feat: add treefmt-nix to dev flake

.prettierrc.yaml

@@ -0,0 +1,11 @@
+---
+printWidth: 100
+tabWidth: 2
+semi: false
+singleQuote: false
+
+overrides:
+  - files: "*.md"
+    options:
+      proseWrap: always
+      tabWidth: 2

dev/flake.nix

@@ -7,15 +7,23 @@
 
     # CI will override `services-flake` to run checks on the latest source
     services-flake.url = "github:juspay/services-flake";
+
+    treefmt-nix = {
+      url = "github:numtide/treefmt-nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
   };
-  outputs = inputs@{ self, nixpkgs, flake-parts, ... }:
+  outputs = inputs@{ nixpkgs, flake-parts, ... }:
     flake-parts.lib.mkFlake { inherit inputs; } {
       systems = nixpkgs.lib.systems.flakeExposed;
+
       imports = [
         (inputs.pre-commit-hooks-nix + /flake-module.nix)
         ./nix/pre-commit.nix
+        ./nix/treefmt.nix
       ];
-      perSystem = { self', pkgs, config, ... }: {
+
+      perSystem = { pkgs, config, ... }: {
         devShells.default = pkgs.mkShell {
           packages = with pkgs; [
             just

dev/nix/pre-commit.nix

@@ -1,13 +1,18 @@
-{ inputs, ... }:
+{ lib, inputs, ... }:
 {
-  perSystem = { pkgs, lib, ... }: {
+  perSystem = { self', ... }: {
     pre-commit = {
       check.enable = true;
       settings = {
         rootSrc = lib.mkForce inputs.services-flake;
         hooks = {
-          nixpkgs-fmt.enable = true;
           commitizen.enable = true;
+
+          treefmt = {
+            enable = true;
+            package = self'.packages.treefmt;
+            pass_filenames = false; # treefmt walks the tree itself.
+          };
         };
       };
     };

dev/nix/treefmt.nix

@@ -0,0 +1,59 @@
+{ lib, inputs, ... }:
+{
+  imports = [
+    inputs.treefmt-nix.flakeModule
+  ];
+
+  perSystem =
+    { config, pkgs, ... }:
+    let
+      treefmt = config.treefmt.build.wrapper;
+    in
+    {
+      # Define formatter as global output.
+      # cause it provides better options than `nix fmt ...`
+      packages = {
+        inherit treefmt;
+      };
+
+      treefmt = {
+        # Overwrite the built in check, since we need to 
+        # run in the root of the repo.
+        build.check = self:
+          let
+            src = ./../..;
+          in
+          pkgs.runCommandLocal "format" { }
+            # Bash 
+            ''
+              PRJ=$TMP/project
+              cp -r "${src}" $PRJ && chmod -R a+w $PRJ && cd $PRJ
+
+              echo "Check formatting of all files."
+
+              "${lib.getExe treefmt}" --no-cache --fail-on-change "$@" . || {
+                echo "Formatting check failed: please run 'just format'."
+                exit 1
+              }
+            '';
+
+        # Used to find the project root
+        # For worktrees we need either `.git` or a file.
+        projectRootFile = "CHANGELOG.md";
+
+        settings.global = {
+          excludes = [
+          ];
+        };
+
+        # Markdown, JSON, YAML, etc.
+        programs.prettier.enable = true;
+        settings.formatter.prettier.excludes = [ ];
+
+        # Nix.
+        programs.deadnix.enable = false;
+        programs.statix.enable = false;
+        programs.nixfmt.enable = true;
+      };
+    };
+}

justfile

@@ -1,3 +1,6 @@
+set positional-arguments
+set shell := ["bash", "-cue"]
+
 # List all the just commands
 default:
     @just --list
@@ -6,6 +9,13 @@ default:
 changelog:
     cz ch --start-rev $(git describe --tags --abbrev=0 HEAD^) --incremental
 
+# Format treewide all files.
+[group('lint')]
+format *args:
+    cd dev && nix run \
+        --override-input services-flake ../. \
+        ".#treefmt" -- "$@" 
+
 # Run example/simple
 [group('example')]
 ex-simple: