Add flake-follows hook

README.md

@@ -470,6 +470,7 @@ hooks](modules/pre-commit.nix).
 - [alejandra](https://github.com/kamadorueda/alejandra)
 - [deadnix](https://github.com/astro/deadnix)
 - [flake-checker](https://github.com/DeterminateSystems/flake-checker)
+- [flake-edit](https://github.com/a-kenji/flake-edit) (for `flake-follows`)
 - [nil](https://github.com/oxalica/nil)
 - [nixf-diagnose](https://github.com/inclyc/nixf-diagnose)
 - [nixfmt](https://github.com/NixOS/nixfmt/) (supports `nixfmt` >=v1.0)

modules/hooks.nix

@@ -534,6 +534,31 @@ in
           };
         };
       };
+      flake-follows = mkOption {
+        description = "flake-follows hook";
+        type = types.submodule {
+          imports = [ hookModule ];
+          options.settings = {
+            flake = mkOption {
+              type = types.oneOf [ types.str types.path ];
+              description = "Path to the flake file to update.";
+              default = "flake.nix";
+            };
+
+            lockFile = mkOption {
+              type = types.oneOf [ types.str types.path ];
+              description = "Path to the flake lock file used as input by `flake-edit`.";
+              default = "flake.lock";
+            };
+
+            noLock = mkOption {
+              type = types.bool;
+              description = "Whether to pass `--no-lock` to avoid updating the lock file.";
+              default = true;
+            };
+          };
+        };
+      };
       flake8 = mkOption {
         description = "flake8 hook";
         type = types.submodule {
@@ -3280,6 +3305,38 @@ in
           entry = "${hooks.fix-encoding-pragma.package}/bin/fix-encoding-pragma";
           types = [ "python" ];
         };
+      flake-follows =
+        let
+          flake = lib.escapeShellArg (toString hooks.flake-follows.settings.flake);
+          lockFile = lib.escapeShellArg (toString hooks.flake-follows.settings.lockFile);
+          noLock = lib.optionalString hooks.flake-follows.settings.noLock "--no-lock";
+          flakeEdit = lib.getExe hooks.flake-follows.package;
+          script = pkgs.writeShellScript "precommit-flake-follows" ''
+            set -euo pipefail
+
+            flake=${flake}
+            lock_file=${lockFile}
+
+            if [ ! -f "$flake" ] || [ ! -f "$lock_file" ]; then
+              exit 0
+            fi
+
+            ${flakeEdit} \
+              --flake "$flake" \
+              --lock-file "$lock_file" \
+              ${noLock} \
+              --non-interactive \
+              follow >/dev/null
+          '';
+        in
+        {
+          name = "flake-follows";
+          description = "Add missing follows declarations to Nix flakes.";
+          package = tools.flake-edit;
+          entry = builtins.toString script;
+          files = "^(flake\\.nix|flake\\.lock)$";
+          pass_filenames = false;
+        };
       flake8 =
         let
           extendIgnoreStr =

nix/tests/default.nix

@@ -2,4 +2,5 @@
 {
   installation-test = pkgs.callPackage ./installation.nix { inherit run; };
   hook-config-test = pkgs.callPackage ./hook-config.nix { inherit run; };
+  flake-follows-test = pkgs.callPackage ./flake-follows.nix { inherit run; };
 }

nix/tests/flake-follows.nix

@@ -0,0 +1,114 @@
+{ pkgs, run }:
+let
+  fakeFlakeEdit = pkgs.writeShellScriptBin "flake-edit" ''
+    set -eu
+
+    flake=
+    : > flake-edit-args
+
+    while [ "$#" -gt 0 ]; do
+      case "$1" in
+        --flake)
+          flake=$2
+          printf '%s\n' "$1" "$2" >> flake-edit-args
+          shift 2
+          ;;
+        --lock-file)
+          printf '%s\n' "$1" "$2" >> flake-edit-args
+          shift 2
+          ;;
+        --no-lock|--non-interactive|follow)
+          printf '%s\n' "$1" >> flake-edit-args
+          shift
+          ;;
+        *)
+          echo "unexpected argument: $1" >&2
+          exit 2
+          ;;
+      esac
+    done
+
+    test -n "$flake"
+    echo '# flake-edit follow ran' >> "$flake"
+  '';
+
+  hook = (run {
+    src = null;
+    addGcRoot = false;
+    tools.flake-edit = fakeFlakeEdit;
+    hooks.flake-follows.enable = true;
+  }).config.hooks.flake-follows;
+
+  hookWithoutNoLock = (run {
+    src = null;
+    addGcRoot = false;
+    tools.flake-edit = fakeFlakeEdit;
+    hooks.flake-follows = {
+      enable = true;
+      settings.noLock = false;
+    };
+  }).config.hooks.flake-follows;
+
+  customPathHook = (run {
+    src = null;
+    addGcRoot = false;
+    tools.flake-edit = fakeFlakeEdit;
+    hooks.flake-follows = {
+      enable = true;
+      settings.flake = "nix/flake.nix";
+      settings.lockFile = "nix/flake.lock";
+    };
+  }).config.hooks.flake-follows;
+in
+pkgs.runCommand "flake-follows-test" { } ''
+  set -euo pipefail
+
+  mkdir enabled
+  cd enabled
+  touch flake.nix flake.lock
+  ${hook.entry}
+  grep -q '# flake-edit follow ran' flake.nix
+  grep -q -- '--flake' flake-edit-args
+  grep -q -- 'flake.nix' flake-edit-args
+  grep -q -- '--lock-file' flake-edit-args
+  grep -q -- 'flake.lock' flake-edit-args
+  grep -q -- '--no-lock' flake-edit-args
+  grep -q -- '--non-interactive' flake-edit-args
+  grep -q -- 'follow' flake-edit-args
+  cd ..
+
+  mkdir no-lock-disabled
+  cd no-lock-disabled
+  touch flake.nix flake.lock
+  ${hookWithoutNoLock.entry}
+  grep -q '# flake-edit follow ran' flake.nix
+  if grep -q -- '--no-lock' flake-edit-args; then
+    echo 'unexpected --no-lock argument' >&2
+    exit 1
+  fi
+  cd ..
+
+  mkdir missing-lock
+  cd missing-lock
+  touch flake.nix
+  ${hook.entry}
+  test ! -e flake-edit-args
+  cd ..
+
+  mkdir missing-flake
+  cd missing-flake
+  touch flake.lock
+  ${hook.entry}
+  test ! -e flake-edit-args
+  cd ..
+
+  mkdir -p custom-path/nix
+  cd custom-path
+  touch nix/flake.nix nix/flake.lock
+  ${customPathHook.entry}
+  grep -q '# flake-edit follow ran' nix/flake.nix
+  grep -q -- 'nix/flake.nix' flake-edit-args
+  grep -q -- 'nix/flake.lock' flake-edit-args
+
+  echo success > $out
+''

nix/tests/hook-config.nix

@@ -7,6 +7,13 @@ let
   fakeNewPreCommit = pkgs.writeShellScriptBin "pre-commit" "" // { pname = "pre-commit"; version = "4.4.0"; };
 
   hookTests = {
+    "flake-follows: runs once for flake inputs" = {
+      conf.hooks.flake-follows.enable = true;
+      hook = "flake-follows";
+      check = raw: raw.files == "^(flake\\.nix|flake\\.lock)$" && raw.pass_filenames == false;
+      expected = "files limited to flake.nix/flake.lock and pass_filenames = false";
+    };
+
     "pre-commit: no priority field when unset" = {
       conf.hooks.shellcheck.enable = true;
       hook = "shellcheck";

nix/tools.nix

@@ -36,6 +36,7 @@
 , elmPackages
 , eslint
 , flake-checker ? placeholder "flake-checker"
+, flake-edit ? placeholder "flake-edit"
 , fprettify
 , git-annex
 , gitlint
@@ -159,6 +160,7 @@ in
     elixir
     eslint
     flake-checker
+    flake-edit
     fprettify
     git-annex
     gitlint