Type checker unsoundly refines both operands of `min/2` and `max/2` from the result’s expected type

[lukaszsamson]

Existing issue

• I have searched existing issues and could not find a duplicate.

Elixir and Erlang/OTP versions

Erlang/OTP 28 [erts-16.4.0.1] [source] [64-bit] [smp:12:12] [ds:12:12:10] [async-threads:1] [jit]

Interactive Elixir (1.21.0-dev)

Operating system

any

Current behavior

The implementation of max and min in Apply module passes result expected type into both args refinement. This is unsound because either argument can be discarded according to erlang term ordering. A consumer constrains only the selected result, not both operands.

Repro:

defmodule Example do
  def run(x) do
    :erlang.binary_part(max(x, ""), 0, 0)
    case x do
      a when is_integer(a) -> :integer
      a when is_binary(a) -> :binary
    end
  end
end

IO.inspect(Example.run(1))

Result: a false positive warning:

warning: the following clause will never match:

    a when is_integer(a) ->

because it attempts to match on the result of:

    x

which has type:

    binary()

where "a" was given the type:

    # type: integer()
    # from: iex:5
    is_integer(a)

└─ iex:5: Example.run/1

The code works and prints "integer"

Expected behavior

Type refinement should be applied to a union of both arguments