Fix nested dim fetch incorrectly preserving list type after container reset

When processing nested array dim fetch assignments like `$arr[$key][$int] = $value`
where the container was previously reset (`$arr[$key] = []`), the list type was
incorrectly preserved. This happened because `produceArrayDimFetchAssignValueToWrite`
used `setExistingOffsetValueType` (which preserves list structure) based on the
general type from the parent's type system, while the actual tracked container type
was an empty array where the offset couldn't exist.

The fix adds a check at container levels (inner dimensions of nested dim fetches)
to verify that the scope's actual tracked type of the container also supports the
offset before using `setExistingOffsetValueType`. This correctly falls through to
`setOffsetValueType` when the container was just reset to `[]`, which properly
degrades the list type.

This addresses the actual reproducer from phpstan/phpstan#14336 where the previous
IntersectionType::setOffsetValueType fix alone was insufficient.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

Author: phpstan-bot

src/Analyser/ExprHandler/AssignHandler.php

@@ -1057,11 +1057,13 @@ private function produceArrayDimFetchAssignValueToWrite(array $dimFetchStack, ar
 			}
 
 			$arrayDimFetch = $dimFetchStack[$i] ?? null;
+			$isContainerLevel = $i + 1 < count($dimFetchStack);
 			if (
 				$offsetType !== null
 				&& $arrayDimFetch !== null
 				&& $scope->hasExpressionType($arrayDimFetch)->yes()
 				&& !$offsetValueType->hasOffsetValueType($offsetType)->no()
+				&& (!$isContainerLevel || !$scope->getType($arrayDimFetch)->hasOffsetValueType($offsetType)->no())
 			) {
 				$hasOffsetType = null;
 				if ($offsetType instanceof ConstantStringType || $offsetType instanceof ConstantIntegerType) {

tests/PHPStan/Analyser/nsrt/bug-14336.php

@@ -4,6 +4,54 @@
 
 use function PHPStan\Testing\assertType;
 
+/**
+ * Actual reproducer from the issue: nested dim fetch with arbitrary int key
+ * after resetting array element to [].
+ *
+ * @param array<string, list<array{xmlNamespace: string, namespace: string, name: string}>> $xsdFiles
+ * @param array<string, list<array{xmlNamespace: string, namespace: string, name: string}>> $groupedByNamespace
+ * @param array<string, list<string>> $extraNamespaces
+ */
+function testIssueReproducer(array $xsdFiles, array $groupedByNamespace, array $extraNamespaces, int $int): void
+{
+	foreach ($extraNamespaces as $mergedNamespace) {
+		if (count($mergedNamespace) < 2) {
+			continue;
+		}
+
+		$targetNamespace = end($mergedNamespace);
+		if (!isset($groupedByNamespace[$targetNamespace])) {
+			continue;
+		}
+		$xmlNamespace = $groupedByNamespace[$targetNamespace][0]['xmlNamespace'];
+
+		assertType('string', $xmlNamespace);
+		assertType('non-empty-list<string>&hasOffsetValue(1, string)', $mergedNamespace);
+
+		$xsdFiles[$xmlNamespace] = [];
+		foreach ($mergedNamespace as $namespace) {
+			foreach ($groupedByNamespace[$namespace] ?? [] as $viewHelper) {
+				$xsdFiles[$xmlNamespace][$int] = $viewHelper;
+			}
+		}
+		// After assigning any int, $xsdFiles[$xmlNamespace] should NOT be a list
+		assertType('array<int, array{xmlNamespace: string, namespace: string, name: string}>', $xsdFiles[$xmlNamespace]);
+		$xsdFiles[$xmlNamespace] = array_values($xsdFiles[$xmlNamespace]);
+	}
+}
+
+/**
+ * Simplified: nested dim fetch after reset with arbitrary int key.
+ *
+ * @param array<string, list<array{name: string}>> $arr
+ */
+function testNestedDimFetchAfterReset(array $arr, int $int, string $key): void
+{
+	$arr[$key] = [];
+	$arr[$key][$int] = ['name' => 'test'];
+	assertType("non-empty-array<int, array{name: string}>", $arr[$key]);
+}
+
 /**
  * Assigning with arbitrary int key in a loop should degrade list to array.
  *