Find duplicate routes in Elixir Phoenix

If you have duplicated routes in your route file like this:

scope "/api", MyAppWeb.Api, as: :api do
  pipe_through [:this]
  
  resources "/users", UserController, except: [:new, :edit]
  scope 
end

scope "/api", MyAppWeb.Api, as: :api do
  pipe_through [:that]

  resources "/users", UserController, except: [:new, :edit]
end

Then you'll get a warning like this:

warning: this clause cannot match because a previous clause at line 2 always matches
  lib/idea_web/router.ex:2

The warning doesn't really let you know which routes are duplicated, but it's really ease to find the duplicated routes by utilizing the uniq command.

mix phx.routes | sort | uniq -d

The -d flag for uniq is duplicates only. -d only considers similar lines in consecutive order as duplicates, so you need to run it through sort first.

The output looks like this:

api_user_path  DELETE  /api/users/:id                   MyAppWeb.Api.UserController :delete
api_user_path  GET     /api/users                       MyAppWeb.Api.UserController :index
api_user_path  GET     /api/users/:id                   MyAppWeb.Api.UserController :show
api_user_path  PATCH   /api/users/:id                   MyAppWeb.Api.UserController :update
api_user_path  POST    /api/users                       MyAppWeb.Api.UserController :create

And those are your duplicate routes!