Check arity with git hook params when using MFA

Author: qgadrian

README.md

@@ -17,7 +17,8 @@ Main features are:
   * Executable files
   * Elixir modules
 * **No limits**: Any git hook is and will be supported out of the box,
- you can [check here the git hooks list](https://git-scm.com/docs/githooks) available.
+ you can [check here the git hooks list](https://git-scm.com/docs/githooks)
+ available.
 
 ## Table of Contents
 
@@ -172,10 +173,9 @@ them as you please.
 It is also possible to use Elixir modules to execute actions for a given git
 hook.
 
-It is recommended the module implement the behaviour `GitHooks` first and then
-add your config as a
+Just add in your config the
 [MFA](https://hexdocs.pm/elixir/typespecs.html#built-in-types) (`{module,
-function, arity}`):
+function, arity}`) definition:
 
 ```elixir
 config :git_hooks,
@@ -189,8 +189,9 @@ config :git_hooks,
   ]
 ```
 
-To see which arguments a git hook receives, [check the git
-documentation](https://git-scm.com/docs/githooks).
+To check how many args you function should expect [check the git
+documentation](https://git-scm.com/docs/githooks) to know which parameters are
+being sent on each hook.
 
 ## Removing a hook
 

config/config.exs

@@ -3,6 +3,12 @@ use Mix.Config
 config :git_hooks,
   auto_install: false,
   hooks: [
+    #prepare_commit_msg: [
+      #verbose: true,
+      #tasks: [
+        #{MyApp.GitHooks.PrepareCommitMsg, :execute, 4}
+      #]
+    #],
     commit_msg: [
       verbose: true,
       tasks: [

lib/git_hooks.ex

@@ -3,14 +3,6 @@ defmodule GitHooks do
 
   alias Mix.Tasks.GitHooks.Install
 
-  @doc """
-  Receives the git hook name and the list of the hook arguments.
-
-  To see how which arguments a git hook has, [check the git
-  documentation](https://git-scm.com/docs/githooks).
-  """
-  @callback execute(atom, list) :: any
-
   if Application.get_env(:git_hooks, :auto_install, true) do
     Install.run(["--quiet"])
   end

lib/mix/tasks/git_hooks/run.ex

@@ -144,18 +144,28 @@ defmodule Mix.Tasks.GitHooks.Run do
       error_exit()
   end
 
-  defp run_task({module, function, _arity}, git_hook_type, git_hook_args) when is_atom(module) do
-    Kernel.apply(module, function, [git_hook_type | git_hook_args])
+  defp run_task({module, function, arity}, git_hook_type, git_hook_args) when is_atom(module) do
+    expected_arity = length(git_hook_args)
+
+    if arity != expected_arity do
+      raise """
+      Invalid #{module}.#{function} arity for #{git_hook_type}, expected #{expected_arity} but got #{
+        arity
+      }. Check the Git hooks documentation to fix the expected parameters.
+      """
+    end
+
+    Kernel.apply(module, function, git_hook_args)
   end
 
   defp run_task(command, git_hook_type, git_hook_args) when is_binary(command) do
     run_task({:cmd, command, []}, git_hook_type, git_hook_args)
   end
 
   defp run_task(task, git_hook_type, _git_hook_args) do
-    raise("""
+    raise """
     Invalid task #{inspect(task)} for hook #{inspect(git_hook_type)}", only String, {:file, ""} or {:cmd, ""} are supported.
-    """)
+    """
   end
 
   @spec get_atom_from_arg(String.t()) :: atom | no_return

test/mix/tasks/git_hooks/run_test.exs

@@ -27,6 +27,29 @@ defmodule Mix.Tasks.RunTest do
              end) =~ "test command"
     end
 
+    test "when it is a MFA then the module function it called" do
+      put_git_hook_config(:pre_commit,
+        tasks: [{GitHooks.TestSupport.MFATest, :execute, 0}],
+        verbose: true
+      )
+
+      assert Run.run(["pre-commit"]) == :ok
+    end
+
+    test "when the arity of the MFA is not the same as the git hook raises an error" do
+      put_git_hook_config(:pre_commit,
+        tasks: [{GitHooks.TestSupport.MFATest, :execute, 5}],
+        verbose: true
+      )
+
+      expect_error_message =
+        "Invalid Elixir.GitHooks.TestSupport.MFATest.execute arity for pre_commit, expected 0 but got 5. Check the Git hooks documentation to fix the expected parameters.\n"
+
+      assert_raise RuntimeError, expect_error_message, fn ->
+        Run.run(["pre-commit"])
+      end
+    end
+
     test "when it is a string then the command it's executed" do
       put_git_hook_config(:pre_commit, tasks: ["echo 'test string command'"], verbose: true)
 

test/support/mfa_test.ex

@@ -0,0 +1,5 @@
+defmodule GitHooks.TestSupport.MFATest do
+  def execute() do
+    :ok
+  end
+end