bug#65068: 29.1; xkb-interception interaction causes problems with key combinations

[Po Lu]

Alexander Prähauser <alexander.praehauser@gmx.at> writes:

> The significance of the U-key is that when I press Space-CapsLock-U
> (or any other key, I think), it doesn't send the signal
> that is configured by xkb but the corresponding key of the default
> English keymap (u for the U-key), which really
> shouldn't happen. Anyway, here the output after pressing the sequence
> you wanted:
>
> keycode: 48, keysym: 65027, 0
> keycode: 192, keysym: 269025093, 0
> keycode: 37, keysym: 65507, 0
> keycode: 37, keysym: 65507, 0 <- Control_R
> keycode: 48, keysym: 65027, 0 <- AC11, ISO_Level3_Shift
> keycode: 192, keysym: 269025093, <- XF86Launch5

This attests to Emacs registering the keysyms you meant it to.  If
ISO_Level3_Shift is registered as a modifier key, it should not be
translated into keyboard input afterwards, let alone the original
apostrophe symbol.

Does this patch resolve your problems with typing level 3 characters
coupled with Control?

diff --git a/src/xterm.c b/src/xterm.c
index 6a1642ff56e..7391041ea0c 100644
--- a/src/xterm.c
+++ b/src/xterm.c
@@ -23734,6 +23734,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
              ptrdiff_t i;
              unsigned int old_state;
              struct xi_device_t *device, *source;
+             bool is_modifier_key;
 
              coding = Qlatin_1;
 
@@ -24175,17 +24176,7 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                       /* Any "vendor-specific" key is ok.  */
                       || (keysym & (1 << 28))
                       || (keysym != NoSymbol && nbytes == 0))
-                     && ! (IsModifierKey (keysym)
-                           /* The symbols from XK_ISO_Lock
-                              to XK_ISO_Last_Group_Lock
-                              don't have real modifiers but
-                              should be treated similarly to
-                              Mode_switch by Emacs. */
-#if defined XK_ISO_Lock && defined XK_ISO_Last_Group_Lock
-                           || (XK_ISO_Lock <= keysym
-                               && keysym <= XK_ISO_Last_Group_Lock)
-#endif
-                           ))
+                     && !is_modifier_key)
                    {
                      STORE_KEYSYM_FOR_DEBUG (keysym);
                      /* make_lispy_event will convert this to a symbolic
@@ -24204,7 +24195,11 @@ handle_one_xevent (struct x_display_info *dpyinfo,
                      STORE_KEYSYM_FOR_DEBUG (copy_bufptr[i]);
                    }
 
-                 if (nbytes)
+                 /* Mind that NBYTES can be set even if KEYSYM
+                    represents a modifier key, but that no character
+                    events should be sent in that case.  */
+
+                 if (nbytes && !is_modifier_key)
                    {
                      inev.ie.kind = MULTIBYTE_CHAR_KEYSTROKE_EVENT;
                      inev.ie.arg = make_unibyte_string (copy_bufptr, nbytes);