Cleanup nix files (#1827)

Drop the classic nix in favor of flakes

Author: zlondrej

CONTRIBUTING.md

@@ -18,10 +18,11 @@ stack test          # Run all the tests
 Or `nix`:
 
 ```shell
-nix-shell nix/shell.nix  # Enter a new development shell with Cabal and Stack
+nix develop  # Enter a new development shell with Cabal and Stack
 
-# Alternatively, another version of GHC can be used. See nix/README.md for more info.
-nix-shell nix/shell.nix --argstr compiler ghc901
+# Alternatively, another version of GHC can be used.
+# See `flake.nix` for all available shells.
+nix develop '#ghc96'
 ```
 
 To build the docs, see `doc/README.md`.

README.md

@@ -66,6 +66,22 @@ You can see the visualised results at https://www.techempower.com/benchmarks/#se
 
 ## Nix
 
-A developer shell.nix file is provided in the `nix` directory
+A developer `flake.nix` file is provided in the root directory.
 
-See  [nix/README.md](nix/README.md)
+Default shell will provide you with tools and dependencies needed to build servant packages.
+
+```sh
+$ nix develop
+```
+
+For the tutorial and the cookbook you can use `tutorial` shell.
+
+```sh
+$ nix develop '#tutorial'
+```
+
+You can also choose a different GHC version.
+
+```sh
+$ nix develop '#ghc96'
+```

default.nix

@@ -38,7 +38,7 @@ nix
 --------
 
 `Nix <https://nixos.org/nix/>`_ users should feel free to take a look at
-the `nix/shell.nix` file in the repository and use it to provision a suitable
+the `flake.nix` file in the repository and use it to provision a suitable
 environment to build and run the examples.
 
 Note for Ubuntu users

doc/tutorial/install.rst

@@ -2,43 +2,94 @@
   description = "Servant development environment";
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-24.05-darwin";
+    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-25.05-darwin";
     flake-utils.url = "github:numtide/flake-utils";
   };
 
-  outputs = { self, nixpkgs, flake-utils }:
-    flake-utils.lib.eachDefaultSystem (system:
+  outputs =
+    {
+      self,
+      nixpkgs,
+      flake-utils,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
       let
         pkgs = import nixpkgs { inherit system; };
 
-        mkDevShell = { compiler ? "ghc92", tutorial ? false }:
+        # We use fourmolu compiled with GHC 9.12
+        # as getting it to compile with lower GHC versions
+        # is complicated and this works out of the box.
+        haskellFormatter = pkgs.haskell.packages.ghc912.fourmolu_0_18_0_0;
+        haskellLinter = pkgs.hlint;
+
+        nixFormatter = pkgs.nixfmt-rfc-style;
+
+        mkDevShell =
+          {
+            compiler ? "ghc92",
+            tutorial ? false,
+          }:
           let
-            ghc = pkgs.haskell.packages.${compiler}.ghcWithPackages (_: []);
-            docstuffs = pkgs.python3.withPackages (ps: with ps; [ recommonmark sphinx sphinx_rtd_theme ]);
+            ghc = pkgs.haskell.packages.${compiler}.ghcWithPackages (ghcPkg: [
+              # Some dependencies don't like being built with
+              # as part of a project, so we pull them from nix.
+              ghcPkg.zlib
+              ghcPkg.lzma
+            ]);
+            docstuffs = pkgs.python3.withPackages (
+              ps: with ps; [
+                recommonmark
+                sphinx
+                sphinx_rtd_theme
+              ]
+            );
           in
           pkgs.mkShell {
-            buildInputs = with pkgs; [
-              ghc
-              zlib
-              python3
-              wget
-              cabal-install
-              postgresql
-              openssl
-              stack
-              haskellPackages.hspec-discover
-            ] ++ (if tutorial then [docstuffs postgresql] else []);
-
-            shellHook = ''
-              eval $(grep export ${ghc}/bin/ghc)
-              export LD_LIBRARY_PATH=$LD_LIBRARY_PATH:"${pkgs.zlib}/lib";
-            '';
+            buildInputs =
+              with pkgs;
+              [
+                ghc
+                python3
+                wget
+                cabal-install
+                postgresql
+                openssl
+                stack
+                haskellPackages.hspec-discover
+                haskellFormatter
+                haskellLinter
+                nixFormatter
+              ]
+              ++ (
+                if tutorial then
+                  [
+                    docstuffs
+                    postgresql
+                  ]
+                else
+                  [ ]
+              );
           };
+
+        mkCiShell = tools: pkgs.mkShell { buildInputs = tools; };
       in
       {
         devShells = {
-          default = mkDevShell {};
+          default = mkDevShell { };
           tutorial = mkDevShell { tutorial = true; };
+
+          # Development shells for different GHC versions.
+          ghc92 = mkDevShell { compiler = "ghc92"; };
+          ghc94 = mkDevShell { compiler = "ghc94"; };
+          ghc96 = mkDevShell { compiler = "ghc96"; };
+          ghc98 = mkDevShell { compiler = "ghc98"; };
+          ghc910 = mkDevShell { compiler = "ghc910"; };
+          ghc912 = mkDevShell { compiler = "ghc912"; };
+
+          # Single-tool shells for CI checks.
+          haskellFormatter = mkCiShell [ haskellFormatter ];
+          haskellLinter = mkCiShell [ haskellLinter ];
         };
       }
     );