Support for GHC-9.0

[mouse07410]

State of support

• The core functionality of haskell-language-server is supported.
• Only some plugins and formatters needs to be updated to make it work with ghc-9.0.1 so they are not included until then.
• So you should consider use other ghc version only if you are specially interested in those plugins o formatters

Has ghc-9.0 support

• ghcide
• haskell-language-server
• hls-haddock-comments-plugin
• hls-hlint-plugin
• hls-importlens-plugin
• hls-pragmas-plugin
• hls-retrie-plugin
• hls-eval-plugin Eval plugin: support ghc 9.0.1 #1997
• hls-module-name-plugin - Actually builds just fine. Was accidentally disabled
• hls-class-plugin - Class plugin bump up #2475
• hls-refine-imports-plugin - All deps build
• hls-splice-plugin - All deps build
• hls-tactic-plugin
  • Blocked upstream by ghc-source-gen (Support GHC 9 google/ghc-source-gen#77 / Add GHC 9 support google/ghc-source-gen#84)
  • Disabled some tests in GHC9 because they expect Wingman to build. See Disable hole fit suggestions when running Wingman #1873 and the expectFailIfGhc9 function
  • Pull request in progress: WIP: GHC-9.0 support for hls-tactics-plugin #2202
  • Finally added with Post ghc-9.2.1 config cleanup #2582, follow up of the previous one

Formatters

• hls-floskell-plugin
• hls-ormolu-plugin - Support added with Switch to ghc-lib-parser-9.0.1.xxx tweag/ormolu#688
• hls-brittany-plugin - Blocked upstream by brittany:ghc-lib-parser (Support for ghc-9.0.1 lspitzner/brittany#352)
• hls-fourmolu-plugin - Bump Fourmolu to 0.4 #2254
• hls-stylish-haskell-plugin blocked upstream by
  • stylish-haskell:ghc-lib-parser (Support for ghc-9.0.1 stylish-haskell#378)
  • Add support for aeson >= 2.0 stylish-haskell#387

Build system and CI

• stack-9.0.1.yaml - Disables not-yet-working plugins and fetches upstream patches
• cabal-ghc901.project - Used for disabling the not yet working plugins and fetching upstream patches
• flake.nix - Needs to fetch upstream patches and disable not-yet-working plugins (nix: add support for ghc 9.0.1 #1995)
• .circleci/config.yml
• .github/workflows/test.yml - Uses the custom cabal.project and disables tests for non-working plugins. Needs to be updated when more plugins gain ghc-9.0.1 support
• .github/workflows/build.yml - The release script is not updated to make a ghc-9.0.1 release yet (PR Add ghc-9.0.1 to the build release script #1940)
• mergify.io We should probably make it manditory for PRs to successfully build/test on ghc-9.0.1 as well

Dependencies which needs updates and hackage release

• blaze-textual: Allow build for GHC 9.0 swamp-agr/blaze-textual#14. Released in hackage.
• czipwith: Fix GHC 9 compatibility lspitzner/czipwith#2.
• th-extras: Add support for ghc-9.0.1 mokus0/th-extras#8. Needs hackage release: Upload to Hackage mokus0/th-extras#10
• hie-bios: Add compatibility for GHC 9.0 and 9.2 hie-bios#300 (needs hackage release)
• dependent-sum: Add support for GHC-9.0.1 obsidiansystems/dependent-sum#57. Needs hackage release, see New release with ghc 9 compat obsidiansystems/dependent-sum#65
• ghc-api-compat: Drop ghc-api-compat from dependency closure #2128
• operational (shake-bench dependency): Fix build for GHC 9.0.1 HeinrichApfelmus/operational#26 (needs hackage release Hackage release with 9.0.1 support HeinrichApfelmus/operational#29)
  • Support added with Remove custom version of operational #2249

Dependencies needed to inlcude brittany in hackage for 9.0:

• multistate: Allow base 4.15 lspitzner/multistate#8, finally added with Fix build with GHC 9.2.1 lspitzner/multistate#11
• data-tree-print: Allow base < 4.17 and ghc <= 9.2.1 lspitzner/data-tree-print#3
• butcher: Support for base-4.15 and ghc-9.0.* lspitzner/butcher#8

[jneira]

STATUS

It still has not been released

upstream packages that should be updated to being buildable with ghc-9.0.4, to build hls-plugin-api alone

• regex-tdfa:base,
• regex-base:base,
• lens:template-haskell,
• lens:setup
• parallel:base,
• haskell-lsp:base, (we are about to change it as the new package lsp that has the upper bound on 4.15 too)
• haskell-lsp-types:base, (same as haskell-lsp)
• hashable:base,
• time-compat:base,
• these:base,
• assoc:base,
• deepseq:base,
• hslogger:base

//cc @Kleidukos

[jneira]

The release candidate has been uploaded: https://www.haskell.org/ghc/blog/20201229-ghc-9.0.1-rc1-released.html
So we could start to add support for it 😄

[poscat0x04]

Now that ghc 9.0.1 has been released, maybe we should bump up the priority?

[jneira]

Yeah, but i guess it will be a complex change, given we are totally tied to ghc

[konn]

As the module structure of the ghc package drastically changed in 9.0.1, it might make sense to provide some compatibility layer in ghcide or its dependency. I once tried ghc-api-compat with GHC 9.0.1-rc1 as a compact layer, but its Hackage version didn't compile at that time.

[jneira]

We have already a compat module in ghcide but it does not export everything we need and it is misused in some code regions (for example i did not use in hlint puglin until recently)
We can leverage it while we add support for the new ghc version.

https://github.com/haskell/haskell-language-server/blob/master/ghcide/src/Development/IDE/GHC/Compat.hs

[jneira]

I've started a branch to give a quick try to ghc-9.0.1. I am afraid that only trying to build hls-plugin-api our simpler subpackage with less dependencies i have needed several allow-newer:

packages: .

allow-newer:
  regex-tdfa:base,
  regex-base:base,
  lens:template-haskell,
  parallel:base,
  haskell-lsp:base,
  haskell-lsp-types:base,
  hashable:base,
  time-compat:base,
  these:base,
  assoc:base,
  deepseq:base,
  hslogger:base

With this in a cabal.project in ./hls-plugin-api i still got:

cabal: Could not resolve dependencies:
[__0] trying: hls-plugin-api-0.7.0.0 (user goal)
[__1] trying: lens-4.19.2 (dependency of hls-plugin-api)
[__2] trying: lens:setup.base-4.15.0.0/installed-4.15.0.0 (dependency of lens)
[__3] next goal: lens:setup.Cabal (dependency of lens)
[__3] rejecting: lens:setup.Cabal-3.4.0.0/installed-3.4.0.0,
lens:setup.Cabal-3.4.0.0 (constraint from maximum version of Cabal used by
Setup.hs requires <3.4)

So the build type setup of lens is preventing the build. Not sure how to avoid it in the call site.

So we have to wait or patch upstream packages. If we would try to install ghcide or hls with plugins the list of pending packages will be interminable so let's start with this one.