[PATCH v2 8/8] grep: given --threads with NO_PTHREADS=YesPlease, warn

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

Add a warning about missing thread support when grep.threads or
--threads is set to a non 0 (default) or 1 (no parallelism) value
under NO_PTHREADS=YesPlease.

This is for consistency with the index-pack & pack-objects commands,
which also take a --threads option & are configurable via
pack.threads, and have long warned about the same under
NO_PTHREADS=YesPlease.

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 builtin/grep.c  |  8 ++++++++
 t/t7810-grep.sh | 18 ++++++++++++++++++
 2 files changed, 26 insertions(+)

diff --git a/builtin/grep.c b/builtin/grep.c
index cb3323060e..c746cdd33c 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -290,6 +290,12 @@ static int grep_cmd_config(const char *var, const char *value, void *cb)
 		if (num_threads < 0)
 			die(_("invalid number of threads specified (%d) for %s"),
 			    num_threads, var);
+#ifdef NO_PTHREADS
+		else if (num_threads && num_threads != 1) {
+			warning(_("no threads support, ignoring %s"), var);
+			num_threads = 0;
+		}
+#endif
 	}
 
 	return st;
@@ -1228,6 +1234,8 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
 	if (num_threads == 1)
 		num_threads = 0;
 #else
+	if (num_threads)
+		warning(_("no threads support, ignoring --threads"));
 	num_threads = 0;
 #endif
 
diff --git a/t/t7810-grep.sh b/t/t7810-grep.sh
index 4523ca926b..f4c225b410 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -787,6 +787,24 @@ do
 	"
 done
 
+test_expect_success !PTHREADS,!GETTEXT_POISON 'grep --threads=N or pack.threads=N warns when no pthreads' '
+	git grep --threads=2 Hello hello_world 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 1 warnings &&
+	grep "no threads support, ignoring --threads" err &&
+	git -c grep.threads=2 grep Hello hello_world 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 1 warnings &&
+	grep "no threads support, ignoring grep\.threads" err &&
+	git -c grep.threads=2 grep --threads=4 Hello hello_world 2>err &&
+	grep ^warning: err >warnings &&
+	test_line_count = 2 warnings &&
+	grep "no threads support, ignoring --threads" err &&
+	grep "no threads support, ignoring grep\.threads" err &&
+	git -c grep.threads=0 grep --threads=0 Hello hello_world 2>err &&
+	test_line_count = 0 err
+'
+
 test_expect_success 'grep from a subdirectory to search wider area (1)' '
 	mkdir -p s &&
 	(
-- 
2.11.0