fix: handle nested :global(...) selectors (#12365)

fixes #10540

.changeset/mean-numbers-cry.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: handle nested `:global(...)` selectors

packages/svelte/src/compiler/phases/2-analyze/css/css-prune.js

@@ -71,7 +71,7 @@ const visitors = {
 		const selectors = truncate(node);
 		const inner = selectors[selectors.length - 1];
 
-		if (node.metadata.rule?.metadata.parent_rule) {
+		if (node.metadata.rule?.metadata.parent_rule && selectors.length > 0) {
 			const has_explicit_nesting_selector = selectors.some((selector) =>
 				selector.selectors.some((s) => s.type === 'NestingSelector')
 			);

packages/svelte/tests/css/samples/global-nested-block/_config.js

@@ -0,0 +1,34 @@
+import { test } from '../../test';
+
+export default test({
+	warnings: [
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector ".unused :global"',
+			start: {
+				line: 25,
+				column: 2,
+				character: 229
+			},
+			end: {
+				line: 25,
+				column: 17,
+				character: 244
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector ".unused :global(.z)"',
+			start: {
+				line: 31,
+				column: 2,
+				character: 283
+			},
+			end: {
+				line: 31,
+				column: 21,
+				character: 302
+			}
+		}
+	]
+});

packages/svelte/tests/css/samples/global-nested-block/expected.css

@@ -0,0 +1,32 @@
+
+	div.svelte-xyz {
+		/* :global {*/
+			.x {
+				color: green;
+			}
+		/*}*/
+
+		.x {
+			color: green;
+		}
+
+		p:where(.svelte-xyz) {
+			.y {
+				color: green;
+			}
+		}
+
+		p:where(.svelte-xyz) .y {
+			color: green;
+		}
+
+		/* (unused) .unused :global {
+			.z {
+				color: red;
+			}
+		}*/
+
+		/* (unused) .unused :global(.z) {
+			color: red;
+		}*/
+	}

packages/svelte/tests/css/samples/global-nested-block/input.svelte

@@ -0,0 +1,35 @@
+<div><p>{@html whatever}</p></div>
+
+<style>
+	div {
+		:global {
+			.x {
+				color: green;
+			}
+		}
+
+		:global(.x) {
+			color: green;
+		}
+
+		p :global {
+			.y {
+				color: green;
+			}
+		}
+
+		p :global(.y) {
+			color: green;
+		}
+
+		.unused :global {
+			.z {
+				color: red;
+			}
+		}
+
+		.unused :global(.z) {
+			color: red;
+		}
+	}
+</style>