feat: add pre-commit-hooks.nix, enforcing conventional commits

enable treefmt and commitizen in pre-commit-hooks.nix

Along with this, we also:

* bump: update nixpkgs of dev flake for pre-commit-hooks.nix to work

the older version didn't have cljfmt

.gitignore

@@ -3,3 +3,4 @@
 /result
 # created when `just run <service>` is used
 /test/data
+/.pre-commit-config.yaml

dev/flake.lock

@@ -1,5 +1,21 @@
 {
   "nodes": {
+    "flake-compat": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1696426674,
+        "narHash": "sha256-kvjfFW7WAETZlt09AgDn1MrtKzP7t90Vf7vypd3OL1U=",
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "rev": "0f9255e01c2351cc7d116c072cb317785dd33b33",
+        "type": "github"
+      },
+      "original": {
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
     "flake-parts": {
       "inputs": {
         "nixpkgs-lib": "nixpkgs-lib"
@@ -33,13 +49,52 @@
         "type": "github"
       }
     },
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1701680307,
+        "narHash": "sha256-kAuep2h5ajznlPMD9rnQyffWG8EM/C73lejGofXvdM8=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "4022d587cbbfd70fe950c1e2083a02621806a725",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "gitignore": {
+      "inputs": {
+        "nixpkgs": [
+          "pre-commit-hooks-nix",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1703887061,
+        "narHash": "sha256-gGPa9qWNc6eCXT/+Z5/zMkyYOuRZqeFZBDbopNZQkuY=",
+        "owner": "hercules-ci",
+        "repo": "gitignore.nix",
+        "rev": "43e1aa1308018f37118e34d3a9cb4f5e75dc11d5",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "gitignore.nix",
+        "type": "github"
+      }
+    },
     "nixpkgs": {
       "locked": {
-        "lastModified": 1697688401,
-        "narHash": "sha256-61QlajY7R9PbK25uFl55zh968CVNspwXX1zzimic4Uo=",
+        "lastModified": 1709613862,
+        "narHash": "sha256-mH+c2gFEzEe49lhUWJ0ieIaMaJ1W85E6G1xLm8ege90=",
         "owner": "nixos",
         "repo": "nixpkgs",
-        "rev": "458ef9126aa380996d77d44f53f886c2d8485f53",
+        "rev": "311a4be96d940a0c673e88bd5bc83ea4f005cc02",
         "type": "github"
       },
       "original": {
@@ -83,11 +138,38 @@
         "type": "github"
       }
     },
+    "pre-commit-hooks-nix": {
+      "inputs": {
+        "flake-compat": "flake-compat",
+        "flake-utils": "flake-utils",
+        "gitignore": "gitignore",
+        "nixpkgs": [
+          "nixpkgs"
+        ],
+        "nixpkgs-stable": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1708018599,
+        "narHash": "sha256-M+Ng6+SePmA8g06CmUZWi1AjG2tFBX9WCXElBHEKnyM=",
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "rev": "5df5a70ad7575f6601d91f0efec95dd9bc619431",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "flake-parts": "flake-parts",
         "flake-root": "flake-root",
         "nixpkgs": "nixpkgs",
+        "pre-commit-hooks-nix": "pre-commit-hooks-nix",
         "services-flake": "services-flake",
         "treefmt-nix": "treefmt-nix"
       }
@@ -107,6 +189,21 @@
         "type": "github"
       }
     },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
+    },
     "treefmt-nix": {
       "inputs": {
         "nixpkgs": "nixpkgs_2"

dev/flake.nix

@@ -4,6 +4,11 @@
     flake-parts.url = "github:hercules-ci/flake-parts";
     flake-root.url = "github:srid/flake-root";
     treefmt-nix.url = "github:numtide/treefmt-nix";
+    pre-commit-hooks-nix = {
+      url = "github:cachix/pre-commit-hooks.nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+      inputs.nixpkgs-stable.follows = "nixpkgs";
+    };
     # CI will override `services-flake` to run checks on the latest source
     services-flake.url = "github:juspay/services-flake";
   };
@@ -13,11 +18,14 @@
       imports = [
         inputs.flake-root.flakeModule
         inputs.treefmt-nix.flakeModule
+        inputs.pre-commit-hooks-nix.flakeModule
+        ./nix/pre-commit.nix
       ];
       perSystem = { pkgs, lib, config, ... }: {
         treefmt = {
           projectRoot = inputs.services-flake;
           projectRootFile = "flake.nix";
+          flakeCheck = false; # pre-commit-hooks.nix checks this
           programs = {
             nixpkgs-fmt.enable = true;
           };
@@ -29,6 +37,7 @@
           # cf. https://flakular.in/haskell-flake/devshell#composing-devshells
           inputsFrom = [
             config.treefmt.build.devShell
+            config.pre-commit.devShell
           ];
           shellHook = ''
             echo

dev/nix/pre-commit.nix

@@ -0,0 +1,14 @@
+{ ... }:
+{
+  perSystem = { pkgs, lib, ... }: {
+    pre-commit = {
+      check.enable = true;
+      settings = {
+        hooks = {
+          treefmt.enable = true;
+          commitizen.enable = true;
+        };
+      };
+    };
+  };
+}