hls-hlint-plugin: Build fails with ghc-lib >= 9.0 and ghc <= 8.10.7

[maralorn]

I am trying to build hls-hlint-plugin in the above mentioned combination.

I get the following error:

src/Ide/Plugin/Hlint.hs:132:44: error:
    • The constructor ‘GHC.RealSrcSpan’ should have 2 arguments, but has been given 1
    • In the pattern: GHC.RealSrcSpan x
      In the pattern: (GHC.RealSrcSpan x, y)
      In the pattern: (, Nothing) -> (GHC.RealSrcSpan x, y)
    |
132 | pattern RealSrcSpan x y <- ((,Nothing) -> (GHC.RealSrcSpan x, y))
    |                                            ^^^^^^^^^^^^^^^^^

src/Ide/Plugin/Hlint.hs:230:23: error:
    • The constructor ‘RealSrcSpan’ should have no arguments, but has been given 2
    • In the pattern: RealSrcSpan span _
      In an equation for ‘srcSpanToRange’:
          srcSpanToRange (RealSrcSpan span _)
            = Range
                {_start = Position
                            {_line = fromIntegral $ srcSpanStartLine span - 1,
                             _character = fromIntegral $ srcSpanStartCol span - 1},
                 _end = Position
                          {_line = fromIntegral $ srcSpanEndLine span - 1,
                           _character = fromIntegral $ srcSpanEndCol span - 1}}
      In an equation for ‘rules’:
          rules plugin
            = do define $ \ GetHlintDiagnostics file -> ...                 defineNoFile $ \ GetHlintSettings -> ...
                 action
                   $ do files <- getFilesOfInterestUntracked
                        ....
            where
                diagnostics ::
                  NormalizedFilePath -> Either ParseError [Idea] -> [FileDiagnostic]
                diagnostics file (Right ideas)
                  = [(file, ShowDiag, ideaToDiagnostic i) |
                       i <- ideas, ideaSeverity i /= Ignore]
                diagnostics file (Left parseErr)
                  = [(file, ShowDiag, parseErrorToDiagnostic parseErr)]
                ideaToDiagnostic :: Idea -> Diagnostic
                ideaToDiagnostic idea
                  = Diagnostic
                      {_range = srcSpanToRange $ ideaSpan idea, _severity = Just DsInfo,
                       _code = Just (InR $ T.pack $ codePre ++ ideaHint idea),
                       _source = Just "hlint", _message = idea2Message idea,
                       _relatedInformation = Nothing, _tags = Nothing}
                  where
                      codePre = ...
                ....
    |
230 |       srcSpanToRange (RealSrcSpan span _) = Range {

I might be holding it wrong, but my impression is, that this line should not compare ghc, but ghc-lib versions.

haskell-language-server/plugins/hls-hlint-plugin/src/Ide/Plugin/Hlint.hs

Line 139 in 3b687a5

#if MIN_VERSION_ghc(9,0,0)

If someone more knowledgeable (e.g. @fendor) could tell me if that’s right, I‘d be very grateful.

[maralorn]

My initial assumption about what the problem is, was wrong.

haskell-language-server/plugins/hls-hlint-plugin/src/Ide/Plugin/Hlint.hs

Line 142 in 3b687a5

pattern RealSrcSpan x y <- ((,Nothing) -> (GHC.RealSrcSpan x, y))

I could fix the problem for this specific config by replacing the above line with

pattern RealSrcSpan x y <- ((,Nothing) -> (GHC.RealSrcSpan x Nothing, y))

The other solution did not work because then I got a mismatch in the type of BufSpan (the ghc or ghc lib BufSpan vs. the IDE Compat BufSpan).

[maralorn]

That fix isn‘t a fix after all. We get the following runtime error:

Source:   compiler
Severity: DsError
Message: 
  src/Ide/Plugin/Hlint.hs:(250,7)-(258,48): Non-exhaustive patterns in function srcSpanToRange

[michaelpj]

cc @pepeiborra

[michaelpj]

I've actually also observed that runtime error in HLS from nixpkgs recently.

[pepeiborra]

Currently you need to build hlint with the ghc-lib flag until ndmitchell/hlint#1376 is fixed and released

[mjrussell]

Is there an example for how to build hlint with the ghc-lib with nix? Do you override the Haskell package HLS inputs somehow?

[pepeiborra]

Looks like there is an incomplete pattern match in the hls-hlint-plugin itself? Perhaps this wasn't noticed before because the code path was CPP'd out.

[mjrussell]

Presumably from here?

https://github.com/haskell/haskell-language-server/blob/master/plugins/hls-hlint-plugin/src/Ide/Plugin/Hlint.hs#L258-L267

It doesn't look non-exhaustive to me and it doesn't look like its changed in a recent GHC version to add a new constructor. Am I missing something obvious?

[maralorn]

The runtime error in nixpkgs could totally be my fault, because I have added this line in nixpkgs to make the setup compile:

https://github.com/NixOS/nixpkgs/blob/8d8b6e8f442c658f53ae4b10a5060adbd1859c56/pkgs/development/haskell-modules/configuration-ghc-8.10.x.nix#L97

[mjrussell]

Ohhhh, yes indeed I think that could be the culprit

Stepping back for a second, and sorry if this is obvious as I'm a bit new to GHC Lib, but shouldn't we be trying to compile GHC-Lib 8.10.7 with GHC 8.10.7? Can we force the package bounds in the nix derivation?

[edit below]

Im wondering if hls-hlint-plugin = addBuildDepend self.ghc-lib_8_10_7 ... would work without a patch.

[anka-213]

I believe your initial assessment was indeed correct. The pragma line should be changed from

#if MIN_VERSION_ghc(9,0,0)

to

#if MIN_GHC_API_VERSION(9,0,0)

It was changed from the latter to the former in #2128, probably by mistake, when updating the pattern synonym to take two arguments instead of one.

[July541]

I believe your initial assessment was indeed correct. The pragma line should be changed from

#if MIN_VERSION_ghc(9,0,0)

to

#if MIN_GHC_API_VERSION(9,0,0)

It was from the latter to the former in #2128, probably by mistake, when updating the pattern synonym to take two arguments instead of one.

I think it has been fixed in a recent commit