fix: properly traverse children when checking matches for `:has` (#13866)

The previous algorithm didn't take control flow blocks etc into account, this fixes that. Fixes #13860

.changeset/tasty-students-peel.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: properly traverse children when checking matches for `:has`

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

@@ -405,19 +405,28 @@ function relative_selector_might_apply_to_node(relative_selector, rule, element,
 		/** @type {Array<Compiler.AST.RegularElement | Compiler.AST.SvelteElement>} */
 		const descendant_elements = [];
 
-		/**
-		 * @param {Compiler.SvelteNode} node
-		 * @param {boolean} is_recursing
-		 */
-		function collect_child_elements(node, is_recursing) {
-			if (node.type === 'RegularElement' || node.type === 'SvelteElement') {
-				descendant_elements.push(node);
-				if (!is_recursing) child_elements.push(node);
-				node.fragment.nodes.forEach((node) => collect_child_elements(node, true));
+		walk(
+			/** @type {Compiler.SvelteNode} */ (element.fragment),
+			{ is_child: true },
+			{
+				_(node, context) {
+					if (node.type === 'RegularElement' || node.type === 'SvelteElement') {
+						descendant_elements.push(node);
+
+						if (context.state.is_child) {
+							child_elements.push(node);
+							context.state.is_child = false;
+							context.next();
+							context.state.is_child = true;
+						} else {
+							context.next();
+						}
+					} else {
+						context.next();
+					}
+				}
 			}
-		}
-
-		element.fragment.nodes.forEach((node) => collect_child_elements(node, false));
+		);
 
 		// :has(...) is special in that it means "look downwards in the CSS tree". Since our matching algorithm goes
 		// upwards and back-to-front, we need to first check the selectors inside :has(...), then check the rest of the

packages/svelte/tests/css/samples/has/_config.js

@@ -6,112 +6,126 @@ export default test({
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector ".unused:has(y)"',
 			start: {
-				line: 28,
+				line: 31,
 				column: 1,
-				character: 277
+				character: 308
 			},
 			end: {
-				line: 28,
+				line: 31,
 				column: 15,
-				character: 291
+				character: 322
 			}
 		},
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector ".unused:has(:global(y))"',
 			start: {
-				line: 31,
+				line: 34,
 				column: 1,
-				character: 312
+				character: 343
 			},
 			end: {
-				line: 31,
+				line: 34,
 				column: 24,
-				character: 335
+				character: 366
 			}
 		},
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector "x:has(.unused)"',
 			start: {
-				line: 34,
+				line: 37,
 				column: 1,
-				character: 356
+				character: 387
 			},
 			end: {
-				line: 34,
+				line: 37,
 				column: 15,
-				character: 370
+				character: 401
 			}
 		},
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector "x:has(y):has(.unused)"',
 			start: {
-				line: 47,
+				line: 50,
 				column: 1,
-				character: 525
+				character: 556
 			},
 			end: {
-				line: 47,
+				line: 50,
 				column: 22,
-				character: 546
+				character: 577
 			}
 		},
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector ".unused"',
 			start: {
-				line: 66,
+				line: 69,
 				column: 2,
-				character: 751
+				character: 782
 			},
 			end: {
-				line: 66,
+				line: 69,
 				column: 9,
-				character: 758
+				character: 789
 			}
 		},
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector ".unused x:has(y)"',
 			start: {
-				line: 82,
+				line: 85,
 				column: 1,
-				character: 905
+				character: 936
 			},
 			end: {
-				line: 82,
+				line: 85,
 				column: 17,
-				character: 921
+				character: 952
 			}
 		},
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector ".unused:has(.unused)"',
 			start: {
-				line: 85,
+				line: 88,
 				column: 1,
-				character: 942
+				character: 973
 			},
 			end: {
-				line: 85,
+				line: 88,
 				column: 21,
-				character: 962
+				character: 993
 			}
 		},
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector "x:has(> z)"',
 			start: {
-				line: 92,
+				line: 98,
+				column: 1,
+				character: 1093
+			},
+			end: {
+				line: 98,
+				column: 11,
+				character: 1103
+			}
+		},
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "x:has(> d)"',
+			start: {
+				line: 101,
 				column: 1,
-				character: 1029
+				character: 1124
 			},
 			end: {
-				line: 92,
+				line: 101,
 				column: 11,
-				character: 1039
+				character: 1134
 			}
 		}
 	]

packages/svelte/tests/css/samples/has/expected.css

@@ -82,9 +82,15 @@
 	x.svelte-xyz:has(> y:where(.svelte-xyz)) {
 		color: green;
 	}
+	y.svelte-xyz:has(> d:where(.svelte-xyz)) {
+		color: green;
+	}
 	/* (unused) x:has(> z) {
 		color: red;
 	}*/
+	/* (unused) x:has(> d) {
+		color: red;
+	}*/
 	x.svelte-xyz > y:where(.svelte-xyz):has(z:where(.svelte-xyz)) {
 		color: green;
 	}

packages/svelte/tests/css/samples/has/input.svelte

@@ -1,6 +1,9 @@
 <x>
 	<y>
 		<z></z>
+		{#if foo}
+			<d></d>
+		{/if}
 	</y>
 </x>
 <c></c>
@@ -89,9 +92,15 @@
 	x:has(> y) {
 		color: green;
 	}
+	y:has(> d) {
+		color: green;
+	}
 	x:has(> z) {
 		color: red;
 	}
+	x:has(> d) {
+		color: red;
+	}
 	x > y:has(z) {
 		color: green;
 	}