remove_dir_recursively(): Add flag for skipping removal of toplevel dir

Add the REMOVE_DIR_KEEP_TOPLEVEL flag to remove_dir_recursively() for
deleting everything inside the given directory, but _not_ the given
directory itself.

Note that this does not pass the REMOVE_DIR_KEEP_NESTED_GIT flag, if set,
to the recursive invocations of remove_dir_recursively().  It is likely to
be a a bug that has been present since REMOVE_DIR_KEEP_NESTED_GIT was
introduced (a0f4afb), but this commit keeps the same behaviour for now.

Signed-off-by: Johan Herland <johan@herland.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

dir.c

@@ -1178,16 +1178,22 @@ int remove_dir_recursively(struct strbuf *path, int flag)
 	struct dirent *e;
 	int ret = 0, original_len = path->len, len;
 	int only_empty = (flag & REMOVE_DIR_EMPTY_ONLY);
+	int keep_toplevel = (flag & REMOVE_DIR_KEEP_TOPLEVEL);
 	unsigned char submodule_head[20];
 
 	if ((flag & REMOVE_DIR_KEEP_NESTED_GIT) &&
 	    !resolve_gitlink_ref(path->buf, "HEAD", submodule_head))
 		/* Do not descend and nuke a nested git work tree. */
 		return 0;
 
+	flag &= ~(REMOVE_DIR_KEEP_TOPLEVEL|REMOVE_DIR_KEEP_NESTED_GIT);
 	dir = opendir(path->buf);
-	if (!dir)
-		return rmdir(path->buf);
+	if (!dir) {
+		if (!keep_toplevel)
+			return rmdir(path->buf);
+		else
+			return -1;
+	}
 	if (path->buf[original_len - 1] != '/')
 		strbuf_addch(path, '/');
 
@@ -1202,7 +1208,7 @@ int remove_dir_recursively(struct strbuf *path, int flag)
 		if (lstat(path->buf, &st))
 			; /* fall thru */
 		else if (S_ISDIR(st.st_mode)) {
-			if (!remove_dir_recursively(path, only_empty))
+			if (!remove_dir_recursively(path, flag))
 				continue; /* happy */
 		} else if (!only_empty && !unlink(path->buf))
 			continue; /* happy, too */
@@ -1214,7 +1220,7 @@ int remove_dir_recursively(struct strbuf *path, int flag)
 	closedir(dir);
 
 	strbuf_setlen(path, original_len);
-	if (!ret)
+	if (!ret && !keep_toplevel)
 		ret = rmdir(path->buf);
 	return ret;
 }

dir.h

@@ -102,6 +102,7 @@ extern void setup_standard_excludes(struct dir_struct *dir);
 
 #define REMOVE_DIR_EMPTY_ONLY 01
 #define REMOVE_DIR_KEEP_NESTED_GIT 02
+#define REMOVE_DIR_KEEP_TOPLEVEL 04
 extern int remove_dir_recursively(struct strbuf *path, int flag);
 
 /* tries to remove the path with empty directories along it, ignores ENOENT */