feat: support ESM-only packages (#701)

Author: stipsan

playground/browser-bundle/package.json

@@ -4,6 +4,15 @@
   "private": true,
   "license": "MIT",
   "type": "module",
+  "exports": {
+    ".": {
+      "source": "./src/index.js",
+      "import": "./dist/index.js",
+      "require": "./dist/index.cjs",
+      "default": "./dist/index.js"
+    },
+    "./package.json": "./package.json"
+  },
   "main": "./dist/index.cjs",
   "module": "./dist/index.js",
   "source": "./src/index.js",

playground/extra-bundles/package.json

@@ -7,6 +7,15 @@
   "main": "./dist/index.js",
   "module": "./dist/index.mjs",
   "source": "./src/index.js",
+  "exports": {
+    ".": {
+      "source": "./src/index.js",
+      "import": "./dist/index.mjs",
+      "require": "./dist/index.js",
+      "default": "./dist/index.js"
+    },
+    "./package.json": "./package.json"
+  },
   "scripts": {
     "build": "run-s clean && pkg build --strict && pkg check --strict",
     "clean": "rimraf dist"

playground/js/package.json

@@ -4,6 +4,15 @@
   "private": true,
   "license": "MIT",
   "type": "commonjs",
+  "exports": {
+    ".": {
+      "source": "./src/index.js",
+      "import": "./dist/index.mjs",
+      "require": "./dist/index.js",
+      "default": "./dist/index.js"
+    },
+    "./package.json": "./package.json"
+  },
   "main": "./dist/index.js",
   "module": "./dist/index.mjs",
   "source": "./src/index.js",

playground/reference-esm-only/package.config.ts

@@ -0,0 +1,5 @@
+import {defineConfig} from '@sanity/pkg-utils'
+
+export default defineConfig({
+  tsconfig: 'tsconfig.dist.json',
+})

playground/reference-esm-only/package.json

@@ -2,5 +2,50 @@
   "name": "reference-esm-only",
   "version": "0.0.0",
   "private": true,
-  "description": "A reference implementation of TypeScript 5.4 best practice for a module that is ESM by default, and does not offer CJS."
+  "description": "A reference implementation of TypeScript 5.4 best practice for a module that is ESM by default, and does not offer CJS.",
+  "license": "MIT",
+  "sideEffects": false,
+  "type": "module",
+  "exports": {
+    ".": {
+      "source": "./src/index.ts",
+      "browser": {
+        "source": "./src/index.ts",
+        "import": "./dist/index.browser.js"
+      },
+      "import": "./dist/index.js",
+      "default": "./dist/index.js"
+    },
+    "./extra": {
+      "source": "./src/extra.ts",
+      "browser": {
+        "source": "./src/extra.ts",
+        "import": "./dist/extra.browser.js"
+      },
+      "import": "./dist/extra.js",
+      "default": "./dist/extra.js"
+    },
+    "./package.json": "./package.json"
+  },
+  "main": "./dist/index.js",
+  "types": "./dist/index.d.ts",
+  "typesVersions": {
+    "*": {
+      "extra": [
+        "./dist/extra.d.ts"
+      ]
+    }
+  },
+  "files": [
+    "dist",
+    "src"
+  ],
+  "scripts": {
+    "build": "run-s clean && pkg build --strict && pkg check --strict",
+    "clean": "rimraf dist"
+  },
+  "devDependencies": {
+    "@tsconfig/node-lts": "20.1.3",
+    "typescript": "5.4.4"
+  }
 }

playground/reference-esm-only/src/extra.ts

@@ -0,0 +1,8 @@
+/** @public */
+export const format = process.env.PKG_FORMAT as string
+
+/** @public */
+export const runtime = process.env.PKG_RUNTIME as string
+
+/** @public */
+export const path = process.env.PKG_FILE_PATH as string

playground/reference-esm-only/src/index.ts

@@ -0,0 +1,8 @@
+/** @public */
+export const format = process.env.PKG_FORMAT as string
+
+/** @public */
+export const runtime = process.env.PKG_RUNTIME as string
+
+/** @public */
+export const path = process.env.PKG_FILE_PATH as string

playground/reference-esm-only/tsconfig.dist.json

@@ -0,0 +1,8 @@
+{
+  "extends": "./tsconfig.settings",
+  "include": ["./src"],
+  "compilerOptions": {
+    "outDir": "./dist",
+    "rootDir": "."
+  }
+}

playground/reference-esm-only/tsconfig.json

@@ -0,0 +1,7 @@
+{
+  "extends": "./tsconfig.settings",
+  "include": ["./src"],
+  "compilerOptions": {
+    "noEmit": true
+  }
+}

playground/reference-esm-only/tsconfig.settings.json

@@ -0,0 +1,10 @@
+{
+  "extends": "@tsconfig/node-lts/tsconfig.json",
+  "compilerOptions": {
+    "module": "Preserve",
+    "moduleResolution": "Bundler",
+    "esModuleInterop": true,
+    "resolveJsonModule": true,
+    "allowSyntheticDefaultImports": true
+  }
+}

pnpm-lock.yaml

@@ -21,9 +21,21 @@ export function parseExports(options: {
       require: pkg.main && pkg.browser[pkg.main],
       import: pkg.module && pkg.browser[pkg.module],
     },
-    require: pkg.main,
-    import: pkg.module,
-    default: pkg.module || pkg.main || '',
+    require: legacyExports
+      ? pkg.main
+      : typeof pkg.exports?.['.'] === 'object' && 'require' in pkg.exports['.']
+        ? pkg.exports['.'].require
+        : '',
+    import: legacyExports
+      ? pkg.module
+      : typeof pkg.exports?.['.'] === 'object' && 'import' in pkg.exports['.']
+        ? pkg.exports['.'].import
+        : '',
+    default: legacyExports
+      ? pkg.module || pkg.main || ''
+      : typeof pkg.exports?.['.'] === 'object' && 'default' in pkg.exports['.']
+        ? pkg.exports['.'].default || ''
+        : pkg.module || pkg.main || '',
   }
 
   const extraExports: (PkgExport & {_path: string})[] = []

src/node/core/pkg/parseExports.ts

@@ -31,7 +31,7 @@ describe('parseExports', () => {
         types: undefined,
         source: './src/index.ts',
         browser: undefined,
-        import: undefined,
+        import: '',
         require: './dist/index.js',
         default: './dist/index.js',
       },
@@ -124,9 +124,7 @@ describe('parseExports', () => {
     }
 
     expect(() => parseExports({pkg, strict: true, legacyExports: false})).toThrow(
-      '\n- package.json: mismatch between "main" and "exports.require". These must be equal.' +
-        '\n- package.json: mismatch between "module" and "exports.import" These must be equal.' +
-        '\n- package.json: `exports["./package.json"] must be "./package.json".' +
+      '\n- package.json: `exports["./package.json"] must be "./package.json".' +
         '\n- package.json with `type: "commonjs"` - `exports["."].require` must end with ".js"' +
         '\n- package.json with `type: "commonjs"` - `exports["."].import` must end with ".mjs"',
     )

test/parseExports.test.ts

@@ -15,6 +15,20 @@ test('should parse tasks (type: module)', () => {
       './dist/index.cjs': './dist/index.browser.cjs',
       './dist/index.js': './dist/index.browser.js',
     },
+    exports: {
+      '.': {
+        source: './src/index.ts',
+        browser: {
+          source: './src/index.ts',
+          import: './dist/index.browser.js',
+          require: './dist/index.browser.cjs',
+        },
+        import: './dist/index.js',
+        require: './dist/index.cjs',
+        default: './dist/index.js',
+      },
+      './package.json': './package.json',
+    },
   }
 
   const exports = parseExports({pkg, strict: true, legacyExports: false})