builtin/gc: move pruning of worktrees into a separate function

In a subsequent commit we will introduce a new "worktree-prune" task for
git-maintenance(1). To prepare for this, refactor the code that spawns
`git worktree prune` into a separate function.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Author: pks-t

builtin/gc.c

@@ -333,6 +333,18 @@ static int maintenance_task_reflog_expire(struct maintenance_run_opts *opts UNUS
 	return run_command(&cmd);
 }
 
+static int maintenance_task_worktree_prune(struct maintenance_run_opts *opts UNUSED,
+					   struct gc_config *cfg)
+{
+	struct child_process prune_worktrees_cmd = CHILD_PROCESS_INIT;
+
+	prune_worktrees_cmd.git_cmd = 1;
+	strvec_pushl(&prune_worktrees_cmd.args, "worktree", "prune", "--expire", NULL);
+	strvec_push(&prune_worktrees_cmd.args, cfg->prune_worktrees_expire);
+
+	return run_command(&prune_worktrees_cmd);
+}
+
 static int too_many_loose_objects(struct gc_config *cfg)
 {
 	/*
@@ -913,16 +925,9 @@ int cmd_gc(int argc,
 		}
 	}
 
-	if (cfg.prune_worktrees_expire) {
-		struct child_process prune_worktrees_cmd = CHILD_PROCESS_INIT;
-
-		prune_worktrees_cmd.git_cmd = 1;
-		strvec_pushl(&prune_worktrees_cmd.args, "worktree", "prune", "--expire", NULL);
-		strvec_push(&prune_worktrees_cmd.args, cfg.prune_worktrees_expire);
-
-		if (run_command(&prune_worktrees_cmd))
-			die(FAILED_RUN, prune_worktrees_cmd.args.v[0]);
-	}
+	if (cfg.prune_worktrees_expire &&
+	    maintenance_task_worktree_prune(&opts, &cfg))
+		die(FAILED_RUN, "worktree");
 
 	rerere_cmd.git_cmd = 1;
 	strvec_pushl(&rerere_cmd.args, "rerere", "gc", NULL);