Is there a way to control key behavior through Rust?

[drewlwhitney]

Basically, is there/will there be something similar to QMK's process_record_user() that we could use in Rust?

Additionally, for combos (and possibly other things), are there/will there be hook functions that let us customize things like re-presses and releases? Something like process_combo_key_repress(). My use case is Alt+Tab on a combo that can go either direction, pretty much what's in the linked example.

Thanks!

[farfromexact]

There is no direct equivalent of QMK's process_record_user() in the current RMK configuration language.

RMK does expose raw matrix press/release events as KeyboardEvent, and the documented processor API lets Rust code subscribe to events:

https://github.com/HaoboGu/rmk/blob/main/rmk/src/event/input.rs
https://github.com/HaoboGu/rmk/blob/main/rmk/src/processor/mod.rs
https://github.com/HaoboGu/rmk/blob/main/docs/docs/main/docs/features/processor.md

A custom processor can therefore observe row/column positions and pressed state, but it is not a synchronous replacement hook that can rewrite the key action before the keyboard keymap handles it. For normal customization, use the built-in behavior that matches the state machine you need:

• behavior.combo for simultaneous key presses;
• behavior.morse for tap, hold, re-press, and release sequences;
• behavior.fork for state-dependent replacement;
• macros for a fixed press/release sequence.

The current combo configuration has actions, output, layer, timeout, and prior-idle handling, but it does not expose QMK's process_combo_key_repress hook. A bidirectional Alt+Tab behavior that depends on the exact re-press/release history would therefore need either a custom core behavior or an upstream extension, not just a TOML mapping.

If you implement it in Rust, subscribe to KeyboardEvent for observation and keep the actual output/state machine in a custom behavior integrated at the keyboard processing stage. A processor that only listens to the event channel may see events after the keymap has already made its decision.

[drewlwhitney]

Gotcha! The event system is neat, I'll dig deeper into it