Emit a deprecation warning when loaded as a default export

See #229

.github/workflows/ci.yml

@@ -72,6 +72,8 @@ jobs:
           npm run init -- --compiler-path=dart-sass --language-path=language $args
 
       - run: npm run test
+      - run: npm run compile
+      - run: node test/after-compile-test.mjs
 
   # The versions should be kept up-to-date with the latest LTS Node releases.
   # They next need to be rotated October 2021. See

lib/index.mjs

@@ -0,0 +1,134 @@
+import * as sass from './index.js';
+
+export const compile = sass.compile;
+export const compileAsync = sass.compileAsync;
+export const compileString = sass.compileString;
+export const compileStringAsync = sass.compileStringAsync;
+export const Logger = sass.Logger;
+export const SassArgumentList = sass.SassArgumentList;
+export const SassBoolean = sass.SassBoolean;
+export const SassColor = sass.SassColor;
+export const SassFunction = sass.SassFunction;
+export const SassList = sass.SassList;
+export const SassMap = sass.SassMap;
+export const SassNumber = sass.SassNumber;
+export const SassString = sass.SassString;
+export const Value = sass.Value;
+export const CustomFunction = sass.CustomFunction;
+export const ListSeparator = sass.ListSeparator;
+export const sassFalse = sass.sassFalse;
+export const sassNull = sass.sassNull;
+export const sassTrue = sass.sassTrue;
+export const Exception = sass.Exception;
+export const PromiseOr = sass.PromiseOr;
+export const info = sass.info;
+export const render = sass.render;
+export const renderSync = sass.renderSync;
+
+let printedDefaultExportDeprecation = false;
+function defaultExportDeprecation() {
+  if (printedDefaultExportDeprecation) return;
+  printedDefaultExportDeprecation = true;
+  console.error(
+      "`import sass from 'sass'` is deprecated.\n" +
+      "Please use `import * as sass from 'sass'` instead.");
+}
+
+export default {
+  get compile() {
+    defaultExportDeprecation();
+    return sass.compile;
+  },
+  get compileAsync() {
+    defaultExportDeprecation();
+    return sass.compileAsync;
+  },
+  get compileString() {
+    defaultExportDeprecation();
+    return sass.compileString;
+  },
+  get compileStringAsync() {
+    defaultExportDeprecation();
+    return sass.compileStringAsync;
+  },
+  get Logger() {
+    defaultExportDeprecation();
+    return sass.Logger;
+  },
+  get SassArgumentList() {
+    defaultExportDeprecation();
+    return sass.SassArgumentList;
+  },
+  get SassBoolean() {
+    defaultExportDeprecation();
+    return sass.SassBoolean;
+  },
+  get SassColor() {
+    defaultExportDeprecation();
+    return sass.SassColor;
+  },
+  get SassFunction() {
+    defaultExportDeprecation();
+    return sass.SassFunction;
+  },
+  get SassList() {
+    defaultExportDeprecation();
+    return sass.SassList;
+  },
+  get SassMap() {
+    defaultExportDeprecation();
+    return sass.SassMap;
+  },
+  get SassNumber() {
+    defaultExportDeprecation();
+    return sass.SassNumber;
+  },
+  get SassString() {
+    defaultExportDeprecation();
+    return sass.SassString;
+  },
+  get Value() {
+    defaultExportDeprecation();
+    return sass.Value;
+  },
+  get CustomFunction() {
+    defaultExportDeprecation();
+    return sass.CustomFunction;
+  },
+  get ListSeparator() {
+    defaultExportDeprecation();
+    return sass.ListSeparator;
+  },
+  get sassFalse() {
+    defaultExportDeprecation();
+    return sass.sassFalse;
+  },
+  get sassNull() {
+    defaultExportDeprecation();
+    return sass.sassNull;
+  },
+  get sassTrue() {
+    defaultExportDeprecation();
+    return sass.sassTrue;
+  },
+  get Exception() {
+    defaultExportDeprecation();
+    return sass.Exception;
+  },
+  get PromiseOr() {
+    defaultExportDeprecation();
+    return sass.PromiseOr;
+  },
+  get info() {
+    defaultExportDeprecation();
+    return sass.info;
+  },
+  get render() {
+    defaultExportDeprecation();
+    return sass.render;
+  },
+  get renderSync() {
+    defaultExportDeprecation();
+    return sass.renderSync;
+  },
+};

package.json

@@ -7,7 +7,10 @@
   "repository": "sass/embedded-host-node",
   "author": "Google Inc.",
   "license": "MIT",
-  "main": "dist/lib/index.js",
+  "exports": {
+    "import": "dist/lib/index.mjs",
+    "default": "dist/lib/index.js"
+  },
   "types": "dist/types/index.d.ts",
   "files": [
     "dist/**/*"
@@ -21,7 +24,7 @@
     "check:gts": "gts check",
     "check:tsc": "tsc --noEmit",
     "clean": "gts clean",
-    "compile": "tsc",
+    "compile": "tsc && cp lib/index.mjs dist/lib/index.mjs",
     "fix": "gts fix",
     "prepublishOnly": "npm run clean && ts-node ./tool/prepare-release.ts",
     "test": "jest"

test/after-compile-test.mjs

@@ -0,0 +1,33 @@
+// Copyright 2023 Google LLC. Use of this source code is governed by an
+// MIT-style license that can be found in the LICENSE file or at
+// https://opensource.org/licenses/MIT.
+
+import * as fs from 'fs';
+
+// Note: this file isn't .test.ts specifically because we _don't_ want Jest to
+// handle it, because Jest chokes on dynamic imports of literal ESM modules.
+
+// This file should only be run _after_ `npm run compile`.
+if (!fs.existsSync('dist/package.json')) {
+  throw new Error('after-compile.test.ts must be run after `npm run compile`.');
+}
+
+// Load these dynamically so we have a better error mesage if `npm run compile`
+// hasn't been run.
+const cjs = await import('../dist/lib/index.js');
+const esm = await import('../dist/lib/index.mjs');
+
+for (const [name, value] of Object.entries(cjs)) {
+  if (name === '__esModule' || name === 'default') continue;
+  if (!esm[name]) {
+    throw new Error(`ESM module is missing export ${name}.`);
+  } else if (esm[name] !== value) {
+    throw new Error(`ESM ${name} isn't the same as CJS.`);
+  }
+
+  if (!esm.default[name]) {
+    throw new Error(`ESM default export is missing export ${name}.`);
+  } else if (esm.default[name] !== value) {
+    throw new Error(`ESM default export ${name} isn't the same as CJS.`);
+  }
+}

test/dependencies.test.ts

@@ -2,7 +2,6 @@
 // MIT-style license that can be found in the LICENSE file or at
 // https://opensource.org/licenses/MIT.
 
-import * as child_process from 'child_process';
 import * as fs from 'fs';
 import * as p from 'path';
 

tool/prepare-release.ts

@@ -16,6 +16,7 @@ import {getLanguageRepo} from './get-language-repo';
 
     console.log('Transpiling TS into dist.');
     shell.exec('tsc');
+    shell.cp('lib/index.mjs', 'dist/lib/index.mjs');
 
     console.log('Copying JS API types to dist.');
     shell.cp('-R', 'lib/src/vendor/sass', 'dist/types');