Fix phpstan/phpstan#11507: Type mismatch when explicitly setting an array key

src/Type/Generic/TemplateTypeHelper.php

@@ -3,8 +3,11 @@
 namespace PHPStan\Type\Generic;
 
 use PHPStan\Reflection\ParametersAcceptor;
+use PHPStan\Type\Accessory\HasOffsetType;
+use PHPStan\Type\Accessory\HasOffsetValueType;
 use PHPStan\Type\ErrorType;
 use PHPStan\Type\GeneralizePrecision;
+use PHPStan\Type\MixedType;
 use PHPStan\Type\NonAcceptingNeverType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeTraverser;
@@ -147,6 +150,14 @@ public static function generalizeInferredTemplateType(TemplateType $templateType
 			} elseif ($type->isConstantValue()->yes() && (!$templateType->getBound()->isScalar()->yes() || $isArrayKey)) {
 				$type = $type->generalize(GeneralizePrecision::templateArgument());
 			}
+
+			$type = TypeTraverser::map($type, static function (Type $type, callable $traverse): Type {
+				if ($type instanceof HasOffsetValueType || $type instanceof HasOffsetType) {
+					return new MixedType();
+				}
+
+				return $traverse($type);
+			});
 		}
 
 		return $type;

tests/PHPStan/Rules/Functions/ReturnTypeRuleTest.php

@@ -411,4 +411,11 @@ public function testBug12397(): void
 		$this->analyse([__DIR__ . '/data/bug-12397.php'], []);
 	}
 
+	public function testBug11507(): void
+	{
+		$this->checkNullables = true;
+		$this->checkExplicitMixed = true;
+		$this->analyse([__DIR__ . '/data/bug-11507.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Functions/data/bug-11507.php

@@ -0,0 +1,50 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug11507;
+
+/**
+ * @template TValue
+ */
+class Collection
+{
+	/**
+	* @param array<int, TValue> $items
+	*/
+	public function __construct(
+		public array $items,
+	) {}
+
+	 /**
+     * Run a map over each of the items.
+     *
+     * @template TMapValue
+     *
+     * @param  callable(TValue, int=): TMapValue  $callback
+     * @return Collection<TMapValue>
+     */
+	public function map(callable $callback): Collection
+	{
+		$keys = array_keys($this->items);
+
+		$items = array_map($callback, $this->items);
+
+        $result = array_combine($keys, $items);
+
+		return new self($result);
+	}
+}
+
+/**
+ * @param  Collection<non-empty-array<string>>  $collection
+ * @return Collection<non-empty-array<string>>
+ */
+function foo(Collection $collection): Collection
+{
+	return $collection->map(function (array $item) {
+		$item['foo'] = '100';
+
+		return $item;
+	});
+}