patch 9.1.0788: <CSI>27;<mod>u is not decoded to literal Escape in kitty/foot

Problem:  <CSI>27;<mod>u is not decoded to literal Escape in kitty/foot
Solution: disable XTerm modifyOtherKeys form 1 when the kitty protocol is enabled
          (Christian Fillion)

References:
- https://invisible-island.net/xterm/modified-keys.html
- https://sw.kovidgoyal.net/kitty/keyboard-protocol/
- e891abdd6a/kitty-keymap.h
- d31459b092/kitty/key_encoding.c (L193)

fixes: #15868
closes: #15881

Signed-off-by: Christian Fillion <contact@cfillion.ca>
Signed-off-by: Christian Brabandt <cb@256bit.org>

src/edit.c

@@ -1625,7 +1625,8 @@ decodeModifyOtherKeys(int c)
     if (typebuf.tb_len >= 4 && (c == CSI || (c == ESC && *p == '[')))
     {
 	idx = (*p == '[');
-	if (p[idx] == '2' && p[idx + 1] == '7' && p[idx + 2] == ';')
+	if (p[idx] == '2' && p[idx + 1] == '7' && p[idx + 2] == ';' &&
+		kitty_protocol_state != KKPS_ENABLED)
 	{
 	    form = 1;
 	    idx += 3;
@@ -1640,9 +1641,10 @@ decodeModifyOtherKeys(int c)
 		break;
 	    ++idx;
 	}
+	int kitty_no_mods = argidx == 0 && kitty_protocol_state == KKPS_ENABLED;
 	if (idx < typebuf.tb_len
 		&& p[idx] == (form == 1 ? '~' : 'u')
-		&& argidx == 1)
+		&& (argidx == 1 || kitty_no_mods))
 	{
 	    // Match, consume the code.
 	    typebuf.tb_off += idx + 1;
@@ -1652,7 +1654,7 @@ decodeModifyOtherKeys(int c)
 		typebuf_was_filled = FALSE;
 #endif
 
-	    mod_mask = decode_modifiers(arg[!form]);
+	    mod_mask = kitty_no_mods ? 0 : decode_modifiers(arg[!form]);
 	    c = merge_modifyOtherKeys(arg[form], &mod_mask);
 	}
     }

src/testdir/test_termcodes.vim

@@ -2001,6 +2001,12 @@ func Test_xx08_kitty_response()
         \ kitty: 'y',
         \ }, terminalprops())
 
+  call feedkeys("\<Esc>[?1u") " simulate the kitty keyboard protocol is enabled
+  call feedkeys(':' .. GetEscCodeCSIu('V', '5') .. GetEscCodeCSIuWithoutModifier("\<Esc>") .. "\<C-B>\"\<CR>", 'Lx!')
+  call assert_equal("\"\<Esc>", @:)
+  call feedkeys(':' .. GetEscCodeCSIu('V', '5') .. GetEscCodeCSIu("\<Esc>", '129') .. "\<C-B>\"\<CR>", 'Lx!')
+  call assert_equal("\"\<Esc>", @:)
+
   set t_RV=
   call test_override('term_props', 0)
 endfunc

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    788,
 /**/
     787,
 /**/