Refactor sticky/oneshot keys

docs/en/README.md

@@ -28,7 +28,7 @@ Before you look further, you probably want to start with our [getting started gu
 - [HoldTap](holdtap.md): Adds support for augmented modifier keys to act as one key when tapped, and modifier when held.
 - [Macros](macros.md): Adds macros.
 - [Mouse keys](mouse_keys.md): Adds mouse keycodes
-- [OneShot](oneshot.md): Adds support for oneshot/sticky keys.
+- [Sticky keys](sticky_keys.md): Adds support for sticky keys.
 - [Power](power.md): Power saving features. This is mostly useful when on battery power.
 - [SerialACE](serialace.md): [DANGER - _see module README_] Arbitrary Code Execution over the data serial.
 - [Split](split_keyboards.md): Keyboards split in two. Seems ergonomic!

docs/en/modules.md

@@ -14,7 +14,7 @@ put on your keyboard.
 when tapped, and modifier when held.
 - [Macros](macros.md): Adds macros.
 - [Mouse keys](mouse_keys.md): Adds mouse keycodes.
-- [OneShot](oneshot.md): Adds support for oneshot/sticky keys.
+- [Sticky keys](sticky_keys.md): Adds support for sticky keys.
 - [Power](power.md): Power saving features. This is mostly useful when on battery power.
 - [Split](split_keyboards.md): Keyboards split in two. Seems ergonomic!
 - [SerialACE](serialace.md): [DANGER - _see module README_] Arbitrary Code Execution over the data serial.

docs/en/sticky_keys.md

@@ -0,0 +1,58 @@
+# Sticky Keys
+
+Sticky keys enable you to have keys that stay pressed for a certain time or
+until another key is pressed and released.
+If the timeout expires or other keys are pressed, and the sticky key wasn't
+released, it is handled as a regular key being held.
+
+## Enable Sticky Keys
+
+```python
+from kmk.modules.sticky_keys import StickyKeys
+sticky_keys = StickyKeys()
+# optional: set a custom release timeout in ms (default: 1000ms)
+# sticky_keys = StickyKeys(release_after=5000)
+keyboard.modules.append(sticky_keys)
+```
+
+## Keycodes
+
+|Keycode          | Aliases      |Description                       |
+|-----------------|--------------|----------------------------------|
+|`KC.SK(KC.ANY)`  | `KC.STICKY`  |make a sticky version of `KC.ANY` |
+
+`KC.STICKY` accepts any valid key code as argument, including modifiers and KMK
+internal keys like momentary layer shifts.
+
+## Custom Sticky Behavior
+
+The full sticky key signature is as follows:
+
+```python
+KC.SK(
+    KC.ANY,              # the key to made sticky
+    defer_release=False  # when to release the key
+)
+```
+
+### `defer_release`
+
+If `False` (default): release sticky key after the first interrupting key
+releases.
+If `True`: stay sticky until all keys are released. Useful when combined with
+non-sticky modifiers, layer keys, etc...
+
+## Sticky Stacks
+
+Sticky keys can be stacked, i.e. tapping a sticky key within the release timeout
+of another will reset the timeout off all previously tapped sticky keys and
+"stack" their effects.
+In this example if you tap `SK_LCTL` and then `SK_LSFT` followed by `KC.TAB`,
+the output will be `ctrl+shift+tab`.
+
+```python
+SK_LCTL = KC.SK(KC.LCTL)
+SK_LSFT = KC.SK(KC.LSFT)
+
+keyboard.keymap = [[SK_LSFT, SK_LCTL, KC.TAB]]
+```

docs/en/tapdance.md

@@ -24,7 +24,7 @@ KC.SOMETHING_ELSE, MAYBE_THIS_IS_A_MACRO, WHATEVER_YO)`, and place it in your
 keymap somewhere. The only limits on how many keys can go in the sequence are,
 theoretically, the amount of RAM your MCU/board has.
 
-Tap dance supports all `HoldTap` based keys, like mod tap, layer tap, oneshot...
+Tap dance supports all `HoldTap` based keys, like mod tap, layer tap...
 it will even honor every option set for those keys.
 Individual timeouts and prefer hold behavior for every tap in the sequence?
 Not a problem.

kmk/modules/sticky_keys.py

@@ -0,0 +1,149 @@
+from micropython import const
+
+from kmk.keys import make_argumented_key
+from kmk.utils import Debug
+
+debug = Debug(__name__)
+
+
+_SK_IDLE = const(0)
+_SK_PRESSED = const(1)
+_SK_RELEASED = const(2)
+_SK_HOLD = const(3)
+_SK_STICKY = const(4)
+
+
+class StickyKeyMeta:
+    def __init__(self, key, defer_release=False):
+        self.key = key
+        self.defer_release = defer_release
+        self.timeout = None
+        self.state = _SK_IDLE
+
+
+class StickyKeys:
+    def __init__(self, release_after=1000):
+        self.active_keys = []
+        self.release_after = release_after
+
+        make_argumented_key(
+            validator=StickyKeyMeta,
+            names=('SK', 'STICKY'),
+            on_press=self.on_press,
+            on_release=self.on_release,
+        )
+
+    def during_bootup(self, keyboard):
+        return
+
+    def before_matrix_scan(self, keyboard):
+        return
+
+    def after_matrix_scan(self, keyboard):
+        return
+
+    def before_hid_send(self, keyboard):
+        return
+
+    def after_hid_send(self, keyboard):
+        return
+
+    def on_powersave_enable(self, keyboard):
+        return
+
+    def on_powersave_disable(self, keyboard):
+        return
+
+    def process_key(self, keyboard, current_key, is_pressed, int_coord):
+        delay_current = False
+
+        for key in self.active_keys.copy():
+            # Ignore keys that will resolve to and emit a different key
+            # eventually, potentially triggering twice.
+            # Handle interactions among sticky keys (stacking) in `on_press`
+            # instead of `process_key` to avoid race conditions / causal
+            # reordering when resetting timeouts.
+            if (
+                isinstance(current_key.meta, StickyKeyMeta)
+                or current_key.meta.__class__.__name__ == 'TapDanceKeyMeta'
+                or current_key.meta.__class__.__name__ == 'HoldTapKeyMeta'
+            ):
+                continue
+
+            meta = key.meta
+
+            if meta.state == _SK_PRESSED and is_pressed:
+                meta.state = _SK_HOLD
+            elif meta.state == _SK_RELEASED and is_pressed:
+                meta.state = _SK_STICKY
+            elif meta.state == _SK_STICKY:
+                # Defer sticky release until last other key is released.
+                if meta.defer_release:
+                    if not is_pressed and len(keyboard._coordkeys_pressed) <= 1:
+                        self.deactivate(keyboard, key)
+                # Release sticky key; if it's a new key pressed: delay
+                # propagation until after the sticky release.
+                else:
+                    self.deactivate(keyboard, key)
+                    delay_current = is_pressed
+
+        if delay_current:
+            keyboard.resume_process_key(self, current_key, is_pressed, int_coord, False)
+        else:
+            return current_key
+
+    def set_timeout(self, keyboard, key):
+        key.meta.timeout = keyboard.set_timeout(
+            self.release_after,
+            lambda: self.on_release_after(keyboard, key),
+        )
+
+    def on_press(self, key, keyboard, *args, **kwargs):
+        # Let sticky keys stack by renewing timeouts.
+        for sk in self.active_keys:
+            keyboard.cancel_timeout(sk.meta.timeout)
+
+        # Reset on repeated taps.
+        if key.meta.state != _SK_IDLE:
+            key.meta.state = _SK_PRESSED
+        else:
+            self.activate(keyboard, key)
+
+        for sk in self.active_keys:
+            self.set_timeout(keyboard, sk)
+
+    def on_release(self, key, keyboard, *args, **kwargs):
+        # No interrupt or timeout happend, mark key as RELEASED, ready to get
+        # STICKY.
+        if key.meta.state == _SK_PRESSED:
+            key.meta.state = _SK_RELEASED
+        # Key in HOLD state is handled like a regular release.
+        elif key.meta.state == _SK_HOLD:
+            for sk in self.active_keys.copy():
+                keyboard.cancel_timeout(sk.meta.timeout)
+                self.deactivate(keyboard, sk)
+
+    def on_release_after(self, keyboard, key):
+        # Key is still pressed but nothing else happend: set to HOLD.
+        if key.meta.state == _SK_PRESSED:
+            for sk in self.active_keys:
+                key.meta.state = _SK_HOLD
+                keyboard.cancel_timeout(sk.meta.timeout)
+        # Key got released but nothing else happend: deactivate.
+        elif key.meta.state == _SK_RELEASED:
+            for sk in self.active_keys.copy():
+                self.deactivate(keyboard, sk)
+
+    def activate(self, keyboard, key):
+        if debug.enabled:
+            debug('activate')
+        key.meta.state = _SK_PRESSED
+        self.active_keys.insert(0, key)
+        keyboard.resume_process_key(self, key.meta.key, True)
+
+    def deactivate(self, keyboard, key):
+        if debug.enabled:
+            debug('deactivate')
+        key.meta.state = _SK_IDLE
+        self.active_keys.remove(key)
+        keyboard.resume_process_key(self, key.meta.key, False)