qmk_firmware/docs/ChangeLog/20230226/PR15741.md

IGNORE_MOD_TAP_INTERRUPT_PER_KEY has been removed and IGNORE_MOD_TAP_INTERRUPT deprecated as a stepping stone towards making IGNORE_MOD_TAP_INTERRUPT the new default behavior for mod-taps in the future.

In place of the now removed IGNORE_MOD_TAP_INTERRUPT_PER_KEY, one must use the pre-existing HOLD_ON_OTHER_KEY_PRESS option.

In most cases, updating get_ignore_mod_tap_interrupt to get_hold_on_other_key_press is simply a matter of renaming the function and swapping every true by false and vice versa. The one subtlety you may need to look out for is that the get_ignore_mod_tap_interrupt was only ever called with mod-taps passed in as the keycode argument, while the keycode argument of get_hold_on_other_key_press can be any dual-role key. This includes not only mod-taps, but also layer-taps, one shot keys, TT(layer) and more. This has an impact on the effect of the default case in a typical per-key configuration making use of a switch(keycode) statement.

To illustrate, let's take the example of a configuration where we'd want all mod-taps to activate the modifier if another key is pressed while held with the exception of LCTL_T(KC_A), which should ignore keys pressed while it is held and activate the modifier only if it has been held for longer than the tapping term. In addition, we would like to keep the default "ignore-interrupt" behavior of layer taps.

An old way to do this would be via the following code:

bool get_ignore_mod_tap_interrupt(uint16_t keycode, keyrecord_t *record) {
    switch(keycode) {
        case LCTL_T(KC_A):
            return true;
        default:
            return false;
    }
}

The correct way to update this code without accidentally changing how the layer-taps work would be the following:

bool get_hold_on_other_key_press(uint16_t keycode, keyrecord_t *record) {
    switch(keycode) {
        // Capture all mod-tap keycodes.
        case QK_MOD_TAP ... QK_MOD_TAP_MAX:
            if (keycode == LCTL_T(KC_A)) {
                // Disable HOLD_ON_OTHER_KEY_PRESS for LCTL_T(KC_A)
                // aka enable IGNORE_MOD_TAP_INTERRUPT for LCTL_T(KC_A).
                return false;
            } else {
                // Enable HOLD_ON_OTHER_KEY_PRESS for every other mod-tap keycode.
                return true;
            }
        default:
            return false;
    }
}

For more information, you are invited to read the sections on IGNORE_MOD_TAP_INTERRUPT and HOLD_ON_OTHER_KEY_PRESS in the page on Tap-Hold configuration options.