Describe the bug

Hello Svelte Team,

I'm reporting a persistent compilation issue observed with Svelte 5's $derived rune when attempting to filter an array based on a $state variable. It appears the compiler incorrectly inserts $.get() calls, leading to TypeErrors at runtime.

A minimal reproduction repository is available here: https://github.com/Gianluca-9/bug

When using $derived to filter an array (storeWarehouse.articles, defined as $state in src/lib/stores/warehouse.svelte.ts) based on a reactive $state string (search in src/routes/Warehouse.svelte), the compiled output seems to incorrectly access the search variable via $.get(search). This $.get() call does not return the expected string value, causing subsequent string methods like .toLowerCase() or array methods like .forEach() to fail with a TypeError.

Reproduction

Steps to Reproduce:

Clone the repository:
Bash

git clone https://github.com/Gianluca-9/bug.git
cd bug
Install dependencies:
Bash

pnpm i
Start the development server:
Bash

pnpm dev
Open the application in your browser (usually http://localhost:5173/).
Observe the console for errors.
Relevant Code Causing the Issue (src/routes/Warehouse.svelte):

Expected Behavior:
The $derived variable wh should evaluate to an Article[] array, containing items filtered correctly based the search string. No TypeError should occur during evaluation or access. console.log($inspect(wh)) should show the internal representation, but its value property should be the filtered array.

Actual Behavior:
A TypeError is thrown at runtime, preventing the table from rendering correctly:
Uncaught TypeError: $.get(...).forEach is not a function (this error occurs when wh is accessed, e.g., in the {#each wh as art} loop or if a derived value depends on wh).

Furthermore, inspecting the wh variable using console.log($inspect(wh)) (when the $derived is enabled in Warehouse.svelte) outputs a function that incorrectly contains $.get(search):

init () => {
return storeWarehouse.articles.filter((item) => item.descr.toLowerCase().includes($.get(search).toLowerCase()));
}
This demonstrates that the compiler is inserting the internal $.get macro unexpectedly, leading to runtime failures.

Workaround:
The filtering functionality is restored by changing wh from a $derived to a $state variable and updating it imperatively within an $effect block that reacts to changes in storeWarehouse.articles and search (as shown in the commented-out code in Warehouse.svelte).

Thank you for your time and assistance in investigating this compiler bug.

Logs

System Info

Svelte: 5.0.0 (Questa è la versione stabile GA! Non più next.1!)
@sveltejs/kit: 2.16.0
@sveltejs/vite-plugin-svelte: 5.0.0
Vite: 6.2.6
TypeScript: 5.0.0 (o più recente, dato che indica ^5.0.0)
Node.js: 22.16.0

Severity

annoyance