Problem:
Too much boilerplate needed to use Lua to impl an excmd or f_xx
function.
Solution:
- Add `nlua_call_vimfn` which takes the args typval, executes
Lua, and returns a typval.
- refactor(excmd): lua impl for :log, :lsp
Problem:
- Builtin "Vimscript" functions (f_xx) are mostly implemented in C.
Partly that's because there is some boilerplate required to call out
to Lua.
- Calls to `vim.fn.foo()` always marshall over the Lua <=> Vimscript
("typval") bridge, even if `fn.foo()` is implemented entirely in Lua:
```
Lua => typval => Object => Lua => Object => typval => Lua.
```
Solution:
Functions declared in eval.lua with `func_lua` are implemented in
entirely in Lua (`_core/vimfn.lua`).
- `gen_eval.lua` wires `func_lua` entries to `lua_wrapper`, which handles
the typval conversion for Vimscript callers (slow path).
- `nlua_call()` detects `func_lua` functions and calls the Lua
implementation directly. This eliminates all conversion overhead for
Lua callers (fast path).
- Validate at build-time that `func`, `func_float`, and `func_lua` are
mutually exclusive.
- Migrate `hostname()` as a toy example, to show the idea.
Problem:
The "tohtml" plugin is loaded by default.
Solution:
- Move it to `pack/dist/opt/nvim.tohtml/`, it is an "opt-in" plugin now.
- Document guidelines.
- Also revert the `plugin/` locations of `spellfile.lua` and `net.lua`.
That idea was not worth the trouble, it will be too much re-education
for too little gain.
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/`
