Dialyzer fails with no_return when using Mix.raise/1 in Elixir 1.17.0

[ypconstante]

Elixir and Erlang/OTP versions

Erlang/OTP 26 [erts-14.2.1] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1] [jit]

Elixir 1.17.0 (compiled with Erlang/OTP 26)

Operating system

macOS 14.5

Current behavior

With Elixir 1.17 dialyzer is failing with no_return when a mix task uses Mix.raise as the return of with/else, using case or raise Mix.Error avoids this issue.

> mix dialyzer
...
lib/mix/tasks/example.ex:6:no_return
The created anonymous function has no local return.

defmodule Mix.Tasks.Example do
  use Mix.Task

  @impl Mix.Task
  def run(argv) do
    with [] <- argv do
      :ok
    else
      _ -> Mix.raise("message")
    end
  end
end

defmodule Mix.Tasks.Example2 do
  use Mix.Task

  @impl Mix.Task
  def run(argv) do
    case argv do
      [] -> :ok
      _ -> Mix.raise("message")
    end
  end
end

defmodule Mix.Tasks.Example3 do
  use Mix.Task

  @impl Mix.Task
  def run(argv) do
    with [] <- argv do
      :ok
    else
      _ -> raise Mix.Error, message: "message"
    end
  end
end

Expected behavior

Dialyzer behaves the same as in previous versions when using Mix.raise/1

[josevalim]

We tag Mix.raise as a no_return, so everything should work. We don't really guarantee Dialyzer compatibility but we would be welcome to review and merge a PR that provides a fix.

[sabiwara]

I think it's because with now defines an anonymous function internally, it would expand to:

where dialyzer complains that The created anonymous function has no local return. fun.
This is only the case when fun isn't explicitly raising but calling a function with a no_return type.

I'm not sure if this could be fixed upstream, or maybe we could try to add more generated: true here to silence it since we're already doing this in a bunch of places for with anyway. Will try to give it a shot.