From 14dba8220243df8b182a83e464eddd78f65b2b74 Mon Sep 17 00:00:00 2001
From: Lorenz A <me@lorenzackermann.xyz>
Date: Tue, 28 Oct 2025 18:17:33 +0100
Subject: [PATCH] LibWeb: Allow whitespace in not after a boolean-expr-group

---
 Libraries/LibWeb/CSS/Parser/Parser.cpp        |  1 +
 .../at-supports-whitespace.txt                | 21 ++++++++++
 .../at-supports-whitespace.html               | 39 +++++++++++++++++++
 3 files changed, 61 insertions(+)
 create mode 100644 Tests/LibWeb/Text/expected/wpt-import/css/css-conditional/at-supports-whitespace.txt
 create mode 100644 Tests/LibWeb/Text/input/wpt-import/css/css-conditional/at-supports-whitespace.html
diff --git a/Libraries/LibWeb/CSS/Parser/Parser.cpp b/Libraries/LibWeb/CSS/Parser/Parser.cpp
index a476a9ce0c..77a890927e 100644
--- a/Libraries/LibWeb/CSS/Parser/Parser.cpp
+++ b/Libraries/LibWeb/CSS/Parser/Parser.cpp
@@ -220,6 +220,7 @@ OwnPtr<BooleanExpression> Parser::parse_boolean_expression(TokenStream<Component
         tokens.discard_whitespace();
 
         if (auto child = parse_boolean_expression_group(tokens, result_for_general_enclosed, parse_test)) {
+            tokens.discard_whitespace();
             transaction.commit();
             return BooleanNotExpression::create(child.release_nonnull());
         }
diff --git a/Tests/LibWeb/Text/expected/wpt-import/css/css-conditional/at-supports-whitespace.txt b/Tests/LibWeb/Text/expected/wpt-import/css/css-conditional/at-supports-whitespace.txt
new file mode 100644
index 0000000000..04393ef395
--- /dev/null
+++ b/Tests/LibWeb/Text/expected/wpt-import/css/css-conditional/at-supports-whitespace.txt
@@ -0,0 +1,21 @@
+Harness status: OK
+
+Found 16 tests
+
+16 Pass
+Pass	@supports ((a)) {}
+Pass	@supports ((a) ) {}
+Pass	@supports ( (a)) {}
+Pass	@supports ( (a) ) {}
+Pass	@supports (not (a)) {}
+Pass	@supports (not (a) ) {}
+Pass	@supports ( not (a)) {}
+Pass	@supports ( not (a) ) {}
+Pass	@supports ((a) and (b)) {}
+Pass	@supports ((a) and (b) ) {}
+Pass	@supports ( (a) and (b)) {}
+Pass	@supports ( (a) and (b) ) {}
+Pass	@supports ((a) or (b)) {}
+Pass	@supports ((a) or (b) ) {}
+Pass	@supports ( (a) or (b)) {}
+Pass	@supports ( (a) or (b) ) {}
\ No newline at end of file
diff --git a/Tests/LibWeb/Text/input/wpt-import/css/css-conditional/at-supports-whitespace.html b/Tests/LibWeb/Text/input/wpt-import/css/css-conditional/at-supports-whitespace.html
new file mode 100644
index 0000000000..3c192ee23f
--- /dev/null
+++ b/Tests/LibWeb/Text/input/wpt-import/css/css-conditional/at-supports-whitespace.html
@@ -0,0 +1,39 @@
+<!DOCTYPE html>
+<title>Parsing of @supports with whitespace</title>
+<link rel="help" href="https://drafts.csswg.org/css-conditional-3/#at-supports">
+<script src=../../resources/testharness.js></script>
+<script src=../../resources/testharnessreport.js></script>
+<main id=main></main>
+<script>
+  let examples = [
+    '@supports ((a)) {}',
+    '@supports ((a) ) {}',
+    '@supports ( (a)) {}',
+    '@supports ( (a) ) {}',
+
+    '@supports (not (a)) {}',
+    '@supports (not (a) ) {}',
+    '@supports ( not (a)) {}',
+    '@supports ( not (a) ) {}',
+
+    '@supports ((a) and (b)) {}',
+    '@supports ((a) and (b) ) {}',
+    '@supports ( (a) and (b)) {}',
+    '@supports ( (a) and (b) ) {}',
+
+    '@supports ((a) or (b)) {}',
+    '@supports ((a) or (b) ) {}',
+    '@supports ( (a) or (b)) {}',
+    '@supports ( (a) or (b) ) {}',
+  ];
+
+  for (let example of examples) {
+    test((t) => {
+      let style = document.createElement('style');
+      t.add_cleanup(() => style.remove());
+      style.textContent = example;
+      main.append(style);
+      assert_equals(style.sheet.rules.length, 1);
+    }, example);
+  }
+</script>
