Create tailwind.config.cjs file in ESM package when running init

CHANGELOG.md

@@ -22,6 +22,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Rewrite default class extractor ([#8204](https://github.com/tailwindlabs/tailwindcss/pull/8204))
 - Move `important` selector to the front when `@apply`-ing selector-modifying variants in custom utilities ([#8313](https://github.com/tailwindlabs/tailwindcss/pull/8313))
 - Error when registering an invalid custom variant ([#8345](https://github.com/tailwindlabs/tailwindcss/pull/8345))
+- Create tailwind.config.cjs file in ESM package when running init ([#8363](https://github.com/tailwindlabs/tailwindcss/pull/8363))
 
 ### Changed
 

integrations/tailwindcss-cli/tests/cli.test.js

@@ -464,4 +464,68 @@ describe('Init command', () => {
       `)
     )
   })
+
+  test('--help in ESM package', async () => {
+    let pkg = await readOutputFile('../package.json')
+
+    await writeInputFile(
+      '../package.json',
+      JSON.stringify({
+        ...JSON.parse(pkg),
+        type: 'module',
+      })
+    )
+
+    let { combined } = await $(`${EXECUTABLE} init --help`)
+
+    expect(dedent(combined)).toEqual(
+      dedent(`
+        tailwindcss v${version}
+
+        Usage:
+           tailwindcss init [options]
+
+        Options:
+           -f, --full               Initialize a full \`tailwind.config.cjs\` file
+           -p, --postcss            Initialize a \`postcss.config.cjs\` file
+               --types              Add TypeScript types for the \`tailwind.config.cjs\` file
+           -h, --help               Display usage information
+      `)
+    )
+
+    await writeInputFile('../package.json', pkg)
+  })
+
+  test('cjs config created when in ESM package', async () => {
+    cleanupFile('tailwind.config.cjs')
+
+    let pkg = await readOutputFile('../package.json')
+
+    await writeInputFile(
+      '../package.json',
+      JSON.stringify({
+        ...JSON.parse(pkg),
+        type: 'module',
+      })
+    )
+
+    let { combined } = await $(`${EXECUTABLE} init`)
+
+    expect(combined).toMatchInlineSnapshot(`
+      "
+      Created Tailwind CSS config file: tailwind.config.cjs
+      "
+    `)
+
+    expect(await fileExists('./tailwind.config.cjs')).toBe(true)
+
+    // Not a clean way to test this.
+    expect(await readOutputFile('../tailwind.config.cjs')).toContain('module.exports =')
+
+    expect(await readOutputFile('../tailwind.config.cjs')).not.toContain(
+      `/** @type {import('tailwindcss/types').Config} */`
+    )
+
+    await writeInputFile('../package.json', pkg)
+  })
 })

src/cli.js

@@ -23,6 +23,27 @@ let env = {
   DEBUG: process.env.DEBUG !== undefined && process.env.DEBUG !== '0',
 }
 
+function isESM() {
+  const pkgPath = path.resolve('./package.json')
+
+  try {
+    let pkg = JSON.parse(fs.readFileSync(pkgPath, 'utf8'))
+    return pkg.type && pkg.type === 'module'
+  } catch (err) {
+    return false
+  }
+}
+
+let configs = isESM()
+  ? {
+      tailwind: 'tailwind.config.cjs',
+      postcss: 'postcss.config.cjs',
+    }
+  : {
+      tailwind: 'tailwind.config.js',
+      postcss: 'postcss.config.js',
+    }
+
 // ---
 
 function indentRecursive(node, indent = 0) {
@@ -160,11 +181,11 @@ let commands = {
   init: {
     run: init,
     args: {
-      '--full': { type: Boolean, description: 'Initialize a full `tailwind.config.js` file' },
-      '--postcss': { type: Boolean, description: 'Initialize a `postcss.config.js` file' },
+      '--full': { type: Boolean, description: `Initialize a full \`${configs.tailwind}\` file` },
+      '--postcss': { type: Boolean, description: `Initialize a \`${configs.postcss}\` file` },
       '--types': {
         type: Boolean,
-        description: 'Add TypeScript types for the `tailwind.config.js` file',
+        description: `Add TypeScript types for the \`${configs.tailwind}\` file`,
       },
       '-f': '--full',
       '-p': '--postcss',
@@ -340,7 +361,7 @@ run()
 function init() {
   let messages = []
 
-  let tailwindConfigLocation = path.resolve(args['_'][1] ?? './tailwind.config.js')
+  let tailwindConfigLocation = path.resolve(args['_'][1] ?? `./${configs.tailwind}`)
   if (fs.existsSync(tailwindConfigLocation)) {
     messages.push(`${path.basename(tailwindConfigLocation)} already exists.`)
   } else {
@@ -367,7 +388,7 @@ function init() {
   }
 
   if (args['--postcss']) {
-    let postcssConfigLocation = path.resolve('./postcss.config.js')
+    let postcssConfigLocation = path.resolve(`./${configs.postcss}`)
     if (fs.existsSync(postcssConfigLocation)) {
       messages.push(`${path.basename(postcssConfigLocation)} already exists.`)
     } else {
@@ -421,7 +442,7 @@ async function build() {
   let configPath = args['--config']
     ? args['--config']
     : ((defaultPath) => (fs.existsSync(defaultPath) ? defaultPath : null))(
-        path.resolve('./tailwind.config.js')
+        path.resolve(`./${configs.tailwind}`)
       )
 
   async function loadPostCssPlugins() {