nix: refactor with flakes

.github/workflows/nix.yml

@@ -24,7 +24,6 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        ghc: ['default']
         os: [ubuntu-latest, macOS-latest]
 
     steps:
@@ -33,13 +32,21 @@ jobs:
       with:
         submodules: true
     - if: ${{ needs.pre_job.outputs.should_skip != 'true' }}
-      uses: cachix/install-nix-action@v12
+      uses: cachix/install-nix-action@v13
       with:
+        install_url: https://nixos-nix-install-tests.cachix.org/serve/lb41az54kzk6j12p81br4bczary7m145/install
+        install_options: '--tarball-url-prefix https://nixos-nix-install-tests.cachix.org/serve'
+        extra_nix_config: |
+          experimental-features = nix-command flakes
         nix_path: nixpkgs=channel:nixos-unstable
     - if: ${{ needs.pre_job.outputs.should_skip != 'true' }}
       uses: cachix/cachix-action@v8
       with:
         name: haskell-language-server
         authToken: ${{ secrets.HLS_CACHIX_AUTH_TOKEN }}
     - if: ${{ needs.pre_job.outputs.should_skip != 'true' }}
-      run: nix-shell --argstr compiler ${{ matrix.ghc }} --run "cabal update && cabal build"
+      run: nix build
+    - if: ${{ needs.pre_job.outputs.should_skip != 'true' }}
+      run: nix develop --profile dev && cachix push haskell-language-server dev
+    - if: ${{ needs.pre_job.outputs.should_skip != 'true' }}
+      run: nix path-info --json | jq -r '.[].path' | cachix push haskell-language-server

.gitignore

@@ -41,3 +41,7 @@ test/testdata/**/hie.yaml
 # ghcide-bench
 *.identifierPosition
 /bench/example
+
+# nix
+result
+result-doc

README.md

@@ -78,6 +78,7 @@ background](https://neilmitchell.blogspot.com/2020/01/one-haskell-ide-to-rule-th
       - [Using Cabal](#using-cabal)
       - [Using Stack](#using-stack)
       - [Using Nix](#using-nix)
+        - [Flakes support](#flakes-support)
       - [Introduction tutorial](#introduction-tutorial)
       - [Test your hacked HLS in your editor](#test-your-hacked-hls-in-your-editor)
     - [Adding support for a new editor](#adding-support-for-a-new-editor)
@@ -807,8 +808,27 @@ $ cabal update
 $ cabal build
 ```
 
+##### Flakes support
+
+If you are using nix 2.4 style command (enabled by `experimental-features = nix-command`),
+you can use `nix develop` instead of `nix-shell` to enter the development shell. To enter the shell with specific GHC versions:
+
+* `nix develop` or `nix develop .#haskell-language-server-dev` - default GHC version
+* `nix develop .#haskell-language-server-8104-dev` - GHC 8.10.4
+* `nix develop .#haskell-language-server-884-dev` - GHC 8.8.4
+* `nix develop .#haskell-language-server-901-dev` - GHC 9.0.1
+
 If you are looking for a Nix expression to create haskell-language-server binaries, see https://github.com/haskell/haskell-language-server/issues/122
 
+To create binaries:
+
+* `nix build` or `nix build .#haskell-language-server` - default GHC version
+* `nix build .#haskell-language-server-8104` - GHC 8.10.4
+* `nix build .#haskell-language-server-884` - GHC 8.8.4
+* `nix build .#haskell-language-server-901` - GHC 9.0.1
+
+GHC 8.6.5 is not supported here because `nixpkgs-unstable` no longer maintains the corresponding packages set.
+
 #### Introduction tutorial
 
 Pepeiborra [wrote an tutorial](https://github.com/pepeiborra/hls-tutorial) on writing a plugin in HLS.

default.nix

@@ -0,0 +1,11 @@
+# This file is the compt layer of flakes: https://github.com/edolstra/flake-compat
+# See flake.nix for details
+(import (
+  let
+    lock = builtins.fromJSON (builtins.readFile ./flake.lock);
+  in fetchTarball {
+    url = "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+    sha256 = lock.nodes.flake-compat.locked.narHash; }
+) {
+  src =  ./.;
+}).defaultNix