Erroneous "typing violation" warning

[marcandre]

Elixir and Erlang/OTP versions

Erlang/OTP 27 [erts-15.0.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [jit]

Elixir 1.17.2 (compiled with Erlang/OTP 25)

Operating system

Mac OS 14.5 (23F79)

Current behavior

The following code compiles with a false warning error:

    x = fn -> 42 end
    if is_atom(x), do: x.__live__()

We get:

    warning: expected a module (an atom) when invoking __live__/0 in expression:

        x.__live__()

    where "x" was given the type:

        # type: fun()
        # from: lib/basic_app_web/live/user_live/index.ex:9
        x = fn x -> x end

    hint: "var.field" (without parentheses) means "var" is a map() while "var.fun()" (with parentheses) means "var" is an atom()

    typing violation found at:
    │
 10 │     if is_atom(x), do: x.__live__()
    │                          ~
    │
    └─ lib/basic_app_web/live/user_live/index.ex:10:26: BasicAppWeb.UserLive.Index.mount/3

Clearly, this code should not error, as x.__live__() will be called only if x is an atom.

This is particularly problematic as our CI is currently set with --warnings-as-errors, and we get this error when calling Phoenix.LiveViewTest.render_component/3 in our tests. Is there a workaround?

Expected behavior

Expecting no warning.

[josevalim]

I believe this has been fixed in LiveVIew (but maybe RC only?).

Also see #13701, #13715, #13727. :)