GitHoox

Git hooks in pure Elixir. Configurable file globs, per-hook options, built-in support for mix format, Credo, ExUnit, and Dialyzer.

GitHoox aims for parity with lefthook's mental model — no implicit stashing, opt-in re-staging of fixed files — while keeping the entire toolchain in Elixir so projects do not need a Node or Python runtime to run hooks.

Installation

Add git_hoox to your dev dependencies in mix.exs:

def deps do
  [
    {:git_hoox, "~> 0.1.0", only: [:dev], runtime: false}
  ]
end

Fetch and install the git hook shims:

mix deps.get
mix git_hoox.install

The installer writes shims into .git/hooks/ and refuses to overwrite any existing user-authored hook. Pass --force to back up the existing hook (saved as <hook>.backup.<utc-timestamp>) and replace it.

mix git_hoox.install --force
mix git_hoox.install --dry-run    # show the install plan, write nothing
mix git_hoox.install --scaffold   # also write a starter .git_hoox.exs

Pass --scaffold (or -s) on first install to drop a starter .git_hoox.exs at the repo root. The scaffolder refuses to overwrite an existing config unless --force is set.

Configuration

GitHoox reads .git_hoox.exs at the repo root. The file is a single map.

# .git_hoox.exs
%{
  hooks: [
    pre_commit: [
      {GitHoox.Hooks.Format, []},
      {GitHoox.Hooks.Credo, []}
    ],
    pre_push: [
      {GitHoox.Hooks.Test, scope: :stale},
      {GitHoox.Hooks.Dialyzer, []}
    ]
  ],
  parallel: false,
  fail_fast: false
}

Top-level options:

Key	Type	Default	Description
`hooks`	keyword	—	Per-stage list of `{Module, opts}` entries.
`parallel`	boolean	`false`	Run hooks within a stage concurrently.
`fail_fast`	boolean	`false`	Stop on first failure within a stage.
`skip_env`	string	`"GIT_HOOX"`	Env var consulted for skip/exclude flags.

Supported stages: pre_commit, prepare_commit_msg, commit_msg, post_commit, pre_rebase, post_checkout, post_merge, pre_push.

Built-in Hooks

`GitHoox.Hooks.Format`

Runs mix format against staged Elixir files and re-stages the result.

{GitHoox.Hooks.Format, []}
{GitHoox.Hooks.Format, check_only: true}     # fail instead of mutating
{GitHoox.Hooks.Format, files: ~w(lib/**/*.ex)}

Defaults: stage_fixed: true, files: ~w(*.ex *.exs *.heex).

`GitHoox.Hooks.Credo`

Runs mix credo against staged Elixir files.

{GitHoox.Hooks.Credo, []}
{GitHoox.Hooks.Credo, strict: true}

Defaults: stage_fixed: false, files: ~w(lib/**/*.ex test/**/*.exs).

`GitHoox.Hooks.Test`

Runs mix test. Three selection strategies:

{GitHoox.Hooks.Test, scope: :all}        # full suite
{GitHoox.Hooks.Test, scope: :stale}      # mix test --stale (fastest)
{GitHoox.Hooks.Test, scope: :related}    # map staged lib/*.ex to test/*_test.exs

Defaults: stage_fixed: false, scope: :all.

`GitHoox.Hooks.Dialyzer`

Runs mix dialyzer --quiet. Slow — PLT builds and whole-project analysis make this unsuitable for pre_commit. Configure on pre_push.

pre_push: [
  {GitHoox.Hooks.Dialyzer, []}
]

`GitHoox.Hooks.Shell`

Escape hatch for anything not covered by a built-in:

{GitHoox.Hooks.Shell,
  run: "mix sobelow --exit",
  files: ~w(lib/**/*.ex)}

{GitHoox.Hooks.Shell,
  run: "mix format {staged_files}",
  files: ~w(*.ex *.exs),
  stage_fixed: true}

Template variables expanded in :run:

Variable	Source
`{staged_files}`	`git diff --cached --name-only --diff-filter=ACMR`
`{all_files}`	`git ls-files`
`{push_files}`	refs received on `pre_push` stdin

Custom Hooks

Implement the GitHoox.Hook behaviour:

defmodule MyApp.Hooks.Sobelow do
  @behaviour GitHoox.Hook

  @impl true
  def default_opts, do: [files: ~w(lib/**/*.ex), stage_fixed: false]

  @impl true
  def run([], _opts), do: :ok
  def run(files, _opts) do
    case System.cmd("mix", ["sobelow", "--exit" | files], stderr_to_stdout: true) do
      {_, 0} -> :ok
      {out, code} -> {:error, {code, out}}
    end
  end
end

pre_commit: [
  {MyApp.Hooks.Sobelow, []}
]

Return values:

Return	Meaning
`:ok`	Hook passed, no files modified.
`{:ok, modified_paths}`	Hook passed; runner re-stages paths if `stage_fixed: true`.
`:skip`	Hook deliberately did nothing.
`{:error, reason}`	Hook failed. Commit aborts unless `fail_fast: false` and other hooks need to run.

Partial Stage and `stage_fixed`

GitHoox does not stash unstaged changes before running hooks. Hooks see the working tree as-is. This matches lefthook's default behavior and avoids the crash and conflict risks of automatic git stash/git stash pop wrappers.

When a formatter or autofixer mutates a file, set stage_fixed: true on that hook entry to re-git add the modified files automatically. Built-in formatter hooks set this default; opt out per-entry if undesired.

Skipping Hooks

Set the configured skip_env (default GIT_HOOX) at commit time:

GIT_HOOX=0 git commit                       # disable all hooks
GIT_HOOX_EXCLUDE=credo,format git commit    # skip specific hook modules
GIT_HOOX_ONLY=test git push                 # run only one

Module names match the suffix after GitHoox.Hooks. (lowercased).

Uninstall

mix git_hoox.uninstall

Removes only the shims GitHoox installed (identified by a marker comment). Foreign hooks are left untouched. If a .backup.* file exists alongside a removed shim, the most recent backup is restored.

Status

GitHoox is pre-1.0. The public API surface (GitHoox, GitHoox.Hook, GitHoox.Config, GitHoox.Git, GitHoox.Installer, the built-in hook modules, and the mix git_hoox.* tasks) follows semver from 0.1.0 onward, but internals under modules marked @moduledoc false (e.g. config schema) may change without notice.

Documentation is published to HexDocs.

Changelog

Released versions are recorded in CHANGELOG.md, generated by release-please.

Unreleased changes accumulate in the open Release PR, which release-please refreshes on every push to main and rewrites the upcoming version and CHANGELOG entries into.

License

BSD 2-Clause. See LICENSE.

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