Recent Erlang versions allow multiline prompts but, to enable it, we no longer can change the prompt on the fly, hence the change.

Hi, welcome to Elixirforum!
I tried to reproduce this, but it worked for me.

Steps I tried:

• Install Elixir 1.16.0-otp26 via asdf.
• Install Erlang 26.1.2 via asdf.
• Create project via mix phx.new demo --no-ecto. Did not want to set up the database. I have phx.new installer for Phoenix 1.7.10.
• Added .tool-versions file to the root of demo project with relevant versions of Elixir and Erlang.
• Installed dependencies.
• Updated the code for lib/demo_web/controllers/page_controller.ex with your example.
• Started the server with iex --dbg pry -S mix phx.server.
• Visited http://localhost:4000, and reached a breakpoint. It worked for both dbg and require IEx; IEx.pry.

Tested on macOS Sonoma 14.4.1.

Can you try to reproduce the same issue on the other device?
Possibly via an Elixir Docker (Podman) container. If it works there, then possibly something is with your local environment.

I remember it was an similar issue with Elixir 1.15.0 and OTP 25, but it is already resolved.

Have tested your code on MacOS Sonoma 14.4.1 on MacMini 2018, Intel based.
It worked for me.

What I have tried:

• Cloned a repo
• Installed dependencies
• Started the app with iex --dbg pry -S mix phx.server
• Visited http://localhost:4000/ and reached a breakpoint.
• Stopped the application.
• Added another breakpoint (2) with require IEx; IEx.pry().
• Started the application with iex -S mix phx.server and refreshed a page in browser.
• Debugger stopped at breakpoint (2).

As I remember, --dbg pry argument appeared at Elixir 1.15.0. dbg macro does not stop at breakpoint without it (though it stopped in Elixir 1.14.x). I mainly use dbg for debug tracing in the code and require IEx; IEx.pry() to set breakpoints (as it always worked).

I think it is not related to the OS, but to the local environment.
Can you try to run your code inside the Docker/Podman?

• Start an Elixir container, something like docker run --rm -it -p 127.0.0.1:4000:4000 elixir:1.16 bash
• Install a git there apt update && apt install git
• Clone your repo git clone https://github.com/onegrx/pry.git
• Visit a repo and install dependencies cd pry; mix deps.get
• Possibly you will want to comment a repo in your configuration. There is no Postgres inside a container. It is not relevant by the way.
• Start the application via iex --dbg pry -S mix phx.server .
• Visit http://localhost:4000 in your browser.

I have written previous commands just to show steps and have not tested them (have not installed Docker on my machine and deleted Podman some time ago). Possibly you will need to install extra dependencies (like PostgreSQL). It should be easy to find solutions for them in the Internet.

I have recently got an interesting error. I played with Erlang and added custom configuration file for it. I have printed a message inside it. When I installed a dependency (erlexec) - the installation process somehow took this message and tried to install dependencies through it. It failed, and I had to update my configuration files. Possibly something similar is in your case, so I suggested to try the same on the other machine.

Erlang looks for configuration in a couple of locations:

• ~/.erlang
• ~/Library/Application Support/erlang/.erlang
• IEX uses ~/.iex.exs
• Environment variable ERL_AFLAGS (you can see its contents via echo $ERL_AFLAGS). I have added this variable to store shell history.

If breakpoints will work inside the Docker/Podman container, then something is with your local configuration.

You may also want to update a listening address in the config/dev.exs here inside a container to:

http: [ip: {0, 0, 0, 0}, port: 4000]

It will allow you to reach the server from outside the container.

Have tried to reproduce with Podman on Apple Silicon:

• installed Podman (brew install podman).
• Prepared a machine (podman machine init).
• Started a machine (podman machine start).
• Started the container with podman run --rm -it -p 127.0.0.1:4000:4000 elixir:1.16 bash. I use --rm flag here, so the container will be deleted after I log out. If you want to keep a container - just remove this flag.
• Git is already installed, cloned the repo.
• Tried to install the dependencies, but got this error, and applied the fix. It happens on Apple Silicon chips, so it should be fine on Intel-based one.
• Installed the dependencies via mix deps.get.
• Installed vim to edit files. You may use nano, if you are not familiar with vim (apt install nano).
• Edited the config/dev.exs - allowed remote connections (ip: {0, 0, 0, 0} thing from above).
• Commented Demo.Repo in lib/demo/application.ex (sole link from my previous message).
• Started the application via iex --dbg pry -S mix phx.server.
• Visited http://localhost:4000 in browser. Reached the breakpoint.

Here is my output:

Interactive Elixir (1.16.2) - press Ctrl+C to exit (type h() ENTER for help)

Rebuilding...

Done in 253ms.
[info] GET /
[debug] Processing with DemoWeb.PageController.home/2
  Parameters: %{}
  Pipelines: [:browser]
Request to pry #PID<0.664.0> at DemoWeb.PageController.foo/1 (lib/demo_web/controllers/page_controller.ex:18)

Request to pry #PID<0.664.0> at DemoWeb.PageController.foo/1 (lib/demo_web/controllers/page_controller.ex:18)
   15:     |> String.split()
   16:     |> Enum.count()
   17:     |> IO.inspect()
   18:     |> dbg
   19:
   20:     conn
   21:   end
Allow? [Yn] y

Interactive Elixir (1.16.2) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> whereami
Location: lib/demo_web/controllers/page_controller.ex:18

   16:     |> Enum.count()
   17:     |> IO.inspect()
   18:     |> dbg
   19:
   20:     conn

    (demo 0.1.0) lib/demo_web/controllers/page_controller.ex:18: DemoWeb.PageController.foo/1
    (demo 0.1.0) lib/demo_web/controllers/page_controller.ex:9: DemoWeb.PageController.home/2
    (demo 0.1.0) lib/demo_web/controllers/page_controller.ex:1: DemoWeb.PageController.action/2
    (demo 0.1.0) lib/demo_web/controllers/page_controller.ex:1: DemoWeb.PageController.phoenix_controller_pipeline/2
    (phoenix 1.7.11) lib/phoenix/router.ex:484: Phoenix.Router.__call__/5
    (demo 0.1.0) lib/demo_web/endpoint.ex:1: DemoWeb.Endpoint.plug_builder_call/2
    (demo 0.1.0) deps/plug/lib/plug/debugger.ex:136: DemoWeb.Endpoint."call (overridable 3)"/2
    (demo 0.1.0) lib/demo_web/endpoint.ex:1: DemoWeb.Endpoint.call/2
    (phoenix 1.7.11) lib/phoenix/endpoint/sync_code_reload_plug.ex:22: Phoenix.Endpoint.SyncCodeReloadPlug.do_call/4
    (bandit 1.4.1) lib/bandit/pipeline.ex:150: Bandit.Pipeline.call_plug!/2
    (bandit 1.4.1) lib/bandit/pipeline.ex:36: Bandit.Pipeline.run/4
    (bandit 1.4.1) lib/bandit/http1/handler.ex:12: Bandit.HTTP1.Handler.handle_data/3
    (bandit 1.4.1) lib/bandit/delegating_handler.ex:18: Bandit.DelegatingHandler.handle_data/3
    (bandit 1.4.1) /pry/deps/thousand_island/lib/thousand_island/handler.ex:411: Bandit.DelegatingHandler.handle_continue/2
    (stdlib 5.2.1) gen_server.erl:1085: :gen_server.try_handle_continue/3
    (stdlib 5.2.1) gen_server.erl:995: :gen_server.loop/7
    (stdlib 5.2.1) proc_lib.erl:241: :proc_lib.init_p_do_apply/3

iex(2)>

Have taken it from container:

• Started the application
• Visited http://localhost:4000 in browser.
• Reached a breakpoint, pressed Y
• got into debugger. The debugger did not change the prompt to pry>, but kept iex> one.
• I was able to run debugging-related commands (for example whereami) in the context of debugged process, though the prompt is still iex>.

Great, that it is not the case.

I see from your example, that you have reached the breakpoint in Elixir 1.16 too. Can you enter debugger-related commands from there (for example whereami)? If yes, then your debugger is working.

Do I understand correctly, that you expected to see the pry> prompt instead of iex> there (and thought pry did not work)?