feat(emotion): add emotion plugin

[sapphi-red]

This PR adds @rolldown/plugin-emotion which utilizes Rolldown's native magic string feature.

In the synthetic benchmark included in this PR, this plugin is

• 1.30x faster than using @swc/plugin-emotion + @rollup/plugin-swc
• 2.64x faster than using @emotion/babel-plugin + @rolldown/plugin-babel

In a real world case, I tested with https://github.com/vanilla/vanilla/tree/release/2025.010 which I found in the GitHub search. Using this plugin was ~10% faster compared to Vite 8 +@swc/plugin-emotion + @rollup/plugin-swc.

The implementation is based on swc-project/plugins/packages/emotion (Apache License 2.0) and test cases are also adapted from it.

This PR also includes an internal package named oxc-unshadowed-visitor which make it easier to find varaibles that are imported.

[Copilot]

Pull request overview

This PR introduces a new @rolldown/plugin-emotion package that transforms Emotion css/styled usage using Rolldown’s native magic string support, and adds supporting infra (fixtures/benchmarks, an internal scope-aware visitor, and e2e examples) to validate behavior and measure performance.

Changes:

• Added @rolldown/plugin-emotion implementation (imports tracking, label generation, sourcemap injection, CSS minification) plus extensive fixtures-based tests.
• Added internal @rolldown/oxc-unshadowed-visitor package to detect unshadowed references in a single pass.
• Expanded repo tooling/config to include internal packages, benchmarks, and Playwright-based examples in workspace + CI.

Reviewed changes

Copilot reviewed 183 out of 186 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
vitest.config.ts	Expands Vitest projects to include internal packages, benchmarks, and examples.
tsconfig.json	Converts root TS config to a solution config referencing shared + examples configs.
tsconfig.common.json	Introduces shared TS compiler options for packages (excludes examples).
pnpm-workspace.yaml	Adds benchmarks, internal packages, and examples to the workspace.
packages/emotion/vitest.config.ts	Adds a dedicated Vitest project for the emotion package.
packages/emotion/tsdown.config.ts	Adds tsdown build config for the new plugin package.
packages/emotion/src/index.ts	Core plugin implementation: transforms css/styled/Global patterns, labels, targets, and sourcemaps.
packages/emotion/src/types.ts	Defines public plugin option types, including importMap and label formatting.
packages/emotion/src/import-map.ts	Maps imports/specifiers to Emotion expression kinds to decide what to transform.
packages/emotion/src/label.ts	Implements label sanitization and label template expansion.
packages/emotion/src/source-map.ts	Inline sourcemap generation + offset-to-line/column mapping.
packages/emotion/src/css-minify.ts	CSS template minification (comments/whitespace compaction).
packages/emotion/src/css-minify.test.ts	Unit tests for the CSS minifier.
packages/emotion/tests/transform.test.ts	Fixture runner that builds via Rolldown and snapshots outputs.
packages/emotion/tests/fixtures/**	Adds many fixture inputs/expected outputs for transform coverage.
packages/emotion/tests/fixtures-labels/**	Adds many label-focused fixtures/expected outputs.
packages/emotion/package.json	Declares the new published plugin package metadata and deps/peers.
packages/emotion/README.md	Documents usage, options, and benchmark results for the plugin.
packages/emotion/LICENSE	Adds a license file placeholder for the package.
packages/emotion/benchmark/**	Adds a benchmark package (generator, app, build configs, vitest bench).
packages/babel/tsdown.config.ts	Aligns Babel package DTS generation to shared TS config.
internal-packages/oxc-unshadowed-visitor/**	Adds the internal scope-aware visitor package + tests + bench.
internal-packages/swc-output-gen/**	Adds an internal tool to generate output.swc.js for fixtures using SWC plugins.
internal-packages/benchmark-utils/**	Adds a seeded RNG utility for deterministic benchmark generation.
examples/**	Adds Playwright-backed E2E test harness + an Emotion example app.
.oxlintrc.json	Disables no-shadow and ignores fixtures/benchmarks for linting.
.oxfmtrc.json	Ignores fixtures directories in formatting.
.gitignore	Ignores .swc, temporary examples dirs, and generated SWC outputs.
.github/workflows/ci.yml	Installs Playwright Chromium in CI to support the new examples tests.
.gitattributes	Forces LF checkout to stabilize hash-based class name generation.
package.json	Adds test:e2e and generate:swc-outputs scripts.

Files not reviewed (1)

• pnpm-lock.yaml: Language not supported

---

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

You can also share your feedback on Copilot code review. Take the survey.