Fix @phpstan-assert not working with union types

- UnionTypeMethodReflection::getAsserts() returned empty assertions,
  causing @phpstan-assert tags to be ignored when calling methods on
  union types like Foo|Bar
- Changed getAsserts() to combine assertions from all union member
  methods, mirroring IntersectionTypeMethodReflection's implementation
- New regression test in tests/PHPStan/Analyser/nsrt/bug-11441.php

Author: ondrejmirtes

CLAUDE.md

@@ -389,6 +389,10 @@ When adding or editing PHPDoc comments in this codebase, follow these guidelines
 - Use imperative voice without "Returns the..." preambles when a brief note suffices. Prefer `/** Replaces unresolved TemplateTypes with their bounds. */` over a multi-line block.
 - Preserve `@api` and type tags on their own lines, with no redundant description alongside them.
 
+### UnionTypeMethodReflection and IntersectionTypeMethodReflection parity
+
+When methods are called on union types (`Foo|Bar`), the resolved method reflection is a `UnionTypeMethodReflection` that wraps the individual method reflections. Similarly, `IntersectionTypeMethodReflection` handles intersection types. These two classes must maintain feature parity for things like `getAsserts()`, `getSelfOutType()`, etc. When one class correctly combines member data (e.g. `IntersectionTypeMethodReflection::getAsserts()` iterating over methods and calling `intersectWith()`), the other should do the same rather than returning empty/null. The `Assertions::intersectWith()` method merges assertion tag lists from multiple sources.
+
 ## Important dependencies
 
 - `nikic/php-parser` ^5.7.0 - PHP AST parsing

src/Reflection/Type/UnionTypeMethodReflection.php

@@ -178,7 +178,13 @@ public function getDocComment(): ?string
 
 	public function getAsserts(): Assertions
 	{
-		return Assertions::createEmpty();
+		$assertions = Assertions::createEmpty();
+
+		foreach ($this->methods as $method) {
+			$assertions = $assertions->intersectWith($method->getAsserts());
+		}
+
+		return $assertions;
 	}
 
 	public function acceptsNamedArguments(): TrinaryLogic

tests/PHPStan/Analyser/nsrt/bug-11441.php

@@ -0,0 +1,58 @@
+<?php // lint >= 8.0
+
+namespace Bug11441;
+
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+	public function __construct(private ?string $param)
+	{
+	}
+
+	public function getParam(): ?string
+	{
+		return $this->param;
+	}
+
+	/**
+	 * @phpstan-assert !null $this->getParam()
+	 */
+	public function checkNotNull(): void
+	{
+		if ($this->getParam() === null) {
+			throw new \Exception();
+		}
+	}
+}
+
+class Bar
+{
+	public function __construct(private ?int $param)
+	{
+	}
+
+	public function getParam(): ?int
+	{
+		return $this->param;
+	}
+
+	/**
+	 * @phpstan-assert !null $this->getParam()
+	 */
+	public function checkNotNull(): void
+	{
+		if ($this->getParam() === null) {
+			throw new \Exception();
+		}
+	}
+}
+
+function test(Foo|Bar $fooOrBar): void
+{
+	assertType('int|string|null', $fooOrBar->getParam());
+
+	$fooOrBar->checkNotNull();
+
+	assertType('int|string', $fooOrBar->getParam());
+}