csi: implement CSI > 4n (reset modifyOtherKeys)

CHANGELOG.md

@@ -60,6 +60,10 @@
   is similar to `show-urls-launch`, but does not automatically exit
   URL mode after activating an URL
   (https://codeberg.org/dnkl/foot/issues/964).
+* Support for `CSI > 4 n`, disable _modifyOtherKeys_. Note that since
+  foot only supports level 1 and 2 (and not level 0), this sequence
+  does not disable _modifyOtherKeys_ completely, but simply reverts it
+  back to level 1 (the default).
 
 
 ### Changed

csi.c

@@ -1497,6 +1497,24 @@ csi_dispatch(struct terminal *term, uint8_t final)
             }
             break; /* final == 'm' */
 
+        case 'n': {
+            int resource = vt_param_get(term, 0, 2);  /* Default is modifyFuncionKeys */
+            switch (resource) {
+            case 0:  /* modifyKeyboard */
+            case 1:  /* modifyCursorKeys */
+            case 2:  /* modifyFunctionKeys */
+                break;
+
+            case 4:  /* modifyOtherKeys */
+                /* We don’t support fully disabling modifyOtherKeys,
+                 * but simply revert back to mode ‘1’ */
+                term->modify_other_keys_2 = false;
+                LOG_DBG("modifyOtherKeys=1");
+                break;
+            }
+            break;
+        }
+
         case 'u': {
             int flags = vt_param_get(term, 0, 0) & KITTY_KBD_SUPPORTED;
 

doc/foot-ctlseqs.7.scd

@@ -563,8 +563,14 @@ manipulation sequences. The generic format is:
 |  \\E[ > 4 ; _Pv_ m
 :  XTMODKEYS
 :  xterm
-:  Set level of the _modifyOtherKey_ property to _Pv_. Note that foot
+:  Set level of the _modifyOtherKeys_ property to _Pv_. Note that foot
    only supports level 1 and 2, where level 1 is the default setting.
+|  \\E[ > 4 n
+:  <unnamed>
+:  xterm
+:  Resets the _modifyOtherKeys_ property to level 1. Note that in foot,
+   this sequence does not completely disable _modifyOtherKeys_, since
+   foot only supports level 1 and level 2 (and not level 0).
 |  \\E[ ? u
 :  <unnamed>
 :  kitty