Fix x-selection-timeout if some keyboard input arrives while waiting

* src/process.c (wait_reading_process_output): Don't allow
skipping calls to select if detect_input_pending when just
waiting for a cell.  (bug#46935)

* src/xselect.c (x_get_foreign_selection): Add more debugging
code.

1 files changed, 11 insertions, 1 deletions

diff --git a/src/process.c b/src/process.c
index 0cbac172fe4..8f654961482 100644
--- a/src/process.c
+++ b/src/process.c
@@ -5492,7 +5492,17 @@ wait_reading_process_output (intmax_t time_limit, int nsecs, int read_kbd,
          triggered by processing X events).  In the latter case, set
          nfds to 1 to avoid breaking the loop.  */
       no_avail = 0;
-      if ((read_kbd || !NILP (wait_for_cell))
+      if ((read_kbd
+           /* The following code doesn't make any sense for just the
+              wait_or_cell case, because detect_input_pending returns
+              whether or not the keyboard buffer isn't empty or there
+              is mouse movement.  Any keyboard input that arrives
+              while waiting for a cell will cause the select call to
+              be skipped, and gobble_input to be called even when
+              there is no input available from the terminal itself.
+              Skipping the call to select also causes the timeout to
+              be ignored.  (bug#46935) */
+           /* || !NILP (wait_for_cell) */)
           && detect_input_pending ())
         {
           nfds = read_kbd ? 0 : 1;