`~p` sigil does not work with non-ascii characters

[aeons]

Environment

• Elixir version (elixir -v): 1.19.1
• Phoenix version (mix deps): 1.8.1
• Operating system: macOS 26

Actual behavior

With a route containing a unicode character, the ~p sigil will warn that the route does not exist.

# in lib/unicode_verified_routes_web/router.ex
    get("/ø", HomeController, :index)
# in eg. a template
<a href={~p"/ø"}>Ø</a>

$ mix compile
    warning: no route path for UnicodeVerifiedRoutesWeb.Router matches "/ø"
    │
  1 │ <a href={~p"/ø"}>Ø</a>
    │ ~~~~~~~~~~~~~~~~~~~~~~
    │
    └─ lib/unicode_verified_routes_web/controllers/page_html/home.html.heex:1: UnicodeVerifiedRoutesWeb.PageHTML.home/1

Reproduction code. However the compile warning is not shown when running as .exs

Application.put_env(:phoenix, :json_library, JSON)

Application.put_env(:sample, SamplePhoenix.Endpoint,
  http: [ip: {127, 0, 0, 1}, port: 5001],
  server: true,
  adapter: Bandit.PhoenixAdapter,
  secret_key_base: String.duplicate("a", 64)
)

Mix.install([
  {:bandit, "~> 1.8"},
  {:phoenix, "~> 1.8"}
])

defmodule SamplePhoenix.SampleController do
  use Phoenix.Controller, formats: [:html, :json]

  use Phoenix.VerifiedRoutes,
    endpoint: SamplePhoenix.Endpoint,
    router: Router

  def index(conn, _) do
    send_resp(conn, 200, ~p"/ø")
  end
end

defmodule Router do
  use Phoenix.Router

  pipeline :browser do
    plug(:accepts, ["html"])
  end

  scope "/", SamplePhoenix do
    pipe_through(:browser)

    get("/", SampleController, :index)
    get("/ø", SampleController, :index)

    # Prevent a horrible error because ErrorView is missing
    get("/favicon.ico", SampleController, :index)
  end
end

defmodule SamplePhoenix.Endpoint do
  use Phoenix.Endpoint, otp_app: :sample
  plug(Router)
end

{:ok, _} = Supervisor.start_link([SamplePhoenix.Endpoint], strategy: :one_for_one)
Process.sleep(:infinity)

Expected behavior

That the route would be detected and work as a regular route would.

[chrismccord]

What happens when you url encoded the ~p? afaik, the spec for URL only allows for percent-encoded chars. We could probably try to make this work, but does ~p"/%C3%B8" work or warn?

[aeons]

That gives the same warning. The rendered url is correctly encoded.