[PATCH v3 29/30] grep: given --threads with NO_PTHREADS=YesPlease, warn

[Ævar Arnfjörð Bjarmason]

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 <ava...@gmail.com>
---
 builtin/grep.c  | 13 +++++++++++++
 t/t7810-grep.sh | 18 ++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/builtin/grep.c b/builtin/grep.c
index a191e2976b..3c721b75a5 100644
--- a/builtin/grep.c
+++ b/builtin/grep.c
@@ -289,6 +289,17 @@ 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) {
+                       /*
+                        * TRANSLATORS: %s is the configuration
+                        * variable for tweaking threads, currently
+                        * grep.threads
+                        */
+                       warning(_("no threads support, ignoring %s"), var);
+                       num_threads = 0;
+               }
+#endif
        }
 
        return st;
@@ -1229,6 +1240,8 @@ int cmd_grep(int argc, const char **argv, const char 
*prefix)
        else if (num_threads < 0)
                die(_("invalid number of threads specified (%d)"), num_threads);
 #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 561709ef6a..f106387820 100755
--- a/t/t7810-grep.sh
+++ b/t/t7810-grep.sh
@@ -791,6 +791,24 @@ do
        "
 done
 
+test_expect_success !PTHREADS,C_LOCALE_OUTPUT '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 -F "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 -F "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 -F "no threads support, ignoring --threads" err &&
+       grep -F "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 &&
        (
-- 
2.13.0.303.g4ebf302169