the_thracian_credo

the_thracian_credo is a Credo plugin and installer for experimental, painfully strict, very opinionated Elixir linting.

mix thx_lint.install --yes
  patches .credo.exs
  writes formatter and Doctor config
  prepares Dialyxir ignore config
  enables The Thracian custom Credo checks

Why Use It

• Credo plugin first: consumers depend on a package instead of copying custom checks into their app.
• Strict defaults: line length, function size, nesting, arity, complexity, debug artifacts, specs, docs, rebinding, and unsafe exec calls are enforced.
• Installer included: fresh projects get a managed config; existing projects are patched carefully.
• Dialyzer-friendly: TheThracianCredo.dialyzer() returns the matching Dialyxir options.
• Built for agentic code review: it rejects patterns that hide intent, swallow errors, or waste review context.

Install

Add the package to mix.exs:

defp deps do
  [
    {:credo, "~> 1.7", only: [:dev, :test], runtime: false},
    {:the_thracian_credo, "~> 0.1.0", only: [:dev, :test], runtime: false}
  ]
end

Install and run:

mix deps.get
mix thx_lint.install --yes
mix credo --strict

Existing Projects

Fresh projects receive a managed .credo.exs with the plugin enabled:

plugins: [{TheThracianCredo, []}]

Existing .credo.exs files are patched in place when the installer can do so safely. Managed regions include a version marker:

# BEGIN the_thracian_credo
# VERSION 0.1.0
# END the_thracian_credo

Legacy regions from @thethracian/elixir-lint-config are migrated automatically.

Dialyxir

If the project uses Dialyxir, add this to project/0:

dialyzer: TheThracianCredo.dialyzer()

What It Enforces

No lexical comments

TheThracianCredo.Check.Readability.NoComments is enabled by default at high priority with exit status 2. The installer activates it in both fresh and existing configurations through TheThracianCredo.checks(); existing consumers receive it when updating the package.

The check uses Elixir's Code.string_to_quoted_with_comments/2. It rejects standalone, trailing, empty, and interpolation comments. Literal # characters inside strings, sigils, charlists, quoted atoms, and heredocs are allowed. @doc and @moduledoc attributes are code, not lexical comments, and remain allowed and required where the existing documentation checks apply.

For parity with the TypeScript and Rust policy, an interpreter shebang such as #!/usr/bin/env elixir is allowed only at the very start of the file (line 1, column 1), with an absolute interpreter path after #! and optional spaces or tabs. Later or indented #! comments and #! without an interpreter path remain forbidden. Invalid syntax remains the responsibility of Credo's parser diagnostics.

The plugin clears Credo's inline suppression directives before analysis in the suggest, list, and diff commands. A directive cannot suppress this check or hide another check's findings. Configuration-file check selections still apply. The policy covers files selected for analysis; installer ownership markers in generated configuration files are not exemptions and will fail if those files are explicitly included.

Credo's official check catalog has no general all-comments prohibition, so this check ships with the package as a custom check.

Local Development

Use a local checkout when changing the package itself:

defp deps do
  [
    {:credo, "~> 1.7", only: [:dev, :test], runtime: false},
    {:the_thracian_credo, path: "/path/to/linters/elixir", only: [:dev, :test], runtime: false}
  ]
end

Then run:

mix deps.get
mix thx_lint.install --yes
mix credo --strict

Registry Links

• Hex.pm: https://hex.pm/packages/the_thracian_credo
• Source: https://github.com/stefan-vatov/code-quality/tree/main/elixir
• Issues: https://github.com/stefan-vatov/code-quality/issues

License

MIT. See LICENSE.