Error: Could not find a declaration file for module

[Bilge]

Describe the bug

Since Svelte v5, one (and only one) of my components gives this error. I cannot determine what is special about this one component, other than it declares no <script> block (but adding one does not fix the error).

• This same file is unchanged since before the v5 migration, where svelte-check detected no error.
• There are no errors with my webpack build.
• The same file importing the problematic component also imports other components without problems.

This combination of circumstances makes me strongly suspect this is a bug.

Reproduction

import WatchListButton from '../component/WatchListButton.svelte';

Error: Could not find a declaration file for module '../component/WatchListButton.svelte'. 'component/WatchListButton.svelte' implicitly has an 'any' type.
import TooltipPage from './tooltip page';
import WatchListButton from '../component/WatchListButton.svelte';
import { mount } from 'svelte';

Expected behaviour

Components don't need declaration files, or such declarations are derived from the component source files.

System Info

• OS: Windows
• IDE: PhpStorm

Which package is the issue about?

svelte-check

Additional Information, eg. Screenshots

No response

[Bilge]

Actually, adding script tags does fix it, but only if you also set lang=ts.

<!-- svelte-check workaround -->
<script lang="ts"></script>

<!-- NOT a svelte-check workaround -->
<script></script>

[jasonlyu123]

Since svelte-check v4 and extension 109, the allowJs typescript compiler option is respected. It was false by default and was previously overridden by the language-server/svelte-check as true. The issue is likely you need to set allowJs to be true to allow module resolution to find js components in your project.

You might also want to check if the include config in your tsconfig/jsconfig.json includes svelte files. Doing so will give your editor a small performance gain and improve your overall experience in type-check or other language features.

[Bilge]

Can confirm: for reasons I don't yet understand, setting "allowJs": true, also resolves the issue.