[PATCH] maint: be defensive in avoiding gnulib's poll module

[Pádraig Brady]

* src/tail.c (check_output_alive): Add a guard that would
trigger on most platforms, to detect if we're using the
gnulib poll module.  That's currently problematic in the
way it emulates poll() using select() and would cause
issues on macos and AIX at least as poll() is replaced there.
---
 src/tail.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/src/tail.c b/src/tail.c
index 3ae6baf52..6c7d59faf 100644
--- a/src/tail.c
+++ b/src/tail.c
@@ -352,6 +352,13 @@ check_output_alive (void)
   if (! monitor_output)
     return;
 
+  /* Check we've not enabled gnulib's poll module
+     as that will emulate poll() in a way not
+     currently compatible with tail's usage.  */
+#if defined HAVE_POLL
+# error "gnulib's poll() replacement is currently incompatible"
+#endif
+
   /* poll(2) is needed on AIX (where 'select' gives a readable
      event immediately) and Solaris (where 'select' never gave
      a readable event).  Also use poll(2) on systems we know work
-- 
2.26.2