gc: support prune --worktrees

Helped-by: Marc Branchaud <marcnarc@xiplink.com>
Signed-off-by: Marc Branchaud <marcnarc@xiplink.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/config.txt

@@ -1229,6 +1229,13 @@ gc.pruneexpire::
 	"now" may be used to disable this  grace period and always prune
 	unreachable objects immediately.
 
+gc.pruneworktreesexpire::
+	When 'git gc' is run, it will call
+	'prune --worktrees --expire 3.months.ago'.
+	Override the grace period with this config variable. The value
+	"now" may be used to disable the grace period and prune
+	$GIT_DIR/worktrees immediately.
+
 gc.reflogexpire::
 gc.<pattern>.reflogexpire::
 	'git reflog expire' removes reflog entries older than

Documentation/git-checkout.txt

@@ -435,8 +435,11 @@ $GIT_DIR or $GIT_COMMON_DIR when you need to directly access something
 inside $GIT_DIR. Use `git rev-parse --git-path` to get the final path.
 
 When you are done with a linked working tree you can simply delete it.
-You can clean up any stale $GIT_DIR/worktrees entries via `git prune
---worktrees` in the main or any linked working tree.
+The working tree's entry in the repository's $GIT_DIR/worktrees
+directory will eventually be removed automatically (see
+`gc.pruneworktreesexpire` in linkgit::git-config[1]), or you can run
+`git prune --worktrees` in the main or any linked working tree to
+clean up any stale entries in $GIT_DIR/worktrees.
 
 If you move a linked working directory to another file system, or
 within a file system that does not support hard links, you need to run
@@ -444,8 +447,8 @@ at least one git command inside the linked working directory
 (e.g. `git status`) in order to update its entry in $GIT_DIR/worktrees
 so that it does not get automatically removed.
 
-To prevent `git prune --worktrees` from deleting a $GIT_DIR/worktrees
-entry (which can be useful in some situations, such as when the
+To prevent a $GIT_DIR/worktrees entry from from being pruned (which
+can be useful in some situations, such as when the
 entry's working tree is stored on a portable device), add a file named
 'locked' to the entry's directory. The file contains the reason in
 plain text. For example, if a linked working tree's `.git` file points

builtin/gc.c

@@ -33,11 +33,13 @@ static int gc_auto_threshold = 6700;
 static int gc_auto_pack_limit = 50;
 static int detach_auto = 1;
 static const char *prune_expire = "2.weeks.ago";
+static const char *prune_worktrees_expire = "3.months.ago";
 
 static struct argv_array pack_refs_cmd = ARGV_ARRAY_INIT;
 static struct argv_array reflog = ARGV_ARRAY_INIT;
 static struct argv_array repack = ARGV_ARRAY_INIT;
 static struct argv_array prune = ARGV_ARRAY_INIT;
+static struct argv_array prune_worktrees = ARGV_ARRAY_INIT;
 static struct argv_array rerere = ARGV_ARRAY_INIT;
 
 static char *pidfile;
@@ -83,6 +85,7 @@ static void gc_config(void)
 	git_config_get_int("gc.autopacklimit", &gc_auto_pack_limit);
 	git_config_get_bool("gc.autodetach", &detach_auto);
 	git_config_date_string("gc.pruneexpire", &prune_expire);
+	git_config_date_string("gc.pruneworktreesexpire", &prune_worktrees_expire);
 	git_config(git_default_config, NULL);
 }
 
@@ -290,6 +293,7 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	argv_array_pushl(&reflog, "reflog", "expire", "--all", NULL);
 	argv_array_pushl(&repack, "repack", "-d", "-l", NULL);
 	argv_array_pushl(&prune, "prune", "--expire", NULL);
+	argv_array_pushl(&prune_worktrees, "prune", "--worktrees", "--expire", NULL);
 	argv_array_pushl(&rerere, "rerere", "gc", NULL);
 
 	gc_config();
@@ -359,6 +363,12 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 			return error(FAILED_RUN, prune.argv[0]);
 	}
 
+	if (prune_worktrees_expire) {
+		argv_array_push(&prune_worktrees, prune_worktrees_expire);
+		if (run_command_v_opt(prune_worktrees.argv, RUN_GIT_CMD))
+			return error(FAILED_RUN, prune_worktrees.argv[0]);
+	}
+
 	if (run_command_v_opt(rerere.argv, RUN_GIT_CMD))
 		return error(FAILED_RUN, rerere.argv[0]);