Fix issue with template of union

src/Type/BenevolentUnionType.php

@@ -19,6 +19,16 @@ public function __construct(array $types, bool $normalized = false)
 		parent::__construct($types, $normalized);
 	}
 
+	public function filterTypes(callable $filterCb): Type
+	{
+		$result = parent::filterTypes($filterCb);
+		if (!$result instanceof self && $result instanceof UnionType) {
+			return TypeUtils::toBenevolentUnion($result);
+		}
+
+		return $result;
+	}
+
 	public function describe(VerbosityLevel $level): string
 	{
 		return '(' . parent::describe($level) . ')';

src/Type/Generic/TemplateBenevolentUnionType.php

@@ -47,4 +47,21 @@ public function withTypes(array $types): self
 		);
 	}
 
+	public function filterTypes(callable $filterCb): Type
+	{
+		$result = parent::filterTypes($filterCb);
+		if (!$result instanceof TemplateType) {
+			return TemplateTypeFactory::create(
+				$this->getScope(),
+				$this->getName(),
+				$result,
+				$this->getVariance(),
+				$this->getStrategy(),
+				$this->getDefault(),
+			);
+		}
+
+		return $result;
+	}
+
 }

src/Type/Generic/TemplateUnionType.php

@@ -34,4 +34,21 @@ public function __construct(
 		$this->default = $default;
 	}
 
+	public function filterTypes(callable $filterCb): Type
+	{
+		$result = parent::filterTypes($filterCb);
+		if (!$result instanceof TemplateType) {
+			return TemplateTypeFactory::create(
+				$this->getScope(),
+				$this->getName(),
+				$result,
+				$this->getVariance(),
+				$this->getStrategy(),
+				$this->getDefault(),
+			);
+		}
+
+		return $result;
+	}
+
 }

src/Type/UnionType.php

@@ -92,14 +92,20 @@ public function getTypes(): array
 	public function filterTypes(callable $filterCb): Type
 	{
 		$newTypes = [];
+		$changed = false;
 		foreach ($this->getTypes() as $innerType) {
 			if (!$filterCb($innerType)) {
+				$changed = true;
 				continue;
 			}
 
 			$newTypes[] = $innerType;
 		}
 
+		if (!$changed) {
+			return $this;
+		}
+
 		return TypeCombinator::union(...$newTypes);
 	}
 

tests/PHPStan/Analyser/nsrt/bug-6609-83.php

@@ -50,7 +50,7 @@ function modify2(\DateTimeInterface $date) {
 	 */
 	function modify3(\DateTimeInterface $date, string $s) {
 		$date = $date->modify($s);
-		assertType('DateTime|DateTimeImmutable', $date);
+		assertType('T of DateTime|DateTimeImmutable (method Bug6609Php83\Foo::modify3(), argument)', $date);
 
 		return $date;
 	}

tests/PHPStan/Analyser/nsrt/bug-6609.php

@@ -50,7 +50,7 @@ function modify2(\DateTimeInterface $date) {
 	 */
 	function modify3(\DateTimeInterface $date, string $s) {
 		$date = $date->modify($s);
-		assertType('(DateTime|DateTimeImmutable|false)', $date);
+		assertType('((T of DateTime|DateTimeImmutable (method Bug6609\Foo::modify3(), argument))|false)', $date);
 
 		return $date;
 	}

tests/PHPStan/Rules/Methods/ReturnTypeRuleTest.php

@@ -1054,4 +1054,9 @@ public function testBug10715(): void
 		$this->analyse([__DIR__ . '/data/bug-10715.php'], []);
 	}
 
+	public function testBug11663(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-11663.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Methods/data/bug-11663.php

@@ -0,0 +1,79 @@
+<?php declare(strict_types = 1);
+
+namespace Bug11663;
+
+class BuilderA
+{
+	/**
+	 * @param string $test
+	 * @return $this
+	 */
+	public function where(string $test)
+	{
+		return $this;
+	}
+}
+
+class BuilderB
+{
+	/**
+	 * @param string $test
+	 * @return $this
+	 */
+	public function where(string $test)
+	{
+		return $this;
+	}
+}
+
+interface A
+{
+	public function doFoo(): static;
+}
+
+interface B
+{
+}
+
+class Test
+{
+	/**
+	 * @template B of BuilderA|BuilderB
+	 * @param B $template
+	 * @return B
+	 */
+	public function test($template)
+	{
+		return $template->where('test');
+	}
+
+	/**
+	 * @param __benevolent<BuilderA|BuilderB|false> $template
+	 * @return __benevolent<BuilderA|BuilderB>
+	 */
+	public function test2($template)
+	{
+		return $template->where('test');
+	}
+
+
+	/**
+	 * @template T of A|B
+	 * @param T $ab
+	 * @return T
+	 */
+	function foo(A|B $ab): A|B
+	{
+		return $ab->doFoo();
+	}
+
+	/**
+	 * @template T of __benevolent<A|B>
+	 * @param T $ab
+	 * @return T
+	 */
+	function foo2(A|B $ab): A|B
+	{
+		return $ab->doFoo();
+	}
+}