Mix Tasks & Generators

Canonical FP bar: docs/fcis-engineering-rules.md — Functional Core, Imperative Shell: pure domain modules; side effects at edges. Generators should emit FCIS-shaped code (thin edges, pure helpers).

RULES — Follow these with no exceptions

1. Always call Mix.Task.run("app.start") first — tasks that access the database or Repo need the app started 2. Create custom tasks for project-specific workflows — don't override standard Mix tasks 3. Register preferred_cli_env in mix.exs — set environment for custom tasks (dev/test/prod) 4. Use transactions for data modifications — wrap Repo.insert_all, Repo.delete_all in Repo.transaction() 5. Test custom tasks with Mix.Project.in_project/4 — ensure tasks work correctly in isolation 6. Follow Mix.Tasks.Namespace.TaskName naming — file path must match: lib/mix/tasks/namespace.task_name.ex

End-to-End Workflow

Follow this sequence when creating a custom Mix task: