fix: correct CapsLock state tracking in waylandim v2

[SHORiN-KiWATA]

Environment

• OS: Arch Linux, Linux 7.0
• Display: Wayland + niri + xwayland-satellite 0.8.1
• fcitx5: 5.1.20
• IM engine: rime (may also affect other engines that use CapsLock state)

Reproduction

1. Switch to rime (Chinese mode)
2. Press CapsLock to enable caps lock
3. Press CapsLock again to disable caps lock
4. Rime remains stuck in English (ASCII) mode — only restarting the IM or manually toggling via F4 menu recovers

Root Cause

WaylandIMInputContextV2::modifiersCallback serializes the modifier state using XKB_STATE_MODS_DEPRESSED | XKB_STATE_MODS_LATCHED. These flags only query held-down (Depressed) and latched (Latch) modifiers, omitting locked modifiers — the category CapsLock belongs to.

Wayland correctly reports mods_locked changes, and xkb_state_update_mask() correctly updates the internal XKB state. However, xkb_state_serialize_mods() reads back only Depressed | Latched, so modifiers_ never contains KeyState::CapsLock. The engine receives key events with uppercase keysyms but no CapsLock modifier in the key states, confusing its internal state machine.

Fix

Replace XKB_STATE_MODS_DEPRESSED | XKB_STATE_MODS_LATCHED with XKB_STATE_MODS_EFFECTIVE. EFFECTIVE includes all three modifier categories (Depressed | Latched | Locked), correctly reflecting CapsLock transitions in modifiers_.

Summary by CodeRabbit

• Bug Fixes
  • Improved modifier-state reporting so keyboard shortcuts and modifier keys are reflected more accurately, including cases like Shift, Caps Lock, Ctrl, Alt, and Num Lock.
  • Updated how modifier updates are forwarded to the virtual keyboard, reducing inconsistencies when input state changes.

[coderabbitai]

📝 Walkthrough

Walkthrough

modifiersCallback now derives Wayland IM modifier updates from the XKB effective modifier state before forwarding them when the virtual keyboard is ready.

Changes

Wayland IM modifier serialization

Layer / File(s)	Summary
Effective modifier mask src/frontend/waylandim/waylandimserverv2.cpp	modifiersCallback now uses XKB_STATE_MODS_EFFECTIVE to populate server_->modifiers_ instead of combining depressed and latched modifier bits.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~10 minutes

Poem

🐇 I hopped through keys with twitching ears,
And found the mask that clears the gears.
Now effective mods dance bright and true,
With every chime of Shift in view.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title accurately summarizes the main fix: WaylandIM v2 now tracks CapsLock state correctly.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.

_{✏️ Tip: You can configure your own custom pre-merge checks in the settings.}

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

---

_{Comment @coderabbitai help to get the list of available commands.}