(arg, "--is-inside-git-dir")) {
diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
index 48ee077..2023208 100755
--- a/t/t1500-rev-parse.sh
+++ b/t/t1500-rev-parse.sh
@@ -3,6 +3,16 @@
 test_description='test git rev-parse'
 . ./test-lib.sh
 
+test_expect_success 'git-common-dir inside sub-dir' '
+   (
+		mkdir -p path/to/child &&
+		cd path/to/child &&
+		echo "$(git rev-parse --show-cdup).git" >expect &&
+		git rev-parse --git-common-dir >actual &&
+		test_cmp expect actual
+	)
+'
+
 test_rev_parse() {
 	name=$1
 	shift
diff --git a/t/t2027-worktree-list.sh b/t/t2027-worktree-list.sh
index 1b1b65a..3780b14 100755
--- a/t/t2027-worktree-list.sh
+++ b/t/t2027-worktree-list.sh
@@ -14,7 +14,7 @@ test_expect_success 'rev-parse --git-common-dir on main worktree' '
 	test_cmp expected actual &&
 	mkdir sub &&
 	git -C sub rev-parse --git-common-dir >actual2 &&
-	echo sub/.git >expected2 &&
+	echo ../.git >expected2 &&
 	test_cmp expected2 actual2
 '
 
-- 
2.8.0