Fix lost list-type if substituted a element via loop

Author: staabm

Diff for: src/Analyser/NodeScopeResolver.php

@@ -5482,6 +5482,10 @@ private function processAssignVar(
 			}
 
 			if ($varType->isArray()->yes() || !(new ObjectType(ArrayAccess::class))->isSuperTypeOf($varType)->yes()) {
+				if ($varType->isList()->yes() && $scope->hasExpressionType($originalVar)->yes()) {
+					$valueToWrite = TypeCombinator::intersect($valueToWrite, new AccessoryArrayListType());
+				}
+
 				if ($var instanceof Variable && is_string($var->name)) {
 					$nodeCallback(new VariableAssignNode($var, $assignedPropertyExpr, $isAssignOp), $scope);
 					$scope = $scope->assignVariable($var->name, $valueToWrite, $nativeValueToWrite, TrinaryLogic::createYes());

Diff for: tests/PHPStan/Analyser/nsrt/bug-12274.php

@@ -0,0 +1,37 @@
+<?php declare(strict_types=1);
+
+namespace Bug12274;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @param non-empty-list<int> $items
+ *
+ * @return non-empty-list<int>
+ */
+function getItems(array $items): array
+{
+	foreach ($items as $index => $item) {
+		$items[$index] = 1;
+	}
+
+	assertType('non-empty-list<int>', $items);
+	return $items;
+}
+
+/**
+ * @param non-empty-list<int> $items
+ *
+ * @return non-empty-list<int>
+ */
+function getItemsByModifiedIndex(array $items): array
+{
+	foreach ($items as $index => $item) {
+		$index++;
+
+		$items[$index] = 1;
+	}
+
+	assertType('non-empty-array<int<0, max>, int>', $items);
+	return $items;
+}

Diff for: tests/PHPStan/Rules/Functions/ReturnTypeRuleTest.php

@@ -345,4 +345,18 @@ public function testBug11301(): void
 		]);
 	}
 
+	public function testBug12274(): void
+	{
+		$this->checkExplicitMixed = true;
+		$this->checkNullables = true;
+
+		$this->analyse([__DIR__ . '/../../Analyser/nsrt/bug-12274.php'], [
+			[
+				'Function Bug12274\getItemsByModifiedIndex() should return non-empty-list<int> but returns non-empty-array<int<0, max>, int>.',
+				36,
+				'non-empty-array<int<0, max>, int> might not be a list.',
+			],
+		]);
+	}
+
 }