Although `nlua_call_excmd` is semantically for implementing Ex-commands,
the `require()` should never fail, so that's a "Lua error".
But if the call itself fails (the later `semsg` call), that's an "Ex
cmd" error.
Problem:
`:lsp restart` detects when a client has exited by using the `LspDetach`
autocommand. This works correctly in common cases, but breaks when
restarting a client which is not attached to any buffer. It also breaks
if a client is detached in between `:lsp restart` and the actual
stopping of the client.
Solution:
Move restart logic into `vim/lsp/client.lua`, so it can hook in to
`_on_exit()`. The public `on_exit` callback cannot be used for this, as
`:lsp restart` needs to ensure the restart only happens once, even if
the command is run multiple times on the same client.
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/`
