add `treefmt` and `pre-commit-hooks`

I can now run `nix fmt` or `nix flake check` to check the syntax for
various files in this repository.

Fixed a deprecation warning for `hugo`:
```
> WARN  The author key in site configuration is deprecated. Use params.author.email instead.
> WARN  The author key in site configuration is deprecated. Use params.author.name instead.
```

6 files changed, 259 insertions, 68 deletions

diff --git a/.gitignore b/.gitignore
index 8ec0a90..81e48e1 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,3 +1,4 @@
 /docs/
 /.hugo_build.lock
 /result
+/.pre-commit-config.yaml
diff --git a/config.toml b/config.toml
index 9d8c464..22cbecc 100644
--- a/config.toml
+++ b/config.toml
@@ -5,70 +5,70 @@ publishDir = "docs"
 enableGitInfo = false
 
 [params]
-  homeText = "A collection of posts"
+homeText = "A collection of posts"
 
-[author]
-  name = "Franck Cuny"
-  email = "franck@fcuny.net"
+[params.author]
+name = "Franck Cuny"
+email = "franck@fcuny.net"
 
 [taxonomies]
-  tag = "tags"
+tag = "tags"
 
 [permalinks]
-  blog = "/blog/:slug/"
-  notes = "/notes/:slug/"
-  tags = "/tags/:slug/"
+blog = "/blog/:slug/"
+notes = "/notes/:slug/"
+tags = "/tags/:slug/"
 
 [menu]
-  [[menu.main]]
-    identifier = "blog"
-    name = "blog"
-    title = "blog"
-    url = "/blog/"
-    weight = 110
+[[menu.main]]
+identifier = "blog"
+name = "blog"
+title = "blog"
+url = "/blog/"
+weight = 110
 
-  [[menu.main]]
-    identifier = "notes"
-    name = "notes"
-    title = "notes"
-    url = "/notes/"
-    weight = 120
+[[menu.main]]
+identifier = "notes"
+name = "notes"
+title = "notes"
+url = "/notes/"
+weight = 120
 
-  [[menu.main]]
-    identifier = "code"
-    name = "code"
-    title = "code"
-    url = "https://github.com/fcuny"
-    weight = 130
+[[menu.main]]
+identifier = "code"
+name = "code"
+title = "code"
+url = "https://github.com/fcuny"
+weight = 130
 
-  [[menu.main]]
-    identifier = "feed"
-    name = "feed"
-    title = "feed"
-    url = "/feed.xml"
-    weight = 140
+[[menu.main]]
+identifier = "feed"
+name = "feed"
+title = "feed"
+url = "/feed.xml"
+weight = 140
 
 [markup]
-  [markup.highlight]
-    anchorLineNos = false
-    codeFences = false
-    guessSyntax = false
-    hl_Lines = ""
-    lineAnchors = ""
-    lineNoStart = 1
-    lineNos = false
-    lineNumbersInTable = false
-    noClasses = true
-    style = "pygments"
-    tabWidth = 4
+[markup.highlight]
+anchorLineNos = false
+codeFences = false
+guessSyntax = false
+hl_Lines = ""
+lineAnchors = ""
+lineNoStart = 1
+lineNos = false
+lineNumbersInTable = false
+noClasses = true
+style = "pygments"
+tabWidth = 4
 
 [mediaTypes."application/atom"]
-  suffixes = ["xml"]
+suffixes = ["xml"]
 
 [outputFormats.Atom]
-  mediaType = "application/atom"
-  baseName = "feed"
-  isPlainText = false
+mediaType = "application/atom"
+baseName = "feed"
+isPlainText = false
 
 [outputs]
-  home = [ "HTML", "Atom" ]
+home = ["HTML", "Atom"]
diff --git a/flake.lock b/flake.lock
index 2dc3d82..677ddcb 100644
--- a/flake.lock
+++ b/flake.lock
@@ -1,5 +1,21 @@
 {
   "nodes": {
+    "flake-compat": {
+      "flake": false,
+      "locked": {
+        "lastModified": 1673956053,
+        "narHash": "sha256-4gtG9iQuiKITOjNQQeQIpoIB6b16fm+504Ch3sNKLd8=",
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "rev": "35bb57c0c8d8b62bbfd284272c928ceb64ddbde9",
+        "type": "github"
+      },
+      "original": {
+        "owner": "edolstra",
+        "repo": "flake-compat",
+        "type": "github"
+      }
+    },
     "flake-utils": {
       "inputs": {
         "systems": "systems"
@@ -18,6 +34,45 @@
         "type": "github"
       }
     },
+    "flake-utils_2": {
+      "inputs": {
+        "systems": "systems_2"
+      },
+      "locked": {
+        "lastModified": 1685518550,
+        "narHash": "sha256-o2d0KcvaXzTrPRIo0kOLV0/QXHhDQ5DTi+OxcjO8xqY=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "a1720a10a6cfe8234c0e93907ffe81be440f4cef",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
+    "gitignore": {
+      "inputs": {
+        "nixpkgs": [
+          "pre-commit-hooks",
+          "nixpkgs"
+        ]
+      },
+      "locked": {
+        "lastModified": 1660459072,
+        "narHash": "sha256-8DFJjXG8zqoONA1vXtgeKXy68KdJL5UaXR8NtVMUbx8=",
+        "owner": "hercules-ci",
+        "repo": "gitignore.nix",
+        "rev": "a20de23b925fd8264fd7fad6454652e142fd7f73",
+        "type": "github"
+      },
+      "original": {
+        "owner": "hercules-ci",
+        "repo": "gitignore.nix",
+        "type": "github"
+      }
+    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1701624383,
@@ -34,10 +89,82 @@
         "type": "github"
       }
     },
+    "nixpkgs-stable": {
+      "locked": {
+        "lastModified": 1685801374,
+        "narHash": "sha256-otaSUoFEMM+LjBI1XL/xGB5ao6IwnZOXc47qhIgJe8U=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "c37ca420157f4abc31e26f436c1145f8951ff373",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-23.05",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs_2": {
+      "locked": {
+        "lastModified": 1689261696,
+        "narHash": "sha256-LzfUtFs9MQRvIoQ3MfgSuipBVMXslMPH/vZ+nM40LkA=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "df1eee2aa65052a18121ed4971081576b25d6b5c",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixpkgs-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "nixpkgs_3": {
+      "locked": {
+        "lastModified": 1695644571,
+        "narHash": "sha256-asS9dCCdlt1lPq0DLwkVBbVoEKuEuz+Zi3DG7pR/RxA=",
+        "owner": "nixos",
+        "repo": "nixpkgs",
+        "rev": "6500b4580c2a1f3d0f980d32d285739d8e156d92",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nixos",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "pre-commit-hooks": {
+      "inputs": {
+        "flake-compat": "flake-compat",
+        "flake-utils": "flake-utils_2",
+        "gitignore": "gitignore",
+        "nixpkgs": "nixpkgs_2",
+        "nixpkgs-stable": "nixpkgs-stable"
+      },
+      "locked": {
+        "lastModified": 1700922917,
+        "narHash": "sha256-ej2fch/T584b5K9sk1UhmZF7W6wEfDHuoUYpFN8dtvM=",
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "rev": "e5ee5c5f3844550c01d2131096c7271cec5e9b78",
+        "type": "github"
+      },
+      "original": {
+        "owner": "cachix",
+        "repo": "pre-commit-hooks.nix",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "flake-utils": "flake-utils",
-        "nixpkgs": "nixpkgs"
+        "nixpkgs": "nixpkgs",
+        "pre-commit-hooks": "pre-commit-hooks",
+        "treefmt-nix": "treefmt-nix"
       }
     },
     "systems": {
@@ -54,6 +181,39 @@
         "repo": "default",
         "type": "github"
       }
+    },
+    "systems_2": {
+      "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_3"
+      },
+      "locked": {
+        "lastModified": 1699786194,
+        "narHash": "sha256-3h3EH1FXQkIeAuzaWB+nK0XK54uSD46pp+dMD3gAcB4=",
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "rev": "e82f32aa7f06bbbd56d7b12186d555223dc399d1",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "treefmt-nix",
+        "type": "github"
+      }
     }
   },
   "root": "root",
diff --git a/flake.nix b/flake.nix
index 878be9f..5ee6f10 100644
--- a/flake.nix
+++ b/flake.nix
@@ -4,16 +4,20 @@
   inputs = {
     nixpkgs.url = "github:nixos/nixpkgs/master";
     flake-utils.url = "github:numtide/flake-utils";
+    pre-commit-hooks.url = "github:cachix/pre-commit-hooks.nix";
+    treefmt-nix.url = "github:numtide/treefmt-nix";
   };
 
-  outputs = { self, nixpkgs, flake-utils }:
+  outputs = { self, nixpkgs, flake-utils, pre-commit-hooks, treefmt-nix, }:
     flake-utils.lib.eachDefaultSystem (system:
       let
         pkgs = nixpkgs.legacyPackages.${system};
-      in
-      {
+        treefmtEval = treefmt-nix.lib.evalModule pkgs ./treefmt.nix;
+      in {
+        formatter = treefmtEval.config.build.wrapper;
+
         packages = {
-          site = with pkgs;
+          default = with pkgs;
             stdenv.mkDerivation {
               pname = "fcuny.net";
               version = self.lastModifiedDate;
@@ -32,20 +36,30 @@
           '';
         };
 
-        apps = {
-          deploy = {
-            type = "app";
-            program = "${self.packages."${system}".deploy}/bin/deploy";
+        checks = {
+          pre-commit-check = pre-commit-hooks.lib.${system}.run {
+            src = ./.;
+            hooks = {
+              hugo = {
+                enable = true;
+                entry = "${pkgs.hugo}/bin/hugo --panicOnWarning";
+                pass_filenames = false;
+              };
+            };
           };
+          formatting = treefmtEval.config.build.check self;
+        };
+
+        apps = {
           default = {
             type = "app";
             program = "${self.packages."${system}".hugo}/bin/hugo";
           };
         };
 
-        defaultPackage = self.packages."${system}".container;
-
-        devShell =
-          pkgs.mkShell { buildInputs = with pkgs; [ hugo git ]; };
+        devShells.default = pkgs.mkShell {
+          inherit (self.checks.${system}.pre-commit-check) shellHook;
+          buildInputs = with pkgs; [ hugo git treefmt ];
+        };
       });
 }
diff --git a/layouts/index.atom.xml b/layouts/index.atom.xml
index 1d73f9b..a80fc53 100644
--- a/layouts/index.atom.xml
+++ b/layouts/index.atom.xml
@@ -2,20 +2,28 @@
   <title>{{ .Site.Title }}</title>
   <link href="{{ .Permalink }}feed.xml" rel="self"/>
   <link href="{{ .Permalink }}"/>
-  <id>{{ .Permalink }}</id>{{ with .Site.Author.name }}
+  <id>{{ .Permalink }}</id>
+
+  {{ with .Site.Params.Author.name }}
   <author>
-    <name>{{.}}</name>{{ with $.Site.Author.email }}
-    <email>{{.}}</email>{{end}}
-  </author>{{end}}
+    <name>{{.}}</name>
+    {{ with $.Site.Params.Author.email }}
+    <email>{{.}}</email>
+    {{end}}
+  </author>
+  {{end}}
+
   <generator>Hugo -- gohugo.io</generator>
   {{ range where (first 10 (where .Site.Pages "Section" "blog")) "Params.hidden" "ne" "true" }}
   <entry>
     {{ `<title type="html"><![CDATA[` | safeHTML }}{{ .Title }}]]></title>
     <link href="{{ .Permalink }}"/>
-    <id>{{ .Permalink }}</id>{{ with .Site.Params.Author }}
+    <id>{{ .Permalink }}</id>
+    {{ with .Site.Params.Author.name }}
     <author>
       <name>{{.}}</name>
-    </author>{{end}}
+    </author>
+    {{end}}
     {{- $fmt := "2006-01-02T15:04:05-07:00" }}
     <published>{{ .Date.Format $fmt | safeHTML }}</published>
     {{ `<content type="html"><![CDATA[` | safeHTML }}{{ .Content }}]]></content>
diff --git a/treefmt.nix b/treefmt.nix
new file mode 100644
index 0000000..e6164a0
--- /dev/null
+++ b/treefmt.nix
@@ -0,0 +1,8 @@
+{
+  projectRootFile = "flake.nix";
+  programs = {
+    nixfmt.enable = true; # nix
+    taplo.enable = true; # toml
+    yamlfmt.enable = true; # yaml
+  };
+}