Fix: consider component and its snippets during css pruning

.changeset/nervous-humans-flash.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: better consider component and its snippets during css pruning

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

@@ -251,7 +251,11 @@ function apply_combinator(relative_selector, rest_selectors, rule, node, directi
 			let sibling_matched = false;
 
 			for (const possible_sibling of siblings.keys()) {
-				if (possible_sibling.type === 'RenderTag' || possible_sibling.type === 'SlotElement') {
+				if (
+					possible_sibling.type === 'RenderTag' ||
+					possible_sibling.type === 'SlotElement' ||
+					possible_sibling.type === 'Component'
+				) {
 					// `{@render foo()}<p>foo</p>` with `:global(.x) + p` is a match
 					if (rest_selectors.length === 1 && rest_selectors[0].metadata.is_global) {
 						sibling_matched = true;
@@ -814,10 +818,10 @@ function get_element_parent(node) {
  * @param {Direction} direction
  * @param {boolean} adjacent_only
  * @param {Set<Compiler.AST.SnippetBlock>} seen
- * @returns {Map<Compiler.AST.RegularElement | Compiler.AST.SvelteElement | Compiler.AST.SlotElement | Compiler.AST.RenderTag, NodeExistsValue>}
+ * @returns {Map<Compiler.AST.RegularElement | Compiler.AST.SvelteElement | Compiler.AST.SlotElement | Compiler.AST.RenderTag | Compiler.AST.Component, NodeExistsValue>}
  */
 function get_possible_element_siblings(node, direction, adjacent_only, seen = new Set()) {
-	/** @type {Map<Compiler.AST.RegularElement | Compiler.AST.SvelteElement | Compiler.AST.SlotElement | Compiler.AST.RenderTag, NodeExistsValue>} */
+	/** @type {Map<Compiler.AST.RegularElement | Compiler.AST.SvelteElement | Compiler.AST.SlotElement | Compiler.AST.RenderTag | Compiler.AST.Component, NodeExistsValue>} */
 	const result = new Map();
 	const path = node.metadata.path;
 
@@ -847,14 +851,18 @@ function get_possible_element_siblings(node, direction, adjacent_only, seen = ne
 				}
 				// Special case: slots, render tags and svelte:element tags could resolve to no siblings,
 				// so we want to continue until we find a definite sibling even with the adjacent-only combinator
-			} else if (is_block(node)) {
-				if (node.type === 'SlotElement') {
+			} else if (is_block(node) || node.type === 'Component') {
+				if (node.type === 'SlotElement' || node.type === 'Component') {
 					result.set(node, NODE_PROBABLY_EXISTS);
 				}
 
 				const possible_last_child = get_possible_nested_siblings(node, direction, adjacent_only);
 				add_to_map(possible_last_child, result);
-				if (adjacent_only && has_definite_elements(possible_last_child)) {
+				if (
+					adjacent_only &&
+					node.type !== 'Component' &&
+					has_definite_elements(possible_last_child)
+				) {
 					return result;
 				}
 			} else if (node.type === 'SvelteElement') {
@@ -907,7 +915,7 @@ function get_possible_element_siblings(node, direction, adjacent_only, seen = ne
 }
 
 /**
- * @param {Compiler.AST.EachBlock | Compiler.AST.IfBlock | Compiler.AST.AwaitBlock | Compiler.AST.KeyBlock | Compiler.AST.SlotElement | Compiler.AST.SnippetBlock} node
+ * @param {Compiler.AST.EachBlock | Compiler.AST.IfBlock | Compiler.AST.AwaitBlock | Compiler.AST.KeyBlock | Compiler.AST.SlotElement | Compiler.AST.SnippetBlock | Compiler.AST.Component} node
  * @param {Direction} direction
  * @param {boolean} adjacent_only
  * @param {Set<Compiler.AST.SnippetBlock>} seen
@@ -942,6 +950,10 @@ function get_possible_nested_siblings(node, direction, adjacent_only, seen = new
 			seen.add(node);
 			fragments.push(node.body);
 			break;
+
+		case 'Component':
+			fragments.push(node.fragment, ...[...node.metadata.snippets].map((s) => s.body));
+			break;
 	}
 
 	/** @type {Map<Compiler.AST.RegularElement | Compiler.AST.SvelteElement, NodeExistsValue>} NodeMap */

packages/svelte/tests/css/samples/general-siblings-combinator-slot/_config.js

@@ -5,32 +5,20 @@ export default test({
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector ".b ~ .c"',
-			start: { character: 137, column: 1, line: 11 },
-			end: { character: 144, column: 8, line: 11 }
+			start: { character: 191, column: 1, line: 13 },
+			end: { character: 198, column: 8, line: 13 }
 		},
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector ".c ~ .f"',
-			start: { character: 162, column: 1, line: 12 },
-			end: { character: 169, column: 8, line: 12 }
-		},
-		{
-			code: 'css_unused_selector',
-			message: 'Unused CSS selector ".f ~ .g"',
-			start: { character: 187, column: 1, line: 13 },
-			end: { character: 194, column: 8, line: 13 }
+			start: { character: 216, column: 1, line: 14 },
+			end: { character: 223, column: 8, line: 14 }
 		},
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector ".b ~ .f"',
-			start: { character: 212, column: 1, line: 14 },
-			end: { character: 219, column: 8, line: 14 }
-		},
-		{
-			code: 'css_unused_selector',
-			message: 'Unused CSS selector ".b ~ .g"',
-			start: { character: 237, column: 1, line: 15 },
-			end: { character: 244, column: 8, line: 15 }
+			start: { character: 241, column: 1, line: 15 },
+			end: { character: 248, column: 8, line: 15 }
 		}
 	]
 });

packages/svelte/tests/css/samples/general-siblings-combinator-slot/expected.css

@@ -2,10 +2,10 @@
 	.d.svelte-xyz ~ .e:where(.svelte-xyz) { color: green; }
 	.a.svelte-xyz ~ .g:where(.svelte-xyz) { color: green; }
 	.a.svelte-xyz ~ .b:where(.svelte-xyz) { color: green; }
+	.f.svelte-xyz ~ .g:where(.svelte-xyz) { color: green; }
+	.b.svelte-xyz ~ .g:where(.svelte-xyz) { color: green; }
 
 	/* no match */
 	/* (unused) .b ~ .c { color: red; }*/
 	/* (unused) .c ~ .f { color: red; }*/
-	/* (unused) .f ~ .g { color: red; }*/
 	/* (unused) .b ~ .f { color: red; }*/
-	/* (unused) .b ~ .g { color: red; }*/

packages/svelte/tests/css/samples/general-siblings-combinator-slot/input.svelte

@@ -6,13 +6,13 @@
 	.d ~ .e { color: green; }
 	.a ~ .g { color: green; }
 	.a ~ .b { color: green; }
+	.f ~ .g { color: green; }
+	.b ~ .g { color: green; }
 
 	/* no match */
 	.b ~ .c { color: red; }
 	.c ~ .f { color: red; }
-	.f ~ .g { color: red; }
 	.b ~ .f { color: red; }
-	.b ~ .g { color: red; }
 </style>
 
 <div class="a"></div>

packages/svelte/tests/css/samples/siblings-combinator-component/Child.svelte

@@ -0,0 +1,5 @@
+<script>
+	let { foo } = $props();
+</script>
+
+{@render foo()}

packages/svelte/tests/css/samples/siblings-combinator-component/_config.js

@@ -0,0 +1,20 @@
+import { test } from '../../test';
+
+export default test({
+	warnings: [
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector "n + m"',
+			end: {
+				character: 468,
+				column: 6,
+				line: 36
+			},
+			start: {
+				character: 463,
+				column: 1,
+				line: 36
+			}
+		}
+	]
+});

packages/svelte/tests/css/samples/siblings-combinator-component/expected.css

@@ -0,0 +1,8 @@
+	x.svelte-xyz + y:where(.svelte-xyz) { color: green; }
+	x.svelte-xyz + v:where(.svelte-xyz) { color: green; }
+	x.svelte-xyz + z:where(.svelte-xyz) { color: green; }
+	y.svelte-xyz + z:where(.svelte-xyz) { color: green; }
+	v.svelte-xyz + z:where(.svelte-xyz) { color: green; }
+	.component + z.svelte-xyz { color: green; }
+
+	/* (unused) n + m { color: red; }*/

packages/svelte/tests/css/samples/siblings-combinator-component/input.svelte

@@ -0,0 +1,37 @@
+<script>
+	import Child from './Child.svelte';
+</script>
+
+<div>
+	<x></x>
+	<Child>
+		<y></y>
+		{#snippet foo()}
+			<v></v>
+		{/snippet}
+	</Child>
+	<z></z>
+
+	<Child>
+		<span>
+			<n></n>
+		</span>
+		{#snippet foo()}
+			<span>
+				<n></n>
+			</span>
+		{/snippet}
+	</Child>
+	<m></m>
+</div>
+
+<style>
+	x + y { color: green; }
+	x + v { color: green; }
+	x + z { color: green; }
+	y + z { color: green; }
+	v + z { color: green; }
+	:global(.component) + z { color: green; }
+
+	n + m { color: red; }
+</style>

packages/svelte/tests/css/samples/siblings-combinator-slot/_config.js

@@ -5,14 +5,8 @@ export default test({
 		{
 			code: 'css_unused_selector',
 			message: 'Unused CSS selector ".b + .c"',
-			start: { character: 110, column: 1, line: 10 },
-			end: { character: 117, column: 8, line: 10 }
-		},
-		{
-			code: 'css_unused_selector',
-			message: 'Unused CSS selector ".c + .f"',
-			start: { character: 135, column: 1, line: 11 },
-			end: { character: 142, column: 8, line: 11 }
+			start: { character: 137, column: 1, line: 11 },
+			end: { character: 144, column: 8, line: 11 }
 		}
 	]
 });

packages/svelte/tests/css/samples/siblings-combinator-slot/expected.css

@@ -1,7 +1,7 @@
 
 	.d.svelte-xyz + .e:where(.svelte-xyz) { color: green; }
 	.a.svelte-xyz + .b:where(.svelte-xyz) { color: green; }
+	.c.svelte-xyz + .f:where(.svelte-xyz) { color: green; }
 
 	/* no match */
 	/* (unused) .b + .c { color: red; }*/
-	/* (unused) .c + .f { color: red; }*/

packages/svelte/tests/css/samples/siblings-combinator-slot/input.svelte

@@ -5,10 +5,10 @@
 <style>
 	.d + .e { color: green; }
 	.a + .b { color: green; }
+	.c + .f { color: green; }
 
 	/* no match */
 	.b + .c { color: red; }
-	.c + .f { color: red; }
 </style>
 
 <div class="a"></div>