Fix issue with template of union

Author: VincentLanglet

src/Analyser/MutatingScope.php

@@ -106,6 +106,7 @@
 use PHPStan\Type\Generic\TemplateTypeHelper;
 use PHPStan\Type\Generic\TemplateTypeMap;
 use PHPStan\Type\Generic\TemplateTypeVarianceMap;
+use PHPStan\Type\Generic\TemplateUnionType;
 use PHPStan\Type\IntegerRangeType;
 use PHPStan\Type\IntegerType;
 use PHPStan\Type\IntersectionType;

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/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 +1,41 @@
+<?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;
+	}
+}
+
+
+class Test
+{
+	/**
+	 * @template B of BuilderA|BuilderB
+	 * @param B $template
+	 * @return B
+	 */
+	public function test($template)
+	{
+		return $template->where('test');
+	}
+}