Postcss7 compatibility (#2773)

* add postcss7 compatibility layers

* add compatibility mode scripts

scripts/compat.js

@@ -0,0 +1,59 @@
+const fs = require('fs')
+const path = require('path')
+const merge = require('lodash/merge')
+
+function fromRootPath(...paths) {
+  return path.resolve(process.cwd(), ...paths)
+}
+
+function backupPath(...paths) {
+  return path.resolve(process.cwd(), 'node_modules', '__tw_cache__', ...paths)
+}
+
+function copy(fromPath, toPath) {
+  fs.mkdirSync(path.dirname(toPath), { recursive: true })
+  fs.copyFileSync(fromPath, toPath)
+}
+
+if (process.argv.includes('--prepare')) {
+  const mainPackageJson = require('../package.json')
+  const compatPackageJson = require('../package.postcss7.json')
+
+  // 1. Backup original package.json file
+  copy(fromRootPath('package.json'), backupPath('package.json'))
+
+  // 2. Backup lib/index.js file
+  copy(fromRootPath('lib', 'index.js'), backupPath('lib', 'index.js'))
+
+  // 3. Use the postcss7 compat file
+  copy(fromRootPath('lib', 'index.postcss7.js'), fromRootPath('lib', 'index.js'))
+
+  // 4. Deep merge package.json contents
+  const packageJson = merge({}, mainPackageJson, compatPackageJson)
+
+  // 5. Write package.json with the new contents
+  fs.writeFileSync(fromRootPath('package.json'), JSON.stringify(packageJson, null, 2), 'utf8')
+
+  // 6. Print some useful information to make publishing easy
+  console.log()
+  console.log('You can safely publish `tailwindcss` in PostCSS 7 compatibility mode:\n')
+  console.log(
+    ['npm version', 'npm publish --tag compat', 'npm run compat:restore']
+      .map((v) => `  ${v}`)
+      .join('\n')
+  )
+  console.log()
+} else if (process.argv.includes('--restore')) {
+  // 1. Restore original package.json file
+  copy(backupPath('package.json'), fromRootPath('package.json'))
+  fs.unlinkSync(backupPath('package.json'))
+
+  // 2. Restore lib/index.js file
+  copy(backupPath('lib', 'index.js'), fromRootPath('lib', 'index.js'))
+  fs.unlinkSync(backupPath('lib', 'index.js'))
+
+  // 3. Done
+  console.log()
+  console.log('Restored from PostCSS 7 mode to latest PostCSS mode!')
+  console.log()
+}