HLS-bundled Fourmolu is outdated (< 0.12)

[georgefst]

It was intended that #883 would cause Fourmolu 0.12 to be used as the dependency version for HLS' Fourmolu plugin. Unfortunately, this doesn't seem to have been the case. We bumped to a version of HLS which supports Fourmolu 0.12, and all else being equal, the latest version of a library should be picked up, so I'm not sure why this has happened.

We should force HLS to use Fourmolu 0.12, but I can't personally work out the right Haskell.Nix incantation to set the constraint.

To demonstrate that this is the case, notice that the HLS-bundled Fourmolu ignores single-constraint-parens, e.g. when formatting n = 1 :: Num a => a, so long as the HLS haskell.plugin.fourmolu.config.external isn't enabled.

[dhess]

Ugh. I don't understand how this happened.

[dhess]

We should force HLS to use Fourmolu 0.12, but I can't personally work out the right Haskell.Nix incantation to set the constraint.

What is the required Cabal incantation? I'll see about translating it to haskell.nix-speak.

[georgefst]

What is the required Cabal incantation?

One way would be to run cabal configure --constraint='fourmolu>=0.12', from the root of the HLS repo.

[dhess]

Hmm, I'm able to convince HLS (via haskell.nix) to use fourmolu-0.12.0.0, but when I do that, the dependency graph breaks on hlint, which is odd:

 nix develop -L                                                                                                                                                   ~/git/primer
warning: Git tree '/Users/dhess/git/primer' is dirty
trace: WARNING: license "LicenseRef-Apache" not found
haskell-project-plan-to-nix-pkgs> Cloning into '/private/tmp/nix-build-haskell-project-plan-to-nix-pkgs.drv-0/tmp.wLWcKJIJNw/dist-newstyle/src/8cip0m236_-695ee5a85f6adb4a'...
haskell-project-plan-to-nix-pkgs> remote: Enumerating objects: 12, done.
haskell-project-plan-to-nix-pkgs> remote: Counting objects: 100% (12/12), done.
haskell-project-plan-to-nix-pkgs> remote: Compressing objects: 100% (9/9), done.
haskell-project-plan-to-nix-pkgs> remote: Total 12 (delta 0), reused 0 (delta 0), pack-reused 0
haskell-project-plan-to-nix-pkgs> Receiving objects: 100% (12/12), 5.91 KiB | 5.91 MiB/s, done.
haskell-project-plan-to-nix-pkgs> HEAD is now at 7341c79 Minimal Repo For Haskell.Nix
haskell-project-plan-to-nix-pkgs> Warning: The package list for 'hackage.haskell.org' is 19493 days old.
haskell-project-plan-to-nix-pkgs> Run 'cabal update' to get the latest list of available packages.
haskell-project-plan-to-nix-pkgs> Warning: Requested index-state 2023-05-13T12:00:00Z is newer than
haskell-project-plan-to-nix-pkgs> 'hackage.haskell.org'! Falling back to older state (2023-05-11T20:39:33Z).
haskell-project-plan-to-nix-pkgs> Resolving dependencies...
haskell-project-plan-to-nix-pkgs> make-install-plan: dieVerbatim: user error (Error: make-install-plan: Could not resolve dependencies:
haskell-project-plan-to-nix-pkgs> [__0] trying: hls-floskell-plugin-1.0.2.1 (user goal)
haskell-project-plan-to-nix-pkgs> [__1] trying: floskell-0.10.7 (dependency of hls-floskell-plugin)
haskell-project-plan-to-nix-pkgs> [__2] trying: haskell-src-exts-1.23.1 (dependency of floskell)
haskell-project-plan-to-nix-pkgs> [__3] trying: bytestring-0.11.4.0/installed-0.11.4.0 (dependency of floskell)
haskell-project-plan-to-nix-pkgs> [__4] trying: aeson-2.1.2.1 (dependency of floskell)
haskell-project-plan-to-nix-pkgs> [__5] trying: base-4.17.1.0/installed-4.17.1.0 (dependency of
haskell-project-plan-to-nix-pkgs> hls-floskell-plugin)
haskell-project-plan-to-nix-pkgs> [__6] trying: hls-fourmolu-plugin-1.1.1.0 (user goal)
haskell-project-plan-to-nix-pkgs> [__7] trying: fourmolu-0.12.0.0 (dependency of hls-fourmolu-plugin)
haskell-project-plan-to-nix-pkgs> [__8] trying: ghc-lib-parser-9.6.1.20230312 (dependency of fourmolu)
haskell-project-plan-to-nix-pkgs> [__9] trying: hls-hlint-plugin-1.1.2.0 (user goal)
haskell-project-plan-to-nix-pkgs> [_10] trying: hlint-3.5 (dependency of hls-hlint-plugin)
haskell-project-plan-to-nix-pkgs> [_11] rejecting: hlint:+ghc-lib (conflict: ghc-lib-parser==9.6.1.20230312,
haskell-project-plan-to-nix-pkgs> hlint +ghc-lib => ghc-lib-parser>=9.4 && <9.5)
haskell-project-plan-to-nix-pkgs> [_11] rejecting: hlint:-ghc-lib (constraint from project config
haskell-project-plan-to-nix-pkgs> /private/tmp/nix-build-haskell-project-plan-to-nix-pkgs.drv-0/tmp.wLWcKJIJNw/cabal.project
haskell-project-plan-to-nix-pkgs> requires opposite flag selection)
haskell-project-plan-to-nix-pkgs> [_11] fail (backjumping, conflict set: ghc-lib-parser, hlint, hlint:ghc-lib)
haskell-project-plan-to-nix-pkgs> After searching the rest of the dependency tree exhaustively, these were the
haskell-project-plan-to-nix-pkgs> goals I've had most trouble fulfilling: hlint, fourmolu, aeson,
haskell-project-plan-to-nix-pkgs> haskell-src-exts, ghc-lib-parser, bytestring, floskell, hls-fourmolu-plugin,
haskell-project-plan-to-nix-pkgs> base, hls-hlint-plugin, hlint:ghc-lib, hls-floskell-plugin
haskell-project-plan-to-nix-pkgs> )
error: builder for '/nix/store/ijc9168n9ria0b749r57y1jdrb9jb0d8-haskell-project-plan-to-nix-pkgs.drv' failed with exit code 1;

The same HLS pin builds fine without the fourmolu-0.12.0.0 constraint.

I'm not sure how to resolve this. Any ideas?

[brprice]

This looks like an incompatibility between hlint and fourmolu's dependencies on ghc-lib-parser. We need (quoting latest versions from hackage):

• hlint requires ghc-lib-parser (>=9.4 && <9.5)
• fourmolu requires ghc-lib-parser (>=9.6 && <9.7)

This also explains why it builds without the constraint: it can just pick an older version of fourmolu which has compatible bounds with hlint.

I think this will be fixed in the next release of hlint, which will contain ndmitchell/hlint#1470 (already merged upstream). I guess we could build hlint from git?

[dhess]

Hmm, so how does anyone get HLS working with fourmolu-0.12.0.0 in that case? Seems like it was premature to merge that support in upstream?

[brprice]

Hmm, so how does anyone get HLS working with fourmolu-0.12.0.0 in that case? Seems like it was premature to merge that support in upstream?

I imagine that one can have either

• HLS+hlint+fourmolu-0.11, or
• HLS+fourmolu-0.12 with no hlint at all

by setting the appropriate flags (for HLS) and constraints (on fourmolu). Just the combination HLS+hlint+fourmolu-0.12 seems problematic (without an unreleased hlint). [Take this with a pinch of salt, I haven't tested anything]

[georgefst]

Yes, I believe @brprice is correct. I've asked HLint about making a release: ndmitchell/hlint#1477 (comment).

There are a few options:

• Use the unreleased HLint, which has ghc-lib-parser-9.6 support.
• I could do some cherry-picking and create a Fourmolu 0.11.1 release containing the necessary fixes, without the dependency bumps.
• Just wait for the imminent HLS 2.0 release (Bump all packages to version 2.0.0.0 and prepare the release haskell/haskell-language-server#3599), and hope that that includes the new HLint.

[dhess]

As this doesn't fix @georgefst's issues, I don't see any point in changing our pin for now, then. We'll wait for, at the latest, the HLS 2.0 release, and hopefully that will fix all the things.

[dhess]

Not sure whether this is fixed in 2.0 because it has other issues: #1009