UnusedVariableSniff: add scope lookup cache to improve performance

SlevomatCodingStandard/Helpers/ScopeHelper.php

@@ -5,6 +5,7 @@
 use PHP_CodeSniffer\Files\File;
 use function array_reverse;
 use function in_array;
+use const T_OPEN_TAG;
 
 /**
  * @internal
@@ -34,4 +35,32 @@ public static function isInSameScope(File $phpcsFile, int $firstPointer, int $se
 		return $getScope($firstPointer) === $getScope($secondPointer);
 	}
 
+	public static function getRootPointer(File $phpcsFile, int $pointer): ?int
+	{
+		$roots = array_reverse(self::getAllRootPointers($phpcsFile));
+		foreach ($roots as $rootPointer) {
+			if ($rootPointer < $pointer) {
+				return $rootPointer;
+			}
+		}
+
+		return null;
+	}
+
+	/**
+	 * @param File $phpcsFile
+	 * @return int[]
+	 */
+	public static function getAllRootPointers(File $phpcsFile): array
+	{
+		static $cache;
+		$cache = $cache ?? new SniffLocalCache();
+
+		$lazyValue = static function () use ($phpcsFile): array {
+			return TokenHelper::findNextAll($phpcsFile, T_OPEN_TAG, 0);
+		};
+
+		return $cache->getAndSetIfNotCached($phpcsFile, $lazyValue);
+	}
+
 }

SlevomatCodingStandard/Sniffs/Variables/UnusedVariableSniff.php

@@ -155,7 +155,7 @@ public function process(File $phpcsFile, $variablePointer): void
 			return;
 		}
 
-		$scopeOwnerPointer = TokenHelper::findPrevious($phpcsFile, T_OPEN_TAG, $variablePointer - 1);
+		$scopeOwnerPointer = ScopeHelper::getRootPointer($phpcsFile, $variablePointer - 1);
 		foreach (array_reverse($tokens[$variablePointer]['conditions'], true) as $conditionPointer => $conditionTokenCode) {
 			if (in_array($conditionTokenCode, TokenHelper::$functionTokenCodes, true)) {
 				$scopeOwnerPointer = $conditionPointer;