How do I suppress the warning for "undefined"?

[Aster89]

I make a massive use of undefined because it helps me filling the holes where I don't know yet what to write; then I often query its type (which is deduced by the surrounding context) and conclulde "oh, yes, then this needs to be a x $ y z).

Having undefined marked in yellow (or whatever, I use HLS on Vim via YouCompleteMe, for what is worth) it's really distracting.

[jhrcek]

Can you share more details about your project?

Afaik there's no setting at the level of haskell language server that would allow disabling this warning.
But I know that for example relude library exports a version of undefined with which a warning is associated:
https://hackage.haskell.org/package/relude-1.2.1.0/docs/src/Relude.Debug.html#undefined

Are you perhaps using relude or similar library?
In general I suspect that you might be dealing with https://downloads.haskell.org/ghc/latest/docs/users_guide/exts/pragmas.html?highlight=pragmas#pragma-WARNING

[Aster89]

I don't think I'm using that Relude thing...

Here's more information that might be useful:

• hovering on undefined shows

  undefined :: forall a. HasCallStack => a

  Defined in ‘GHC.Err’ (base-4.17.2.1)

  ---

  _ :: IO Report

  ---

  _ :: forall a. HasCallStack => a

• Compiler: GHC 9.4.8
• Language server: HLS 2.5.0.0

What other information can I provide?

[michaelpj]

What is the diagnostic that you actually get?

[Aster89]

  ✲ Name:        Anti-pattern: unsafe functions
  ✲ Description: Usage of unsafe functions breaks referential transparency
  ✲ Severity:    Error
  ✲ Category:    #Unsafe #AntiPattern
 Possible solutions:
   - Remove 'undefined' or at least replace with 'error' to give better error messages
   - Replace 'unsafeCoerce' with 'coerce'
   - Rewrite the code to avoid using 'unsafePerformIO' and other unsafe IO functions
  [STAN-0212]

[michaelpj]

This is a stan diagnostic. The stan plugin is off in more recent versions of HLS, or you can turn it off in your editor's config.

[jhrcek]

Ah, I didn't think of that, because I never saw stan working :)
There should be two ways to disable stan warning:

1. disable stan plugin at the level of haskell-language-server configuration
2. disable this particular diagnostic at the level of stan (the stan itself can be configured via config files). Though you should be aware that the way that stan plugin is loading config files has been modified/fixed only recently - after the official hls 2.6.0.0 release (cf PR)