NonexistentOffsetInArrayDimFetchRule - do not report errors on expressions after truthy isset check

Author: ondrejmirtes

src/Rules/Arrays/NonexistentOffsetInArrayDimFetchRule.php

@@ -54,6 +54,10 @@ public function processNode(Node $node, Scope $scope): array
 			return $isOffsetAccessibleTypeResult->getUnknownClassErrors();
 		}
 
+		if ($scope->hasExpressionType($node)->yes()) {
+			return [];
+		}
+
 		$isOffsetAccessible = $isOffsetAccessibleType->isOffsetAccessible();
 
 		if ($scope->isInExpressionAssign($node) && $isOffsetAccessible->yes()) {
@@ -87,7 +91,7 @@ public function processNode(Node $node, Scope $scope): array
 			return [];
 		}
 
-		if ($dimType === null || $scope->hasExpressionType($node)->yes()) {
+		if ($dimType === null) {
 			return [];
 		}
 

tests/PHPStan/Rules/Arrays/NonexistentOffsetInArrayDimFetchRuleTest.php

@@ -552,14 +552,6 @@ public function testBug7229(): void
 				'Cannot access offset string on mixed.',
 				24,
 			],
-			[
-				'Cannot access offset string on mixed.',
-				29,
-			],
-			[
-				'Cannot access offset string on mixed.',
-				32,
-			],
 		]);
 	}
 
@@ -729,4 +721,15 @@ public function testBug6605(): void
 		]);
 	}
 
+	public function testBug9991(): void
+	{
+		$this->checkExplicitMixed = true;
+		$this->analyse([__DIR__ . '/data/bug-9991.php'], [
+			[
+				'Cannot access offset \'title\' on mixed.',
+				9,
+			],
+		]);
+	}
+
 }

tests/PHPStan/Rules/Arrays/data/bug-9991.php

@@ -0,0 +1,14 @@
+<?php
+
+namespace Bug9991;
+
+function (): void {
+	$data = json_decode(file_get_contents('') ?: '', flags: JSON_THROW_ON_ERROR | JSON_OBJECT_AS_ARRAY);
+
+	if (
+		isset($data['title'])
+		&& is_string($data['title'])
+	) {
+		echo $data['title'];
+	}
+};