builtin/receive-pack: convert to use git-maintenance(1)

In 850b6ed (auto-gc: extract a reusable helper from "git fetch",
2020-05-06), we have introduced a helper function `run_auto_gc()` that
kicks off `git gc --auto`. The intent of this function was to pass down
the "--quiet" flag to git-gc(1) as required without duplicating this at
all callsites. In 7c3e9e8 (auto-gc: pass --quiet down from am,
commit, merge and rebase, 2020-05-06) we then converted callsites that
need to pass down this flag to use the new helper function. This has the
notable omission of git-receive-pack(1), which is the only remaining
user of `git gc --auto` that sets up the proccess manually. This is
probably because it unconditionally passes down the `--quiet` flag and
thus didn't benefit much from the new helper function.

In a95ce12 (maintenance: replace run_auto_gc(), 2020-09-17) we then
replaced `run_auto_gc()` with `run_auto_maintenance()` which invokes
git-maintenance(1) instead of git-gc(1). This command is the modern
replacement for git-gc(1) and is both more thorough and also more
flexible because administrators can configure which tasks exactly to run
during maintenance.

But due to git-receive-pack(1) not using `run_auto_gc()` in the first
place it did not get converted to use git-maintenance(1) like we do
everywhere else now. Address this oversight and start to use the newly
introduced function `prepare_auto_maintenance()`. This will also make it
easier for us to adapt this code together with all the other callsites
that invoke auto-maintenance in the future.

This removes the last internal user of `git gc --auto`.

Signed-off-by: Patrick Steinhardt <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: pks-t

Documentation/config/receive.txt

@@ -8,7 +8,7 @@ receive.advertisePushOptions::
 	capability to its clients. False by default.
 
 receive.autogc::
-	By default, git-receive-pack will run "git-gc --auto" after
+	By default, git-receive-pack will run "git maintenance run --auto" after
 	receiving data from git-push and updating refs.  You can stop
 	it by setting this variable to false.
 

builtin/receive-pack.c

@@ -2581,17 +2581,16 @@ int cmd_receive_pack(int argc, const char **argv, const char *prefix)
 		if (auto_gc) {
 			struct child_process proc = CHILD_PROCESS_INIT;
 
-			proc.no_stdin = 1;
-			proc.stdout_to_stderr = 1;
-			proc.err = use_sideband ? -1 : 0;
-			proc.git_cmd = proc.close_object_store = 1;
-			strvec_pushl(&proc.args, "gc", "--auto", "--quiet",
-				     NULL);
-
-			if (!start_command(&proc)) {
-				if (use_sideband)
-					copy_to_sideband(proc.err, -1, NULL);
-				finish_command(&proc);
+			if (prepare_auto_maintenance(1, &proc)) {
+				proc.no_stdin = 1;
+				proc.stdout_to_stderr = 1;
+				proc.err = use_sideband ? -1 : 0;
+
+				if (!start_command(&proc)) {
+					if (use_sideband)
+						copy_to_sideband(proc.err, -1, NULL);
+					finish_command(&proc);
+				}
 			}
 		}
 		if (auto_update_server_info)