maintenance: add --task option

A user may want to only run certain maintenance tasks in a certain
order. Add the --task=<task> option, which allows a user to specify an
ordered list of tasks to run. These cannot be run multiple times,
however.

Here is where our array of maintenance_task pointers becomes critical.
We can sort the array of pointers based on the task order, but we do not
want to move the struct data itself in order to preserve the hashmap
references. We use the hashmap to match the --task=<task> arguments into
the task struct data.

Keep in mind that the 'enabled' member of the maintenance_task struct is
a placeholder for a future 'maintenance.<task>.enabled' config option.
Thus, we use the 'enabled' member to specify which tasks are run when
the user does not specify any --task=<task> arguments. The 'enabled'
member should be ignored if --task=<task> appears.

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

1 files changed, 63 insertions, 3 deletions

diff --git a/builtin/gc.c b/builtin/gc.c
index 86b807a008e..00fff59bdb2 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -701,7 +701,7 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 }
 
 static const char * const builtin_maintenance_run_usage[] = {
-	N_("git maintenance run [--auto] [--[no-]quiet]"),
+	N_("git maintenance run [--auto] [--[no-]quiet] [--task=<task>]"),
 	NULL
 };
 
@@ -759,6 +759,9 @@ struct maintenance_task {
 	const char *name;
 	maintenance_task_fn *fn;
 	unsigned enabled:1;
+
+	/* -1 if not selected. */
+	int selected_order;
 };
 
 enum maintenance_task_label {
@@ -781,13 +784,32 @@ static struct maintenance_task tasks[] = {
 	},
 };
 
+static int compare_tasks_by_selection(const void *a_, const void *b_)
+{
+	const struct maintenance_task *a, *b;
+
+	a = (const struct maintenance_task *)&a_;
+	b = (const struct maintenance_task *)&b_;
+
+	return b->selected_order - a->selected_order;
+}
+
 static int maintenance_run_tasks(struct maintenance_run_opts *opts)
 {
-	int i;
+	int i, found_selected = 0;
 	int result = 0;
 
+	for (i = 0; !found_selected && i < TASK__COUNT; i++)
+		found_selected = tasks[i].selected_order >= 0;
+
+	if (found_selected)
+		QSORT(tasks, TASK__COUNT, compare_tasks_by_selection);
+
 	for (i = 0; i < TASK__COUNT; i++) {
-		if (!tasks[i].enabled)
+		if (found_selected && tasks[i].selected_order < 0)
+			continue;
+
+		if (!found_selected && !tasks[i].enabled)
 			continue;
 
 		if (tasks[i].fn(opts)) {
@@ -799,20 +821,58 @@ static int maintenance_run_tasks(struct maintenance_run_opts *opts)
 	return result;
 }
 
+static int task_option_parse(const struct option *opt,
+			     const char *arg, int unset)
+{
+	int i, num_selected = 0;
+	struct maintenance_task *task = NULL;
+
+	BUG_ON_OPT_NEG(unset);
+
+	for (i = 0; i < TASK__COUNT; i++) {
+		if (tasks[i].selected_order >= 0)
+			num_selected++;
+		if (!strcasecmp(tasks[i].name, arg)) {
+			task = &tasks[i];
+		}
+	}
+
+	if (!task) {
+		error(_("'%s' is not a valid task"), arg);
+		return 1;
+	}
+
+	if (task->selected_order >= 0) {
+		error(_("task '%s' cannot be selected multiple times"), arg);
+		return 1;
+	}
+
+	task->selected_order = num_selected + 1;
+
+	return 0;
+}
+
 static int maintenance_run(int argc, const char **argv, const char *prefix)
 {
+	int i;
 	struct maintenance_run_opts opts;
 	struct option builtin_maintenance_run_options[] = {
 		OPT_BOOL(0, "auto", &opts.auto_flag,
 			 N_("run tasks based on the state of the repository")),
 		OPT_BOOL(0, "quiet", &opts.quiet,
 			 N_("do not report progress or other information over stderr")),
+		OPT_CALLBACK_F(0, "task", NULL, N_("task"),
+			N_("run a specific task"),
+			PARSE_OPT_NONEG, task_option_parse),
 		OPT_END()
 	};
 	memset(&opts, 0, sizeof(opts));
 
 	opts.quiet = !isatty(2);
 
+	for (i = 0; i < TASK__COUNT; i++)
+		tasks[i].selected_order = -1;
+
 	argc = parse_options(argc, argv, prefix,
 			     builtin_maintenance_run_options,
 			     builtin_maintenance_run_usage,