builtin/maintenance: make "gc" strategy accessible

While the user can pick the "incremental" maintenance strategy, it is
not possible to explicitly use the "gc" strategy. This has two
downsides:

  - It is impossible to use the default "gc" strategy for a specific
    repository when the strategy was globally set to a different strategy.

  - It is not possible to use git-gc(1) for scheduled maintenance.

Address these issues by making making the "gc" strategy configurable.
Furthermore, extend the strategy so that git-gc(1) runs for both manual
and scheduled maintenance.

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

Documentation/config/maintenance.adoc

@@ -30,6 +30,8 @@ The possible strategies are:
 +
 * `none`: This strategy implies no tasks are run at all. This is the default
   strategy for scheduled maintenance.
+* `gc`: This strategy runs the `gc` task. This is the default strategy for
+  manual maintenance.
 * `incremental`: This setting optimizes for performing small maintenance
   activities that do not delete any data. This does not schedule the `gc`
   task, but runs the `prefetch` and `commit-graph` tasks hourly, the

builtin/gc.c

@@ -1843,10 +1843,11 @@ struct maintenance_strategy {
 
 static const struct maintenance_strategy none_strategy = { 0 };
 
-static const struct maintenance_strategy default_strategy = {
+static const struct maintenance_strategy gc_strategy = {
 	.tasks = {
 		[TASK_GC] = {
-			.type = MAINTENANCE_TYPE_MANUAL,
+			.type = MAINTENANCE_TYPE_MANUAL | MAINTENANCE_TYPE_SCHEDULED,
+			.schedule = SCHEDULE_DAILY,
 		},
 	},
 };
@@ -1894,6 +1895,8 @@ static struct maintenance_strategy parse_maintenance_strategy(const char *name)
 {
 	if (!strcasecmp(name, "incremental"))
 		return incremental_strategy;
+	if (!strcasecmp(name, "gc"))
+		return gc_strategy;
 	die(_("unknown maintenance strategy: '%s'"), name);
 }
 
@@ -1937,7 +1940,7 @@ static void initialize_task_config(struct maintenance_run_opts *opts,
 		strategy = none_strategy;
 		type = MAINTENANCE_TYPE_SCHEDULED;
 	} else {
-		strategy = default_strategy;
+		strategy = gc_strategy;
 		type = MAINTENANCE_TYPE_MANUAL;
 	}
 

t/t7900-maintenance.sh

@@ -915,7 +915,7 @@ test_expect_success 'maintenance.strategy is respected' '
 		git gc --quiet --no-detach --skip-foreground-tasks
 		EOF
 
-		test_strategy incremental --schedule=weekly <<-\EOF
+		test_strategy incremental --schedule=weekly <<-\EOF &&
 		git pack-refs --all --prune
 		git prune-packed --quiet
 		git multi-pack-index write --no-progress
@@ -923,6 +923,18 @@ test_expect_success 'maintenance.strategy is respected' '
 		git multi-pack-index repack --no-progress --batch-size=1
 		git commit-graph write --split --reachable --no-progress
 		EOF
+
+		test_strategy gc <<-\EOF &&
+		git pack-refs --all --prune
+		git reflog expire --all
+		git gc --quiet --no-detach --skip-foreground-tasks
+		EOF
+
+		test_strategy gc --schedule=weekly <<-\EOF
+		git pack-refs --all --prune
+		git reflog expire --all
+		git gc --quiet --no-detach --skip-foreground-tasks
+		EOF
 	)
 '