Simplified `Scope.define`'s implementation by taking two arguments.

src/Bundle.js

@@ -29,8 +29,11 @@ export default class Bundle {
 			transform: ensureArray( options.transform )
 		};
 
+		// The global scope, and the bundle's internal scope.
 		this.globals = new Scope();
 		this.scope = new Scope( this.globals );
+		// Alias for entryModule.exports.
+		this.exports = null;
 
 		this.toExport = null;
 
@@ -51,6 +54,7 @@ export default class Bundle {
 			.then( id => this.fetchModule( id ) )
 			.then( entryModule => {
 				this.entryModule = entryModule;
+				this.exports = entryModule.exports;
 
 				entryModule.markAllStatements( true );
 				this.markAllModifierStatements();
@@ -200,10 +204,9 @@ export default class Bundle {
 		});
 
 		if ( format !== 'es6' && exportMode === 'named' ) {
-			keys( this.entryModule.exports )
-				.concat( keys( this.entryModule.reexports ) )
+			keys( this.exports.names )
 				.forEach( name => {
-					const canonicalName = this.traceExport( this.entryModule, name );
+					const canonicalName = this.exports.lookup( name ).name;
 
 					if ( isReassignedVarDeclaration[ canonicalName ] ) {
 						varExports[ name ] = true;
@@ -221,12 +224,13 @@ export default class Bundle {
 
 		// since we're rewriting variable exports, we want to
 		// ensure we don't try and export them again at the bottom
-		this.toExport = this.entryModule.exports.usedNames();
+		this.toExport = keys( this.exports.names )
+			.filter( key => !varExports[ key ] );
 
 		let magicString = new MagicString.Bundle({ separator: '\n\n' });
 
 		this.orderedModules.forEach( module => {
-			const source = module.render( this.toExport, format );
+			const source = module.render( allBundleExports, format );
 			if ( source.toString().length ) {
 				magicString.addSource( source );
 			}

src/ExternalModule.js

@@ -24,9 +24,16 @@ export default class ExternalModule {
 		// Override reference.
 		this.exports.reference = name => {
 			if ( !this.exports.defines( name ) ) {
-				this.exports.define({
-					originalName: name,
-					name,
+				let idName = name;
+
+				if (name === 'default' ) {
+					idName = this.name;
+					this.needsDefault = true;
+				}
+
+				this.exports.define( name, {
+					originalName: idName,
+					name: idName,
 
 					module: this
 				});

src/Module.js

@@ -106,8 +106,7 @@ export default class Module {
 				// If the default export has an identifier, bind to it.
 				this.exports.bind( 'default', this.locals.reference( identifier ) );
 			} else {
-				// Define the default identifier.
-				const id = {
+				this.exports.define( this.name, {
 					originalName: 'default',
 					name: 'default',
 
@@ -118,13 +117,7 @@ export default class Module {
 					isDeclaration,
 					isAnonymous,
 					isModified: false // in case of `export default foo; foo = somethingElse`
-				};
-
-				this.exports.define( id );
-
-				// Rename it to avoid generating the `default` identifier,
-				// which is invalid.
-				id.name = this.name;
+				});
 			}
 
 		}
@@ -196,6 +189,15 @@ export default class Module {
 				this.locals.bind( localName, module );
 			} else {
 				this.locals.bind( localName, module.exports.reference( name ) );
+
+				// For compliance with earlier Rollup versions.
+				// If the module is external, and we access the default.
+				// Rewrite the module name, and the default name to the
+				// `localName` we use for it.
+				if ( module.isExternal && isDefault ) {
+					const id = module.exports.lookup( name );
+					module.name = id.name = localName;
+				}
 			}
 		});
 	}
@@ -210,7 +212,7 @@ export default class Module {
 
 			// consolidate names that are defined/modified in this module
 			keys( statement.defines ).forEach( name => {
-				this.locals.define({
+				this.locals.define( name, {
 					originalName: name,
 					name,
 
@@ -537,14 +539,16 @@ export default class Module {
 				.concat( keys( statement.defines ) )
 				.forEach( name => {
 					const bundleName = this.locals.lookup( name ).name;
+					console.log( name, bundleName, toExport[ bundleName ] );
 
-					if ( ~toExport.indexOf( bundleName ) ) {
-						bundleExports[ name ] = replacements[ name ] = bundleName;
+					if ( toExport[ bundleName ] ) {
+						bundleExports[ name ] = replacements[ name ] = toExport[ bundleName ];
 					} else if ( bundleName !== name ) { // TODO weird structure
 						replacements[ name ] = bundleName;
 					}
 				});
 
+			console.log( replacements );
 			statement.replaceIdentifiers( magicString, replacements, bundleExports );
 
 			// modify exports as necessary

src/Scope.js

@@ -64,13 +64,10 @@ export default class Scope {
 		});
 	}
 
-	// Defines `name` in the scope. `name` must be a `string` or an `Identifier`.
-	define ( name ) {
-		if ( typeof name === 'string' ) {
-			this.ids[ this.index( name ) ] = new Identifier( name );
-		} else {
-			this.ids[ this.index( name.name ) ] = name;
-		}
+	// Defines `name` in the scope to be `id`.
+	// If no `id` is supplied, a plain `Identifier` is created.
+	define ( name, id = new Identifier( name ) ) {
+		this.ids[ this.index( name ) ] = id;
 	}
 
 	// TODO: rename! Too similar to `define`.