I'm not entirely sure how to reproduce this, not even how it actually happens, but I'm currently working on a codebase where running mix phx.routes --info [ROUTE] raises an exception with the following message:

Function: :index
** (ArgumentError) cannot convert the given list to a string.

To be converted to a string, a list must either be empty or only
contain the following elements:

  * strings
  * integers representing Unicode code points
  * a list containing one of these three elements

Please check the given list or call inspect/1 to get the list representation, got:

[generated: true, location: 32]

    (elixir 1.15.5) lib/list.ex:1084: List.to_string/1
    (phoenix 1.7.8) lib/mix/tasks/phx.routes.ex:109: Mix.Tasks.Phx.Routes.get_url_info/2
    (mix 1.15.5) lib/mix/task.ex:447: anonymous fn/3 in Mix.Task.run_task/5
    (mix 1.15.5) lib/mix/cli.ex:92: Mix.CLI.run_task/2
    /Users/dino/.asdf/installs/elixir/1.15.5-otp-26/bin/mix:2: (file)

After reviewing the code for mix phx.routes I noticed that it relies on Code.fetch_docs/1 to find the line number for a specific function in a module's file.

However, it assumes that Code.fetch_docs/1 will always return the function's location as the second element of the tuple, which is not always the case, as Code.fetch_docs/1 can return a list of annotations - :erl_anno.anno() - as a Keyword list. When that's the case, the line number is actually the value for the :location key.

As such, this Pull Request updates the Mix.Tasks.Phx.Routes.get_line_number/2 to make sure that both situations are supported.