import defaults from external modules, with an interop layer

src/ExternalModule.js

@@ -8,11 +8,14 @@ export default class ExternalModule {
 
 		this.canonicalNames = {};
 		this.defaultExportName = null;
+
+		this.needsDefault = null;
+		this.needsNamed = null;
 	}
 
 	getCanonicalName ( name ) {
 		if ( name === 'default' ) {
-			return `${this.name}__default`; // TODO...
+			return this.needsNamed ? `${this.name}__default` : this.name;
 		}
 
 		if ( name === '*' ) {

src/Module.js

@@ -190,6 +190,12 @@ export default class Module {
 					}
 
 					if ( module.isExternal ) {
+						if ( importDeclaration.name === 'default' ) {
+							module.needsDefault = true;
+						} else {
+							module.needsNamed = true;
+						}
+
 						module.importedByBundle.push( importDeclaration );
 						return emptyArrayPromise;
 					}

src/finalisers/cjs.js

@@ -6,7 +6,16 @@ export default function cjs ( bundle, magicString ) {
 	// TODO handle ambiguous default imports
 	// TODO handle empty imports, once they're supported
 	const importBlock = bundle.externalModules
-		.map( module => `var ${module.name} = require('${module.id}');` )
+		.map( module => {
+			let requireStatement = `var ${module.name} = require('${module.id}');`;
+
+			if ( module.needsDefault ) {
+				requireStatement += '\n' + ( module.needsNamed ? `var ${module.name}__default = ` : `${module.name} = ` ) +
+					`'default' in ${module.name} ? ${module.name}['default'] : ${module.name};`;
+			}
+
+			return requireStatement;
+		})
 		.join( '\n' );
 
 	if ( importBlock ) {

test/samples/allows-external-modules/_config.js

@@ -1,3 +0,0 @@
-module.exports = {
-	description: 'Non-absolute and non-relative modules are assumed to be external'
-};

test/samples/import-default-from-external/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'imports default from external module'
+};

test/samples/import-default-from-external/main.js

@@ -0,0 +1,7 @@
+// would be a namespace import in real life, obvs
+import path from 'path';
+
+var path1 = 'foo/bar/baz';
+var path2 = 'foo/baz/bar';
+
+assert.equal( path.relative( path1, path2 ), '../../baz/bar' );

test/samples/import-named-from-external/_config.js

@@ -0,0 +1,3 @@
+module.exports = {
+	description: 'imports names from an external module'
+};