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.

2 files changed, 18 insertions, 2 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;
diff --git a/src/xselect.c b/src/xselect.c
index dd82a906af1..fcf0ee944e2 100644
--- a/src/xselect.c
+++ b/src/xselect.c
@@ -1261,7 +1261,13 @@ x_get_foreign_selection (Lisp_Object selection_symbol, Lisp_Object target_type,
   intmax_t timeout = max (0, x_selection_timeout);
   intmax_t secs = timeout / 1000;
   int nsecs = (timeout % 1000) * 1000000;
-  TRACE1 ("  Start waiting %"PRIdMAX" secs for SelectionNotify", secs);
+  TRACE1 ("  Start waiting %"PRIdMAX" secs for SelectionNotify.", secs);
+
+  if (input_blocked_p ())
+    TRACE0 ("    Input is blocked.");
+  else
+    TRACE1 ("    Waiting for %d nsecs in addition.", nsecs);
+
   /* This function can be called with input blocked inside Xt or GTK
      timeouts run inside popup menus, so use a function that works
      when input is blocked.  Prefer wait_reading_process_output