Code action to remove redundant imports is sometimes not created

[jhrcek]

Using hls 2.7.0.0 in vscode with ghc 9.4.8, I sometimes don't get "remove redundant imports" code action.

Here's a one-module reproducer (assuming you have a cabal project with postgresql-simple dependency):

module Main where

import Database.PostgreSQL.Simple.Types (In (..), PGArray (..), Values (..), fromIdentifier, fromQuery)

main :: IO ()
main = do
    let array = PGArray []
        in_ = In []
        values = Values [] []
    putStrLn "Hello, Haskell!"

Although warning is generated and displayed on hover:

The import of ‘Identifier(fromIdentifier), Query(fromQuery)’
from module ‘Database.PostgreSQL.Simple.Types’ is redundanttypecheck(-Wunused-imports)

The usual code action to remove unused import is not created. Not a big deal, but it's breaking my flow, as now I have to focus on what the warning is exactly saying and fix it manually :smile:

[jhrcek]

Hint for anyone looking into fixing this

This seems to happen when the unused field is a record field selector (for both data and newtypes). When these are unused, GHC warning actually mentions `RecordConstructor(recordFieldName)` in the diagnostic.

The place where this breaks down is in this function: https://github.com/haskell/haskell-language-server/blob/23005f8b1dd6a6d8b9248138629a3c4561bd8843/plugins/hls-refactor-plugin/src/Development/IDE/Plugin/CodeAction.hs#L1942-L1955 which gets passed b::String like RecordConstructor(recordFieldName), tries to compare it with printOutputable b' which at this point is just recordFieldName, which are not equal and so no code action is generated for these.

[battermann]

Looking into this