Trogon.Credo

Trogon.Credo is a shared library of Credo checks you depend on instead of copy. It turns the custom check modules that accumulate in a project's .credo/checks/ directory into a versioned Hex package that many repositories can point at.

The package ships check modules and Credo plugins that enable them. Each check lives under the Trogon.Credo.Check.<Category>.<Name> namespace, mirroring Credo's own layout, and is built on Credo's public API so a Credo patch release cannot break it. A consumer either enables the checks it wants one by one in its own .credo.exs, or adds a plugin under Trogon.Credo.Plugin that enables the checks for one library, such as Ecto, in a single line.

Custom Credo checks have no distribution story of their own. A check written for one repository gets copied into the next, then the two drift: a false positive fixed in one copy stays broken in the other, and neither version is tested anywhere. Shipping the checks as a dependency gives them a single source, a test suite, and a version number, so a fix reaches every project that upgrades.

This is for teams running Credo across more than one Elixir repository, and for anyone who has already written a custom check worth keeping. Checks that encode an architectural convention, such as where a layer's modules must live, are parameterized and ship inert, so the conventions stay in each project's configuration while the code that enforces them stays here.

How-to

Enable a check

Add the check module to the checks: %{enabled: [...]} list in your project's .credo.exs:

%{
  configs: [
    %{
      name: "default",
      checks: %{
        enabled: [
          {Trogon.Credo.Check.Warning.ForbiddenImport,
           [modules: [{MyApp.Fixtures, "Call MyApp.Fixtures functions with the full name."}]]}
        ]
      }
    }
  ]
}

Run mix credo as usual and the enabled checks run alongside Credo's built-in ones.

Use a plugin

Add the plugin to the plugins: list of the config in your project's .credo.exs, with the params it accepts:

%{
  configs: [
    %{
      name: "default",
      plugins: [{Trogon.Credo.Plugin.Ecto, [repos: [MyApp.Repo]]}]
    }
  ]
}

The plugin enables its checks whether the config lists checks with enabled:, extra:, or a plain list, and whichever config --config-name selects. Each plugin documents the checks it enables and the params it forwards to them in its own module documentation.

To leave one of the plugin's checks out, name it in except::

plugins: [{Trogon.Credo.Plugin.Ecto, [except: [Trogon.Credo.Check.Ecto.RepoTransact]]}]

To configure one of them differently, list it in checks: yourself. Your entry replaces the one the plugin would add, so {Trogon.Credo.Check.Ecto.RepoTransact, false} disables it, and a # credo:disable-for-next-line Trogon.Credo.Check.Ecto.RepoTransact comment silences a single line.

References

Every check documents what it flags and the parameters it accepts in its own module documentation, so the two never drift apart. Browse them under Trogon.Credo.Check in the published documentation, or read one from a project that already depends on the package:

$ mix credo explain Trogon.Credo.Check.Warning.ForbiddenImport