[PATCH v2] tests: commandhelper: Accept POLLNVAL on macOS

[Roman Bolshakov <r.bolshakov@xxxxxxxxx>]

commandhelper hangs indefinitely in poll() on macOS on commandtest test2
and later because POLLNVAL is returned on revents for input file
descriptor opened from /dev/null, i.e this hangs:

  $ tests/commandhelper < /dev/null
  BEGIN STDOUT
  BEGIN STDERR
  ^C

But it works fine with regular stdin:

  $ tests/commandhelper <<< test
  BEGIN STDOUT
  BEGIN STDERR
  test
  test
  END STDOUT
  END STDERR

The issue is mentioned in poll(2):

  BUGS
    The poll() system call currently does not support devices.

With the change all 28 cases in commandtest pass.

Signed-off-by: Roman Bolshakov <r.bolshakov@xxxxxxxxx>
---
Chnges since v1:
 - Extract expected events into a variable (Andrea)
 - Provide upstream issue # and fix a typo (Ján)

 tests/commandhelper.c | 12 +++++++++++-
 1 file changed, 11 insertions(+), 1 deletion(-)

diff --git a/tests/commandhelper.c b/tests/commandhelper.c
index 7c260c4e13..ba5681b715 100644
--- a/tests/commandhelper.c
+++ b/tests/commandhelper.c
@@ -190,7 +190,17 @@ int main(int argc, char **argv) {
         }
 
         for (i = 0; i < numpollfds; i++) {
-            if (fds[i].revents & (POLLIN | POLLHUP | POLLERR)) {
+            short revents = POLLIN | POLLHUP | POLLERR;
+
+# ifdef __APPLE__
+            /*
+             * poll() on /dev/null will return POLLNVAL
+             * Apple-Feedback: FB8785208
+             */
+            revents |= POLLNVAL;
+# endif
+
+            if (fds[i].revents & revents) {
                 fds[i].revents = 0;
 
                 got = read(fds[i].fd, buf, sizeof(buf));
-- 
2.28.0