fix: throw clear error when prettier is not installed instead of hanging

[isamu]

Summary

• Add a require.resolve('prettier') check before creating the synckit worker thread
• When prettier is not installed, ESLint now throws a clear error message instead of hanging indefinitely

Fixes #781

Root Cause

worker.mjs imports prettier as a top-level static import. When prettier is not installed, the worker thread crashes on startup. synckit doesn't handle worker startup failures — the main thread blocks forever on Atomics.wait().

Fix

Check for prettier availability via require.resolve('prettier') before creating the worker. If not found, throw:

Error: eslint-plugin-prettier requires "prettier" package to be installed. Please install it with: npm install -D prettier

Test plan

• All existing tests pass (pnpm test)
• Manual verification: remove prettier from node_modules and confirm ESLint fails with the new error message instead of hanging

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Important

Adds a check for Prettier's installation in eslint-plugin-prettier.js to prevent ESLint from hanging, throwing a clear error if missing.

• Behavior:
  • Adds require.resolve('prettier') check in eslint-plugin-prettier.js before creating the synckit worker thread.
  • Throws error if Prettier is not installed, preventing ESLint from hanging.
• Error Handling:
  • Throws error: eslint-plugin-prettier requires "prettier" package to be installed. Please install it with: npm install -D prettier.
• Testing:
  • All existing tests pass.
  • Manual verification to ensure ESLint fails with the new error message when Prettier is not installed.

^{This description was created by for 297bc40. You can customize this summary. It will automatically update as commits are pushed.}

Summary by CodeRabbit

• Bug Fixes
  • Now fails fast with a clear error if Prettier is not installed, instead of hanging during formatting.
• Documentation
  • Added a changelog entry describing the patch that clarifies the new failure behavior when Prettier is missing.

[changeset-bot]

🦋 Changeset detected

Latest commit: 1318b9b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 1 package

Name	Type
eslint-plugin-prettier	Patch

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Click here if you're a maintainer who wants to add another changeset to this PR

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[coderabbitai]

📝 Walkthrough

Walkthrough

Adds a defensive check to eslint-plugin-prettier to verify the prettier package can be resolved before lazy-loading it; if unresolved, the plugin now throws a clear error message instead of hanging.

Changes

Cohort / File(s)	Summary
Prettier Module Validation eslint-plugin-prettier.js	Add explicit resolve check for the prettier module before loading the Prettier worker; throw a descriptive error when prettier is not installed to avoid an indefinite hang.
Changelog .changeset/fix-prettier-not-installed-hang.md	Add patch release note documenting the fix where missing prettier now causes a clear failure instead of hanging.

Estimated code review effort

🎯 2 (Simple) | ⏱️ ~8 minutes

Suggested reviewers

• JounQin

Poem

🐰 I sniffed the code where errors hide,
Prettier absent — no longer bide.
Now when it’s gone, a trumpet calls,
No silent hangs in linting halls.
Hop on, install — the rabbit winks and smiles.

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title accurately describes the main change: adding error handling to fail fast with a clear error when Prettier is not installed, rather than hanging.
Linked Issues check	✅ Passed	The PR implements the core requirement from #781: checking Prettier availability at rule creation time and throwing a descriptive error instead of hanging.
Out of Scope Changes check	✅ Passed	All changes are directly related to fixing the issue: the defensive check in eslint-plugin-prettier.js and the corresponding changelog entry.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

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✨ Finishing touches

• 📝 Generate docstrings

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Post copyable unit tests in a comment

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