Recover from incomplete ESM using acorn-loose

[jp-knj]

Initial checklist

• I read the support docs
• I read the contributing guide
• I agree to follow the code of conduct
• I searched issues and discussions and couldn’t find anything or linked relevant results below
• I made sure the docs are up to date
• I included tests (or that’s not needed)

Description of changes

Closes #267

Problem

When users type incomplete ESM (e.g. export const x = or import { } from) in an MDX file, the strict acorn parser fails and the language service loses all IntelliSense — completions, diagnostics, and hover information disappear for the entire file until the syntax is corrected.

This is a poor editing experience because ESM is always incomplete while the user is actively typing it.

Approach

Introduce a "hybrid acorn" strategy that uses acorn-loose for ESM parsing and the strict acorn parser (with JSX) for expressions

Long-term perspective

This is a minimal, low-risk first step. Possible future improvements include working with micromark-extension-mdxjs-esm to support pluggable error recovery, reducing the need for patching at the language-service level.

[changeset-bot]

⚠️ No Changeset found

Latest commit: ce0c182

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[github-actions]

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 92.47%. Comparing base (660067a) to head (ce0c182).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #528      +/-   ##
==========================================
+ Coverage   92.43%   92.47%   +0.04%     
==========================================
  Files          13       13              
  Lines        1982     1994      +12     
==========================================
+ Hits         1832     1844      +12     
  Misses        150      150              

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