Filter out falsy values in plugins and middleware array

.changeset/grumpy-olives-call.md

@@ -0,0 +1,5 @@
+---
+'wmr': patch
+---
+
+Fix error when `plugins` or `middleware` array contains falsy values in the parsed configuration. This typically happens due to conditionally setting items. All falsy values are now filtered out by default.

packages/wmr/src/lib/normalize-options.js

@@ -204,16 +204,23 @@ export async function normalizeOptions(options, mode, configWatchFiles = []) {
 	// Sort plugins by "enforce" phase. Default is "normal".
 	// The execution order is: "pre" -> "normal" -> "post"
 	if (options.plugins) {
-		options.plugins = options.plugins.flat().sort((a, b) => {
-			const aScore = a.enforce === 'post' ? 1 : a.enforce === 'pre' ? -1 : 0;
-			const bScore = b.enforce === 'post' ? 1 : b.enforce === 'pre' ? -1 : 0;
-			return aScore - bScore;
-		});
+		options.plugins = options.plugins
+			.flat()
+			// Filter out falsy values caused by conditionals
+			.filter(Boolean)
+			.sort((a, b) => {
+				const aScore = a.enforce === 'post' ? 1 : a.enforce === 'pre' ? -1 : 0;
+				const bScore = b.enforce === 'post' ? 1 : b.enforce === 'pre' ? -1 : 0;
+				return aScore - bScore;
+			});
 	}
 
 	await runConfigHook('config', options.plugins);
 	await runConfigHook('configResolved', options.plugins);
 
+	// Filter out falsy values caused by conditionals
+	options.middleware = options.middleware.filter(Boolean);
+
 	if (prevPublicFolder !== options.public) {
 		// If the CWD has a public/ directory, all files are assumed to be within it.
 		// From here, everything except node_modules and `out` are relative to public:

packages/wmr/test/fixtures/plugin-config-falsy/public/index.html

@@ -0,0 +1,2 @@
+<p>Nothing to see here!</p>
+<script src="index.js" type="module"></script>

packages/wmr/test/fixtures/plugin-config-falsy/wmr.config.mjs

@@ -0,0 +1,17 @@
+export default {
+	middleware: [false, undefined, null, 0],
+	plugins: [
+		false,
+		undefined,
+		null,
+		0,
+		{
+			name: 'foo',
+			configResolved() {
+				return {
+					middleware: [false, undefined, null, 0]
+				};
+			}
+		}
+	]
+};

packages/wmr/test/plugins/plugins.test.js

@@ -76,4 +76,15 @@ describe('config', () => {
 		await waitForMessage(instance.output, 'configResolved() A');
 		await waitForMessage(instance.output, 'configResolved() C');
 	});
+
+	it('should filter out falsy values in arrays inside configuration', async () => {
+		await loadFixture('plugin-config-falsy', env);
+		instance = await runWmrFast(env.tmp.path);
+		await getOutput(env, instance);
+
+		await waitForMessage(
+			instance.output,
+			/plugins: \[ { name: 'foo', configResolved: \[Function: configResolved\] } \]/
+		);
+	});
 });