Symbol renaming work in simple modules without any exports does not work

[halloleo]

Your environment

Using VS Code as LSP client with Haskell 9.2.5 via ghcup on macOS. HLS is on 1.9.1

Steps to reproduce

Write a simple module Cnt.hs:

-- File Cnt.hs
module Cnt where

mostFrequentChar' :: String -> Char -> Int -> (Char, Int)
mostFrequentChar' [] maxChar maxFreq = (maxChar, maxFreq)
mostFrequentChar' (c:cs) maxChar maxFreq =
    let freq = count c (c:cs)
    in if freq > maxFreq
        then mostFrequentChar' cs c freq
        else mostFrequentChar' cs maxChar maxFreq
    where count x xs = length $ filter (== x) xs

No exports needed. (I will load the file into ghci to play with it.)

Then try to rename mostFrequentChar' to mostFrequentChar.

Expected behaviour

I expected that mostFrequentChar' is changed to mostFrequentChar.

Actual behaviour

No renaming is performed, but you get (in VS Code):

See also

I discussed this problem first on the Haskell discourse.

[July541]

Thanks for your report! It's a known limitation for hls-rename-plugin, see #3130 for details.

[halloleo]

Thanks for picking this up, @July541.

I had a look at #3130 and I saw the tip about "haskell.plugin.rename.config.crossModule": true. Interesting, but how can a crossModule setting help in a local rename situation?

I think I don't understand...

[July541]

but how can a crossModule setting help in a local rename situation?

Rename only work for local symbols, without the explicit export list, hls with consider all function as exported symbols, that doesn't work.

So you have two choices:

1. Supply an explicit export list, and rename local symbols.
2. Enable crossModule even if it's an experimental item.

[halloleo]

Ah, makes sense: The initial error means I can normally rename local symbols only with export list, but with the crossModule setting I can rename local symbols even without export list, right?

Then excuse my newbie question, but in which file do I need to set this HLS setting haskell.plugin.rename.config.crossModule: true when I use HLS in VS Code?

[July541]

Precisely, you are renaming exported symbols with crossModule enabled since all symbols will be exported implicitly.

On the Settings page, and search haskell rename, you'll find it.

[halloleo]

Thank you, @July541! This works brilliantly!

PS: Not sure whether I should close this issue...

[OlegAlexander]

Hello, and thank you for creating HLS! I'm on Windows in VSCode, and I just ran into the "Explicit export list required for renaming." Luckily, setting haskell.plugin.rename.config.crossModule: true seems to have fixed the problem. I'm new to Haskell, and I want to say that this error was very unexpected coming from other languages. I hope the crossModule renaming settings will be on by default in the future. Again, thank you for making HLS!