[PATCH v3 2/6] run-command: add hide_output to run_processes_parallel_opts

[Calvin Wan <calvinwan@google.com>]

Output from child processes and callbacks may not be necessary to
print out for every invoker of run_processes_parallel. Add
hide_output as an option to not print said output.

Signed-off-by: Calvin Wan <calvinwan@google.com>
---
 run-command.c               | 8 +++++---
 run-command.h               | 9 +++++++++
 t/helper/test-run-command.c | 6 ++++++
 t/t0061-run-command.sh      | 6 ++++++
 4 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/run-command.c b/run-command.c
index 03787bc7f5..3aa28ad6dc 100644
--- a/run-command.c
+++ b/run-command.c
@@ -1603,7 +1603,8 @@ static void pp_cleanup(struct parallel_processes *pp,
 	 * When get_next_task added messages to the buffer in its last
 	 * iteration, the buffered output is non empty.
 	 */
-	strbuf_write(&pp->buffered_output, stderr);
+	if (!opts->hide_output)
+		strbuf_write(&pp->buffered_output, stderr);
 	strbuf_release(&pp->buffered_output);
 
 	sigchain_pop_common();
@@ -1754,7 +1755,7 @@ static int pp_collect_finished(struct parallel_processes *pp,
 			pp->pfd[i].fd = -1;
 		child_process_init(&pp->children[i].process);
 
-		if (opts->ungroup) {
+		if (opts->ungroup || opts->hide_output) {
 			; /* no strbuf_*() work to do here */
 		} else if (i != pp->output_owner) {
 			strbuf_addbuf(&pp->buffered_output, &pp->children[i].err);
@@ -1826,7 +1827,8 @@ void run_processes_parallel(const struct run_process_parallel_opts *opts)
 				pp.children[i].state = GIT_CP_WAIT_CLEANUP;
 		} else {
 			pp_buffer_stderr(&pp, opts, output_timeout);
-			pp_output(&pp);
+			if (!opts->hide_output)
+				pp_output(&pp);
 		}
 		code = pp_collect_finished(&pp, opts);
 		if (code) {
diff --git a/run-command.h b/run-command.h
index b4584c3698..4570812c08 100644
--- a/run-command.h
+++ b/run-command.h
@@ -496,6 +496,11 @@ struct run_process_parallel_opts
 	 */
 	unsigned int ungroup:1;
 
+	/**
+	 * hide_output: see 'hide_output' in run_processes_parallel() below.
+	 */
+	unsigned int hide_output:1;
+
 	/**
 	 * get_next_task: See get_next_task_fn() above. This must be
 	 * specified.
@@ -547,6 +552,10 @@ struct run_process_parallel_opts
  * NULL "struct strbuf *out" parameter, and are responsible for
  * emitting their own output, including dealing with any race
  * conditions due to writing in parallel to stdout and stderr.
+ * 
+ * If the "hide_output" option is set, any output in the "struct strbuf
+ * *out" parameter will not be printed by this function. This includes
+ * output from child processes as well as callbacks.
  */
 void run_processes_parallel(const struct run_process_parallel_opts *opts);
 
diff --git a/t/helper/test-run-command.c b/t/helper/test-run-command.c
index e9b41419a0..1af443db4d 100644
--- a/t/helper/test-run-command.c
+++ b/t/helper/test-run-command.c
@@ -446,6 +446,12 @@ int cmd__run_command(int argc, const char **argv)
 		opts.ungroup = 1;
 	}
 
+	if (!strcmp(argv[1], "--hide-output")) {
+		argv += 1;
+		argc -= 1;
+		opts.hide_output = 1;
+	}
+
 	if (!strcmp(argv[1], "--pipe-output")) {
 		argv += 1;
 		argc -= 1;
diff --git a/t/t0061-run-command.sh b/t/t0061-run-command.sh
index e50e57db89..a0219f6093 100755
--- a/t/t0061-run-command.sh
+++ b/t/t0061-run-command.sh
@@ -180,6 +180,12 @@ test_expect_success 'run_command runs ungrouped in parallel with more tasks than
 	test_line_count = 4 err
 '
 
+test_expect_success 'run_command hides output when run in parallel' '
+	test-tool run-command --hide-output run-command-parallel 4 sh -c "printf \"%s\n%s\n\" Hello World" >out 2>err &&
+	test_must_be_empty out &&
+	test_must_be_empty err
+'
+
 cat >expect <<-EOF
 preloaded output of a child
 asking for a quick stop
-- 
2.38.0.135.g90850a2211-goog