Can’t install specific version of haskell-language-server with reflex-platform

[bradrn]

I have a project using reflex-platform with GHC 8.6.5. Therefore, this project requires haskell-language-server built with GHC 8.6.5. The haskell4nix documentation is very clear on how to install a specific version of HLS, and after looking around the reflex-platform source a bit, I managed to produce the following Nix expression:

{ system ? builtins.currentSystem }:
let config = {
  packageOverrides = pkgs: {
    haskell-language-server = pkgs.haskell-language-server.override { supportedGhcVersions = [ "865" ]; };
  };
}; in
(import ./reflex-platform { inherit system config; }).project ({ pkgs, ... }: {
# snip
})

Of course, I soon discovered that this doesn’t work: supplying config to ./reflex-platform only affects the expression resulting from the import, so installing HLS using nix-env -i haskell-language-server (inside nix-shell) still gets the wrong version, because it’s still looking in <nixpkgs>.

I then did some debugging with nix repl, and this produced the curious result that nixpkgs inside ./reflex-platform does not even appear to contain haskell-language-server:

$ nix repl
Welcome to Nix version 2.3.16. Type :? for help.

nix-repl> config = { packageOverrides = pkgs: { haskell-language-server = pkgs.haskell-language-server.override { supportedGhcVersions = [ "865" ]; }; }; }

nix-repl> system = builtins.currentSystem

nix-repl> rplat = import ./reflex-platform { inherit system config; }

nix-repl> rplat.nixpkgs.haskell-language-server
error: attribute 'haskell-language-server' missing, at (string):1:57

By contrast, it contained other packages I’d expect, for instance GCC:

nix-repl> rplat.nixpkgs.gcc
«derivation /nix/store/hhdqlmw9z0kmnhfcc48ng6bfd8ng4fy0-gcc-wrapper-9.3.0.drv»

And the global nixpkgs certainly contained HLS as expected:

nix-repl> (import <nixpkgs> {}).haskell-language-server
«derivation /nix/store/rg188igj8bscm9wml7riqyblyb2pdf0r-haskell-language-server-1.4.0.0.drv»

Furthermore, even if (import ./reflex-platform { inherit system config; }).nixpkgs were to contain HLS as expected, I’m not sure how I would even go about installing it within my Nix shell, given that said version of nixpkgs is accessible only within the function call in default.nix.

Thus I enquire: does there exist any way to install a specific version of HLS using reflex-platform? And if there is, could it please be added to the documentation? (I know it’s a beginner topic, but then again, HLS is likely one of the first things a beginner would want to install.)

[alexfmpe]

I then did some debugging with nix repl, and this produced the curious result that nixpkgs inside ./reflex-platform does not even appear to contain haskell-language-server:

IIRC the nixpkgs pinned down here had HLS in a different place than more recent nixpkgs.

so installing HLS using nix-env -i haskell-language-server (inside nix-shell) still gets the wrong version, because it’s still looking in <nixpkgs>.

I think you want to add shellToolOverrides to the body of project:

reflex-platform/project/default.nix

Lines 89 to 92 in 53ef944

	, shellToolOverrides ? _: _: {}
	# A function returning a record of tools to provide in the
	# nix-shells.
	#

Haven't tried supportedGhcVersions, but what worked for me was using the HLS from the ghc 8.6.5 package set (default for pinned nixpkgs is 8.10) and launching my editor inside nix-shell -A shells.ghc:

  shellToolOverrides = self: super: {
    inherit (pkgs.haskell.packages.ghc865) haskell-language-server;
  };

Thus I enquire: does there exist any way to install a specific version of HLS using reflex-platform?

The above method gives you the pinned nixpkgs's HLS which is 0.4.0.0. @fendor had a shot at using newer ones but I think it turned out to be complicated.

[bradrn]

IIRC the nixpkgs pinned down here had HLS in a different place than more recent nixpkgs.

Hmm, in that case do you know where it is?

I think you want to add shellToolOverrides to the body of project:

reflex-platform/project/default.nix

Lines 89 to 92 in 53ef944

	, shellToolOverrides ? _: _: {}
	# A function returning a record of tools to provide in the
	# nix-shells.
	#

I must have looked through that file about five times for a field like that, and still I managed to miss it — thanks for pointing this out! shellToolOverrides is indeed what I was looking for.

The above method gives you the pinned nixpkgs's HLS which is 0.4.0.0. @fendor had a shot at using newer ones but I think it turned out to be complicated.

In that case, I think I’ll leave this issue open. After all HLS is one of the most widely-used packages for Haskell development, and I think most people (including me) would prefer to use a newer version.

[rubenmoor]

Using this approach with nixpkgs 20.09:

shellToolOverrides = self: super: {
    inherit (pkgs.haskell.packages.ghc865) haskell-language-server;
  };

I get an error:

Unexpected usage error
can't load .so/.DLL for: /nix/store/pnd2kl27sag76h23wa5kl95a76n3k9i3-glibc-2.27/lib/librt.so
(/nix/store/pnd2kl27sag76h23wa5kl95a76n3k9i3-glibc-2.27/lib/librt.so: undefined symbol:
__clock_nanosleep, version GLIBC_PRIVATE)

[iogrt]

If anyone else comes across this thread, I was able to get a haskell-language-server with the latest reflex-platform (1.1.1.0) (uses ghc 8.10.7 ) by doing the steps mentioned here (btw I'm not using obelisk):
https://discourse.haskell.org/t/haskell-language-server-ghc-version-could-not-be-determined/5856/10

These are the steps in the link:

• checkout haskell-language-server (I used the 1.8-release branch since that's the last version for ghc 8.10.7)
• go into your reflex platform project nix-shell
• cd into haskell language-server directory
• run cabal install
• configure your ide LSP settings to find the hls server executable at $HOME/.cabal/bin/haskell-language-server (the wrapper doesn’t work)

I think reflex-platform should provide an option to install hls. Nix could probably automate the cabal install manual step right?