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

[Po Lu via "Bug reports for GNU Emacs, the Swiss army knife of text editors" <bug-gnu-emacs@gnu.org>]

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

> It does seem to register the correct level shifts now, but it seems to
> evaluate each key immediately after having been
> pressed. For instance, when I press Space-CapsLock-U, this should
> evaluate to C-; and it does, but this is the output
> I'm receiving in-between:
>
> <Control_R> is undefined
> C-' is undefined
> C-; is undefined
>
> Po Lu [2023-08-24 Thu 17:56] wrote:
>
>> 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);

Please excuse my carelessness, I appear to have ommitted a chunk of the
diff:

diff --git a/src/xterm.c b/src/xterm.c
index 6a1642ff56e..4b2da066694 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;
 
@@ -24091,6 +24092,18 @@ handle_one_xevent (struct x_display_info *dpyinfo,
 		      goto xi_done_keysym;
 		    }
 
+		  is_modifier_key = (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
+				     );
+
 		  /* Random non-modifier sorts of keysyms.  */
 		  if (((keysym >= XK_BackSpace && keysym <= XK_Escape)
 		       || keysym == XK_Delete
@@ -24175,17 +24188,7 @@ 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 +24207,11 @@ 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);