[fix] support using arrays for kit.vite.resolve.alias (#2328)

Author: bluwy

.changeset/sour-waves-return.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+support using arrays for kit.vite.resolve.alias

packages/kit/src/core/config/index.js

@@ -170,6 +170,12 @@ function merge_into(a, b, conflicts = [], path = []) {
 	const is_plain_object = (x) => typeof x === 'object' && x.constructor === Object;
 
 	for (const prop in b) {
+		// normalize alias objects to array
+		if (prop === 'alias' && path[path.length - 1] === 'resolve') {
+			if (a[prop]) a[prop] = normalize_alias(a[prop]);
+			if (b[prop]) b[prop] = normalize_alias(b[prop]);
+		}
+
 		if (is_plain_object(b[prop])) {
 			if (!is_plain_object(a[prop])) {
 				if (a[prop] !== undefined) {
@@ -233,3 +239,17 @@ export function print_config_conflicts(conflicts, pathPrefix = '', scope) {
 		);
 	});
 }
+
+/**
+ * normalize kit.vite.resolve.alias as an array
+ * @param {import('vite').AliasOptions} o
+ * @returns {import('vite').Alias[]}
+ */
+export function normalize_alias(o) {
+	return Array.isArray(o)
+		? o
+		: Object.entries(o).map(([find, replacement]) => ({
+				find,
+				replacement
+		  }));
+}

packages/kit/src/core/config/index.spec.js

@@ -501,4 +501,30 @@ deepMergeSuite('merge including toString', () => {
 	assert.equal(Object.keys(merged), ['toString', 'constructor', 'y']);
 });
 
+deepMergeSuite('merge resolve.alias', () => {
+	const [merged, conflicts] = deep_merge(
+		{
+			resolve: {
+				alias: [{ find: /foo/, replacement: 'bar' }]
+			}
+		},
+		{
+			resolve: {
+				alias: {
+					alpha: 'beta'
+				}
+			}
+		}
+	);
+	assert.equal(conflicts.length, 0);
+	assert.equal(merged, {
+		resolve: {
+			alias: [
+				{ find: /foo/, replacement: 'bar' },
+				{ find: 'alpha', replacement: 'beta' }
+			]
+		}
+	});
+});
+
 deepMergeSuite.run();

packages/kit/src/core/dev/index.js

@@ -107,8 +107,6 @@ class Watcher extends EventEmitter {
 
 		this.server = await get_server(this.https, vite_config, (req, res) => handler(req, res));
 
-		const alias = vite_config.resolve && vite_config.resolve.alias;
-
 		// don't warn on overriding defaults
 		const [modified_vite_config] = deep_merge(default_config, vite_config);
 
@@ -119,21 +117,10 @@ class Watcher extends EventEmitter {
 			configFile: false,
 			root: this.cwd,
 			resolve: {
-				alias: Array.isArray(alias)
-					? [
-							{
-								find: '$app',
-								replacement: path.resolve(`${this.dir}/runtime/app`)
-							},
-							{
-								find: '$lib',
-								replacement: this.config.kit.files.lib
-							}
-					  ]
-					: {
-							$app: path.resolve(`${this.dir}/runtime/app`),
-							$lib: this.config.kit.files.lib
-					  }
+				alias: {
+					$app: path.resolve(`${this.dir}/runtime/app`),
+					$lib: this.config.kit.files.lib
+				}
 			},
 			build: {
 				rollupOptions: {