NonexistentOffsetInArrayDimFetchCheck - be less strict about Benevole…

…ntUnionType

src/Rules/Arrays/NonexistentOffsetInArrayDimFetchCheck.php

@@ -7,6 +7,7 @@
 use PHPStan\Rules\RuleError;
 use PHPStan\Rules\RuleErrorBuilder;
 use PHPStan\Rules\RuleLevelHelper;
+use PHPStan\Type\BenevolentUnionType;
 use PHPStan\Type\ErrorType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeUtils;
@@ -68,7 +69,12 @@ static function (Type $type) use ($dimType): bool {
 		}
 
 		if (!$report && $this->reportMaybes) {
-			foreach (TypeUtils::flattenTypes($type) as $innerType) {
+			if ($type instanceof BenevolentUnionType) {
+				$flattenedTypes = [$type];
+			} else {
+				$flattenedTypes = TypeUtils::flattenTypes($type);
+			}
+			foreach ($flattenedTypes as $innerType) {
 				if ($dimType instanceof UnionType) {
 					if ($innerType->hasOffsetValueType($dimType)->no()) {
 						$report = true;

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -268,4 +268,14 @@ public function testBug2689(): void
 		]);
 	}
 
+	public function testBug5169(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-5169.php'], [
+			[
+				'Cannot access offset mixed on (float|int).',
+				29,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Arrays/data/bug-5169.php

@@ -0,0 +1,31 @@
+<?php declare(strict_types=1);
+
+namespace Bug5169;
+
+class HelloWorld
+{
+	/**
+	 * @param array<mixed> $configs
+	 *
+	 * @return array<mixed>
+	 */
+	protected function merge(array $configs): array
+	{
+		$result = [];
+		foreach ($configs as $config) {
+			$result += $config;
+
+			foreach ($config as $name => $dto) {
+				$result[$name] += $dto;
+			}
+		}
+
+		return $result;
+	}
+
+	public function merge2($mixed): void
+	{
+		$f = $mixed - $mixed;
+		$f[$mixed] = true;
+	}
+}