fix: emit error on wrong placement of the :global block selector

.changeset/pretty-beers-care.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: emit error on wrong placement of the `:global` block selector

documentation/docs/98-reference/.generated/compile-errors.md

@@ -274,6 +274,12 @@ A `:global` selector cannot modify an existing selector
 A `:global` selector can only be modified if it is a descendant of other selectors
 ```
 
+### css_global_block_invalid_placement
+
+```
+A `:global` selector cannot be inside a pseudoclass
+```
+
 ### css_global_invalid_placement
 
 ```

packages/svelte/messages/compile-errors/style.md

@@ -50,6 +50,10 @@ x y {
 
 > A `:global` selector can only be modified if it is a descendant of other selectors
 
+## css_global_block_invalid_placement
+
+> A `:global` selector cannot be inside a pseudoclass
+
 ## css_global_invalid_placement
 
 > `:global(...)` can be at the start or end of a selector sequence, but not in the middle

packages/svelte/src/compiler/errors.js

@@ -581,6 +581,15 @@ export function css_global_block_invalid_modifier_start(node) {
 	e(node, 'css_global_block_invalid_modifier_start', `A \`:global\` selector can only be modified if it is a descendant of other selectors\nhttps://svelte.dev/e/css_global_block_invalid_modifier_start`);
 }
 
+/**
+ * A `:global` selector cannot be inside a pseudoclass
+ * @param {null | number | NodeLike} node
+ * @returns {never}
+ */
+export function css_global_block_invalid_placement(node) {
+	e(node, 'css_global_block_invalid_placement', `A \`:global\` selector cannot be inside a pseudoclass\nhttps://svelte.dev/e/css_global_block_invalid_placement`);
+}
+
 /**
  * `:global(...)` can be at the start or end of a selector sequence, but not in the middle
  * @param {null | number | NodeLike} node

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

@@ -68,8 +68,12 @@ const css_visitors = {
 			const global = node.children.find(is_global);
 
 			if (global) {
-				const idx = node.children.indexOf(global);
+				const is_nested = context.path.at(-2)?.type === 'PseudoClassSelector';
+				if (is_nested && !global.selectors[0].args) {
+					e.css_global_block_invalid_placement(global.selectors[0]);
+				}
 
+				const idx = node.children.indexOf(global);
 				if (global.selectors[0].args !== null && idx !== 0 && idx !== node.children.length - 1) {
 					// ensure `:global(...)` is not used in the middle of a selector (but multiple `global(...)` in sequence are ok)
 					for (let i = idx + 1; i < node.children.length; i++) {

packages/svelte/tests/compiler-errors/samples/css-global-block-in-pseudoclass/_config.js

@@ -0,0 +1,9 @@
+import { test } from '../../test';
+
+export default test({
+	error: {
+		code: 'css_global_block_invalid_placement',
+		message: 'A `:global` selector cannot be inside a pseudoclass',
+		position: [28, 35]
+	}
+});

packages/svelte/tests/compiler-errors/samples/css-global-block-in-pseudoclass/main.svelte

@@ -0,0 +1,4 @@
+<style>
+	/* invalid */
+	:is(:global) { color: red }
+</style>