[BUGFIX] Handle strings in at-rule preludes

CHANGELOG.md

@@ -28,6 +28,7 @@ Please also have a look at our
 ### Fixed
 
 - Render very small numbers in `Size` without rounding them to zero (#1647)
+- Ignore braces and semicolons inside quoted strings when parsing at-rule preludes (#1650)
 
 ### Documentation
 

src/CSSList/CSSList.php

@@ -212,7 +212,7 @@ private static function parseAtRule(ParserState $parserState): ?CSSListItem
             return new CSSNamespace($url, $prefix, $identifierLineNumber);
         } else {
             // Unknown other at rule (font-face, @layer, or such)
-            $arguments = \trim($parserState->consumeUntil(['{', ';'], false, false));
+            $arguments = self::consumeAtRuleArguments($parserState);
             if ($parserState->comes(';')) {
                 $parserState->consume(';');
                 return new AtRuleStatement($identifier, $arguments, $identifierLineNumber);
@@ -246,6 +246,44 @@ private static function parseAtRule(ParserState $parserState): ?CSSListItem
         }
     }
 
+    /**
+     * Consumes an at-rule prelude without treating braces or semicolons inside strings as delimiters.
+     *
+     * @phpstan-impure This method advances the parser state.
+     */
+    private static function consumeAtRuleArguments(ParserState $parserState): string
+    {
+        $arguments = '';
+        while (!$parserState->isEnd()) {
+            $arguments .= $parserState->consumeUntil(['{', ';', '"', "'"]);
+            if ($parserState->comes('{') || $parserState->comes(';')) {
+                return \trim($arguments);
+            }
+
+            $quote = $parserState->consume(1);
+            $trailingBackslashMatches = [];
+            $matchCount = \preg_match('/(\\\\+)\\z/', $arguments, $trailingBackslashMatches);
+            // An odd run escapes the quote; an even run leaves it as a delimiter.
+            $isEscaped = $matchCount === 1 && (\strlen($trailingBackslashMatches[1]) % 2) === 1;
+            $arguments .= $quote;
+            if ($isEscaped) {
+                continue;
+            }
+
+            while (true) {
+                $character = $parserState->consume(1);
+                $arguments .= $character;
+                if ($character === '\\') {
+                    $arguments .= $parserState->consume(1);
+                } elseif ($character === $quote) {
+                    break;
+                }
+            }
+        }
+
+        return \trim($arguments);
+    }
+
     /**
      * Tests an identifier for a given value. Since identifiers are all keywords, they can be vendor-prefixed.
      * We need to check for these versions too.

tests/Functional/Property/AtRuleStatementTest.php

@@ -130,4 +130,52 @@ public function rendersParsedLayerStatementWithTrailingSemicolon(): void
 
         self::assertStringContainsString('@layer reset;', $rendered);
     }
+
+    /**
+     * @test
+     */
+    public function doesNotTreatBracesOrSemicolonsInsideStringsAsAtRuleDelimiters(): void
+    {
+        $css = '@media (custom: "a;b{c}") { .inside { color: red; } } .after { color: blue; }';
+
+        $contents = (new Parser($css))->parse()->getContents();
+
+        self::assertCount(2, $contents);
+        self::assertInstanceOf(AtRuleBlockList::class, $contents[0]);
+        self::assertSame('(custom: "a;b{c}")', $contents[0]->atRuleArgs());
+    }
+
+    /**
+     * @test
+     */
+    public function handlesOddAndEvenBackslashRunsBeforeQuotesInAtRuleArguments(): void
+    {
+        $oddBackslashCss = '@media (custom: "a\\";{b}") { .inside { color: red; } } .after { color: blue; }';
+        $oddBackslashContents = (new Parser($oddBackslashCss))->parse()->getContents();
+
+        self::assertCount(2, $oddBackslashContents);
+        self::assertInstanceOf(AtRuleBlockList::class, $oddBackslashContents[0]);
+        self::assertSame('(custom: "a\\";{b}")', $oddBackslashContents[0]->atRuleArgs());
+
+        $evenBackslashCss = '@custom "a\\\\"; .after { color: blue; }';
+        $evenBackslashContents = (new Parser($evenBackslashCss))->parse()->getContents();
+
+        self::assertCount(2, $evenBackslashContents);
+        self::assertInstanceOf(AtRuleStatement::class, $evenBackslashContents[0]);
+        self::assertSame('"a\\\\"', $evenBackslashContents[0]->atRuleArgs());
+    }
+
+    /**
+     * @test
+     */
+    public function doesNotTreatDelimitersAfterBackslashInsideStringAsAtRuleDelimiters(): void
+    {
+        $css = '@media (custom: "a\\b;c{d}") { .inside { color: red; } } .after { color: blue; }';
+
+        $contents = (new Parser($css))->parse()->getContents();
+
+        self::assertCount(2, $contents);
+        self::assertInstanceOf(AtRuleBlockList::class, $contents[0]);
+        self::assertSame('(custom: "a\\b;c{d}")', $contents[0]->atRuleArgs());
+    }
 }