modify-dependencies

name	modify-dependencies
description	Umbrella dependency management patterns for the CheddarFlow project. TRIGGER when: adding dependencies, creating new apps, modifying mix.exs files, working with CFX.MixHelpers, or changing the mix_helpers.exs file. Also trigger when adding tags like :root, :web, :http to app configurations. DO NOT TRIGGER when: working with code that doesn't involve dependency or project configuration.

Umbrella Dependency Management

Dependencies are centralized via CFX.MixHelpers in mix_helpers.exs at the project root.

How It Works

1. umbrella_deps/0 defines all shared external dependencies with versions and optional tags
2. sibling_deps/0 auto-discovers all umbrella apps as in_umbrella: true
3. Individual apps call CFX.MixHelpers.deps/1 with atom names and/or tags

Tags

Tag	Dependencies Included
:root	libcluster, libcluster_ec2_tag_strategy
:web	Phoenix web dependencies
:http	finch, tesla, jason, error_message, castore, mint

App mix.exs Pattern

Code.require_file("mix_helpers.exs", "../..")

defmodule MyApp.MixProject do
  use Mix.Project
  @tags [:root, :http]
  @siblings [:schemas, :shared_utils]

  def project do
    CFX.MixHelpers.merge_umbrella_opts(
      app: :my_app,
      deps: deps()
    )
  end

  defp deps do
    CFX.MixHelpers.deps(
      @tags ++ @siblings ++ [
        :oban,
        {:some_dep, "~> 1.0"}
      ]
    )
  end
end

merge_umbrella_opts/1

Merges standard umbrella options:

• Elixir version constraint (~> 1.16)
• Build/config/deps/lockfile paths to umbrella root
• elixirc_paths (includes test/support in dev/test)
• ExCoveralls test coverage
• Dialyzer configuration

Key Rules

• Never add a dep directly to an app's mix.exs if it's already in umbrella_deps/0 — reference by name
• Always add new shared deps to umbrella_deps/0 in mix_helpers.exs
• Use tags for category-wide deps (e.g., :http for all HTTP clients)
• Sibling deps are auto-discovered — just list the app name as atom
• Some older apps manage deps directly without CFX.MixHelpers
• sobelow is always included regardless of tags

Adding a New Umbrella App

1. Create app under apps/
2. Add Code.require_file("mix_helpers.exs", "../..") at top of mix.exs
3. Use CFX.MixHelpers.merge_umbrella_opts/1 for project config
4. Use CFX.MixHelpers.deps/1 for dependency resolution
5. If release app, add to releases/0 in root mix.exs
6. Add tags: :root if joining cluster, :http if making HTTP requests