feat: support Babel 8

.babelrc

@@ -3,6 +3,7 @@
     [
       "@babel/preset-env",
       {
+        "modules": "commonjs",
         "targets": {
           "node": 12
         }

.changeset/support-babel-8.md

@@ -0,0 +1,5 @@
+---
+'babel-plugin-styled-components': minor
+---
+
+Support Babel 8. The plugin now installs alongside `@babel/core@8` without peer dependency warnings or errors, and the `css` prop transform no longer crashes with `t.jSXIdentifier is not a function` on Babel 8. The plugin also no longer depends on `@babel/plugin-syntax-jsx`, which only accepted Babel 7 as a peer. Babel 7 output is unchanged.

.github/workflows/test.yml

@@ -33,3 +33,6 @@ jobs:
 
       - name: Run tests
         run: pnpm test
+
+      - name: Run fixtures on Babel 8
+        run: pnpm build && pnpm test:babel8

AGENTS.md

@@ -11,6 +11,7 @@ Commands
 - `pnpm exec jest -u`: regenerate fixture outputs, only after the snapshot-drift rule below is satisfied
 - `pnpm exec jest --coverage`: prints live coverage
 - `pnpm build`: compile `src/` to `lib/`; run it to verify every set of changes. Don't start a dev server unless asked
+- `pnpm test:babel8`: the built `lib/` over the fixtures on Babel 8, outside Jest because Babel 8 is ESM-only; run `pnpm build` first
 - `pnpm bench [--base <ref>] [--config default|all|bare] [--rounds N] [--normalize-aliases]`: interleaved A/B of the plugin at `<ref>` (default `origin/main`) against the working tree over generated inputs; fails when outputs differ
 - `pnpm bench:profile [--input small|medium|large|large-cjs]`: CPU profile with the plugin frames that drive Babel's work
 - `node scripts/compat.js [--base <ref>]`: styled-components v5, v6, and v7 prerelease smoke against the working tree and `<ref>` (default `origin/main`)

README.md

@@ -10,7 +10,7 @@ This plugin is a highly recommended supplement to the base styled-components lib
 
 This plugin is tested against:
 
-- `@babel/core` `^7`
+- `@babel/core` `^7` and `^8`
 - `styled-components` `>= 6` (earlier majors may still work but aren't exercised in CI)
 
 ## Quick start

package.json

@@ -23,11 +23,14 @@
   "devDependencies": {
     "@babel/cli": "^7.26.4",
     "@babel/core": "^7.26.0",
+    "@babel/plugin-syntax-jsx": "^7.28.6",
     "@babel/plugin-transform-class-properties": "^7.25.9",
     "@babel/plugin-transform-modules-commonjs": "^7.26.3",
     "@babel/preset-env": "^7.26.0",
     "@changesets/cli": "2.31.0",
     "babel-test": "^0.2.4",
+    "babel8": "npm:@babel/core@^8.0.9",
+    "babel8-preset-typescript": "npm:@babel/preset-typescript@^8",
     "jest": "^29.7.0",
     "jest-file-snapshot": "^0.5.0",
     "prettier": "^3.4.2",
@@ -37,18 +40,18 @@
   "dependencies": {
     "@babel/helper-annotate-as-pure": "^7.25.9",
     "@babel/helper-module-imports": "^7.25.9",
-    "@babel/plugin-syntax-jsx": "^7.25.9",
     "picomatch": "^4.0.2"
   },
   "peerDependencies": {
-    "@babel/core": "^7.0.0",
+    "@babel/core": "^7.0.0 || ^8.0.0",
     "styled-components": ">= 2"
   },
   "scripts": {
     "clean": "rimraf lib",
     "style": "prettier --write src/**/*.js",
     "build": "babel src -d lib",
     "test": "jest",
+    "test:babel8": "node scripts/babel8.js",
     "test:watch": "pnpm test -- --watch",
     "bench": "node scripts/bench/index.js",
     "bench:profile": "node scripts/bench/profile.js",