Derived stores with multiple dependencies don't always update.

[pngwn]

When a store has multiple dependencies it won't always update when those dependencies update. This is only present when one of the dependencies is derived from the other dependency (I think).

REPL

Thanks to @Conduitry's detective work, it seems like this bug was possibly introduced by #2955.

[mrkishi]

The issue here is that deriveds are always invalidated:

svelte/src/runtime/store/index.ts

Lines 162 to 165 in 83be1f3

	() => {
	run_all(invalidators);
	pending |= (1 << i);
	}),

But not necessarily updated:

svelte/src/runtime/store/index.ts

Lines 68 to 75 in 83be1f3

	if (safe_not_equal(value, new_value)) {
	value = new_value;
	if (!stop) {
	return; // not ready
	}
	subscribers.forEach((s) => s[1]());
	subscribers.forEach((s) => s[0](value));
	}

pending needs to be reset even if !safe_not_equal().

[btakita]

One of my apps (>1000 stores) is dead in the water until this is fixed. Any thoughts on what can be done?

[btakita]

To get around this issue, one can use a writable & manually set it's value using subscribe.

https://svelte.dev/repl/14d838206c5c4114b16ce51a4bb3ec71?version=3.6.7

[btakita]

I have a hotfix for v3.6.7 at:

"svelte": "btakita/svelte#gh-3191-hotfix"

[btakita]

v3.6.8 hotfix "svelte": "btakita/svelte#3.6.8-gh-3191-hotfix"

@Rich-Harris What are your thoughts on #3219? Thank you