dir: new flag to remove_dir_recurse() to spare the original_cwd

remove_dir_recurse(), and its non-static wrapper called
remove_dir_recursively(), both take flags for modifying its behavior.
As with the previous commits, we would generally like to protect
the original_cwd, but we want to forced user commands (e.g. 'git rm -rf
...') or other special cases to remove it.  Add a flag for this purpose.
After reading through every caller of remove_dir_recursively() in the
current codebase, there was only one that should be adjusted and that
one only in a very unusual circumstance.  Add a pair of new testcases to
highlight that very specific case involving submodules && --git-dir &&
--work-tree.

Acked-by: Derrick Stolee <stolee@gmail.com>
Acked-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
Signed-off-by: Elijah Newren <newren@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/rm.c

@@ -399,12 +399,13 @@ int cmd_rm(int argc, const char **argv, const char *prefix)
 	if (!index_only) {
 		int removed = 0, gitmodules_modified = 0;
 		struct strbuf buf = STRBUF_INIT;
+		int flag = force ? REMOVE_DIR_PURGE_ORIGINAL_CWD : 0;
 		for (i = 0; i < list.nr; i++) {
 			const char *path = list.entry[i].name;
 			if (list.entry[i].is_submodule) {
 				strbuf_reset(&buf);
 				strbuf_addstr(&buf, path);
-				if (remove_dir_recursively(&buf, 0))
+				if (remove_dir_recursively(&buf, flag))
 					die(_("could not remove '%s'"), path);
 
 				removed = 1;

dir.c

@@ -3204,6 +3204,7 @@ static int remove_dir_recurse(struct strbuf *path, int flag, int *kept_up)
 	int ret = 0, original_len = path->len, len, kept_down = 0;
 	int only_empty = (flag & REMOVE_DIR_EMPTY_ONLY);
 	int keep_toplevel = (flag & REMOVE_DIR_KEEP_TOPLEVEL);
+	int purge_original_cwd = (flag & REMOVE_DIR_PURGE_ORIGINAL_CWD);
 	struct object_id submodule_head;
 
 	if ((flag & REMOVE_DIR_KEEP_NESTED_GIT) &&
@@ -3259,9 +3260,14 @@ static int remove_dir_recurse(struct strbuf *path, int flag, int *kept_up)
 	closedir(dir);
 
 	strbuf_setlen(path, original_len);
-	if (!ret && !keep_toplevel && !kept_down)
-		ret = (!rmdir(path->buf) || errno == ENOENT) ? 0 : -1;
-	else if (kept_up)
+	if (!ret && !keep_toplevel && !kept_down) {
+		if (!purge_original_cwd &&
+		    startup_info->original_cwd &&
+		    !strcmp(startup_info->original_cwd, path->buf))
+			ret = -1; /* Do not remove current working directory */
+		else
+			ret = (!rmdir(path->buf) || errno == ENOENT) ? 0 : -1;
+	} else if (kept_up)
 		/*
 		 * report the uplevel that it is not an error that we
 		 * did not rmdir() our directory.

dir.h

@@ -495,6 +495,9 @@ int get_sparse_checkout_patterns(struct pattern_list *pl);
 /* Remove the contents of path, but leave path itself. */
 #define REMOVE_DIR_KEEP_TOPLEVEL 04
 
+/* Remove the_original_cwd too */
+#define REMOVE_DIR_PURGE_ORIGINAL_CWD 0x08
+
 /*
  * Remove path and its contents, recursively. flags is a combination
  * of the above REMOVE_DIR_* constants. Return 0 on success.

t/t2501-cwd-empty.sh

@@ -291,11 +291,6 @@ test_submodule_removal () {
 	test_status=
 	test "$path_status" = dir && test_status=test_must_fail
 
-	# Actually, while path_status=dir && test_status=test_must_fail
-	# reflect our desired behavior, current behavior is:
-	path_status=missing
-	test_status=
-
 	test_when_finished "git reset --hard HEAD~1" &&
 	test_when_finished "rm -rf .git/modules/my_submodule" &&