Finds the cookbooks available to the current project.

Discovery is a convention lookup, not a scan. For each dependency app (and the current project), composer checks whether Composer.<App> is loaded and defines a cookbook. A dependency that ships lib/composer/<app>.ex is found with no configuration.

The cookbooks, in order:

• core, composer's built-in cookbook, always
• the current project's own cookbook, if it defines one
• every dependency's cookbook
• local, the user's config directory (see Composer.Local)

The virtual hex cookbook is not listed; Composer.Resolver knows it.

Limiting cookbooks

The host app can allow or deny package cookbooks by name. core and local are always available.

# config/config.exs
config :composer, cookbooks: [except: [:some_cookbook]]
config :composer, cookbooks: [only: [:composer_lab]]

Dependencies must be compiled before discovery, which is why composer's tasks run mix compile first; an uncompiled dependency's cookbook is not loaded and so not found.