![\"pre-commit.png\"](\"https://github.com/DeterminateSystems/flakehub-mirror/raw/HEAD/pre-commit.png\")
Trivial integration for Nix projects (wires up a few things behind the scenes)
\nProvide a low-overhead build of all the tooling available for the hooks to use\n(naive implementation of calling nix-shell does bring some latency when committing)
\nCommon hooks for languages like Python, Haskell, Elm, etc. See all hook options
\nRun hooks as part of development and during CI
\nSupport for alternative pre-commit implementations, like prek.
{ inputs, ... }:\n\n{\n git-hooks.hooks = {\n # Format Nix code\n nixfmt.enable = true;\n\n # Format Python code\n black.enable = true;\n\n # Lint shell scripts\n shellcheck.enable = true;\n\n # Execute shell examples in Markdown files\n mdsh.enable = true;\n\n # Override a package with a different version\n ormolu.enable = true;\n ormolu.package = pkgs.haskellPackages.ormolu;\n\n # Some hooks have more than one package, like clippy:\n clippy.enable = true;\n clippy.packageOverrides.cargo = pkgs.cargo;\n clippy.packageOverrides.clippy = pkgs.clippy;\n # Some hooks provide settings\n clippy.settings.allFeatures = true;\n\n # Define your own custom hooks\n # See all options: https://github.com/cachix/git-hooks.nix#custom-hooks\n my-custom-hook = {\n enable = true;\n entry = \"./on-pre-commit.sh\";\n };\n };\n\n # Use alternative pre-commit implementations\n git-hooks.package = pkgs.prek;\n}\nSee getting started.
\nGiven the following flake.nix example:
{\n description = \"An example project\";\n\n inputs = {\n systems.url = \"github:nix-systems/default\";\n git-hooks.url = \"github:cachix/git-hooks.nix\";\n };\n\n outputs =\n {\n self,\n systems,\n nixpkgs,\n ...\n }@inputs:\n let\n forEachSystem = nixpkgs.lib.genAttrs (import systems);\n in\n {\n # Run the hooks with `nix fmt`.\n formatter = forEachSystem (\n system:\n let\n pkgs = nixpkgs.legacyPackages.${system};\n config = self.checks.${system}.pre-commit-check.config;\n inherit (config) package configFile;\n script = ''\n ${pkgs.lib.getExe package} run --all-files --config ${configFile}\n '';\n in\n pkgs.writeShellScriptBin \"pre-commit-run\" script\n );\n\n # Run the hooks in a sandbox with `nix flake check`.\n # Read-only filesystem and no internet access.\n checks = forEachSystem (system: {\n pre-commit-check = inputs.git-hooks.lib.${system}.run {\n src = ./.;\n hooks = {\n nixfmt.enable = true;\n };\n };\n });\n\n # Enter a development shell with `nix develop`.\n # The hooks will be installed automatically.\n # Or run pre-commit manually with `nix develop -c pre-commit run --all-files`\n devShells = forEachSystem (system: {\n default =\n let\n pkgs = nixpkgs.legacyPackages.${system};\n inherit (self.checks.${system}.pre-commit-check) shellHook enabledPackages;\n in\n pkgs.mkShell {\n inherit shellHook;\n buildInputs = enabledPackages;\n };\n });\n };\n}\nAdd /.pre-commit-config.yaml to .gitignore.\nThis file is auto-generated from the Nix configuration and doesn't need to be committed.
Enter a development shell with pre-commit hooks enabled:
\nRun all hooks sandboxed:
\nKeep in mind that nix flake check runs in a sandbox.\nIt doesn't have access to the internet and cannot modify files.\nThis makes it a poor choice for formatting hooks that attempt to fix files automatically, or hooks that cannot easily be packaged to avoid impure access to the internet.
A better alternative in such cases is to run pre-commit through nix develop:
Or configure a formatter like in the example above and use nix fmt:
If your flake uses flake-parts, we provide a flake-parts module as well. Checkout ./template/flake.nix for an example.
Optionally use binary caches to avoid compilation:
\nIntegrate hooks to be built as part of default.nix:
let\n nix-pre-commit-hooks = import (builtins.fetchTarball \"https://github.com/cachix/git-hooks.nix/tarball/master\");\n in {\n # Configured with the module options defined in `modules/pre-commit.nix`:\n pre-commit-check = nix-pre-commit-hooks.run {\n src = ./.;\n # If your hooks are intrusive, avoid running on each commit with a default_states like this:\n # default_stages = [\"manual\" \"pre-push\"];\n hooks = {\n elm-format.enable = true;\n\n # override a package with a different version\n ormolu.enable = true;\n ormolu.package = pkgs.haskellPackages.ormolu;\n ormolu.settings.defaultExtensions = [ \"lhs\" \"hs\" ];\n\n # some hooks have more than one package, like clippy:\n clippy.enable = true;\n clippy.packageOverrides.cargo = pkgs.cargo;\n clippy.packageOverrides.clippy = tools.clippy;\n # some hooks provide settings\n clippy.settings.allFeatures = true;\n };\n };\n }\nRun $ nix-build -A pre-commit-check to perform the checks as a Nix derivation.
Integrate hooks to prepare environment as part of shell.nix:
let\n pre-commit = import ./default.nix;\n in (import <nixpkgs> {}).mkShell {\n shellHook = ''\n ${pre-commit.pre-commit-check.shellHook}\n '';\n buildInputs = pre-commit.pre-commit-check.enabledPackages;\n }\nAdd /.pre-commit-config.yaml to .gitignore.
Run $ nix-shell to execute shellHook which will:
.pre-commit-config.yaml config file symlink which\nreferences the binaries, for speed and safe garbage collectionpre-commit executable that git commit will invoke.envrc:
use nix\nSometimes it is useful to add a project specific command as an extra check that\nis not part of the pre-defined set of hooks provided by this project.
\nExample configuration:
\n let\n nix-pre-commit-hooks = import (builtins.fetchTarball \"https://github.com/cachix/git-hooks.nix/tarball/master\");\n in {\n pre-commit-check = nix-pre-commit-hooks.run {\n hooks = {\n # ...\n\n # Example custom hook for a C project using Make:\n unit-tests = {\n enable = true;\n\n # The name of the hook (appears on the report table):\n name = \"Unit tests\";\n\n # The command to execute (mandatory):\n entry = \"make check\";\n\n # The pattern of files to run on (default: \"\" (all))\n # see also https://pre-commit.com/#hooks-files\n files = \"\\\\.(c|h)$\";\n\n # List of file types to run on (default: [ \"file\" ] (all files))\n # see also https://pre-commit.com/#filtering-files-with-types\n # You probably only need to specify one of `files` or `types`:\n types = [ \"text\" \"c\" ];\n\n # Exclude files that were matched by these patterns (default: [ ] (none)):\n excludes = [ \"irrelevant\\\\.c\" ];\n\n # The language of the hook - tells pre-commit\n # how to install the hook\n # (default: \"system\", or \"unsupported\" for pre-commit >= 4.4.0)\n # see also https://pre-commit.com/#supported-languages\n language = \"unsupported\";\n\n # Set this to false to not pass the changed files\n # to the command (default: true):\n pass_filenames = false;\n\n # Which git hooks the command should run for (default: [ \"pre-commit\" ]):\n stages = [\"pre-push\"];\n };\n };\n };\n }\nCustom hooks are defined with the same schema as pre-defined\nhooks.
\n\n\nNote on
\nlanguage = \"system\"vs\"unsupported\":Pre-commit >= 4.4.0 renamed
\n\"system\"to\"unsupported\".This does not mean deprecated —
\n\"unsupported\"is just a new name to\nreflect that when using this language, pre-commit does not provision the tools,\nand using externally managed tools (e.g. via Nix) is not an officially\nsupported workflow.Both values are functionally equivalent.\nThe default is set automatically based on the pre-commit package version.
\nWe recommend switching to
\nprek.
clang-format.
\nYou may restrict which languages should be formatted by clang-format using\nclang-format.types_or. For example to check only C and C++ files:
clang-format = {\n enable = true;\n types_or = lib.mkForce [ \"c\" \"c++\" ];\n};\nOtherwise, the default internal list is used which includes everything that\nclang-format supports.
\ngo fmtgo testnixfmt >=v1.0)poetry check.poetry lock.terraform-format: built-in formatter (using\nOpenTofu's\nfmt or\nTerraform's\nfmt)terraform-validate: built-in validator (using\nOpenTofu's\nvalidate\nTerraform's\nvalidate)Everyone is encouraged to add new hooks.
\n\nHave a look at the existing hooks and the options.
\nThere's no guarantee the hook will be accepted, but the general guidelines are:
\n< 50MB. A problematic example: