Slim down flake inputs using flake-parts partitions

.envrc

@@ -1,5 +1,6 @@
 watch_file \
   *.cabal \
-  nix/modules/flake/*.nix
+  haskell.nix \
+  dev/*
 
 use flake

README.md

@@ -13,18 +13,11 @@ If you have an *existing* Haskell project, you should probably use https://githu
 
 ## Getting Started
 
-Initialize this template using:
-
-```sh
-nix run nixpkgs#omnix -- \
-  init github:srid/haskell-template -o ./yourproject
-```
-
-*tldr: [Install Nix](https://nixos.asia/en/install), [setup direnv](https://nixos.asia/en/direnv), open in VSCode, install recommended extensions and run `just run`.*
+Initialize this template using the green "Use this template" button above or just clone it, and then [rename it](https://srid.ca/haskell-template/start#rename-the-project).
 
 Full instructions: https://srid.ca/haskell-template/start
 
-Recommended dev environment setup: https://nixos.asia/en/direnv
+*tldr: [Install Nix](https://nixos.asia/en/install), [setup direnv](https://nixos.asia/en/direnv), open in VSCode, install recommended extensions and run `just run`.*
 
 ## Tips
 
@@ -39,6 +32,6 @@ Recommended dev environment setup: https://nixos.asia/en/direnv
 
 ## Discussions
 
-Questions? Ideas? Suggestions? Join our [NixOS Asia community](https://nixos.asia/en/#community) or post in [Github Discussions](https://github.com/srid/haskell-template/discussions).
+Questions? Ideas? Suggestions? Post in [Github Discussions](https://github.com/srid/haskell-template/discussions).
 
 [pre-commit]: https://github.com/cachix/git-hooks.nix

nix/modules/flake/pre-commit.nix → dev/flake-module.nix

@@ -1,12 +1,35 @@
-# Git pre-commit hooks are defined here.
+# Development-only flake-parts module
+# This module is loaded in the "dev" partition and includes devShell, pre-commit hooks, etc.
 
 { inputs, ... }:
 {
   imports = [
     (inputs.git-hooks + /flake-module.nix)
     inputs.fourmolu-nix.flakeModule
+    ../haskell.nix
   ];
-  perSystem = { config, ... }: {
+
+  perSystem = { config, pkgs, ... }: {
+    # Development shell
+    devShells.default = pkgs.mkShell {
+      name = "haskell-template";
+      meta.description = "Haskell development environment";
+
+      # See https://community.flake.parts/haskell-flake/devshell#composing-devshells
+      inputsFrom = [
+        config.haskellProjects.default.outputs.devShell
+        config.pre-commit.devShell
+      ];
+
+      # Development packages
+      packages = with pkgs; [
+        just
+        nixd
+        ghciwatch
+      ];
+    };
+
+    # Git pre-commit hooks
     pre-commit.settings = {
       hooks = {
         nixpkgs-fmt.enable = true;

dev/flake.nix

@@ -0,0 +1,14 @@
+{
+  description = "Development inputs for haskell-template";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
+    git-hooks.url = "github:cachix/git-hooks.nix";
+    git-hooks.flake = false;
+    fourmolu-nix.url = "github:jedimahdi/fourmolu-nix";
+    haskell-flake.url = "github:srid/haskell-flake";
+  };
+
+  # This flake exists only for its inputs; see ./flake-module.nix for outputs.
+  outputs = { ... }: { };
+}

dev/partition.nix

@@ -0,0 +1,24 @@
+# Partition configuration for development outputs
+# This routes devShells and checks to the dev partition
+{ inputs, ... }:
+
+{
+  imports = [
+    inputs.flake-parts.flakeModules.partitions
+  ];
+  # Partition development outputs to avoid fetching dev-only inputs
+  # when users only need packages/apps
+  partitionedAttrs = {
+    devShells = "dev";
+    checks = "dev";
+  };
+
+  partitions.dev = {
+    extraInputsFlake = ./.;
+    module = {
+      imports = [
+        ./flake-module.nix
+      ];
+    };
+  };
+}

flake.nix

@@ -3,20 +3,15 @@
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/nixpkgs-unstable";
     flake-parts.url = "github:hercules-ci/flake-parts";
-    flake-parts.inputs.nixpkgs-lib.follows = "nixpkgs";
-    nixos-unified.url = "github:srid/nixos-unified";
     haskell-flake.url = "github:srid/haskell-flake";
-    fourmolu-nix.url = "github:jedimahdi/fourmolu-nix";
-
-    git-hooks.url = "github:cachix/git-hooks.nix";
-    git-hooks.flake = false;
   };
 
-  outputs = inputs:
-    # This will import ./nix/modules/flake/*.nix
-    # cf. https://nixos-unified.org/autowiring.html#flake-parts
-    #
-    # To write your own Nix, add or edit files in ./nix/modules/flake/
-    inputs.nixos-unified.lib.mkFlake
-      { inherit inputs; root = ./.; };
+  outputs = inputs@{ flake-parts, ... }:
+    flake-parts.lib.mkFlake { inherit inputs; } {
+      systems = [ "x86_64-linux" "aarch64-linux" "x86_64-darwin" "aarch64-darwin" ];
+      imports = [
+        ./haskell.nix
+        ./dev/partition.nix # Development stuff decoupled; https://flake.parts/options/flake-parts-partitions.html
+      ];
+    };
 }

nix/modules/flake/haskell.nix → haskell.nix

@@ -1,26 +1,29 @@
 # haskell-flake configuration goes in this module.
 
-{ root, inputs, ... }:
+{ inputs, ... }:
 {
   imports = [
     inputs.haskell-flake.flakeModule
   ];
-  perSystem = { self', lib, config, pkgs, ... }: {
+  perSystem = { self', lib, ... }: {
     # Our only Haskell project. You can have multiple projects, but this template
     # has only one.
     # See https://github.com/srid/haskell-flake/blob/master/example/flake.nix
     haskellProjects.default = {
+      # The base project is at the flake root
       # To avoid unnecessary rebuilds, we filter projectRoot:
       # https://community.flake.parts/haskell-flake/local#rebuild
-      projectRoot = builtins.toString (lib.fileset.toSource {
-        inherit root;
-        fileset = lib.fileset.unions [
-          (root + /src)
-          (root + /haskell-template.cabal)
-          (root + /LICENSE)
-          (root + /README.md)
-        ];
-      });
+      projectRoot =
+        let root = ./.;
+        in builtins.toString (lib.fileset.toSource {
+          inherit root;
+          fileset = lib.fileset.unions [
+            (root + /src)
+            (root + /haskell-template.cabal)
+            (root + /LICENSE)
+            (root + /README.md)
+          ];
+        });
 
       # The base package set (this value is the default)
       # basePackages = pkgs.haskellPackages;