Stale error displayed in VScode

[FrancisToth]

Hi guys, Haskell noob here. I start playing with VSCode (1.40.2) and Haskell IDE Engine (0.14.0.0) with Haskell Language Server (0.0.31) , and got a really weird behaviour. Given the following code:

module Chap9
    ( 
    )
where

loop3 :: (String, String) -> [String]
loop3 (_, (_ : _)) = loop3 $ ([], [])

foo :: String -> String
foo s = s

If I add another function named like foo

foo :: String -> String
foo s = s

wait for the error to be displayed, and then fix the name of the duplicated function like this:

foo2 :: String -> String
foo2 s = s

the code compiles (when loaded from the terminal) but the editor still shows the stale error telling there are multiple declarations of foo. I do not get the error if the loop3 function is declared like this:

loop3 :: (String, String) -> [String]
loop3 (_, _ : _) = loop3 $ ([], [])

So it looks like the problem comes from pattern matching but I cannot explain why. If this is not the right place to talk about this, I sincerely apologize. In any case, thank you in advance.

[FrancisToth]

I actually ended up thinking that pattern matching against lists inside tuples does not work (it seems to compile though)

foo :: (String, String) -> String
foo (l , (h : t)) = l

triggers the bug and is fixed by:

foo :: (String, String) -> String
foo (l , h : t) = l

[jneira]

I can reproduce with latest versions of hie and the extension

[fendor]

haskell/haskell-ide-engine#1629 seems related to this and not specific to vscode.

[jneira]

We are using haskell-language-server now as backend lsp server, @FrancisToth do you continue expereincing the issue with last hls (1.0.0) version?

[jneira]

In fact hls does not have the quick fix for duplicate functions so the error cant be even reproduced 😟

[jneira]

Opened feature request, i hope the bug will be not present when it will be added 😉 #1532