Support Svelte

[sushichan044]

Summary

Add first-class transformation for import.meta.* inside Svelte components. Handle both script blocks and template/expression contexts with correct offset mapping.

Motivation

• Parity with JS/TS and Astro support.
• Svelte apps may reference import.meta.* in scripts, reactive statements, and templates.

Scope

• Parse Svelte files with the official compiler.
• Transform in:
  • <script> (instance) and <script context="module"> (honor lang="ts").
  • Template expressions: mustache, attribute expressions, and directive expressions.

Important Caveat

Svelte has unique syntax and directives beyond plain HTML/JS:

• Reactive statements/declarations: $: x = ..., $: { ... }.
• Store shorthand: $store reads.
• Block syntax: {#if}, {#each}, {#await}.
• Directives: on:, bind:, class:, use:, as well as transitions/animations.
  We must only transform JavaScript expression substrings and keep offsets precise when applying replacements.

Non-Goals

• Implementing a Svelte compiler.
• Transforming raw HTML or string-only attributes.
• Changing Svelte semantics; only replace import.meta.* with literal results.

Design Proposal

• Parser: use svelte/compiler to obtain AST and node positions.
• Scripts: run analyzeTypeScript on instance and module scripts.
• Template: traverse expression-bearing nodes (mustache, attribute values, on:, bind:, class:, use: directives, and reactive statements). For each expression string, run analyzeTypeScript and map replacements back via node offsets.
• Special cases: do not modify directive names/modifiers; operate only on expression content.

Implementation Plan

1. Add src/core/languages/svelte.ts processor using svelte/compiler via tryImport.
2. Extend detection in src/core/languages/index.ts to include .svelte.
3. Add optional peer dep: svelte.
4. Tests & fixtures under tests/fixtures/svelte/ covering:
   • Instance and module scripts (TS on/off)
   • { import.meta.FOO }, on:click={import.meta.fn()}
   • bind:value={import.meta.V}, class:active={import.meta.FLAG}
   • Reactive $: x = import.meta.V and $: { console.log(import.meta.V) }
5. Docs: update README (Language Support) once merged.

Testing Strategy

• Snapshot-based fixtures; ensure no-op when import.meta is absent.
• Edge cases: store shorthand $store, nested block structures.

Risks

• Offset mapping bugs; mitigate with helper utilities and thorough fixtures.
• Compiler version drift; guard with tryImport and pinned peer deps.

Acceptance Criteria

• .svelte files with import.meta.* are transformed in scripts and template expressions.
• Unsupported contexts remain unchanged. All tests pass.

Open Questions

• Should certain directives be ignored by default to reduce false positives?

How to Contribute

• Comment to claim. Incremental PRs welcome.
• Use AST node positions from the official compiler; avoid ad-hoc string parsing.