I think this is not backwards compatible, best to keep the defaults.

Sorry, yesterday I had to go and forgot to mention that I didn't fix the tests yet.

It is not backwards compatible in the sense that now the message won't include the error code by default, as seen in the failing test:

Passed in:
(string) 'Very important error message'
Expected:
(string) 'Very important error message[error code 114514]'

Configuration doesn't (shouldn't) need to be changed and the code can be readded by using vim.diagnostic.config if the user prefers. Maybe a note on how to do it should be added to the docs with a simple example.

Good point.

I fixed the tests, but it's my first time using busted and idk if I did something wrong or the tests don't test what I would expect. The tests in spec/lint_spec.lua didn't fail before my changes, and even modifing the expected messages to gibberish it doesn't fail. I did ""fix"" them anyway to what I would expect, but idk what's wrong with the tests or my understanding of them. I did test it in my local neovim and it worked as expected.

Didn't add any example of customization, idk if that's needed or not. In any case it's outside of the plugin's scope, it's just the neovim api.

ok