Generate project documentation

Rationale

The correct invocation of helper modules and functions can be intimidating because

these are generated dynamically (e.g., when creating a new project or adding a new resource)
they are not documented explicitly (e.g., MyApp.ErrorHelpers.error_tag)
the documentation does not cover all examples (e.g., MyApp.Router.Helpers.*_path in Phoenix.Router).

Although the created helpers are scattered all over your project but their location follows a solid logic. You can get used to them pretty quick and fortunately, when you generate a project with Phoenix, the code is shipped with documentation via Elixir’s @doc and @moduledoc module attributes.

These docs are not limited to helpers only but you can also

see your project broken down by submodules/functions/macros
add your own documentation
look up any functions that were generated under the namespace of your project (e.g., MyApp.Repo contains callback function implementations from Ecto.Repo)

Generating the docs

To generate documentation from your source code, add ex_doc as dependency into your mix.exs file:

# config/mix.exs

def deps do
  [{:ex_doc, "~> 0.11", only: :dev}]
end

You can use Markdown within Elixir @doc and @moduledoc attributes.

Then, run mix deps.get to fetch and compile the new modules and generate the project documentation with mix docs. An example output is the official Elixir Docs.

To serve them immediately use mix docs --output priv/static/doc and navigate to my_app_url_or_ip/doc/index.html.

Additional reading:

The bulk of this guide is referenced from Elixir Recipes.