TypeScript type assertions lose opening parenthesis in bind:value expressions, causing syntax errors

[beshanoe]

TypeScript type assertions lose opening parenthesis in bind:value expressions, causing syntax errors

Bug Description

When using Prettier with prettier-plugin-svelte, TypeScript type assertions in bind:value expressions lose their opening parenthesis, resulting in invalid syntax that breaks parsing.

Example

Before formatting (correct syntax):

<script lang="ts">
  interface Config {
    value: string;
  }
  
  let config: Config | Record<string, never> = { value: 'test' };
</script>

<input bind:value={(config as Config).value} />

After prettier --write (broken syntax):

<script lang="ts">
  interface Config {
    value: string;
  }

  let config: Config | Record<string, never> = { value: 'test' };
</script>

<input bind:value={config as Config).value} />

Notice the missing opening parenthesis: (config as Config) becomes config as Config).

Impact

This creates a cascade of problems:

1. Syntax Error: The code becomes unparseable due to mismatched parentheses
2. ESLint Failure: eslint --fix breaks the file, making it impossible to lint on subsequent runs
3. Build Failure: Svelte compiler cannot parse the invalid syntax

Environment

• prettier: 3.6.2
• prettier-plugin-svelte: 3.4.0 (latest)
• svelte: 5.0.0
• Node.js: 20.19.4
• npm: 10.8.2

Reproduction

1. Create a .svelte file with TypeScript type assertion in bind:value
2. Run prettier --write file.svelte
3. Observe the missing opening parenthesis

Minimal Reproduction Case

<script lang="ts">
  interface Config { value: string; }
  let config: Config | Record<string, never> = { value: 'test' };
</script>

<input bind:value={(config as Config).value} />

Run: prettier --write file.svelte

Result: bind:value={config as Config).value} (missing opening parenthesis)

Related Issues

This appears related to:

• Prettier adding surrounding parentheses on new function bindings #477 (opposite problem: unwanted parentheses addition in function bindings)

Expected Behavior

Prettier should preserve the parentheses around TypeScript type assertions in bind:value expressions to maintain valid syntax.

Workaround

Use <!-- prettier-ignore --> comments before affected lines:

<!-- prettier-ignore -->
<input bind:value={(config as Config).value} />