Always recreate paths for external modules

src/Chunk.ts

@@ -514,7 +514,7 @@ export default class Chunk {
 			let id: string;
 			let globalName: string;
 			if (dep instanceof ExternalModule) {
-				id = dep.renderPath || dep.setRenderPath(options, inputBase);
+				id = dep.setRenderPath(options, inputBase);
 				if (options.format === 'umd' || options.format === 'iife') {
 					globalName = getGlobalName(
 						dep,

src/ExternalModule.ts

@@ -37,9 +37,11 @@ export default class ExternalModule {
 	}
 
 	setRenderPath(options: OutputOptions, inputBase: string) {
-		if (options.paths)
+		this.renderPath = '';
+		if (options.paths) {
 			this.renderPath =
 				typeof options.paths === 'function' ? options.paths(this.id) : options.paths[this.id];
+		}
 		if (!this.renderPath) {
 			if (!isAbsolute(this.id)) {
 				this.renderPath = this.id;

test/function/samples/mixed-external-paths/_config.js

@@ -0,0 +1,22 @@
+module.exports = {
+	description: 'allows using the path option selectively',
+	options: {
+		external: ['dep-a', 'dep-b'],
+		output: {
+			paths: {
+				'dep-a': 'secret-dep'
+			}
+		}
+	},
+	context: {
+		require(id) {
+			if (id === 'secret-dep') {
+				return 'secret';
+			}
+			if (id === 'dep-b') {
+				return 'b';
+			}
+			throw new Error(`Unexpected dependency ${id}`);
+		}
+	}
+};

test/function/samples/mixed-external-paths/main.js

@@ -0,0 +1,5 @@
+import a from 'dep-a';
+import b from 'dep-b';
+
+assert.equal(a, 'secret');
+assert.equal(b, 'b');

test/misc/misc.js

@@ -98,4 +98,28 @@ describe('misc', () => {
 			plugins: [loader({ x: `console.log( 42 );` }), null, false, undefined]
 		});
 	});
+
+	it('handles different import paths for different outputs', () => {
+		return rollup
+			.rollup({
+				input: 'x',
+				external: ['the-answer'],
+				plugins: [loader({ x: `import 'the-answer'` })]
+			})
+			.then(bundle =>
+				Promise.all([
+					bundle
+						.generate({ format: 'esm' })
+						.then(generated => assert.equal(generated.output[0].code, "import 'the-answer';\n", 'no render path 1')),
+					bundle
+						.generate({ format: 'esm', paths: id => `//unpkg.com/${id}@?module` })
+						.then(generated =>
+							assert.equal(generated.output[0].code, "import '//unpkg.com/the-answer@?module';\n", 'with render path')
+						),
+					bundle
+						.generate({ format: 'esm' })
+						.then(generated => assert.equal(generated.output[0].code, "import 'the-answer';\n", 'no render path 2'))
+				])
+			);
+	});
 });