dev: Configure nixfmt (rfc style)

doc/manual/source/development/building.md

@@ -278,6 +278,8 @@ You may run the formatters as a one-off using:
 ./maintainers/format.sh
 ```
 
+### Pre-commit hooks
+
 If you'd like to run the formatters before every commit, install the hooks:
 
 ```
@@ -292,3 +294,30 @@ If it fails, run `git add --patch` to approve the suggestions _and commit again_
 To refresh pre-commit hook's config file, do the following:
 1. Exit the development shell and start it again by running `nix develop`.
 2. If you also use the pre-commit hook, also run `pre-commit-hooks-install` again.
+
+### VSCode
+
+Insert the following json into your `.vscode/settings.json` file to configure `nixfmt`.
+This will be picked up by the _Format Document_ command, `"editor.formatOnSave"`, etc.
+
+```json
+{
+  "nix.formatterPath": "nixfmt",
+  "nix.serverSettings": {
+    "nixd": {
+      "formatting": {
+        "command": [
+          "nixfmt"
+        ],
+      },
+    },
+    "nil": {
+      "formatting": {
+        "command": [
+          "nixfmt"
+        ],
+      },
+    },
+  },
+}
+```

flake.lock

@@ -36,6 +36,24 @@
         "type": "github"
       }
     },
+    "flake-utils": {
+      "inputs": {
+        "systems": "systems"
+      },
+      "locked": {
+        "lastModified": 1710146030,
+        "narHash": "sha256-SZ5L6eA7HJ/nmkzGG7/ISclqe6oZdOZTNoesiInkXPQ=",
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "rev": "b1d9ab70662946ef0850d488da1c9019f3a9752a",
+        "type": "github"
+      },
+      "original": {
+        "owner": "numtide",
+        "repo": "flake-utils",
+        "type": "github"
+      }
+    },
     "git-hooks-nix": {
       "inputs": {
         "flake-compat": [],
@@ -61,6 +79,24 @@
         "type": "github"
       }
     },
+    "nixfmt": {
+      "inputs": {
+        "flake-utils": "flake-utils"
+      },
+      "locked": {
+        "lastModified": 1736283758,
+        "narHash": "sha256-hrKhUp2V2fk/dvzTTHFqvtOg000G1e+jyIam+D4XqhA=",
+        "owner": "NixOS",
+        "repo": "nixfmt",
+        "rev": "8d4bd690c247004d90d8554f0b746b1231fe2436",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "repo": "nixfmt",
+        "type": "github"
+      }
+    },
     "nixpkgs": {
       "locked": {
         "lastModified": 1734359947,
@@ -114,10 +150,26 @@
         "flake-compat": "flake-compat",
         "flake-parts": "flake-parts",
         "git-hooks-nix": "git-hooks-nix",
+        "nixfmt": "nixfmt",
         "nixpkgs": "nixpkgs",
         "nixpkgs-23-11": "nixpkgs-23-11",
         "nixpkgs-regression": "nixpkgs-regression"
       }
+    },
+    "systems": {
+      "locked": {
+        "lastModified": 1681028828,
+        "narHash": "sha256-Vy1rq5AaRuLzOxct8nz4T6wlgyUR7zLU309k9mBC768=",
+        "owner": "nix-systems",
+        "repo": "default",
+        "rev": "da67096a3b9bf56a91d16901293e51ba5b49a27e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "nix-systems",
+        "repo": "default",
+        "type": "github"
+      }
     }
   },
   "root": "root",

flake.nix

@@ -17,6 +17,7 @@
   # work around 7730 and https://github.com/NixOS/nix/issues/7807
   inputs.git-hooks-nix.inputs.flake-compat.follows = "";
   inputs.git-hooks-nix.inputs.gitignore.follows = "";
+  inputs.nixfmt.url = "github:NixOS/nixfmt";
 
   outputs = inputs@{ self, nixpkgs, nixpkgs-regression, ... }:
 
@@ -301,7 +302,7 @@
       });
 
       devShells = let
-        makeShell = import ./packaging/dev-shell.nix { inherit lib devFlake; };
+        makeShell = import ./packaging/dev-shell.nix { inherit inputs lib devFlake; };
         prefixAttrs = prefix: lib.concatMapAttrs (k: v: { "${prefix}-${k}" = v; });
       in
         forAllSystems (system:

maintainers/flake-module.nix

@@ -31,6 +31,35 @@
             touch $out
           ''}";
         };
+        nixfmt-rfc-style = {
+          enable = true;
+          package = inputs.nixfmt.packages.${pkgs.hostPlatform.system}.default;
+          excludes = [
+            # Invalid
+            ''^tests/functional/lang/parse-.*\.nix$''
+
+            # Formatting-sensitive
+            ''^tests/functional/lang/eval-okay-curpos\.nix$''
+            ''^tests/functional/lang/.*comment.*\.nix$''
+            ''^tests/functional/lang/.*newline.*\.nix$''
+            ''^tests/functional/lang/.*eol.*\.nix$''
+
+            # Syntax tests
+            ''^tests/functional/shell.shebang\.nix$''
+            ''^tests/functional/lang/eval-okay-ind-string\.nix$''
+
+            # Not supported by nixfmt
+            ''^tests/functional/lang/eval-okay-deprecate-cursed-or\.nix$''
+            ''^tests/functional/lang/eval-okay-attrs5\.nix$''
+
+            # More syntax tests
+            # These tests, or parts of them, should have been parse-* test cases.
+            ''^tests/functional/lang/eval-fail-eol-2\.nix$''
+            ''^tests/functional/lang/eval-fail-path-slash\.nix$''
+            ''^tests/functional/lang/eval-fail-toJSON-non-utf-8\.nix$''
+            ''^tests/functional/lang/eval-fail-set\.nix$''
+          ];
+        };
         clang-format = {
           enable = true;
           # https://github.com/cachix/git-hooks.nix/pull/532
@@ -660,7 +689,6 @@
             ''^src/libutil-tests/data/git/check-data\.sh$''
           ];
         };
-        # TODO: nixfmt, https://github.com/NixOS/nixfmt/issues/153
       };
     };
   };

packaging/dev-shell.nix

@@ -1,4 +1,4 @@
-{ lib, devFlake }:
+{ lib, inputs, devFlake }:
 
 { pkgs }:
 
@@ -108,6 +108,7 @@ in {
       modular.pre-commit.settings.package
       (pkgs.writeScriptBin "pre-commit-hooks-install"
         modular.pre-commit.settings.installationScript)
+      inputs.nixfmt.packages.${pkgs.hostPlatform.system}.default
     ]
     # TODO: Remove the darwin check once
     # https://github.com/NixOS/nixpkgs/pull/291814 is available