Feature request: Sticky key “cancel” key

[dxmh]

Current behaviour:

• Sticky keys are cancelled after a timeout

Desired behaviour:

• Sticky keys are cancelled after a timeout, OR
• Sticky keys are cancelled with a key

Examples:

With &kp ESCAPE configured as cancel key:

• Tap &sk LSHIFT, &kp A = A (uppercase)
• Tap &sk LSHIFT, &kp ESC, &kp A = a (lowercase)

With &mo NAV configured as cancel key:

• Tap &sk LSHIFT, &mo NAV, &kp A = a (lowercase)

[dxmh]

Another idea... In #829 (comment) this was suggested:

Could you not have it look at whether the key pressed is another sticky key instead of modifier?

This made me think - when checking if the key being pressed is also sticky, or a modifier, or whatever, it could also check if the key being pressed is itself and then cancel/unstick if so.

This would allow for an experience very similar to Callum Oakley's popular one-shot key implementation: https://github.com/callum-oakley/qmk_firmware/blob/master/users/callum/readme.md (documentation link).

[daliusd]

I have improved Callum one-shot key implementation with layers (details here https://blog.ffff.lt/posts/callum-layers/) and found out that potentially I need different cancel keys for one-shot modifiers and one-shot layers. Just to make everything more complicated 😄

[ldebritto]

Working around this I've faked a cancel function by creating a macro to trigger a F22 tap when hitting any of the thumb layer switches:

    macros {
        la_nav: cancel_queued_os_mods_and_toggle_nav {
            label = "LA_NAV";
            compatible = "zmk,behavior-macro";
            #binding-cells = <0>;
            bindings
                = <&macro_press &mo NAV>
                , <&macro_tap &kp F22>
                , <&macro_pause_for_release>
                , <&macro_release &mo NAV>
                ;
        };
        la_sym: cancel_queued_os_mods_and_toggle_sym {
            label = "LA_SYM";
            compatible = "zmk,behavior-macro";
            #binding-cells = <0>;
            bindings
                = <&macro_press &mo SYM>
                , <&macro_tap &kp F22>
                , <&macro_pause_for_release>
                , <&macro_release &mo SYM>
                ;
        };