maintenance: add [un]register subcommands

In preparation for launching background maintenance from the 'git
maintenance' builtin, create register/unregister subcommands. These
commands update the new 'maintenance.repos' config option in the global
config so the background maintenance job knows which repositories to
maintain.

These commands allow users to add a repository to the background
maintenance list without disrupting the actual maintenance mechanism.

For example, a user can run 'git maintenance register' when no
background maintenance is running and it will not start the background
maintenance. A later update to start running background maintenance will
then pick up this repository automatically.

The opposite example is that a user can run 'git maintenance unregister'
to remove the current repository from background maintenance without
halting maintenance for other repositories.

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-maintenance.txt

@@ -29,6 +29,15 @@ Git repository.
 SUBCOMMANDS
 -----------
 
+register::
+	Initialize Git config values so any scheduled maintenance will
+	start running on this repository. This adds the repository to the
+	`maintenance.repo` config variable in the current user's global
+	config and enables some recommended configuration values for
+	`maintenance.<task>.schedule`. The tasks that are enabled are safe
+	for running in the background without disrupting foreground
+	processes.
+
 run::
 	Run one or more maintenance tasks. If one or more `--task` options
 	are specified, then those tasks are run in that order. Otherwise,
@@ -36,6 +45,11 @@ run::
 	config options are true. By default, only `maintenance.gc.enabled`
 	is true.
 
+unregister::
+	Remove the current repository from background maintenance. This
+	only removes the repository from the configured list. It does not
+	stop the background maintenance processes from running.
+
 TASKS
 -----
 

builtin/gc.c

@@ -1407,7 +1407,56 @@ static int maintenance_run(int argc, const char **argv, const char *prefix)
 	return maintenance_run_tasks(&opts);
 }
 
-static const char builtin_maintenance_usage[] = N_("git maintenance run [<options>]");
+static int maintenance_register(void)
+{
+	struct child_process config_set = CHILD_PROCESS_INIT;
+	struct child_process config_get = CHILD_PROCESS_INIT;
+
+	/* There is no current repository, so skip registering it */
+	if (!the_repository || !the_repository->gitdir)
+		return 0;
+
+	config_get.git_cmd = 1;
+	strvec_pushl(&config_get.args, "config", "--global", "--get", "maintenance.repo",
+		     the_repository->worktree ? the_repository->worktree
+					      : the_repository->gitdir,
+			 NULL);
+	config_get.out = -1;
+
+	if (start_command(&config_get))
+		return error(_("failed to run 'git config'"));
+
+	/* We already have this value in our config! */
+	if (!finish_command(&config_get))
+		return 0;
+
+	config_set.git_cmd = 1;
+	strvec_pushl(&config_set.args, "config", "--add", "--global", "maintenance.repo",
+		     the_repository->worktree ? the_repository->worktree
+					      : the_repository->gitdir,
+		     NULL);
+
+	return run_command(&config_set);
+}
+
+static int maintenance_unregister(void)
+{
+	struct child_process config_unset = CHILD_PROCESS_INIT;
+
+	if (!the_repository || !the_repository->gitdir)
+		return error(_("no current repository to unregister"));
+
+	config_unset.git_cmd = 1;
+	strvec_pushl(&config_unset.args, "config", "--global", "--unset",
+		     "maintenance.repo",
+		     the_repository->worktree ? the_repository->worktree
+					      : the_repository->gitdir,
+		     NULL);
+
+	return run_command(&config_unset);
+}
+
+static const char builtin_maintenance_usage[] =	N_("git maintenance <subcommand> [<options>]");
 
 int cmd_maintenance(int argc, const char **argv, const char *prefix)
 {
@@ -1417,6 +1466,10 @@ int cmd_maintenance(int argc, const char **argv, const char *prefix)
 
 	if (!strcmp(argv[1], "run"))
 		return maintenance_run(argc - 1, argv + 1, prefix);
+	if (!strcmp(argv[1], "register"))
+		return maintenance_register();
+	if (!strcmp(argv[1], "unregister"))
+		return maintenance_unregister();
 
 	die(_("invalid subcommand: %s"), argv[1]);
 }

t/t7900-maintenance.sh

@@ -9,7 +9,7 @@ GIT_TEST_MULTI_PACK_INDEX=0
 
 test_expect_success 'help text' '
 	test_expect_code 129 git maintenance -h 2>err &&
-	test_i18ngrep "usage: git maintenance run" err &&
+	test_i18ngrep "usage: git maintenance <subcommand>" err &&
 	test_expect_code 128 git maintenance barf 2>err &&
 	test_i18ngrep "invalid subcommand: barf" err &&
 	test_expect_code 129 git maintenance 2>err &&
@@ -300,4 +300,19 @@ test_expect_success '--schedule inheritance weekly -> daily -> hourly' '
 	test_subcommand git multi-pack-index write --no-progress <weekly.txt
 '
 
+test_expect_success 'register and unregister' '
+	test_when_finished git config --global --unset-all maintenance.repo &&
+	git config --global --add maintenance.repo /existing1 &&
+	git config --global --add maintenance.repo /existing2 &&
+	git config --global --get-all maintenance.repo >before &&
+	git maintenance register &&
+	git config --global --get-all maintenance.repo >actual &&
+	cp before after &&
+	pwd >>after &&
+	test_cmp after actual &&
+	git maintenance unregister &&
+	git config --global --get-all maintenance.repo >actual &&
+	test_cmp before actual
+'
+
 test_done