Fix TypeScript generic parameters being stripped with Prettier 3.7.0+

[Copilot]

Prettier 3.7.0+ strips TypeScript generic parameters from expressions in Svelte templates:

<!-- Before formatting -->
<a href={resolve('/path', { ...(page.params as Required<typeof page.params>), baz: 2 })}>

<!-- After formatting with Prettier 3.7.0+ -->
<a href={resolve('/path', { ...(page.params as Required), baz: 2 })}>

Changes

• Use babel-ts/babel parsers directly instead of custom AST-manipulating parsers. The custom parsers extracted just the expression node from the AST, which became incompatible with Prettier 3.7.0's formatting engine.

• Add removeLeadingSemicolon helper to strip protective semicolons that Prettier adds for ASI protection (e.g., ;('foo') → 'foo')

• Update removeParentheses with conservative heuristics to remove wrapper parentheses while preserving semantically important ones in function calls and grouped expressions

Trade-off

Using babel-ts directly means Prettier removes some parentheses it considers unnecessary (e.g., (x = !x) → x = !x). These are functionally equivalent but stylistically different. 9 existing tests reflect this formatting change.

Testing

Verified with Prettier 3.0.0, 3.7.0, and 3.7.3. Generic parameters now preserved correctly while maintaining backward compatibility.

Warning

Firewall rules blocked me from connecting to one or more addresses (expand for details)

I tried to connect to the following addresses, but was blocked by firewall rules:

• https://api.github.com/repos/prettier/prettier/compare/3.6.2...3.7.0
  • Triggering command: /usr/bin/curl curl -s REDACTED (http block)
• prettier.io
  • Triggering command: /usr/bin/curl curl -s REDACTED (dns block)

If you need me to access, download, or install something from one of these locations, you can either:

• Configure Actions setup steps to set up my environment, which run before the firewall is enabled
• Add the appropriate URLs or hosts to the custom allowlist in this repository's Copilot coding agent settings (admins only)

Original prompt

---

This section details on the original issue you should resolve

<issue_title>Generic parameters being removed</issue_title>
<issue_description>Given the following sveltekit file:

<script lang="ts">
  import { page } from '$app/state';
  import { resolve } from '$app/paths';
</script>

<a href={resolve('/[foo]/[bar]/[baz]', { ...(page.params as Required<typeof page.params>), baz: 2 })}>Go</a>

and the following config:

/**
 * @see https://prettier.io/docs/configuration
 * @type {import("prettier").Config}
 */
export default {
  singleQuote: true,
  printWidth: 100,
  plugins: ['prettier-plugin-svelte'],
  overrides: [{ files: '*.svelte', options: { parser: 'svelte' } }],
};

Prettier 3.7.3 and prettier-plugin-svelte 3.4.0 remove the generic passed to Required:

<script lang="ts">
  import { page } from '$app/state';
  import { resolve } from '$app/paths';
</script>

<a href={resolve('/[foo]/[bar]/[baz]', { ...(page.params as Required), baz: 2 })}>Go</a>

The only work-around I've found for now is to declare the type in the script block:

<script lang="ts">
  import { page } from '$app/state';
  import { resolve } from '$app/paths';

  type RequiredParameters = Required<typeof page.params>;
</script>

<a href={resolve('/[foo]/[bar]/[baz]', { ...(page.params as RequiredParameters), baz: 2 })}>Go</a>
```</issue_description>

## Comments on the Issue (you are @copilot in this section)

<comments>
</comments>

• Fixes Generic parameters being removed #506

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