master 304c373c98: Improve input extension version checks on GTK 3

[Po Lu]

branch: master
commit 304c373c98ffdba8f946072f15fd109c4cef533f
Author: Po Lu <luangruo@yahoo.com>
Commit: Po Lu <luangruo@yahoo.com>

    Improve input extension version checks on GTK 3
    
    * src/xterm.c (x_term_init): If newer versions of XInput 2 don't
    work, then look for an older one.
---
 src/xterm.c | 62 ++++++++++++++++++++++++++++++++++++++++++++++++-------------
 1 file changed, 49 insertions(+), 13 deletions(-)

diff --git a/src/xterm.c b/src/xterm.c
index caacf8336c..d78c5d7250 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -16398,32 +16398,68 @@ x_term_init (Lisp_Object display_name, char 
*xrm_option, char *resource_name)
                       &xi_first_error))
     {
 #ifdef HAVE_GTK3
-      /* Catch errors caused by GTK requesting a different version of
-        XInput 2 than what Emacs was built with.  */
-      x_catch_errors (dpyinfo->display);
+      bool move_backwards = false;
+      int original_minor = minor;
 
     query:
+
+      /* Catch errors caused by GTK requesting a different version of
+        XInput 2 than what Emacs was built with.  Usually, the X
+        server tolerates these mistakes, but a BadValue error can
+        result if only one of GTK or Emacs wasn't built with support
+        for XInput 2.2.
+
+        To work around the first, it suffices to increase the minor
+        version until the X server is happy if the XIQueryVersion
+        request results in an error.  If that doesn't work, however,
+        then it's the latter, so decrease the minor until the version
+        that GTK requested is found.  */
+      x_catch_errors (dpyinfo->display);
 #endif
 
       rc = XIQueryVersion (dpyinfo->display, &major, &minor);
 
 #ifdef HAVE_GTK3
+      /* Increase the minor version until we find one the X
+        server agrees with.  If that didn't work, then
+        decrease the version until it either hits zero or
+        becomes agreeable to the X server.  */
+
       if (x_had_errors_p (dpyinfo->display))
        {
-         /* Some unreasonable value that will probably not be
-            exceeded in the future.  */
-         if (minor > 100)
-           rc = BadRequest;
+         x_uncatch_errors_after_check ();
+
+         /* Since BadValue errors can't be generated if both the
+            prior and current requests specify a version of 2.2 or
+            later, this means the prior request specified a version
+            of the input extension less than 2.2.  */
+         if (minor >= 2)
+           {
+             move_backwards = true;
+             minor = original_minor;
+
+             if (--minor < 0)
+               rc = BadRequest;
+             else
+               goto query;
+           }
          else
            {
-             /* Increase the minor version until we find one the X server
-                agrees with.  */
-             minor++;
-             goto query;
+             if (!move_backwards)
+               {
+                 minor++;
+                 goto query;
+               }
+
+             if (--minor < 0)
+               rc = BadRequest;
+             else
+               goto query;
+
            }
        }
-
-      x_uncatch_errors ();
+      else
+       x_uncatch_errors_after_check ();
 #endif
 
       if (rc == Success)