builtin-rm: fix index lock file path

When hold_locked_index() is called with a relative git_dir and you are
outside the work tree, the lock file become relative to the current
directory. So when later setup_work_tree() change the current directory
it breaks lock file path and commit_locked_index() fails.

This patch move index locking code after setup_work_tree() call to make
lock file relative to the working tree as it should be and add a test
case.

Noticed by Nick Andrew.

Signed-off-by: Olivier Marin <dkr@freesurf.fr>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-rm.c

@@ -146,11 +146,6 @@ int cmd_rm(int argc, const char **argv, const char *prefix)
 
 	git_config(git_default_config, NULL);
 
-	newfd = hold_locked_index(&lock_file, 1);
-
-	if (read_cache() < 0)
-		die("index file corrupt");
-
 	argc = parse_options(argc, argv, builtin_rm_options, builtin_rm_usage, 0);
 	if (!argc)
 		usage_with_options(builtin_rm_usage, builtin_rm_options);
@@ -158,6 +153,11 @@ int cmd_rm(int argc, const char **argv, const char *prefix)
 	if (!index_only)
 		setup_work_tree();
 
+	newfd = hold_locked_index(&lock_file, 1);
+
+	if (read_cache() < 0)
+		die("index file corrupt");
+
 	pathspec = get_pathspec(prefix, argv);
 	seen = NULL;
 	for (i = 0; pathspec[i] ; i++)

t/t3600-rm.sh

@@ -217,4 +217,16 @@ test_expect_success 'Remove nonexistent file returns nonzero exit status' '
 	! git rm nonexistent
 '
 
+test_expect_success 'Call "rm" from outside the work tree' '
+	mkdir repo &&
+	cd repo &&
+	git init &&
+	echo something > somefile &&
+	git add somefile &&
+	git commit -m "add a file" &&
+	(cd .. &&
+	 git --git-dir=repo/.git --work-tree=repo rm somefile) &&
+	test_must_fail git ls-files --error-unmatch somefile
+'
+
 test_done