Ensure CSS is applied to nested route layouts

src/core/create_compilers/RollupCompiler.ts

@@ -241,7 +241,7 @@ export default class RollupCompiler {
 			async generateBundle(this: PluginContext, options: NormalizedOutputOptions, bundle: OutputBundle): Promise<void> {
 
 				function is_route(file_path: string) {
-					return file_path.includes(that.routes) && !file_path.includes(path.sep + '_') && !file_path.endsWith('.css');
+					return file_path.includes(that.routes) && !file_path.endsWith('.css');
 				}
 
 				function js_deps(chunk: RenderedChunk, opts?: DependencyTreeOptions) {

test/apps/css/src/routes/_components/NestedRouteTest.svelte

@@ -0,0 +1,8 @@
+<h3>This is content defined in a component imported by a layout in a nested routes.</h3>
+
+<style>
+	h3 {
+		background-color: rgb(255, 0, 0);
+		color: #fff;
+	}
+</style>

test/apps/css/src/routes/nested/_layout.svelte

@@ -0,0 +1,17 @@
+<script>
+    import NestedRouteTest from '../_components/NestedRouteTest.svelte';
+</script>
+
+<h2>This is content defined in a layout in a nested route. It should have a green background.</h2>
+
+<NestedRouteTest/>
+
+<slot></slot>
+
+<style>
+    h2 {
+        background-color: rgb(0, 128, 0);
+        color: #fff;
+        margin-bottom: 2rem;
+    }
+</style>

test/apps/css/src/routes/nested/index.svelte

@@ -0,0 +1 @@
+<p>This is slotted page content in a nested routes.</p>

test/apps/css/test.ts

@@ -25,6 +25,24 @@ describe('css', function() {
 		);
 	});
 
+	it('includes CSS defined in nested layout with server render', async () => {
+		await r.load('/nested');
+
+		assert.strictEqual(
+			await r.page.$eval('h2', node => getComputedStyle(node).backgroundColor),
+			'rgb(0, 128, 0)'
+		);
+	});
+
+	it('includes CSS defined in component imported by nested layout with server render', async () => {
+		await r.load('/nested');
+
+		assert.strictEqual(
+			await r.page.$eval('h3', node => getComputedStyle(node).backgroundColor),
+			'rgb(255, 0, 0)'
+		);
+	});
+
 	it('includes CSS on error page', async () => {
 		await r.load('/doesnotexist');