Legacy #await problem

[valmarv]

Describe the bug

Await block unexpectedly evaluates expression upon state changes in legacy mode.
Expected behavior is to only have the expression evaluated when its variables change.

Reproduction

https://svelte.dev/playground/53cc8a72175c41c6bebb2bbb75d069a7?version=5.2.3

Logs

No response

System Info

System:
    OS: Windows 10 10.0.19045
    CPU: (16) x64 Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz
    Memory: 9.01 GB / 25.53 GB
  Binaries:
    Node: 18.12.1 - C:\Program Files\nodejs\node.EXE
    npm: 9.1.3 - C:\Program Files\nodejs\npm.CMD
  Browsers:
    Edge: Chromium (130.0.2849.80)
    Internet Explorer: 11.0.19041.4355
  npmPackages:
    rollup: ^4.22.4 => 4.27.3
    svelte: ^5.1.6 => 5.2.3

Severity

blocking an upgrade

[patrikpessi]

I ran into the same problem and worked around it by turning the function calls into plain promises like so
https://svelte.dev/playground/1c7393b8c9a5457f8261ec65c33fdf48?version=5.2.8

[dummdidumm]

cnt becomes a dependency of the await block by being read inside init, and that causes the await block to rerun. We likely need to wrap these calls in untrack in legacy mode

[valmarv]

@dummdidumm What exactly is this dependency tracking, when does it come up? Function calls haven't been invalidated by dependencies in the past.

[patrikpessi]

Invalidating function calls when deps change causes code like this to break too
In svelte 5:
https://svelte.dev/playground/hello-world?version=5.2.9#H4sIAAAAAAAACm2MwUrEMBRFf-XxVi0tdnBZ04A7_8G4mEnfQDDzEpIXRwn5dwlV3Li7HM65Ffl8I1zxhbwPcA_J7zDQ7oT2EWe8Ok8Z19eK8hW71wHOv9VzjA_5g7x0djln-o_bwEIsGVdU2SYXRRs24knAhsICG5yeDHd2LWzFBYY-hhFqh0YSSUn8Y0_w2G1phtXy98cq6npkTS1RG1aXIhIYAlvv7PtWhxE2fbxMU9OObaIbsajlMLVhnFHoU3CVVKi9tW9ABERgIAEAAA==
In svelte 4:
https://svelte.dev/playground/hello-world?version=4.2.18#H4sIAAAAAAAACm2MwUrEMBRFf-XxVi0tdnBZ04A7_8G4mEnfQDDzEpIXRwn5dwlV3Li7HM65Ffl8I1zxhbwPcA_J7zDQ7oT2EWe8Ok8Z19eK8hW71wHOv9VzjA_5g7x0djln-o_bwEIsGVdU2SYXRRs24knAhsICG5yeDHd2LWzFBYY-hhFqh0YSSUn8Y0_w2G1phtXy98cq6npkTS1RG1aXIhIYAlvv7PtWhxE2fbxMU9OObaIbsajlMLVhnFHoU3CVVKi9tW9ABERgIAEAAA==

[patrikpessi]

cnt becomes a dependency of the await block by being read inside init, and that causes the await block to rerun. We likely need to wrap these calls in untrack in legacy mode

I find this hidden reactivity somewhat counterintuitive, given that we have runes specifically designed for declaring reactive values. Wasn't one of the key selling points of runes that they provide a clearer and more intentional way to define reactivity?