Ports leak between apps when compiled together

[lydell]

Here are two minimal Elm programs, that both use ports with different names:

port module A exposing (main)


port a_outgoing : String -> Cmd msg


port a_incoming : (String -> msg) -> Sub msg


main : Program () String String
main =
    Platform.worker
        { init = \() -> ( "", Cmd.none )
        , update = \_ s -> ( s, a_outgoing s )
        , subscriptions = \_ -> a_incoming identity
        }

port module B exposing (main)


port b_outgoing : String -> Cmd msg


port b_incoming : (String -> msg) -> Sub msg


main : Program () String String
main =
    Platform.worker
        { init = \() -> ( "", Cmd.none )
        , update = \_ s -> ( s, b_outgoing s )
        , subscriptions = \_ -> b_incoming identity
        }

Let’s compile them together into the same JavaScript file:

elm make src/A.elm src/B.elm --output combined.js

Then let’s initialize both:

const appA = Elm.A.init();
const appB = Elm.A.init();

console.log("A ports", appA.ports);
console.log("B ports", appB.ports);

Both logs show 4 ports available: a_outgoing, a_incoming, b_outgoing, b_incoming

I would have expected:

• appA: a_outgoing, a_incoming
• appB: b_outgoing, b_incoming

If you do appA.b_outgoing.subscribe(console.log) nothing is ever logged, and if you do appA.b_incoming.send("") nothing ever gets to A and not to B either. So the extra ports are harmless, they’re just confusing.

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