Fix phpstan/phpstan#5357: Intersection of generics are not simplified, calling method on it returns *NEVER*

phpstan-baseline.neon

@@ -1713,6 +1713,12 @@ parameters:
 			count: 2
 			path: src/Type/TypeCombinator.php
 
+		-
+			rawMessage: Doing instanceof PHPStan\Type\Generic\GenericObjectType is error-prone and deprecated.
+			identifier: phpstanApi.instanceofType
+			count: 2
+			path: src/Type/TypeCombinator.php
+
 		-
 			rawMessage: Doing instanceof PHPStan\Type\IntersectionType is error-prone and deprecated.
 			identifier: phpstanApi.instanceofType

src/Type/TypeCombinator.php

@@ -20,6 +20,7 @@
 use PHPStan\Type\Constant\ConstantIntegerType;
 use PHPStan\Type\Constant\ConstantStringType;
 use PHPStan\Type\Generic\GenericClassStringType;
+use PHPStan\Type\Generic\GenericObjectType;
 use PHPStan\Type\Generic\TemplateArrayType;
 use PHPStan\Type\Generic\TemplateBenevolentUnionType;
 use PHPStan\Type\Generic\TemplateMixedType;
@@ -1503,9 +1504,42 @@ public static function intersect(Type ...$types): Type
 					continue 2;
 				}
 
-				if ($isSuperTypeA->no()) {
-					return new NeverType();
+				if (!$isSuperTypeA->no()) {
+					continue;
 				}
+
+				if (
+					$types[$i] instanceof GenericObjectType
+					&& $types[$j] instanceof GenericObjectType
+					&& $types[$i]->getClassName() === $types[$j]->getClassName()
+					&& count($types[$i]->getTypes()) === count($types[$j]->getTypes())
+				) {
+					$mergedParams = [];
+					foreach ($types[$i]->getTypes() as $k => $paramTypeI) {
+						$paramTypeJ = $types[$j]->getTypes()[$k];
+						$merged = self::intersect($paramTypeI, $paramTypeJ);
+						if ($merged instanceof NeverType) {
+							return $merged;
+						}
+						$mergedParams[] = $merged;
+					}
+					$subtractedType = $types[$i]->getSubtractedType();
+					if ($subtractedType !== null && $types[$j]->getSubtractedType() !== null) {
+						$subtractedType = self::union($subtractedType, $types[$j]->getSubtractedType());
+					} elseif ($types[$j]->getSubtractedType() !== null) {
+						$subtractedType = $types[$j]->getSubtractedType();
+					}
+					$types[$j] = new GenericObjectType(
+						$types[$j]->getClassName(),
+						$mergedParams,
+						$subtractedType,
+					);
+					array_splice($types, $i--, 1);
+					$typesCount--;
+					continue 2;
+				}
+
+				return new NeverType();
 			}
 		}
 

tests/PHPStan/Analyser/nsrt/bug-5357.php

@@ -0,0 +1,103 @@
+<?php declare(strict_types = 1);
+
+namespace Bug5357;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @phpstan-template T of object
+ */
+interface AdminInterface {}
+
+/**
+ * @phpstan-template T of ProxyQueryInterface
+ */
+interface PagerInterface {}
+
+/**
+ * @phpstan-template T of ProxyQueryInterface
+ * @phpstan-implements PagerInterface<T>
+ */
+class Pager implements PagerInterface
+{}
+
+/**
+ * @phpstan-template T of ProxyQueryInterface
+ */
+interface DatagridInterface
+{
+	/**
+	 * @phpstan-return PagerInterface<T>
+	 */
+	public function getPager(): PagerInterface;
+}
+
+/**
+ * @phpstan-template T of ProxyQueryInterface
+ * @phpstan-implements DatagridInterface<T>
+ */
+class Datagrid implements DatagridInterface
+{
+	/**
+	 * @phpstan-return PagerInterface<T>
+	 */
+	public function getPager(): PagerInterface
+	{
+		throw new \Exception();
+	}
+}
+
+interface ProxyQueryInterface {}
+
+class Proxy implements ProxyQueryInterface {}
+
+class MockObject {}
+
+/**
+ * @phpstan-template T of ProxyQueryInterface
+ */
+interface DatagridBuilderInterface
+{
+	/**
+	 * @param AdminInterface<object> $admin
+	 * @param array<string, mixed>   $values
+	 *
+	 * @phpstan-return DatagridInterface<T>
+	 */
+	public function getBaseDatagrid(AdminInterface $admin, array $values = []): DatagridInterface;
+}
+
+/**
+ * @phpstan-implements DatagridBuilderInterface<Proxy>
+ */
+class DatagridBuilder implements DatagridBuilderInterface
+{
+	/**
+	 * @param AdminInterface<object> $admin
+	 * @param array<string, mixed>   $values
+	 *
+	 * @phpstan-return DatagridInterface<Proxy>
+	 */
+	public function getBaseDatagrid(AdminInterface $admin, array $values = []): DatagridInterface
+	{
+		throw new \Exception();
+	}
+}
+
+class HelloWorld
+{
+	/**
+	 * @var MockObject&AdminInterface<object>
+	 */
+	public $admin;
+
+	public DatagridBuilder $datagridBuilder;
+
+	public function sayHello(): void
+	{
+		$datagrid = $this->datagridBuilder->getBaseDatagrid($this->admin);
+		assert($datagrid instanceof Datagrid);
+		assertType('Bug5357\Datagrid&Bug5357\DatagridInterface<Bug5357\Proxy>', $datagrid);
+		assertType('Bug5357\PagerInterface<Bug5357\Proxy>', $datagrid->getPager());
+	}
+}