$derived doesn't update if dependent $state has nested objects

[ampatspell]

Describe the bug

If $state contains nested objects (that passes prototype === object_prototype) and they are mutated outside of $effect (?) and accessed, $derived doesn't return the latest value.

class {
  data = $state<{ position: { x: number }>();
  position = $derived(this.data?.position);
}

Reproduction

sorry for the messy repro. this is the simplest I could get it to.

data.name and name correctly returns 1
data.position.x correctly returns 1
position returns undefined

this happens only if position is accessed outside of an $effect.active() (?).

comment out this.content.map(e => e.position); in models.svelte.ts line 36, and position then correctly returns 1

https://svelte-5-preview.vercel.app/#H4sIAAAAAAAAE51TwW6jMBD9lZEbqZAi6JkkrXrotXvJrVQqxUPjFdgID5QK-d9XtoEkTXPZU8LMm5k3741HVooKNUtfRybzGlnKnpqGRYy-G_uhe6wIWcS06trCRra6aEVDD5kEEHWjWoIR9gchPzUYKFtVw22c1IpjpWNffrvJpIVXSOASsAOJX1NVEG5scoVliQUFQQi7Bw-Ldfdhp31gEFrQNllmZ3K8wbw4TMBCSUJJkGsg29TYjlsueiiqXOtdxlr1lTFbSBnxnPLYbgs7GB0-tqFHFzMWs0246B36apPz-iuVpwMbpQUJJePh59hjxsDVHr-Vz7HHeDgbPiZWG5NJFrFacVEK5CyltkMTLT6fWXR0_K8-dRsH57ATwPsFo9XWEocdrDTlhJODQnK05O4nuyUOFIQeD1AoqWnB3N3RQejYfW48wAWmvlMNgOWawvuLFftmNTq8eY_m9CxAeqwAGFI_Zo4Y_8e4OcZzO7msuVQj7UWNqptvcGnpmPltJq4mgvvw2G-5hhXHVvTIg2UZf1QeO7O9ApzTodPPNb6UX3ta88EvFry-hZv_WM274q7p9FEui07LT-PiptOHwKHPAPLz9Klu_MFmNP8mCazXL3_2z-l6DaJ0LUFoKFRdoyTkoDqKYJLkKFNeaQUtlhUWpKGTHNvq2zLt86rDXwnWeROg3RDP5LzwzFy-jDfzDzS1mo0NBQAA

Logs

No response

System Info

System:
  OS: macOS 14.2.1
  CPU: (8) arm64 Apple M1
  Memory: 102.20 MB / 8.00 GB
  Shell: 5.9 - /bin/zsh
Binaries:
  Node: 18.19.0 - ~/.nvm/versions/node/v18.19.0/bin/node
  Yarn: 1.22.21 - ~/.nvm/versions/node/v18.19.0/bin/yarn
  npm: 10.2.3 - ~/.nvm/versions/node/v18.19.0/bin/npm
  pnpm: 8.6.12 - ~/.nvm/versions/node/v18.19.0/bin/pnpm
  bun: 1.0.15 - ~/.bun/bin/bun
  Watchman: 2023.12.04.00 - /opt/homebrew/bin/watchman
Browsers:
  Chrome: 123.0.6312.59
  Safari: 17.2.1
npmPackages:
  rollup: ^4.9.5 => 4.13.0

Severity

blocking all usage of svelte

[ampatspell]

Just for the context, this repro is based on the setup I have for Firebase query onSnapshot callbacks that mutates – adds, moves or removes documents array while some of the documents also get data updates.

[7nik]

I simplified the code.

The $derived seems to break if its first read is done outside a reactive context.

Both REPLs start to work when you wrap reading .position with $effect.root.