Bug: Refactoring "Rename Symbol" (F2) in a `.ts` file corrupts Svelte components code that uses the renamed type**

[thomas-mindruptive]

Describe the bug

1. Description

Describe the bug clearly and concisely.

When using the "Rename Symbol" (F2) refactoring feature in VS Code on a TypeScript type within a .ts file, the Svelte language extension incorrectly modifies and corrupts the code of a .svelte file that imports and uses this type. Instead of just updating the type name, the refactoring injects malformed code and extraneous function calls throughout the Svelte component's script block, rendering it syntactically invalid.

2. To Reproduce

Note: It's not easy to reproduce, because I already converted my commit. But these are some samples:

1. Create a forms.types.ts file with several exported TypeScript types:

   // src/lib/forms.types.ts
   export type SubmitCallback<T = any> = (data: T) => unknown | Promise<unknown>;
   // ... other types

2. Create a FormShell.svelte component that imports and uses these types in its props definition:

   <!-- src/lib/components/FormShell.svelte -->
   <script lang="ts" generics="T extends Record<string, any>">
     import type { SubmitCallback, /* other types */ } from '$lib/forms.types';
     import { coerceErrorMessage } from "$lib/utils/errorUtils"; // This was a new import, intended to replace existing, local "coerceMessage()"
   
     interface FormShellProps<T> {
       submitCbk: SubmitCallback<T>;
       // ... other props
     }
   
     const { submitCbk }: FormShellProps<T> = $props();
     // ... component logic
   </script>

3. Perform the refactoring:

   • Open the forms.types.ts file.
   • Place the cursor on the SubmitCallback type name.
   • Press F2 to trigger "Rename Symbol".
   • Rename it to SubmitFn and press Enter.

3. Expected behavior

I expected the refactoring to only change the type name SubmitCallback to SubmitFn within the FormShell.svelte component, leaving the rest of the code untouched.

The expected result in FormShell.svelte should be:

<script lang="ts" generics="T extends Record<string, any>">
  import type { SubmitFn, /* other types */ } from '$lib/forms.types';

  interface FormShellProps<T> {
    submitCbk: SubmitFn<T>; // Correctly renamed
    // ... other props
  }
  // ...
</script>

4. Actual behavior

The FormShell.svelte file was corrupted with multiple syntax errors. The refactoring tool seems to have incorrectly injected code fragments into various places within the <script> block.

Here is a snippet of the corrupted code:

// ...
import type {
  Errors,
  ValidateFn, // This was renamed from ValidateCallback
  SubmitFn,   // This was renamed from SubmitCallback
  CancelFn,   // This was renamed from CancelCallback
  // ...
} from "./forms.types";
  

// ...

function internalSet<P extends NonEmptyPath<T>>(
  path: readonly [...P],
  value: PathValue<T, P>,
) {
  try {
    coerceErrorMessage[it added additional characters here].set<T, P>(formState.data, path, value); // ERROR
  } catch (e) {
    // ...
  }
} 

function get<P extends NonEmptyPath<T>>(
  path: readonly [...P],
): PathValue<T, P> | undefined {
  try {
    return pathUtils.get(formState.data, path);
  } catch (e) {
    log.error("get failed", {
      //...
      error: coerceErrorMessage(e),coerceErrorMessage 
    });
    return undefined;
  }
}

function markTouched(path: string) {
  formState.touched.add(path);
  if (autoValidate === "blur") {
    void runValidate(path);
  }
}coerceErrorMessage // ERROR!

// ....
log.error("get failed", {
    // ...
    error: coerceErrorMessage(e),coerceErrorMessage // Error
});

5. System Info

• Svelte for VS Code extension version: 109.11.0
• VS Code version: v103.2.0
• OS: Windows 11
• SvelteKit version: ^2.22.0"
• Node.js version: 24.4.1

6. Additional context

This issue makes refactoring TypeScript types that are consumed by Svelte components very unreliable and potentially destructive. It seems to be related to how the language server processes changes across .ts and .svelte file boundaries, especially when dealing with generic types.

Reproduction

Note: It's not easy to reproduce, because I already converted my commit. But these are some samples:

1. Create a forms.types.ts file with several exported TypeScript types:

   // src/lib/forms.types.ts
   export type SubmitCallback<T = any> = (data: T) => unknown | Promise<unknown>;
   // ... other types

2. Create a FormShell.svelte component that imports and uses these types in its props definition:

   <!-- src/lib/components/FormShell.svelte -->
   <script lang="ts" generics="T extends Record<string, any>">
     import type { SubmitCallback, /* other types */ } from '$lib/forms.types';
     import { coerceErrorMessage } from "$lib/utils/errorUtils"; // This was a new import, intended to replace existing, local "coerceMessage()"
   
     interface FormShellProps<T> {
       submitCbk: SubmitCallback<T>;
       // ... other props
     }
   
     const { submitCbk }: FormShellProps<T> = $props();
     // ... component logic
   </script>

3. Perform the refactoring:

   • Open the forms.types.ts file.
   • Place the cursor on the SubmitCallback type name.
   • Press F2 to trigger "Rename Symbol".
   • Rename it to SubmitFn and press Enter.

Expected behaviour

I expected the refactoring to only change the type name SubmitCallback to SubmitFn within the FormShell.svelte component, leaving the rest of the code untouched.

The expected result in FormShell.svelte should be:

<script lang="ts" generics="T extends Record<string, any>">
  import type { SubmitFn, /* other types */ } from '$lib/forms.types';

  interface FormShellProps<T> {
    submitCbk: SubmitFn<T>; // Correctly renamed
    // ... other props
  }
  // ...
</script>

System Info

• Svelte for VS Code extension version: 109.11.0
• VS Code version: v103.2.0
• OS: Windows 11
• SvelteKit version: ^2.22.0"
• Node.js version: 24.4.1

Which package is the issue about?

No response

Additional Information, eg. Screenshots

This issue makes refactoring TypeScript types that are consumed by Svelte components very unreliable and potentially destructive. It seems to be related to how the language server processes changes across .ts and .svelte file boundaries, especially when dealing with generic types.

[jasonlyu123]

I can't reproduce this. Did you save the Svelte file before you renamed the symbol? This is a limitation for renaming from a ts/js file because the TypeScript language service plugin can't see unsaved Svelte documents. If you do, please provide a reproduction repository.

[thomas-mindruptive]

Thank you, yes I save everything before refactoring. VSC changed multiple files, and many of them were broken.
Sorry, I don't have the files anymore. Next time, I will save them immediately.