Add flake template & test in Github Actions (#54)

.github/workflows/ci.yaml

@@ -0,0 +1,27 @@
+name: "CI"
+on:
+  push:
+    branches:
+      - '*'
+  pull_request:
+jobs:
+  checks:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: cachix/install-nix-action@v18
+        with:
+          extra_nix_config: |
+            experimental-features = nix-command flakes
+            access-tokens = github.com=${{ secrets.GITHUB_TOKEN }}
+      - name: Test template
+        id: template
+        run: |
+          FLAKE=$(pwd)
+          TEMP_DIR=$(mktemp -d)
+          cd $TEMP_DIR
+          nix flake init -t $FLAKE
+          # Build haskell executable
+          nix build --override-input haskell-flake path:${FLAKE}
+          # Test haskell devshell (via HLS check)
+          nix develop --override-input haskell-flake path:${FLAKE} -c haskell-language-server

README.md

@@ -8,37 +8,16 @@ To keep `flake.nix` smaller (see examples below) and declarative ([what](https:/
 
 ## Usage
 
-To use `haskell-flake` in your Haskell projects, create a `flake.nix` containing the following:
-
-```nix
-{
-  inputs = {
-    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
-    flake-parts.url = "github:hercules-ci/flake-parts";
-    haskell-flake.url = "github:srid/haskell-flake";
-  };
-  outputs = inputs@{ self, nixpkgs, flake-parts, ... }:
-    flake-parts.lib.mkFlake { inherit self; } {
-      systems = nixpkgs.lib.systems.flakeExposed;
-      imports = [ inputs.haskell-flake.flakeModule ];
-      perSystem = { self', pkgs, ... }: {
-        haskellProjects.default = {
-          packages = { 
-            # You can add more than one local package here.
-            my-package.root = ./.;  # Assumes ./my-package.cabal
-          };
-          # buildTools = hp: { fourmolu = hp.fourmolu; ghcid = null; };
-          # overrides = self: super: { };
-          # hlintCheck.enable = true;
-          # hlsCheck.enable = true;
-        };
-        # haskell-flake doesn't set the default package, but you can do it here.
-        packages.default = self'.packages.my-package;
-      };
-    };
-}
+To use `haskell-flake` in your Haskell projects, run:
+
+``` nix
+nix flake init -t github:srid/haskell-flake
 ```
 
+This will generate a template Haskell project with a `flake.nix`. If you already have a Haskell project, copy over this `flake.nix` and adjust accordingly.
+
+## Documentation
+
 Check out the [list of options](https://flake.parts/options/haskell-flake.html). `haskell-flake` uses `callCabal2nix` and `shellFor` [under the hood](https://github.com/srid/haskell-multi-nix/blob/master/flake.nix).
 
 ## Template

example/example.cabal

@@ -0,0 +1,17 @@
+cabal-version:   3.0
+name:            example
+version:         0.1.0.0
+license:         NONE
+author:          Joe
+maintainer:      joe@example.com
+build-type:      Simple
+
+common warnings
+    ghc-options: -Wall
+
+executable example
+    import:           warnings
+    main-is:          Main.hs
+    build-depends:    base
+    hs-source-dirs:   src
+    default-language: Haskell2010

example/flake.nix

@@ -0,0 +1,26 @@
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    flake-parts.url = "github:hercules-ci/flake-parts";
+    haskell-flake.url = "github:srid/haskell-flake";
+  };
+  outputs = inputs@{ self, nixpkgs, flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = nixpkgs.lib.systems.flakeExposed;
+      imports = [ inputs.haskell-flake.flakeModule ];
+      perSystem = { self', pkgs, ... }: {
+        haskellProjects.default = {
+          packages = {
+            # You can add more than one local package here.
+            example.root = ./.;  # Assumes ./example.cabal
+          };
+          # buildTools = hp: { fourmolu = hp.fourmolu; ghcid = null; };
+          # overrides = self: super: { };
+          # hlintCheck.enable = true;
+          # hlsCheck.enable = true;
+        };
+        # haskell-flake doesn't set the default package, but you can do it here.
+        packages.default = self'.packages.example;
+      };
+    };
+}

example/src/Main.hs

@@ -0,0 +1,4 @@
+module Main where
+
+main :: IO ()
+main = putStrLn "Hello, Haskell!"

flake.nix

@@ -2,5 +2,9 @@
   description = "A `flake-parts` module for Haskell development";
   outputs = { self, ... }: {
     flakeModule = ./flake-module.nix;
+    templates.default = {
+      description = "Example project using haskell-flake";
+      path = ./example;
+    };
   };
 }