PDO::prepare returns BenevolentUnionType

Author: ondrejmirtes

Diff for: conf/config.neon

@@ -1144,6 +1144,11 @@ services:
 		tags:
 			- phpstan.dynamicFunctionThrowTypeExtension
 
+	-
+		class: PHPStan\Type\Php\PdoPrepareDynamicReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicMethodReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\ReflectionClassConstructorThrowTypeExtension
 		tags:

Diff for: src/Type/Php/PdoPrepareDynamicReturnTypeExtension.php

@@ -0,0 +1,37 @@
+<?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\DynamicMethodReturnTypeExtension;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeUtils;
+
+class PdoPrepareDynamicReturnTypeExtension implements DynamicMethodReturnTypeExtension
+{
+
+	public function getClass(): string
+	{
+		return 'PDO';
+	}
+
+	public function isMethodSupported(MethodReflection $methodReflection): bool
+	{
+		return $methodReflection->getName() === 'prepare';
+	}
+
+	public function getTypeFromMethodCall(MethodReflection $methodReflection, MethodCall $methodCall, Scope $scope): Type
+	{
+		$returnType = ParametersAcceptorSelector::selectFromArgs(
+			$scope,
+			$methodCall->getArgs(),
+			$methodReflection->getVariants(),
+		)->getReturnType();
+
+		return TypeUtils::toBenevolentUnion($returnType);
+	}
+
+}

Diff for: tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -594,6 +594,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/classPhpDocs-phpstanPropertyPrefix.php');
 
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/array-destructuring-types.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/pdo-prepare.php');
 	}
 
 	/**

Diff for: tests/PHPStan/Analyser/data/pdo-prepare.php

@@ -0,0 +1,17 @@
+<?php
+
+namespace PDOPrepare;
+
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+
+	public function doFoo()
+	{
+		$database = new \PDO('dsn');
+		$logDeleteQuery = $database->prepare('DELETE FROM log');
+		assertType('(PDOStatement|false)', $logDeleteQuery);
+	}
+
+}