follow up on state_unsafe_mutation for SvelteMap created inside $derived

[gyzerok]

Describe the bug

Yesterday I've got a fix merged, that was related to this. And it seems to work almost perfectly except for one strange case.

There is one place in our code that is still failing. I can see why it's happening, but I've spent several hours today trying to create a failing test for it without any success.

In the following code calls to map.set in the first loop are working just fine without any issues. However the last call triggers state_unsafe_mutation.

class Chat {
  adminParticipants: $derived.by(() => {
    const map = new SvelteMap();

    for (const [id, apiAdmin] of Object.entries(this.$.adminParticipants ?? {})) {
      const contactId = AbstractContact.resolveId(+id);
      map.set(contactId, AdminParticipant.fromApi(this.pool, apiAdmin));
    }

    if (this.ownerId) {
      // state_unsafe_mutation is happening on this .set
      map.set(
        this.ownerId,
        AdminParticipant.fromApi(this.pool, {
          id: this.ownerId,
          permissions: Number.MAX_SAFE_INTEGER,
        }),
      );
    }

    return map;
  });
}

Here you can see how it looks in the debugger - reaction_sources do not include source for some reason.

Reproduction

Would love to have one, but seems like I need help

Logs

System Info

Using version from this PR: https://github.com/sveltejs/svelte/pull/16221

Severity

annoyance

[paoloricciuti]

I think this is exactly what i was talking about in #16230 ...there's still some variable that uses source instead of state and the only difference is that state pushes itself on the reaction_sources array...I was already talking with the other maintainers to see if there's something obvious I'm missing but I don't think we should EVER use source internally so I plan to just remove it and replace it with state...let me open a PR to see if this fixes it.

[gyzerok]

@paoloricciuti in map and set source is used inside set/add methods. I've tried to swap it for state, but then tests for SvelteMap and SvelteSet are failing. I've tried investigating how to fix the logic there, but without any success.

[paoloricciuti]

@paoloricciuti in map and set source is used inside set/add methods. I've tried to swap it for state, but then tests for SvelteMap and SvelteSet are failing. I've tried investigating how to fix the logic there, but without any success.

I'm trying to look into this too...let's see who does it first 😄

[paoloricciuti]

So this is the minimal repro

https://svelte.dev/playground/fc0e9a6ba3ea4743b72f294dbd733f1e?version=pr-16221

The problem is that the second time around it's actually setting the source created before so it's problematic...i think it's safe to use state here for this very but I'm not sure if it's a long term solution

[gyzerok]

Awesome! I was trying to call multiple sets, but never reset the same key. Now tests from my PR are failing, which is great. Will give it a fresh look

[paoloricciuti]

I have a solution locally technically but i'm not convinced by the fix so i'm gonna try to see if there's a better solution

[gyzerok]

Mind sharing your code? Planning to spend couple more hours tomorrow by looking into this. If nothing else will at least learn more about the internals

[paoloricciuti]

I'll open a PR in a bit even tho I'm not fully convinced yet