fix(behaviors): Make multiple sticky keys work on same key position

[caksoylar]

Sticky keys have logic implemented so that if you press the same sticky key a second time, it releases the first press before activating a sticky key press again. However, multiple sticky keys are only disambiguated by key position, which means that you currently cannot have active multiple sticky keys that are triggered from the same key position. This scenario occurs under a couple conditions:

• You activate a sticky key (e.g. &sk LCTRL), then activate a different sticky key e.g. (&sk LSHIFT) on a different layer but at the same key position
• You activate multiple sticky keys on a macro invocation (e.g. with bindings = <&sk LSHIFT>, <&sl 1>;)

Using only the key position is usually enough to disambiguate multiple active instances of a behavior; for instance for hold-taps, you cannot press the same key position again while one hold-tap is active at that position. However this doesn't apply to sticky keys since they stay active after you release the key that activates them.

In order to support above scenarios, add three tests covering them and modify the implementation to use behavior binding (e.g. &kp vs. &mo) and parameter (e.g. LCTRL vs. LSHIFT) in addition to key position to disambiguate between active sticky keys.

Also remove the redundant param2 storage in sticky keys since they only accept one binding cell, can drop this refactor commit if it is unnecessary.

Fixes #508 and #1421.

PR check-list

• Branch has a clean commit history
• Additional tests are included, if changing behaviors/core code that is testable.
• Proper Copyright + License headers added to applicable files (Generally, we stick to "The ZMK Contributors" for copyrights to help avoid churn when files get edited)
• Pre-commit used to check formatting of files, commit messages, etc.
• Includes any necessary documentation changes.

[Nick-Munnich]

All LGTM, don't think docs changes or copyright stuff is missing

[urob]

Related: #508 and #1421. Two small comments below.

[caksoylar]

@urob thanks for the issue pointers, I had a vague memory of issues with macros but I never thought to search for existing issues!

[caksoylar]

Interestingly Okke attempted to solve the issue in #670 by implementing a general trace ID. That might be a more robust solution in general, but this implementation is more self-contained and seems robust enough to me.

[friendlylambda]

Thank you so much @caksoylar!

I did some manual testing of this change here to verify it and can confirm it's all working as I would expect. Here are my test notes:

Action is the action I took on the keyboard. Result is the key input received by the OS.

Key layout is here: https://my.glove80.com/#/layout/user/2a9bbbdb-ca3d-4bab-b0cd-214c59581ae0

Run 1: Before Patch (24.02)

Current Behavior

Result:

Test 1: Sticky shift -> &sl layer switch -> sticky command (on same key but different layer) -> letter key (on base layer)

Time (Approx)	Action	Result
0ms	sticky shift key down	shift DOWN
200ms	sticky shift key up
500ms	Layer switch key down
600ms	Layer switch key up
700ms	sticky command key down	shift UP
700ms		command DOWN
800ms	sticky command key up
900ms	letter key "h" down	h DOWN (OS command+h shortcut triggers)
1000ms	letter key "h" up	command UP
1000ms		h UP

Result: 😞 command+h is triggered because the sticky shift is ended when the sticky command is triggered, even though they're on different layers.

Test 2: Macro that sets sticky shift then switches to a sticky layer

Time (Approx)	Action	Result
0ms	macro button down	shift DOWN
100ms	macro button up
400ms	letter key "j" down	"j"
450ms	letter key "j" up	j UP
450ms		shift UP

Result: 😞 lowercase j is outputted instead of an uppercase one due to the sticky layer in the macro ending the sticky shift when triggered

Test 3: Macro that sets sticky shift then sticky alt then switches to a sticky layer (layer 2)

Time (Approx)	Action	Result
0ms	macro button down	shift DOWN
0ms		shift UP
0ms		alt DOWN
0ms		alt UP
100ms	macro button up
200ms	letter key "m" down	"m"
450ms	letter key "m" up	m UP

Result: 😞 lowercase m (which exists only on layer 2) is typed and the modifiers have no effect because they end when the sticky layer is triggered

Run 2: After Patch

Updated Behavior

Test 1: Sticky shift -> &sl layer switch -> sticky command (on same key but different layer) -> letter key (on base layer)

Time (Approx)	Action	Result
0ms	sticky shift key down	shift DOWN
200ms	sticky shift key up
500ms	Layer switch key down
600ms	Layer switch key up
700ms	sticky command key down	command DOWN
800ms	sticky command key up
900ms	letter key "h" down	h DOWN (OS shortcut for command+shift+h triggered)
2000ms	letter key "h" up	h UP
2000ms		shift UP
2000ms		command UP

Result: ✅ both sticky modifiers become active and then resolve when the "h" key is pressed, just like they would if they were on different physical keys.

Test 2: Macro that sets sticky shift then switches to a sticky layer

Time (Approx)	Action	Result
0ms	macro button down	shift DOWN
100ms	macro button up
400ms	letter key "j" down	"J"
450ms	letter key "j" up	j UP
450ms		shift UP

Result: ✅ capital J is typed

Test 3: Macro that sets sticky shift then sticky alt then switches to a sticky layer

Time (Approx)	Action	Result
0ms	macro button down	shift DOWN
0ms		alt DOWN
100ms	macro button up
400ms	letter key "j" down	j DOWN (OS shortcut for shift+option+j triggered)
450ms	letter key "j" up	j UP
450ms		shift UP
450ms		alt UP

Result: ✅ shift+alt+j shortcut is triggered, just like it would be each sticky modifier and the j key were on different physical keys.

Existing Functionality

Test 4: Sticky shift then a letter

Time (Approx)	Action	Result
0ms	sticky shift key down	shift DOWN
100ms	letter key "h" down	"H"
200ms	letter key "h" up	h UP
200ms		shift UP

Result: ✅

Test 5: Sticky shift then sticky shift (same key)

Time (Approx)	Action	Result
0ms	sticky shift key down	shift DOWN
200ms	sticky shift key up
400ms	sticky shift key down	shift UP
400ms		shift DOWN
1400ms	sticky shift key up	shift UP

Result: ✅

Test 6: Sticky shift then sticky gui (different keys)

Time (Approx)	Action	Result
0ms	sticky shift key down	shift DOWN
250ms	sticky shift key up
500ms	sticky gui key down	gui DOWN
750ms	sticky gui key up
1250ms		shift UP
1750ms		gui UP

Result: ✅