Svelte: Function hoisting is too aggressive

[mrkishi]

Functions that contain instance data are hoisted; see REPL.

Note that the DOM update code is generated even though the variable never gets invalidated.

Tangentially related to #2731.

[NicolasHz]

I don't understand your point. it's working as it should, I mean, you're reassigning get_answer to another function... even with hoisting you're overriding it

[mrkishi]

Yeah, we're still overriding something — but it's the global function, not the per-instance one which is what should happen.

Granted, I believe this is a very low priority bug, but we should eventually get to it.

Plain javascript version to clarify what I mean:

// this is what we write
function component_init(props) {
    function secret() {
        return secret.value;
    }

    secret.value = props.value;
    return secret;
}

// this is how svelte currently hoists functions
function secret() {
    return secret.value;
}

function component_init_transformed(props) {
    secret.value = props.value;
    return secret;
}

const a = component_init(10);
const b = component_init(20);
const c = component_init_transformed(30);
const d = component_init_transformed(40);

console.log(a(), b(), c(), d()); // 10 20 40 40 instead of 10 20 30 40

[dasZGFz]

It looks like this was fixed unless I'm misunderstanding.

REPL

[mrkishi]

It's now indeed not as aggressive, but when the value escapes our code through function calls it should still be deemed mutable: repl.

And in order to be compliant, getters also need to be considered unsafe, even though that's more of a fringe aspect.