fix: match class and style directives against attribute selector (#16179)

Co-authored-by: 7nik <kifiranet@gmail.com>

.changeset/fair-laws-appear.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: match class and style directives against attribute selector

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

@@ -532,12 +532,7 @@ function relative_selector_might_apply_to_node(relative_selector, rule, element,
 			}
 
 			case 'ClassSelector': {
-				if (
-					!attribute_matches(element, 'class', name, '~=', false) &&
-					!element.attributes.some(
-						(attribute) => attribute.type === 'ClassDirective' && attribute.name === name
-					)
-				) {
+				if (!attribute_matches(element, 'class', name, '~=', false)) {
 					return false;
 				}
 
@@ -633,6 +628,16 @@ function attribute_matches(node, name, expected_value, operator, case_insensitiv
 		if (attribute.type === 'SpreadAttribute') return true;
 		if (attribute.type === 'BindDirective' && attribute.name === name) return true;
 
+		// match attributes against the corresponding directive but bail out on exact matching
+		if (attribute.type === 'StyleDirective' && name.toLowerCase() === 'style') return true;
+		if (attribute.type === 'ClassDirective' && name.toLowerCase() === 'class') {
+			if (operator == '~=') {
+				if (attribute.name === expected_value) return true;
+			} else {
+				return true;
+			}
+		}
+
 		if (attribute.type !== 'Attribute') continue;
 		if (attribute.name.toLowerCase() !== name.toLowerCase()) continue;
 

packages/svelte/tests/css/samples/attribute-selector-matches-derictive/expected.css

@@ -0,0 +1,2 @@
+	span[class].svelte-xyz { color: green }
+	div[style].svelte-xyz { color: green }

packages/svelte/tests/css/samples/attribute-selector-matches-derictive/input.svelte

@@ -0,0 +1,7 @@
+<span class:foo={true}></span>
+<div style:--foo="bar"></div>
+
+<style>
+	span[class] { color: green }
+	div[style] { color: green }
+</style>

packages/svelte/tests/css/samples/class-directive/_config.js

@@ -0,0 +1,20 @@
+import { test } from '../../test';
+
+export default test({
+	warnings: [
+		{
+			code: 'css_unused_selector',
+			message: 'Unused CSS selector ".third"\nhttps://svelte.dev/e/css_unused_selector',
+			start: {
+				line: 6,
+				column: 2,
+				character: 115
+			},
+			end: {
+				line: 6,
+				column: 8,
+				character: 121
+			}
+		}
+	]
+});

packages/svelte/tests/css/samples/class-directive/expected.css

@@ -0,0 +1,3 @@
+  .first.svelte-xyz { color: green }
+  .second.svelte-xyz { color: green }
+  /* (unused) .third { color: red }*/

packages/svelte/tests/css/samples/class-directive/input.svelte

@@ -0,0 +1,7 @@
+<div class:first={true} class:second={true}></div>
+
+<style>
+  .first { color: green }
+  .second { color: green }
+  .third { color: red }
+</style>