Add esModule: 'if-default-prop' and make it the default value

docs/999-big-list-of-options.md

@@ -591,15 +591,11 @@ const foo = null;
 export { foo as void };
 
 // cjs output with reservedNamesAsProps: false
-Object.defineProperty(exports, '__esModule', { value: true });
-
 const foo = null;
 
 exports['void'] = foo;
 
 // cjs output with reservedNamesAsProps: true
-Object.defineProperty(exports, '__esModule', { value: true });
-
 const foo = null;
 
 exports.void = foo;
@@ -614,25 +610,18 @@ Whether to allow the use of `Symbol` in auto-generated code snippets. Currently,
 export const foo = 42;
 
 // cjs output with symbols: false
-Object.defineProperty(exports, '__esModule', { value: true });
-
 const foo = 42;
 
 exports.foo = foo;
 
 // cjs output with symbols: true
-Object.defineProperties(exports, {
-  __esModule: { value: true },
-  [Symbol.toStringTag]: { value: 'Module' }
-});
+Object.defineProperty(exports, Symbol.toStringTag, { value: 'Module' });
 
 const foo = 42;
 
 exports.foo = foo;
 ```
 
-Note: The `__esModule` flag in the example can be prevented via the [`output.esModule`](https://rollupjs.org/guide/en/#outputesmodule) option.
-
 #### output.hoistTransitiveImports
 
 Type: `boolean`<br> CLI: `--hoistTransitiveImports`/`--no-hoistTransitiveImports`<br> Default: `true`
@@ -1412,9 +1401,15 @@ export default {
 
 #### output.esModule
 
-Type: `boolean`<br> CLI: `--esModule`/`--no-esModule`<br> Default: `true`
+Type: `boolean | "if-default-prop"`<br> CLI: `--esModule`/`--no-esModule`<br> Default: `"if-default-prop"`
+
+Whether to add a `__esModule: true` property when generating exports for non-ES formats. This property signifies that the exported value is the namespace of an ES module and that the default export of this module corresponds to the `.default` property of the exported object.
 
-Whether to add a `__esModule: true` property when generating exports for non-ES formats. This property signifies that the exported value is the namespace of an ES module and that the default export of this module corresponds to the `.default` property of the exported object. By default, Rollup adds this property when using [named exports mode](guide/en/#outputexports) for a chunk. See also [`output.interop`](https://rollupjs.org/guide/en/#outputinterop).
+- `true` will always add the property when using [named exports mode](guide/en/#outputexports), which is similar to what other tools do.
+- `"if-default-prop"` will only add the property when using named exports mode and there also is a default export. The subtle difference is that if there is no default export, consumers of the CommonJS version of your library will get all named exports as default export instead of an error or `undefined`. We chose to make this the default value as the `__esModule` property is not a standard followed by any JavaScript runtime and leads to many interop issues, so we want to limit its use to the cases where it is really needed.
+- `false` on the other hand will never add the property even if the default export would become a property `.default`.
+
+See also [`output.interop`](https://rollupjs.org/guide/en/#outputinterop).
 
 #### output.exports
 
@@ -1488,8 +1483,6 @@ Example:
 export { x } from 'external';
 
 // CJS output with externalLiveBindings: true
-Object.defineProperty(exports, '__esModule', { value: true });
-
 var external = require('external');
 
 Object.defineProperty(exports, 'x', {
@@ -1500,8 +1493,6 @@ Object.defineProperty(exports, 'x', {
 });
 
 // CJS output with externalLiveBindings: false
-Object.defineProperty(exports, '__esModule', { value: true });
-
 var external = require('external');
 
 exports.x = external.x;

src/Chunk.ts

@@ -583,9 +583,25 @@ export default class Chunk {
 
 		const renderedDependencies = [...this.getRenderedDependencies().values()];
 		const renderedExports = exportMode === 'none' ? [] : this.getChunkExportDeclarations(format);
-		const hasExports =
-			renderedExports.length !== 0 ||
-			renderedDependencies.some(dep => (dep.reexports && dep.reexports.length !== 0)!);
+		let hasExports = renderedExports.length !== 0;
+		let hasDefaultExport = false;
+		for (const { reexports } of renderedDependencies) {
+			if (reexports?.length) {
+				hasExports = true;
+				if (reexports.some(reexport => reexport.reexported === 'default')) {
+					hasDefaultExport = true;
+					break;
+				}
+			}
+		}
+		if (!hasDefaultExport) {
+			for (const { exported } of renderedExports) {
+				if (exported === 'default') {
+					hasDefaultExport = true;
+					break;
+				}
+			}
+		}
 
 		const { intro, outro, banner, footer } = await createAddons(
 			outputOptions,
@@ -598,6 +614,7 @@ export default class Chunk {
 				accessedGlobals,
 				dependencies: renderedDependencies,
 				exports: renderedExports,
+				hasDefaultExport,
 				hasExports,
 				id: preliminaryFileName.fileName,
 				indent,

src/finalisers/amd.ts

@@ -13,6 +13,7 @@ export default function amd(
 		accessedGlobals,
 		dependencies,
 		exports,
+		hasDefaultExport,
 		hasExports,
 		id,
 		indent: t,
@@ -84,7 +85,7 @@ export default function amd(
 	);
 	let namespaceMarkers = getNamespaceMarkers(
 		namedExportsMode && hasExports,
-		isEntryFacade && esModule,
+		isEntryFacade && (esModule === true || (esModule === 'if-default-prop' && hasDefaultExport)),
 		isModuleFacade && namespaceToStringTag,
 		snippets
 	);

src/finalisers/cjs.ts

@@ -12,6 +12,7 @@ export default function cjs(
 		accessedGlobals,
 		dependencies,
 		exports,
+		hasDefaultExport,
 		hasExports,
 		indent: t,
 		intro,
@@ -36,7 +37,7 @@ export default function cjs(
 	const useStrict = strict ? `'use strict';${n}${n}` : '';
 	let namespaceMarkers = getNamespaceMarkers(
 		namedExportsMode && hasExports,
-		isEntryFacade && esModule,
+		isEntryFacade && (esModule === true || (esModule === 'if-default-prop' && hasDefaultExport)),
 		isModuleFacade && namespaceToStringTag,
 		snippets
 	);

src/finalisers/iife.ts

@@ -20,6 +20,7 @@ export default function iife(
 		accessedGlobals,
 		dependencies,
 		exports,
+		hasDefaultExport,
 		hasExports,
 		indent: t,
 		intro,
@@ -118,7 +119,7 @@ export default function iife(
 	);
 	let namespaceMarkers = getNamespaceMarkers(
 		namedExportsMode && hasExports,
-		esModule,
+		esModule === true || (esModule === 'if-default-prop' && hasDefaultExport),
 		namespaceToStringTag,
 		snippets
 	);

src/finalisers/index.ts

@@ -13,6 +13,7 @@ export interface FinaliserOptions {
 	accessedGlobals: Set<string>;
 	dependencies: ChunkDependency[];
 	exports: ChunkExports;
+	hasDefaultExport: boolean;
 	hasExports: boolean;
 	id: string;
 	indent: string;

src/finalisers/umd.ts

@@ -39,6 +39,7 @@ export default function umd(
 		accessedGlobals,
 		dependencies,
 		exports,
+		hasDefaultExport,
 		hasExports,
 		id,
 		indent: t,
@@ -201,7 +202,7 @@ export default function umd(
 	);
 	let namespaceMarkers = getNamespaceMarkers(
 		namedExportsMode && hasExports,
-		esModule,
+		esModule === true || (esModule === 'if-default-prop' && hasDefaultExport),
 		namespaceToStringTag,
 		snippets
 	);

src/rollup/types.d.ts

@@ -619,7 +619,7 @@ export interface OutputOptions {
 	/** @deprecated Use the "renderDynamicImport" plugin hook instead. */
 	dynamicImportFunction?: string;
 	entryFileNames?: string | ((chunkInfo: PreRenderedChunk) => string);
-	esModule?: boolean;
+	esModule?: boolean | 'if-default-prop';
 	exports?: 'default' | 'named' | 'none' | 'auto';
 	extend?: boolean;
 	externalLiveBindings?: boolean;
@@ -669,7 +669,7 @@ export interface NormalizedOutputOptions {
 	/** @deprecated Use the "renderDynamicImport" plugin hook instead. */
 	dynamicImportFunction: string | undefined;
 	entryFileNames: string | ((chunkInfo: PreRenderedChunk) => string);
-	esModule: boolean;
+	esModule: boolean | 'if-default-prop';
 	exports: 'default' | 'named' | 'none' | 'auto';
 	extend: boolean;
 	externalLiveBindings: boolean;

src/utils/options/normalizeOutputOptions.ts

@@ -44,7 +44,7 @@ export function normalizeOutputOptions(
 		dir: getDir(config, file),
 		dynamicImportFunction: getDynamicImportFunction(config, inputOptions, format),
 		entryFileNames: getEntryFileNames(config, unsetOptions),
-		esModule: config.esModule ?? true,
+		esModule: config.esModule ?? 'if-default-prop',
 		exports: getExports(config, unsetOptions),
 		extend: config.extend || false,
 		externalLiveBindings: config.externalLiveBindings ?? true,

test/chunking-form/samples/amd-id-auto-base-path-concat/_expected/amd/some/where/main.js

@@ -6,8 +6,6 @@ define('some/where/main', ['require', 'exports'], (function (require, exports) {
 
 	exports.getA = getA;
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));
 
 define('some/where/generated-a', ['exports'], (function (exports) { 'use strict';

test/chunking-form/samples/amd-id-auto-base-path-concat/_expected/cjs/some/where/main.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 function getA() {
 	return Promise.resolve().then(function () { return require('./generated-a.js'); });
 }

test/chunking-form/samples/amd-id-auto-base-path/_expected/amd/some/where/main.js

@@ -6,6 +6,4 @@ define('some/where/main', ['require', 'exports'], (function (require, exports) {
 
 	exports.getA = getA;
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/amd-id-auto-base-path/_expected/cjs/some/where/main.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 function getA() {
 	return Promise.resolve().then(function () { return require('./chunks/generated-a.js'); });
 }

test/chunking-form/samples/amd-id-auto/_expected/amd/main.js

@@ -6,6 +6,4 @@ define('main', ['require', 'exports'], (function (require, exports) { 'use stric
 
 	exports.getA = getA;
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/amd-id-auto/_expected/cjs/main.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 function getA() {
 	return Promise.resolve().then(function () { return require('./generated-a.js'); });
 }

test/chunking-form/samples/chunk-export-renaming/_expected/amd/main1.js

@@ -4,6 +4,4 @@ define(['exports', './generated-one'], (function (exports, one) { 'use strict';
 
 	exports.ItemOne = one.One;
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/chunk-export-renaming/_expected/amd/main2.js

@@ -8,6 +8,4 @@ define(['exports', './generated-one'], (function (exports, one) { 'use strict';
 
     exports.ItemTwo = Two;
 
-    Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/chunk-export-renaming/_expected/cjs/main1.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 var one = require('./generated-one.js');
 
 

test/chunking-form/samples/chunk-export-renaming/_expected/cjs/main2.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 var one = require('./generated-one.js');
 
 class Two {

test/chunking-form/samples/chunking-reexport/_expected/amd/main1.js

@@ -7,6 +7,4 @@ define(['exports', './generated-dep', 'external'], (function (exports, dep, exte
 		get: function () { return external.asdf; }
 	});
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/chunking-reexport/_expected/amd/main2.js

@@ -7,6 +7,4 @@ define(['exports', './generated-dep', 'external'], (function (exports, dep, exte
 		get: function () { return external.asdf; }
 	});
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/chunking-reexport/_expected/cjs/main1.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 require('./generated-dep.js');
 var external = require('external');
 

test/chunking-form/samples/chunking-reexport/_expected/cjs/main2.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 require('./generated-dep.js');
 var external = require('external');
 

test/chunking-form/samples/chunking-star-external/_expected/amd/main1.js

@@ -15,6 +15,4 @@ define(['exports', 'starexternal1', 'external1', './generated-dep', 'starexterna
 		});
 	});
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/chunking-star-external/_expected/amd/main2.js

@@ -15,6 +15,4 @@ define(['exports', './generated-dep', 'external2', 'starexternal2'], (function (
 		});
 	});
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/chunking-star-external/_expected/cjs/main1.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 var starexternal1 = require('starexternal1');
 var external1 = require('external1');
 var dep = require('./generated-dep.js');

test/chunking-form/samples/chunking-star-external/_expected/cjs/main2.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 var dep = require('./generated-dep.js');
 var external2 = require('external2');
 var starexternal2 = require('starexternal2');

test/chunking-form/samples/circular-entry-points/_expected/amd/main1.js

@@ -4,6 +4,4 @@ define(['exports', './generated-main1'], (function (exports, main2) { 'use stric
 
 	exports.p = main2.p$1;
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/circular-entry-points/_expected/amd/main2.js

@@ -4,6 +4,4 @@ define(['exports', './generated-main1'], (function (exports, main2) { 'use stric
 
 	exports.p = main2.p;
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/circular-entry-points/_expected/cjs/main1.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 var main2 = require('./generated-main1.js');
 
 

test/chunking-form/samples/circular-entry-points/_expected/cjs/main2.js

@@ -1,7 +1,5 @@
 'use strict';
 
-Object.defineProperty(exports, '__esModule', { value: true });
-
 var main2 = require('./generated-main1.js');
 
 

test/chunking-form/samples/circular-entry-points2/_expected/amd/main1.js

@@ -4,6 +4,4 @@ define(['exports', './main2'], (function (exports, main2) { 'use strict';
 
 	exports.p = main2.p2;
 
-	Object.defineProperty(exports, '__esModule', { value: true });
-
 }));

test/chunking-form/samples/circular-entry-points2/_expected/amd/main2.js

@@ -23,6 +23,4 @@ define(['exports'], (function (exports) { 'use strict';
   exports.p = p$1;
   exports.p2 = p;
 
-  Object.defineProperty(exports, '__esModule', { value: true });
-
 }));