builtin/gc: avoid global state in gc_before_repack()

The `gc_before_repack()` should only ever run once in git-gc(1), but we
may end up calling it twice when the "--detach" flag is passed. The
duplicated call is avoided though via a static flag in this function.

This pattern is somewhat unintuitive though. Refactor it to drop the
static flag and instead guard the second call of `gc_before_repack()`
via `opts.detach`.

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

Author: pks-t

builtin/gc.c

@@ -816,22 +816,14 @@ static int report_last_gc_error(void)
 	return ret;
 }
 
-static void gc_before_repack(struct maintenance_run_opts *opts,
-			     struct gc_config *cfg)
+static int gc_before_repack(struct maintenance_run_opts *opts,
+			    struct gc_config *cfg)
 {
-	/*
-	 * We may be called twice, as both the pre- and
-	 * post-daemonized phases will call us, but running these
-	 * commands more than once is pointless and wasteful.
-	 */
-	static int done = 0;
-	if (done++)
-		return;
-
 	if (cfg->pack_refs && maintenance_task_pack_refs(opts, cfg))
-		die(FAILED_RUN, "pack-refs");
+		return error(FAILED_RUN, "pack-refs");
 	if (cfg->prune_reflogs && maintenance_task_reflog_expire(opts, cfg))
-		die(FAILED_RUN, "reflog");
+		return error(FAILED_RUN, "reflog");
+	return 0;
 }
 
 int cmd_gc(int argc,
@@ -965,7 +957,8 @@ int cmd_gc(int argc,
 			goto out;
 		}
 
-		gc_before_repack(&opts, &cfg); /* dies on failure */
+		if (gc_before_repack(&opts, &cfg) < 0)
+			die(NULL);
 		delete_tempfile(&pidfile);
 
 		/*
@@ -995,7 +988,8 @@ int cmd_gc(int argc,
 		free(path);
 	}
 
-	gc_before_repack(&opts, &cfg);
+	if (opts.detach <= 0)
+		gc_before_repack(&opts, &cfg);
 
 	if (!repository_format_precious_objects) {
 		struct child_process repack_cmd = CHILD_PROCESS_INIT;