Fix generic callback return type on union of generic objects

- When calling a method with template parameters on a union type (e.g.,
  Collection<int, A>|Collection<int, B>), resolve return types for each
  union member separately instead of combining variants first
- The root cause was that combineAcceptors merged variants from different
  generic instantiations, losing proper template type resolution for
  callable return types
- Excludes TemplateUnionType from decomposition to preserve template
  type wrapping
- Updated static-late-binding test assertion to match now-correct result
- New regression test in tests/PHPStan/Analyser/nsrt/bug-14203.php

Closes phpstan/phpstan#14203

Author: phpstan-bot

src/Analyser/ExprHandler/Helper/MethodCallReturnTypeHelper.php

@@ -9,8 +9,10 @@
 use PHPStan\DependencyInjection\AutowiredService;
 use PHPStan\DependencyInjection\Type\DynamicReturnTypeExtensionRegistryProvider;
 use PHPStan\Reflection\ParametersAcceptorSelector;
+use PHPStan\Type\Generic\TemplateType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeCombinator;
+use PHPStan\Type\UnionType;
 use function count;
 
 #[AutowiredService]
@@ -35,6 +37,21 @@ public function methodCallReturnType(
 			return null;
 		}
 
+		if ($typeWithMethod instanceof UnionType && !$typeWithMethod instanceof TemplateType) {
+			$memberTypes = [];
+			foreach ($typeWithMethod->getTypes() as $memberType) {
+				$memberResult = $this->methodCallReturnType($scope, $memberType, $methodName, $methodCall);
+				if ($memberResult === null) {
+					continue;
+				}
+				$memberTypes[] = $memberResult;
+			}
+			if (count($memberTypes) > 0) {
+				return TypeCombinator::union(...$memberTypes);
+			}
+			return null;
+		}
+
 		$methodReflection = $typeWithMethod->getMethod($methodName, $scope);
 		$parametersAcceptor = ParametersAcceptorSelector::selectFromArgs(
 			$scope,

tests/PHPStan/Analyser/nsrt/bug-14203.php

@@ -0,0 +1,90 @@
+<?php // lint >= 8.1
+
+declare(strict_types = 1);
+
+namespace Bug14203;
+
+use function PHPStan\Testing\assertType;
+
+/**
+ * @template TKey of array-key
+ * @template TValue
+ */
+class Collection
+{
+    /**
+     * Create a new collection.
+     *
+     * @param  array<TKey, TValue>  $items
+     */
+    final public function __construct(protected $items = [])
+    {
+    }
+
+    /**
+	 * @template TMapValue
+     *
+     * @param  callable(TValue, TKey): TMapValue  $callback
+     * @return static<TKey, TMapValue>
+     */
+    public function map(callable $callback)
+    {
+        $newItems = [];
+
+		foreach ($this->items as $key => $value) {
+			$newItems[$key] = $callback($value, $key);
+		}
+
+		return new static($newItems);
+    }
+}
+
+class SpecificA {
+    public function __construct(
+		public readonly int $valueA,
+		public readonly string $someSharedValue,
+	) {}
+}
+
+class SpecificB {
+    public function __construct(
+		public readonly int $valueB,
+		public readonly string $someSharedValue,
+	) {}
+}
+
+class MyDTO {
+    public function __construct(
+		public readonly string $thatSharedValue,
+	) {}
+}
+
+function works(): void {
+    $myCollection = new Collection([new SpecificA(1, 'A'), new SpecificB(2, 'B')]);
+
+	$result = $myCollection->map(static fn (SpecificA|SpecificB $specific): MyDTO => new MyDTO($specific->someSharedValue));
+	assertType('Bug14203\Collection<int, Bug14203\MyDTO>', $result);
+}
+
+/**
+ * @return Collection<int, SpecificA>
+ */
+function getA(): Collection {
+	return new Collection([new SpecificA(1, 'A')]);
+}
+
+/**
+ * @return Collection<int, SpecificB>
+ */
+function getB(): Collection {
+	return new Collection([new SpecificB(2, 'B')]);
+}
+
+function breaks(): void {
+    $myCollection = random_int(0, 1) === 0
+		? getA()
+		: getB();
+
+	$result = $myCollection->map(static fn (SpecificA|SpecificB $specific): MyDTO => new MyDTO($specific->someSharedValue));
+	assertType('Bug14203\Collection<int, Bug14203\MyDTO>', $result);
+}

tests/PHPStan/Analyser/nsrt/static-late-binding.php

@@ -85,7 +85,7 @@ public function foo(): void
         assertType('static(StaticLateBinding\B)', parent::retStatic());
         assertType('static(StaticLateBinding\B)', $this->retStatic());
         assertType('bool', X::retStatic());
-        assertType('bool|StaticLateBinding\A|StaticLateBinding\X', $clUnioned::retStatic()); // should be bool|StaticLateBinding\A https://github.com/phpstan/phpstan/issues/11687
+        assertType('bool|StaticLateBinding\A', $clUnioned::retStatic());
 
         assertType('StaticLateBinding\A', A::retStatic(...)());
         assertType('StaticLateBinding\B', B::retStatic(...)());