Elixir Project Guardrails

✓ Policy Beta Devex Build And Ci

Enforce Elixir-specific project standards including mix manifest presence, Elixir version requirement, lockfile commit, test directory layout, Credo/Dialyzer configuration, and umbrella app detection.

Add elixir to your lunar-config.yml:

uses: github://earthly/lunar-lib/policies/elixir@v1.0.5

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Included Guardrails

This policy includes 6 guardrails that enforce standards for your devex build and ci.

Guardrail

`mix-project-exists`

Ensures the project has a mix.exs file. Required for all Elixir projects managed with Mix.

mix.exs elixir project mix manifest

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Guardrail

`elixir-version-constraint-set`

Ensures the project declares an Elixir version requirement (e.g., elixir: "~> 1.15") in mix.exs. Pinning a minimum Elixir version prevents drift and surprises on build machines.

elixir version version requirement mix.exs

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Guardrail

`dependencies-locked`

Ensures mix.lock is committed for reproducible dependency resolution. Without a lockfile, builds can pull different Hex versions over time.

mix.lock lockfile reproducibility hex

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Guardrail

`test-directory-exists`

Ensures a test/ directory exists. An explicit test dir is the conventional layout for ExUnit. Skips on non-Elixir projects when .lang.elixir is absent.

test/ exunit testing test layout

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Guardrail

`credo-or-dialyzer-configured`

Ensures Credo or Dialyzer is configured. Credo is detected via .credo.exs. Dialyzer is detected via {:dialyxir, ...} dep, a dialyzer/0 block in mix.exs, or a mix dialyzer command observed in CI. Static analysis catches bugs and enforces consistent idiomatic Elixir.

credo dialyzer dialyxir static analysis code quality

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Guardrail

`umbrella-app-detected`

Reports whether the project is an umbrella application. Informational — passes if the project is NOT an umbrella or if umbrella structure is correctly detected.

umbrella apps monorepo elixir umbrella

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Required Integrations

This policy evaluates data gathered by one or more of the following integration(s). Make sure to enable them in your lunar-config.yml.

Collector LanguagesBuild Required

Elixir Collector

Provides Elixir project metadata

Configuration

Configure this policy in your lunar-config.yml.

Inputs

Input	Required	Default	Description

Documentation

View on GitHub

Elixir Project Guardrails

Enforce Elixir-specific project standards including mix manifest presence, Elixir version pinning, lockfile commit, test layout, Credo/Dialyzer configuration, and umbrella detection.

Overview

This policy validates Elixir projects against best practices for mix project layout, version pinning, dependency reproducibility, testing conventions, and static analysis. All checks skip gracefully on non-Elixir projects (i.e., .lang.elixir missing).

Policies

This plugin provides the following policies (use include to select a subset):

Policy	Description	Failure Meaning
`mix-project-exists`	Validates mix.exs exists	Project lacks a mix manifest
`elixir-version-constraint-set`	Validates `elixir: "~> X.Y"` in mix.exs	Missing Elixir version requirement
`dependencies-locked`	Validates mix.lock exists	Missing dependency lockfile
`test-directory-exists`	Validates `test/` directory	No tests committed
`credo-or-dialyzer-configured`	Validates Credo or Dialyzer config	No static analysis configured
`umbrella-app-detected`	Reports umbrella app layout	— (informational)

Required Data

This policy reads from the following Component JSON paths:

Path	Type	Provided By
`.lang.elixir`	object	`elixir` collector
`.lang.elixir.mix_exs_exists`	boolean	`elixir` collector
`.lang.elixir.mix_lock_exists`	boolean	`elixir` collector
`.lang.elixir.elixir_requirement`	string	`elixir` collector
`.lang.elixir.test_directory_exists`	boolean	`elixir` collector
`.lang.elixir.credo_configured`	boolean	`elixir` collector
`.lang.elixir.dialyzer_configured`	boolean	`elixir` collector
`.lang.elixir.cicd.cmds`	array	`elixir` collector (additional signal for Dialyzer — `mix dialyzer` invocations)
`.lang.elixir.umbrella`	object	`elixir` collector

Installation

Add to your lunar-config.yml:

policies:
  - uses: github://earthly/lunar-lib/policies/elixir@main
    on: ["domain:your-domain"]  # replace with your own domain or tags
    enforcement: report-pr
    # include: [mix-project-exists, dependencies-locked]  # Only run specific checks

Examples

Passing Example

{
  "lang": {
    "elixir": {
      "mix_exs_exists": true,
      "mix_lock_exists": true,
      "elixir_requirement": "~> 1.15",
      "test_directory_exists": true,
      "credo_configured": true,
      "dialyzer_configured": false,
      "umbrella": { "is_umbrella": false }
    }
  }
}

Failing Example

{
  "lang": {
    "elixir": {
      "mix_exs_exists": true,
      "mix_lock_exists": false,
      "elixir_requirement": "",
      "test_directory_exists": false,
      "credo_configured": false,
      "dialyzer_configured": false,
      "umbrella": { "is_umbrella": false }
    }
  }
}

Failure messages:

"mix.lock not found. Run 'mix deps.get' and commit mix.lock for reproducible builds."
"Elixir version requirement missing in mix.exs. Add 'elixir: \"~> 1.15\"' to the project/0 block."
"test/ directory not found. Create a test/ directory and add ExUnit tests."
"Neither Credo (.credo.exs) nor Dialyzer detected. Add {:credo, ...} or {:dialyxir, ...} to deps for static analysis."

Remediation

mix-project-exists

Run mix new <project-name> to initialize a new Elixir project
Ensure mix.exs is at the project root

elixir-version-constraint-set

Open mix.exs and find the project/0 function
Add or update elixir: "~> 1.15" (or desired minimum) to the keyword list

Example:

def project do
  [
    app: :my_app,
    version: "0.1.0",
    elixir: "~> 1.15",
    ...
  ]
end

dependencies-locked

Run mix deps.get to fetch dependencies
Commit the resulting mix.lock to version control
Ensure mix.lock is not in .gitignore

test-directory-exists

Create a test/ directory: mkdir test
Add a test helper: touch test/test_helper.exs with ExUnit.start()
Add at least one test file under test/

credo-or-dialyzer-configured

Add Credo: {:credo, "~> 1.7", only: [:dev, :test], runtime: false} to deps
Run mix credo.gen.config to create .credo.exs
Or add Dialyzer: {:dialyxir, "~> 1.4", only: [:dev], runtime: false} to deps
Run mix dialyzer to generate PLTs. The policy also passes if mix dialyzer is observed running in CI even without a local config block — wiring it into your pipeline counts.

umbrella-app-detected

Informational — no remediation needed. This check surfaces whether the project is structured as an umbrella app.

Open Source

This policy is open source and available on GitHub. Contribute improvements, report issues, or fork it for your own use.

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Common Use Cases

Explore how individual guardrails work with specific integrations.

Mix Project Exists + Elixir Collector Ensures the project has a mix.exs file. Required for all Elixir projects managed...

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Elixir Version Constraint Set + Elixir Collector Ensures the project declares an Elixir version requirement (e.g., `elixir: "~>...

→

Dependencies Locked + Elixir Collector Ensures mix.lock is committed for reproducible dependency resolution. Without a...

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Test Directory Exists + Elixir Collector Ensures a `test/` directory exists. An explicit test dir is the conventional...

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Credo Or Dialyzer Configured + Elixir Collector Ensures Credo or Dialyzer is configured. Credo is detected via `.credo.exs`....

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Umbrella App Detected + Elixir Collector Reports whether the project is an umbrella application. Informational — passes...

→

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