flake: add pre-commit-hooks

flake.lock

@@ -32,10 +32,35 @@
         "type": "github"
       }
     },
+    "pre-commit-hooks": {
+      "inputs": {
+        "flake-utils": [
+          "futils"
+        ],
+        "nixpkgs": [
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1624971177,
+        "narHash": "sha256-Amf/nBj1E77RmbSSmV+hg6YOpR+rddCbbVgo5C7BS0I=",
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "rev": "397f0713d007250a2c7a745e555fa16c5dc8cadb",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "ref": "master",
+        "repo": "pre-commit-hooks.nix",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "futils": "futils",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "pre-commit-hooks": "pre-commit-hooks"
       }
     }
   },

flake.nix

@@ -15,10 +15,21 @@
       repo = "nixpkgs";
       ref = "nixpkgs-unstable";
     };
+
+    pre-commit-hooks = {
+      type = "github";
+      owner = "cachix";
+      repo = "pre-commit-hooks.nix";
+      ref = "master";
+      inputs = {
+        flake-utils.follows = "futils";
+        nixpkgs.follows = "nixpkgs";
+      };
+    };
   };
 
-  outputs = { self, nixpkgs, futils } @ inputs:
+  outputs = { self, futils, nixpkgs, pre-commit-hooks } @ inputs:
-    futils.lib.eachSystem futils.lib.allSystems (system:
+    futils.lib.eachDefaultSystem (system:
       let
         inherit (nixpkgs) lib;
         pkgs = nixpkgs.legacyPackages.${system};
@@ -37,9 +48,36 @@
         ];
       in
       {
+        checks = {
+          pre-commit = pre-commit-hooks.lib.${system}.run {
+            src = ./.;
+
+            hooks = {
+              nixpkgs-fmt = {
+                enable = true;
+              };
+
+              markdown-lint = {
+                enable = true;
+
+                name = "Lint each post's markdown";
+
+                entry =
+                  let
+                    pkg = pkgs.nodePackages.markdownlint-cli;
+                  in
+                  "${pkg}/bin/markdownlint";
+
+                types = [ "markdown" ];
+              };
+            };
+          };
+        };
+
         devShell = pkgs.mkShell {
           name = "report";
           inherit buildInputs;
+          inherit (self.checks.${system}.pre-commit) shellHook;
         };
 
         defaultPackage = pkgs.stdenvNoCC.mkDerivation {