CI: replace luacheck with luals (for headless/automated linting)

[justinmk]

Problem

(This is a tracking issue, to invite discussion/counterpoints/investigation.)

luacheck might be redundant with luals.

Expected behavior

• determine if luacheck adds value beyond what luals is capable of
• if luals has a non-interactive mode, use that instead of luacheck to check code in CI
  • con: this requires lintlua build target to use/install luals
• remove luacheck

[clason]

Possible alternative: https://github.com/JohnnyMorganz/luau-lsp, which has a stand-alone mode

(disclaimer: I don't know how close luau is to lua, so whether that can be leveraged at all)

[lewis6991]

Luau is almost a completely different language so I'm not sure we can use it.

[clason]

https://luau-lang.org claims that

Luau is syntactically backwards-compatible with Lua 5.1 (code that is valid Lua 5.1 is also valid Luau)

However, it is typed, and I would expect any static analyzer would rely on that rather than our annotations, which would kind of defeat the purpose.

[clason]

LuaLS does seem to support a --check mode: https://luals.github.io/wiki/usage/

lua-language-server/bin/lua-language-server --check runtime --checklevel=Error --logpath=. runtime/

Diagnosis complete, 41 problems found, see ./check.json

check.json.txt

Would need some postprocessing...

[clason]

Other relevant data points:

• LuaLS can be installed via homebrew
• LuaLS makes frequent (and sometimes breaking) updates; expect reported diagnostics to change rapidly (although if we explicitly extract diagnostics from the JSON, new checks won't be a problem).

[lewis6991]

I've opened LuaLS/lua-language-server#3051 to try to progress this.