Use mutable bindings for default exports (#4182)

Escape "default" when used as named export
Create new variable for TDZ default exports

src/Chunk.ts

@@ -1015,7 +1015,7 @@ export default class Chunk {
 				}
 			} else if (variable instanceof SyntheticNamedExportVariable) {
 				expression = local;
-				if (format === 'es' && exportName !== 'default') {
+				if (format === 'es') {
 					local = variable.renderName!;
 				}
 			}

src/ast/nodes/Identifier.ts

@@ -175,6 +175,40 @@ export default class Identifier extends NodeBase implements PatternNode {
 		this.getVariableRespectingTDZ().includeCallArguments(context, args);
 	}
 
+	isPossibleTDZ(): boolean {
+		// return cached value to avoid issues with the next tree-shaking pass
+		if (this.isTDZAccess !== null) return this.isTDZAccess;
+
+		if (
+			!(this.variable instanceof LocalVariable) ||
+			!this.variable.kind ||
+			!(this.variable.kind in tdzVariableKinds)
+		) {
+			return (this.isTDZAccess = false);
+		}
+
+		let decl_id;
+		if (
+			this.variable.declarations &&
+			this.variable.declarations.length === 1 &&
+			(decl_id = this.variable.declarations[0] as any) &&
+			this.start < decl_id.start &&
+			closestParentFunctionOrProgram(this) === closestParentFunctionOrProgram(decl_id)
+		) {
+			// a variable accessed before its declaration
+			// in the same function or at top level of module
+			return (this.isTDZAccess = true);
+		}
+
+		if (!this.variable.initReached) {
+			// Either a const/let TDZ violation or
+			// var use before declaration was encountered.
+			return (this.isTDZAccess = true);
+		}
+
+		return (this.isTDZAccess = false);
+	}
+
 	markDeclarationReached(): void {
 		this.variable!.initReached = true;
 	}
@@ -231,40 +265,6 @@ export default class Identifier extends NodeBase implements PatternNode {
 		}
 		return this.variable!;
 	}
-
-	private isPossibleTDZ(): boolean {
-		// return cached value to avoid issues with the next tree-shaking pass
-		if (this.isTDZAccess !== null) return this.isTDZAccess;
-
-		if (
-			!(this.variable instanceof LocalVariable) ||
-			!this.variable.kind ||
-			!(this.variable.kind in tdzVariableKinds)
-		) {
-			return (this.isTDZAccess = false);
-		}
-
-		let decl_id;
-		if (
-			this.variable.declarations &&
-			this.variable.declarations.length === 1 &&
-			(decl_id = this.variable.declarations[0] as any) &&
-			this.start < decl_id.start &&
-			closestParentFunctionOrProgram(this) === closestParentFunctionOrProgram(decl_id)
-		) {
-			// a variable accessed before its declaration
-			// in the same function or at top level of module
-			return (this.isTDZAccess = true);
-		}
-
-		if (!this.variable.initReached) {
-			// Either a const/let TDZ violation or
-			// var use before declaration was encountered.
-			return (this.isTDZAccess = true);
-		}
-
-		return (this.isTDZAccess = false);
-	}
 }
 
 function closestParentFunctionOrProgram(node: any): any {

src/ast/variables/ExportDefaultVariable.ts

@@ -54,6 +54,7 @@ export default class ExportDefaultVariable extends LocalVariable {
 		return this.originalId &&
 			(this.hasId ||
 				!(
+					this.originalId.isPossibleTDZ() ||
 					this.originalId.variable.isReassigned ||
 					this.originalId.variable instanceof UndefinedVariable ||
 					// this avoids a circular dependency

src/finalisers/es.ts

@@ -114,18 +114,14 @@ function getExportBlock(exports: ChunkExports, _: string, varOrConst: string): s
 	const exportBlock: string[] = [];
 	const exportDeclaration: string[] = [];
 	for (const specifier of exports) {
-		if (specifier.exported === 'default') {
-			exportBlock.push(`export default ${specifier.local};`);
-		} else {
-			if (specifier.expression) {
-				exportBlock.push(`${varOrConst} ${specifier.local}${_}=${_}${specifier.expression};`);
-			}
-			exportDeclaration.push(
-				specifier.exported === specifier.local
-					? specifier.local
-					: `${specifier.local} as ${specifier.exported}`
-			);
+		if (specifier.expression) {
+			exportBlock.push(`${varOrConst} ${specifier.local}${_}=${_}${specifier.expression};`);
 		}
+		exportDeclaration.push(
+			specifier.exported === specifier.local
+				? specifier.local
+				: `${specifier.local} as ${specifier.exported}`
+		);
 	}
 	if (exportDeclaration.length) {
 		exportBlock.push(`export${_}{${_}${exportDeclaration.join(`,${_}`)}${_}};`);

src/finalisers/shared/getExportBlock.ts

@@ -5,6 +5,7 @@ import {
 	isDefaultAProperty,
 	namespaceInteropHelpersByInteropType
 } from '../../utils/interopHelpers';
+import { RESERVED_NAMES } from '../../utils/reservedNames';
 
 export function getExportBlock(
 	exports: ChunkExports,
@@ -65,9 +66,9 @@ export function getExportBlock(
 		}
 	}
 
-	for (const chunkExport of exports) {
-		const lhs = `exports.${chunkExport.exported}`;
-		const rhs = chunkExport.local;
+	for (const { exported, local } of exports) {
+		const lhs = `exports${RESERVED_NAMES[exported] ? `['${exported}']` : `.${exported}`}`;
+		const rhs = local;
 		if (lhs !== rhs) {
 			if (exportBlock) exportBlock += n;
 			exportBlock += `${lhs}${_}=${_}${rhs};`;

test/chunking-form/samples/basic-chunking/_expected/es/main1.js

@@ -11,4 +11,4 @@ class Main1 {
   }
 }
 
-export default Main1;
+export { Main1 as default };

test/chunking-form/samples/basic-chunking/_expected/es/main2.js

@@ -16,4 +16,4 @@ class Main2 {
   }
 }
 
-export default Main2;
+export { Main2 as default };

test/chunking-form/samples/chunk-export-deshadowing/_expected/es/main1.js

@@ -6,4 +6,4 @@ class Main1 {
   }
 }
 
-export default Main1;
+export { Main1 as default };

test/chunking-form/samples/chunk-export-deshadowing/_expected/es/main2.js

@@ -6,4 +6,4 @@ class Main2 {
   }
 }
 
-export default Main2;
+export { Main2 as default };

test/chunking-form/samples/chunk-live-bindings/_expected/es/main1.js

@@ -7,4 +7,4 @@ class Main1 {
   }
 }
 
-export default Main1;
+export { Main1 as default };

test/chunking-form/samples/chunk-live-bindings/_expected/es/main2.js

@@ -7,4 +7,4 @@ class Main2 {
   }
 }
 
-export default Main2;
+export { Main2 as default };

test/chunking-form/samples/chunk-namespace-boundary/_expected/es/main1.js

@@ -5,4 +5,4 @@ var cjs = commonjsGlobal.fn;
 
 var main1 = shared.map(cjs);
 
-export default main1;
+export { main1 as default };

test/chunking-form/samples/chunk-namespace-boundary/_expected/es/main2.js

@@ -2,4 +2,4 @@ import { s as shared } from './generated-shared.js';
 
 var main2 = shared.map(d => d + 2);
 
-export default main2;
+export { main2 as default };

test/chunking-form/samples/chunking-compact/_expected/es/main1.js

@@ -5,4 +5,4 @@ import {f as fn$1}from'./generated-dep2.js';function fn () {
     fn();
     fn$1();
   }
-}export default Main1;
+}export{Main1 as default};

test/chunking-form/samples/chunking-compact/_expected/es/main2.js

@@ -9,4 +9,4 @@ import {f as fn$3}from'./generated-dep2.js';import {fn as fn$2}from'external';fu
     fn();
     fn$3();
   }
-}export default Main2;
+}export{Main2 as default};

test/chunking-form/samples/chunking-externals/_expected/es/main1.js

@@ -11,4 +11,4 @@ class Main1 {
   }
 }
 
-export default Main1;
+export { Main1 as default };

test/chunking-form/samples/chunking-externals/_expected/es/main2.js

@@ -18,4 +18,4 @@ class Main2 {
   }
 }
 
-export default Main2;
+export { Main2 as default };

test/chunking-form/samples/deconflict-system-default-export-variable/_expected/es/main.js

@@ -2,4 +2,4 @@ import * as other from './other.js';
 
 var main = other + "extended";
 
-export default main;
+export { main as default };

test/chunking-form/samples/default-identifier-renaming/_expected/es/main1.js

@@ -2,4 +2,4 @@ import { d as data } from './generated-shared.js';
 
 var main1 = data.map(d => d + 1);
 
-export default main1;
+export { main1 as default };

test/chunking-form/samples/default-identifier-renaming/_expected/es/main2.js

@@ -2,4 +2,4 @@ import { d as data } from './generated-shared.js';
 
 var main2 = data.map(d => d + 2);
 
-export default main2;
+export { main2 as default };

test/chunking-form/samples/default-reexport-namespace/_expected/es/one.js

@@ -1,3 +1,3 @@
 const __icon__ = {};
 
-export default __icon__;
+export { __icon__ as default };

test/chunking-form/samples/deprecated/configure-asset-url/_expected/amd/nested/chunk.js

@@ -2,6 +2,6 @@ define(['require', 'exports'], function (require, exports) { 'use strict';
 
 	var solved = 'nested/chunk.js:solved:assets/asset-solved-28a7ac89.txt:../assets/asset-solved-28a7ac89.txt';
 
-	exports.default = solved;
+	exports['default'] = solved;
 
 });

test/chunking-form/samples/deprecated/configure-asset-url/_expected/cjs/nested/chunk.js

@@ -2,4 +2,4 @@
 
 var solved = 'nested/chunk.js:solved:assets/asset-solved-28a7ac89.txt:../assets/asset-solved-28a7ac89.txt';
 
-exports.default = solved;
+exports['default'] = solved;

test/chunking-form/samples/deprecated/configure-asset-url/_expected/es/nested/chunk.js

@@ -1,3 +1,3 @@
 var solved = 'nested/chunk.js:solved:assets/asset-solved-28a7ac89.txt:../assets/asset-solved-28a7ac89.txt';
 
-export default solved;
+export { solved as default };

test/chunking-form/samples/deprecated/emit-chunk-existing/_expected/es/generated-dep.js

@@ -1,3 +1,3 @@
 var value = 42;
 
-export default value;
+export { value as default };

test/chunking-form/samples/deprecated/indirect-reexports-preserve-modules/_expected/amd/components/sub/index.js

@@ -3,7 +3,7 @@ define(['exports'], function (exports) { 'use strict';
 	const foo = 'bar';
 	var bar = () => {};
 
-	exports.default = bar;
+	exports['default'] = bar;
 	exports.foo = foo;
 
 	Object.defineProperty(exports, '__esModule', { value: true });

test/chunking-form/samples/deprecated/indirect-reexports-preserve-modules/_expected/cjs/components/sub/index.js

@@ -5,5 +5,5 @@ Object.defineProperty(exports, '__esModule', { value: true });
 const foo = 'bar';
 var bar = () => {};
 
-exports.default = bar;
+exports['default'] = bar;
 exports.foo = foo;

test/chunking-form/samples/deprecated/indirect-reexports-preserve-modules/_expected/es/components/sub/index.js

@@ -1,5 +1,4 @@
 const foo = 'bar';
 var bar = () => {};
 
-export default bar;
-export { foo };
+export { bar as default, foo };

test/chunking-form/samples/deprecated/manual-chunks/_expected/es/main.js

@@ -13,4 +13,4 @@ class Main {
   }
 }
 
-export default Main;
+export { Main as default };

test/chunking-form/samples/deprecated/preserve-modules-auto-export-mode/_expected/es/default.js

@@ -1,3 +1,3 @@
 var foo = 'default';
 
-export default foo;
+export { foo as default };

test/chunking-form/samples/deprecated/preserve-modules-commonjs/_expected/es/commonjs.js

@@ -9,4 +9,4 @@ console.log(external, value);
 
 var commonjs = 42;
 
-export default commonjs;
+export { commonjs as default };

test/chunking-form/samples/deprecated/preserve-modules-dynamic-namespace/_expected/es/m2.js

@@ -1,3 +1,3 @@
 var m2 = {a:1};
 
-export default m2;
+export { m2 as default };

test/chunking-form/samples/deprecated/preserve-modules-dynamic-namespace/_expected/es/m3.js

@@ -1,3 +1,3 @@
 var m3 = {b:2};
 
-export default m3;
+export { m3 as default };

test/chunking-form/samples/deprecated/preserve-modules-empty/_expected/es/two.js

@@ -1,3 +1,3 @@
 var a = {};
 
-export default a;
+export { a as default };

test/chunking-form/samples/deprecated/preserve-modules-filename-pattern/_expected/es/entry-foo-es-ts.ts.js

@@ -1,3 +1,3 @@
 var foo = 42;
 
-export default foo;
+export { foo as default };

test/chunking-form/samples/deprecated/preserve-modules-filename-pattern/_expected/es/entry-no-ext-es-.js

@@ -1,3 +1,3 @@
 var noExt = 'no-ext';
 
-export default noExt;
+export { noExt as default };

test/chunking-form/samples/deprecated/preserve-modules-filename-pattern/_expected/es/nested/entry-bar-es-ts.ts.js

@@ -1,3 +1,3 @@
 var bar = 'banana';
 
-export default bar;
+export { bar as default };

test/chunking-form/samples/deprecated/preserve-modules-filename-pattern/_expected/es/nested/entry-baz-es-ts.ts.js

@@ -1,3 +1,3 @@
 var baz = 'whatever';
 
-export default baz;
+export { baz as default };

test/chunking-form/samples/deprecated/preserve-modules-id-case-sensitive/_expected/es/_virtual/_One1.js

@@ -1,3 +1,3 @@
 var c = 'One1.js';
 
-export default c;
+export { c as default };

test/chunking-form/samples/deprecated/preserve-modules-id-case-sensitive/_expected/es/_virtual/_One2.js

@@ -1,3 +1,3 @@
 var b = 'One.js';
 
-export default b;
+export { b as default };

test/chunking-form/samples/deprecated/preserve-modules-id-case-sensitive/_expected/es/_virtual/_one.js

@@ -1,3 +1,3 @@
 var a = 'one.js';
 
-export default a;
+export { a as default };

test/chunking-form/samples/deprecated/preserve-modules-named-export-mode/_expected/amd/default.js

@@ -2,7 +2,7 @@ define(['exports'], function (exports) { 'use strict';
 
 	var foo = 'default';
 
-	exports.default = foo;
+	exports['default'] = foo;
 
 	Object.defineProperty(exports, '__esModule', { value: true });
 

test/chunking-form/samples/deprecated/preserve-modules-named-export-mode/_expected/cjs/default.js

@@ -4,4 +4,4 @@ Object.defineProperty(exports, '__esModule', { value: true });
 
 var foo = 'default';
 
-exports.default = foo;
+exports['default'] = foo;

test/chunking-form/samples/deprecated/preserve-modules-named-export-mode/_expected/es/default.js

@@ -1,3 +1,3 @@
 var foo = 'default';
 
-export default foo;
+export { foo as default };

test/chunking-form/samples/deprecated/preserve-modules-non-entry-imports/_expected/es/dep2.js

@@ -1,3 +1,3 @@
 function foo() {}
 
-export default foo;
+export { foo as default };