from Resike:

luacheck - --formatter=plain --std none --only [111,112,113] --no-unused --no-redefined --no-unused-args --no-unused-secondaries --no-self --no-max-line-length --no-max-code-line-length --no-max-string-line-length --no-max-comment-line-length --codes --ranges --filename @


111    Setting an undefined global variable.
112    Mutating an undefined global variable.
113    Accessing an undefined global variable.

https://luacheck.readthedocs.io/en/stable/warnings.html

I used to use findglobals, a very simple script to check for global accesses, and obviously this is much better. It is a good idea to use something like this to make sure that you didn't forget to declare some local variable, but unless it can be configured to ignore globals from the WoW API and from other addons most of these are going to be false positives.

I've seen findglobals. Seems good, but I'm probably going to write a small script to detect it without needing a lua runtime.