do not reject "grep -qr . > out"

The recent fix to avoid an infinite disk-filling loop, commit 5e20a38a,
introduced a minor regression.  If you use grep with -q and -r, and
redirect output to a file that will be traversed, then grep would
reject the command, even though it will generate no output.
In that case, there is no risk of an infinite loop.
* src/main.c (grepfile): Do not reject input == output when
using --quiet/--silent (-q).
Reported by J H Wilson in http://bugs.mageia.org/show_bug.cgi?id=3501
forwarded by Nicolas Vigier to https://savannah.gnu.org/bugs/?34917

1 files changed, 4 insertions, 2 deletions

diff --git a/src/main.c b/src/main.c
index c70156f6..c81342fe 100644
--- a/src/main.c
+++ b/src/main.c
@@ -1225,8 +1225,10 @@ grepfile (char const *file, struct stats *stats)
          disk before we open this file, we can end up reading and matching
          those lines and appending them to the file from which we're reading.
          Then we'd have what appears to be an infinite loop that'd terminate
-         only upon filling the output file system or reaching a quota.  */
-      if (S_ISREG (stats->stat.st_mode) && out_stat.st_ino
+         only upon filling the output file system or reaching a quota.
+         However, there is no risk of an infinite loop when we know that
+         grep will generate no output (-q).  */
+      if (!out_quiet && S_ISREG (stats->stat.st_mode) && out_stat.st_ino
           && SAME_REGULAR_FILE (stats->stat, out_stat))
         {
           error (0, 0, _("input file %s is also the output"), quote (file));