fix!: remove rollup, extraneous types and migrate to ESM-only

[lumirlumir]

Prerequisites checklist

• I have read the contributing guidelines.

What is the purpose of this pull request?

In this PR, I've resolved the issue mentioned in eslint/json#196, removing rollup and extraneous types and migrating the package to ESM-only.

The main focus of this PR is removing much of the logic and the workarounds we previously used to support a dual CommonJS/ESM package.

Some notable parts are as follows:

• tsconfig.json: I mostly followed the convention used in the Markdown plugin, which is now an ESM-only package. (Ref: https://github.com/eslint/markdown/blob/main/tsconfig.json)
• package.json: Likewise, I mostly followed the convention used in the Markdown plugin. (Ref: https://github.com/eslint/markdown/blob/main/package.json)
• .github/workflows/ci.yml: Added @arethetypeswrong/cli to verify that type exports work correctly.

What changes did you make? (Give an overview)

In this PR, I've resolved the issue mentioned in #196, removing rollup and extraneous types and migrating the package to ESM-only.

Related Issues

• Counterpart: fix!: remove rollup, extraneous types and migrate to ESM-only json#197
• Prior Arts:
  • fix!: remove rollup and extraneous types markdown#383
  • ci: run arethetypeswrong in CI markdown#598
• Closes: Change Request: Remove rollup and migrate to ESM-only as part of the upcoming v1.0.0 (JSON/CSS) json#196

Is there anything you'd like reviewers to focus on?

I didn't intentionally remove tests/types/cjs-import.test.cts since require(ESM) is now enabled. However, if removing it is the right course of action, I'm happy to do so.

[Copilot]

Pull request overview

This pull request migrates the @eslint/css package from a dual CommonJS/ESM format to ESM-only, following the pattern established in the @eslint/markdown plugin. The migration simplifies the build process by removing Rollup bundling and the associated workarounds previously needed to support both module systems.

• Removes Rollup build configuration and related tooling (dedupe-types.js, update-cts.js)
• Simplifies TypeScript configuration to output directly to dist/ instead of separate dist/esm and dist/cjs directories
• Updates package.json exports to provide only ESM entry points
• Adds @arethetypeswrong/cli to CI pipeline to validate type definitions

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
tsconfig.json	Simplified configuration to use include instead of files, removed dual-output setup, and updated outDir to single dist/ directory
tsconfig.esm.json	Removed as no longer needed for ESM-only package
tools/update-cts.js	Removed tool that converted .js references to .cjs (no longer needed without CommonJS support)
tools/dedupe-types.js	Removed tool that deduplicated types in rolled-up files (no longer needed without Rollup)
rollup.config.js	Removed Rollup bundler configuration entirely
package.json	Updated entry points to single ESM format, simplified build scripts, added @arethetypeswrong/cli dependency, and reorganized lint-staged configuration
jsr.json	Updated export path from dist/esm to dist
.github/workflows/ci.yml	Added new CI job to validate type definitions using @arethetypeswrong/cli

---

💡 Add Copilot custom instructions for smarter, more guided reviews. Learn how to get started.