Svelte 5: Misleading error message "Cannot reassign or bind to each block argument in runes mode."

[felix-roehrich]

Describe the bug

If you look at the code in the REPL, you will very quickly notice that code in App.svelte will not have the desired effect, but the error message is very confusing, since at no point there is an assignment to an each block element.

Reproduction

https://svelte-5-preview.vercel.app/#H4sIAAAAAAAAE31Qy2rDMBD8lUXtwQYT93kxsmnxJ_QY5eA6ayIqS0JaB4Lwv1eK3Rra0uPOzA4zE9ggFXpW7QPT3YisYq_WsoLRxabDn1ERxtubyfUJ4b530lIjtCA5WuMIWhicGUGwXdnulg_BhOblJtV8wStjSRrtwU0aPZSR4-3VK9x4La1FAtVdzERZgHOnJoQ5nxOfFNj1J9jfFw_FY_FUPB-g86BXVhB_n4iMBqN7JfuPOmQ51M3qUkdh84bEy0XVrJ5l8rxahHINMKfobRNLj-YoB4lHVpGbcC6-N2r_WyiV3TYSpGKnsLaCOSa5tc5Yn-Ub_ZXx7sdq4cWhPqL7Y5Pf8Q7zJ0lZY4POAQAA

Logs

No response

System Info

REPL

Severity

annoyance

[dm-de]

I rewrote your code, but it is useless... value does nothing - maybe replace with console.log

LINK

[MacFJA]

I rewrote your code, but it is useless... value does nothing - maybe replace with console.log

LINK

The rewrite is incorrect, you declare a new variable inside the scope of the function, it's not the same value from the layout, so the code run, but it has no effect in the component C.svelte

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The value from a snippet instruction seem to be immutable, similar to getContext/setContext

If it's the case, then maybe the documentation should indicate this limitation, and maybe the same workaround as getContext

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So, if, instead of a simple value, a plain old store is used, then the code work as expected (as far as I understand the goal of this code) (See my version with store, I add a <fieldset> that contains the content of value to visualize the changes)