Fix broken --alias option

package.json

@@ -57,6 +57,7 @@
     "gzip-size": "^5.0.0",
     "pretty-bytes": "^5.1.0",
     "rollup": "^0.67.3",
+    "rollup-plugin-alias": "^1.5.1",
     "rollup-plugin-babel": "^4.1.0-0",
     "rollup-plugin-buble": "^0.19.4",
     "rollup-plugin-bundle-size": "^1.0.1",

src/index.js

@@ -11,6 +11,7 @@ import babel from 'rollup-plugin-babel';
 import nodeResolve from 'rollup-plugin-node-resolve';
 import buble from 'rollup-plugin-buble';
 import { terser } from 'rollup-plugin-terser';
+import alias from 'rollup-plugin-alias';
 import postcss from 'rollup-plugin-postcss';
 import gzipSize from 'gzip-size';
 import brotliSize from 'brotli-size';
@@ -35,6 +36,9 @@ const parseMappingArgument = globalStrings => {
 	return globals;
 };
 
+// Extensions to use when resolving modules
+const EXTENSIONS = ['.ts', '.tsx', '.js', '.jsx', '.es6', '.es', '.mjs'];
+
 const WATCH_OPTS = {
 	exclude: 'node_modules/**',
 };
@@ -287,15 +291,16 @@ function createConfig(options, entry, format, writeMeta) {
 		options.entries.filter(e => e !== entry),
 	);
 
-	let aliases = {};
+	let outputAliases = {};
 	// since we transform src/index.js, we need to rename imports for it:
 	if (options.multipleEntries) {
-		aliases['.'] = './' + basename(options.output);
-	}
-	if (options.alias) {
-		aliases = Object.assign(aliases, parseMappingArgument(options.alias));
+		outputAliases['.'] = './' + basename(options.output);
 	}
 
+	const moduleAliases = options.alias
+		? parseMappingArgument(options.alias)
+		: {};
+
 	const peerDeps = Object.keys(pkg.peerDependencies || {});
 	if (options.external === 'none') {
 		// bundle everything (external=[])
@@ -396,6 +401,12 @@ function createConfig(options, entry, format, writeMeta) {
 						inject: false,
 						extract: !!writeMeta,
 					}),
+					Object.keys(moduleAliases).length > 0 &&
+						alias(
+							Object.assign({}, moduleAliases, {
+								resolve: EXTENSIONS,
+							}),
+						),
 					nodeResolve({
 						module: true,
 						jsnext: true,
@@ -431,7 +442,7 @@ function createConfig(options, entry, format, writeMeta) {
 						// supplied configurations we set this option to false. Note
 						// that we never supported using custom babel configs anyway.
 						babelrc: false,
-						extensions: ['.ts', '.tsx', '.js', '.jsx', '.es6', '.es', '.mjs'],
+						extensions: EXTENSIONS,
 						exclude: 'node_modules/**',
 						plugins: [
 							require.resolve('@babel/plugin-syntax-jsx'),
@@ -542,7 +553,7 @@ function createConfig(options, entry, format, writeMeta) {
 		},
 
 		outputOptions: {
-			paths: aliases,
+			paths: outputAliases,
 			globals,
 			strict: options.strict === true,
 			legacy: true,

test/__snapshots__/index.test.js.snap

@@ -1,5 +1,30 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`fixtures alias 1`] = `
+"Used script: microbundle --no-sourcemap -f cjs --alias ./constants=./constants-debug
+
+Directory tree:
+
+alias
+  dist
+    alias-mapping.js
+  package.json
+  src
+    constants-debug.js
+    constants.js
+    index.js
+
+
+Build \\"aliasMapping\\" to dist:
+62 B: alias-mapping.js.gz
+46 B: alias-mapping.js.br"
+`;
+
+exports[`fixtures alias 2`] = `
+"console.log(\\"DEBUG should be true: \\",!0);
+"
+`;
+
 exports[`fixtures async-iife-ts 1`] = `
 "Used script: microbundle
 

test/fixtures/alias/package.json

@@ -0,0 +1,6 @@
+{
+  "name": "alias-mapping",
+  "scripts": {
+    "build": "microbundle --no-sourcemap -f cjs --alias ./constants=./constants-debug"
+  }
+}

test/fixtures/alias/src/constants-debug.js

@@ -0,0 +1 @@
+export const DEBUG = true;

test/fixtures/alias/src/constants.js

@@ -0,0 +1 @@
+export const DEBUG = false;

test/fixtures/alias/src/index.js

@@ -0,0 +1,2 @@
+import { DEBUG } from './constants';
+console.log('DEBUG should be true: ', DEBUG);