input: kitty: fix alternate codepoint sometimes not being reported

When alternate key reporting is enabled (i.e. when we're supposed to
report the shifted key along with the unshifted key), we try to figure
out whether the key really is shifted or not (and thus which xkb
keysym to use for the unshifted and shifted keys in the escape).

This was done by getting the layout's *all* modifier combinations that
produce the shifted keysym, and if any of of them contained a modifier
that isn't supported by the kitty protocol, the shifted and unshifted
keys are derived from the same keysym. This is to ensure we handle
things like AltGr-combos correctly.

The issue is, since there may be more than one modifier combination
generating the shifted keysym, we may end up using the wrong keysym
just because _another_ combination set contains modifiers not
supported by the kitty protocol. What we're interrested in is whether
the *pressed* set of modifiers contains such modifiers.

Closes #1918

CHANGELOG.md

@@ -71,6 +71,13 @@
 ### Deprecated
 ### Removed
 ### Fixed
+
+* Kitty keyboard protocol: alternate key reporting failing to report
+  the alternate codepoint in some corner cases ([#1918][1918]).
+
+[1918]: https://codeberg.org/dnkl/foot/issues/1918
+
+
 ### Security
 ### Contributors
 

input.c

@@ -1315,29 +1315,8 @@ emit_escapes:
          * (yes, this matches what kitty does, as of 0.23.1)
          */
 
-        /* Get the key's shift level */
+        const bool use_level0_sym = (ctx->mods & ~seat->kbd.kitty_significant) == 0;
-        xkb_level_index_t lvl = xkb_state_key_get_level(
+        const xkb_keysym_t sym_to_use = use_level0_sym && ctx->level0_syms.count > 0
-            seat->kbd.xkb_state, ctx->key, ctx->layout);
-
-        /* And get all modifier combinations that, combined with
-         * the pressed key, results in the current shift level */
-        xkb_mod_mask_t masks[32];
-        size_t mask_count = xkb_keymap_key_get_mods_for_level(
-            seat->kbd.xkb_keymap, ctx->key, ctx->layout, lvl,
-            masks, ALEN(masks));
-
-        /* Check modifier combinations - if a combination has
-         * modifiers not in our set of 'significant' modifiers,
-         * use key sym as-is */
-        bool use_level0_sym = true;
-        for (size_t i = 0; i < mask_count; i++) {
-            if ((masks[i] & ~seat->kbd.kitty_significant) > 0) {
-                use_level0_sym = false;
-                break;
-            }
-        }
-
-        xkb_keysym_t sym_to_use = use_level0_sym && ctx->level0_syms.count > 0
             ? ctx->level0_syms.syms[0]
             : sym;