Add SimpleXmlElementXpathMethodReturnTypeExtension

conf/config.neon

@@ -1183,6 +1183,11 @@ services:
 		tags:
 			- phpstan.broker.dynamicMethodReturnTypeExtension
 
+	-
+		class: PHPStan\Type\Php\SimpleXMLElementXpathMethodReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicMethodReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\StrSplitFunctionReturnTypeExtension
 		tags:

src/Type/Php/SimpleXMLElementXpathMethodReturnTypeExtension.php

@@ -0,0 +1,63 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\MethodCall;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\MethodReflection;
+use PHPStan\Reflection\ParametersAcceptorSelector;
+use PHPStan\Type\ArrayType;
+use PHPStan\Type\Constant\ConstantBooleanType;
+use PHPStan\Type\MixedType;
+use PHPStan\Type\NeverType;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
+use PHPStan\Type\TypeUtils;
+
+class SimpleXMLElementXpathMethodReturnTypeExtension implements \PHPStan\Type\DynamicMethodReturnTypeExtension
+{
+
+	public function getClass(): string
+	{
+		return \SimpleXMLElement::class;
+	}
+
+	public function isMethodSupported(MethodReflection $methodReflection): bool
+	{
+		return $methodReflection->getName() === 'xpath';
+	}
+
+	public function getTypeFromMethodCall(MethodReflection $methodReflection, MethodCall $methodCall, Scope $scope): Type
+	{
+		if (!isset($methodCall->args[0])) {
+			return ParametersAcceptorSelector::selectSingle($methodReflection->getVariants())->getReturnType();
+		}
+
+		$argType = $scope->getType($methodCall->args[0]->value);
+
+		$xmlElement = new \SimpleXMLElement('<foo />');
+
+		$result = null;
+		foreach (TypeUtils::getConstantStrings($argType) as $constantString) {
+			$newResult = @$xmlElement->xpath($constantString->getValue());
+
+			if ($result !== null && gettype($result) !== gettype($newResult)) {
+				return ParametersAcceptorSelector::selectSingle($methodReflection->getVariants())->getReturnType();
+			}
+
+			$result = $newResult;
+			$argType = TypeCombinator::remove($argType, $constantString);
+		}
+
+		if ($result === null || !$argType instanceof NeverType) {
+			return ParametersAcceptorSelector::selectSingle($methodReflection->getVariants())->getReturnType();
+		}
+
+		if ($result === false) {
+			return new ConstantBooleanType(false);
+		}
+
+		return new ArrayType(new MixedType(), $scope->getType($methodCall->var));
+	}
+
+}

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -3226,6 +3226,18 @@ public function dataBinaryOperations(): array
 				'bool',
 				'$simpleXMLWritingXML',
 			],
+			[
+				'array<SimpleXMLElement>',
+				'$simpleXMLRightXpath',
+			],
+			[
+				'false',
+				'$simpleXMLWrongXpath',
+			],
+			[
+				'array<static(SimpleXMLElement)>|false',
+				'$simpleXMLUnknownXpath',
+			],
 		];
 	}
 

tests/PHPStan/Analyser/data/binary.php

@@ -170,6 +170,13 @@ public function doFoo(array $generalArray)
 
 		$simpleXMLWritingXML = $simpleXML->asXML('path.xml');
 
+		/** @var string $stringForXpath */
+		$stringForXpath = doFoo();
+
+		$simpleXMLRightXpath = $simpleXML->xpath('/a/b/c');
+		$simpleXMLWrongXpath = $simpleXML->xpath('[foo]');
+		$simpleXMLUnknownXpath = $simpleXML->xpath($stringForXpath);
+
 		if (rand(0, 1)) {
 			$maybeDefinedVariable = 'foo';
 		}