[PATCH v2 10/22] run-command API: don't fall back on online_cpus()

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

When a "jobs = 0" is passed let's BUG() out rather than fall back on
online_cpus(). The default behavior was added when this API was
implemented in c553c72eed6 (run-command: add an asynchronous parallel
child processor, 2015-12-15).

Most of our code in-tree that scales up to "online_cpus()" by default
calls that function by itself. By having these callers of the
"run_processes_parallel()" API do the same we can in subsequent
commits pass all arguments down as a "const struct".

The preceding commit has an overview of the API callers that passed
"jobs = 0". There were only two of them (actually three, but they
resolved to these two config parsing codepaths).

The "fetch.parallel" caller already had a test for the
"fetch.parallel=0" case added in 0353c688189 (fetch: do not run a
redundant fetch from submodule, 2022-05-16), but there was no such
test for "submodule.fetchJobs". Let's add one here.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 builtin/fetch.c             | 2 ++
 run-command.c               | 7 +++----
 submodule-config.c          | 2 ++
 t/t5526-fetch-submodules.sh | 5 +++++
 4 files changed, 12 insertions(+), 4 deletions(-)

diff --git a/builtin/fetch.c b/builtin/fetch.c
index 78043fb67ef..82f1da14ec1 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -122,6 +122,8 @@ static int git_fetch_config(const char *k, const char *v, void *cb)
 		fetch_parallel_config = git_config_int(k, v);
 		if (fetch_parallel_config < 0)
 			die(_("fetch.parallel cannot be negative"));
+		if (!fetch_parallel_config)
+			fetch_parallel_config = online_cpus();
 		return 0;
 	}
 
diff --git a/run-command.c b/run-command.c
index 5a63008b6e1..21c00a48823 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1562,8 +1562,8 @@ static void pp_init(struct parallel_processes *pp,
 		    task_finished_fn task_finished,
 		    void *data, int ungroup)
 {
-	if (n < 1)
-		n = online_cpus();
+	if (!n)
+		BUG("you must provide a non-zero number of processes!");
 
 	pp->max_processes = n;
 
@@ -1831,8 +1831,7 @@ void run_processes_parallel_tr2(size_t n, get_next_task_fn get_next_task,
 				task_finished_fn task_finished, void *pp_cb,
 				const char *tr2_category, const char *tr2_label)
 {
-	trace2_region_enter_printf(tr2_category, tr2_label, NULL, "max:%d",
-				   ((n < 1) ? online_cpus() : n));
+	trace2_region_enter_printf(tr2_category, tr2_label, NULL, "max:%d", n);
 
 	run_processes_parallel(n, get_next_task, start_failure,
 			       task_finished, pp_cb);
diff --git a/submodule-config.c b/submodule-config.c
index cd7ee236a12..4dc61b3a78a 100644
--- a/submodule-config.c
+++ b/submodule-config.c
@@ -303,6 +303,8 @@ int parse_submodule_fetchjobs(const char *var, const char *value)
 	int fetchjobs = git_config_int(var, value);
 	if (fetchjobs < 0)
 		die(_("negative values not allowed for submodule.fetchJobs"));
+	if (!fetchjobs)
+		fetchjobs = online_cpus();
 	return fetchjobs;
 }
 
diff --git a/t/t5526-fetch-submodules.sh b/t/t5526-fetch-submodules.sh
index e36f9fdf242..98a287ffb90 100755
--- a/t/t5526-fetch-submodules.sh
+++ b/t/t5526-fetch-submodules.sh
@@ -724,6 +724,11 @@ test_expect_success 'fetching submodules respects parallel settings' '
 		GIT_TRACE=$(pwd)/trace.out git fetch --jobs 9 &&
 		grep "9 tasks" trace.out &&
 		>trace.out &&
+
+		GIT_TRACE=$(pwd)/trace.out git -c submodule.fetchJobs=0 fetch &&
+		grep "preparing to run up to [0-9]* tasks" trace.out &&
+		! grep "up to 0 tasks" trace.out &&
+		>trace.out
 	)
 '
 
-- 
2.38.0.971.ge79ff6d20e7