Problem:
We want to encourage implementing core features in Lua instead of C, but
it's clumsy because:
- Core Lua code (built into `nvim` so it is available even if VIMRUNTIME
is missing/invalid) requires manually updating CMakeLists.txt, or
stuffing it into `_editor.lua`.
- Core Lua modules are not organized similar to C modules, `_editor.lua`
is getting too big.
Solution:
- Introduce `_core/` where core Lua code can live. All Lua modules added
there will automatically be included as bytecode in the `nvim` binary.
- Move these core modules into `_core/*`:
```
_defaults.lua
_editor.lua
_options.lua
_system.lua
shared.lua
```
TODO:
- Move `_extui/ => _core/ui2/`
Problem:
Every CI log has a lot of noise at the end, which makes it harder to
find relevant test failures:
Running tests from test/functional/terminal/tui_spec.lua
...
T5831 TUI bg color queries the terminal for background color:
T5832 TUI bg color triggers OptionSet from automatic background processing:
T5833 TUI bg color sends theme update notifications when background changes #31652:
...
Running tests from test/functional/ui/output_spec.lua
...
WRN 2025-12-02T03:36:47.304 ui/c/T5831.28003.0 tui_handle_term_mode:223: TUI: terminal mode 2026 unavailable, state 0
WRN 2025-12-02T03:36:47.359 ui/c/T5832.28006.0 tui_handle_term_mode:223: TUI: terminal mode 2048 unavailable, state 0
WRN 2025-12-02T03:36:47.414 ui/c/T5833.28009.0 tui_handle_term_mode:223: TUI: terminal mode 2048 unavailable, state 0
Solution:
- Skip logging in test-mode.
- This can be reverted later, when these logs are changed to "INFO"
level, per this TODO comment:
```
// TODO(bfredl): This is really ILOG but we want it in all builds.
// add to show_verbose_terminfo() without being too racy ????
WLOG("TUI: terminal mode %d unavailable, state %d", mode, state);
```
