eslint returns incorrect Svelte error

[hamilton]

The following code (reduced for clarity) caused an error:

export let whatever = 10;
let internal = writable(whatever);
$: $internal = whatever;

let someOtherStore = derived(internal, $internal => $internal + 10);

This should not technically be an error, but it's breaking a PR that was passing last night. Has something changed?

[openjck]

I'm looking into this. Do you mean you're seeing a no-unused-vars error about $internal? That error is correct; it isn't used. The $internal that's used on line 5 is the argument of the anonymous function.

[openjck]

If that's not what you meant, let me know.

[hamilton]

$: $internal = whatever is a fairly normal way of shorthanding $: internal.set(whatever), and the part in packages/datagraphic/DataGraphic.svelte the caused the issue didn't to date raise this eslint error before, so something must have changed in our eslint setup to make it raise an error now. I would argue that it shouldn't raise an error for these kinds of reactive autosubscribed set operations, and in fact it didn't before. I think whether it is used / unused is largely semantics since a derived store reactively uses the store value itself. But I guess eslint is largely concerned with semantics :)

Don't know the right course of action, I guess we're ruled by whatever eslint prescribes. I've already fixed the error where it occurred. I just think this is kind of useless and arbitrary. Let's chalk this issue up to grumbling. Closing now

[openjck]

Oh, I see. This sounds like a bug, then. I'll find a GitHub issue against eslint-plugin-svelte3 or open one.

[openjck]

I opened an issue:
sveltejs/eslint-plugin-svelte3#66

There's a related issue which has already been filed, which mine might be a duplicate of:
sveltejs/eslint-plugin-svelte3#64

[openjck]

Reminder:

We can close this when sveltejs/eslint-plugin-svelte3#66 is fixed and we have upgraded to a version of eslint-plugin-svelte3 which includes the fix.