Type error on Elixir 1.19.0-dev with OTP 28

[kipcole9]

Elixir and Erlang/OTP versions

• OTP 28.0-rc2
• Elixir 1.19.0-dev

Operating system

MacOS

Current behavior

The following module produces a type warning that (as best I can tell) is not correct. Note that replacing the interpolated value #{known_locale_count} with #{inspect known_locale_count} result in no type warning. Somehow the interpolation is affecting the assumption of the type of known_locale_count - the relevant part of the warning seems to be:

# from: lib/type_check.ex:17
to_string(known_locale_count)

Example module

defmodule TypeCheck do
  @warn_if_greater_than 100

  @locales [
    :ar, :ca, :"ca-ES-valencia", :de, :doi, :en, :"en-001", :"en-AU", :"en-GB",
    :es, :fr, :"fr-CA", :it, :ja, :nb, :no, :pl, :th, :und
  ]

  def install_locales(config) do
    known_locale_count =
      @locales
      |> Enum.count()

    locale_string = if known_locale_count > 1, do: "locales named ", else: "locale named "

    IO.puts(
      "Generating #{inspect(config.backend)} for #{known_locale_count} " <>
        locale_string <>
        "#{inspect(@locales, limit: 5)} with " <>
        "a default locale named #{:en}"
    )

    if known_locale_count > @warn_if_greater_than do
      IO.puts("Please be patient, generating functions for many locales " <> "can take some time")
    end
  end
end

Type message

iex -S mix
Erlang/OTP 28 [RELEASE CANDIDATE 2] [erts-16.0] [source] [64-bit] [smp:10:10] [ds:10:10:10] [async-threads:1] [jit]

    warning: comparison with structs found:

        known_locale_count > 100

    given types:

        dynamic(
          %Date{} or %DateTime{} or %NaiveDateTime{} or %Time{} or %URI{} or %Version{} or
            %Version.Requirement{} or atom() or binary() or float() or integer() or list(term())
        ) > integer()

    where "known_locale_count" was given the type:

        # type: dynamic(
          %Date{} or %DateTime{} or %NaiveDateTime{} or %Time{} or %URI{} or %Version{} or
            %Version.Requirement{} or atom() or binary() or float() or integer() or list(term())
        )
        # from: lib/type_check.ex:17
        to_string(known_locale_count)

    Comparison operators (>, <, >=, <=, min, and max) perform structural and not semantic comparison. Comparing with a struct won't give meaningful results. Structs that can be compared typically define a compare/2 function within their modules that can be used for semantic comparison.

    typing violation found at:
    │
 23 │     if known_locale_count > @warn_if_greater_than do
    │                           ~
    │
    └─ lib/type_check.ex:23:27: TypeCheck.install_locales/1

Expected behavior

No type error is expected since:

    known_locale_count =
      @locales
      |> Enum.count()

is determined by the result of Enum.count/1.

[sabiwara]

Sharing another smaller example for the record

defmodule Foo do
  def foo(x, y) do
    msg = "#{x} > #{y}"
    if x > y do
      IO.puts(msg)
    end
  end
end