Add DatePeriod::getEndDate dynamic return type

conf/config.neon

@@ -1051,6 +1051,11 @@ services:
 		tags:
 			- phpstan.dynamicStaticMethodThrowTypeExtension
 
+	-
+		class: PHPStan\Type\Php\DatePeriodGetEndDateMethodReturnTypeExtension
+		tags:
+			- phpstan.broker.dynamicMethodReturnTypeExtension
+
 	-
 		class: PHPStan\Type\Php\DsMapDynamicReturnTypeExtension
 		tags:

resources/functionMap.php

@@ -1591,7 +1591,7 @@
 'DatePeriod::__construct\'2' => ['void', 'iso'=>'string', 'options='=>'int'],
 'DatePeriod::__wakeup' => ['void'],
 'DatePeriod::getDateInterval' => ['DateInterval'],
-'DatePeriod::getEndDate' => ['DateTimeInterface'],
+'DatePeriod::getEndDate' => ['?DateTimeInterface'],
 'DatePeriod::getStartDate' => ['DateTimeInterface'],
 'DateTime::__construct' => ['void', 'time='=>'string', 'timezone='=>'?DateTimeZone'],
 'DateTime::__set_state' => ['static', 'array'=>'array'],

src/Type/Php/DatePeriodGetEndDateMethodReturnTypeExtension.php

@@ -0,0 +1,56 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Type\Php;
+
+use PhpParser\Node\Expr\MethodCall;
+use PhpParser\Node\Expr\New_;
+use PHPStan\Analyser\Scope;
+use PHPStan\Reflection\MethodReflection;
+use PHPStan\Type\DynamicMethodReturnTypeExtension;
+use PHPStan\Type\IntegerType;
+use PHPStan\Type\NullType;
+use PHPStan\Type\ObjectType;
+use PHPStan\Type\Type;
+use PHPStan\Type\TypeCombinator;
+
+class DatePeriodGetEndDateMethodReturnTypeExtension implements DynamicMethodReturnTypeExtension
+{
+
+	public function getClass(): string
+	{
+		return \DatePeriod::class;
+	}
+
+	public function isMethodSupported(MethodReflection $methodReflection): bool
+	{
+		return $methodReflection->getName() === 'getEndDate';
+	}
+
+	public function getTypeFromMethodCall(MethodReflection $methodReflection, MethodCall $methodCall, Scope $scope): Type
+	{
+		/** @var New_ $new */
+		$new = $methodCall->var;
+		$argument = $new->getRawArgs()[2] ?? null;
+
+		// initialize with iso parameter
+		if ($argument === null) {
+			return new NullType();
+		}
+
+		$dateTimeType = new ObjectType(\DateTimeInterface::class);
+		$argumentType = $scope->getType($argument->value);
+
+		// initialize with end parameter
+		if ($dateTimeType->isSuperTypeOf($argumentType)->yes()) {
+			return $dateTimeType;
+		}
+
+		// initialize with recurrences parameter
+		if ((new IntegerType())->isSuperTypeOf($argumentType)->yes()) {
+			return new NullType();
+		}
+
+		return TypeCombinator::addNull($dateTimeType);
+	}
+
+}

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -543,6 +543,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-2760.php');
 
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/filesystem-functions.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/DatePeriodGetEndDateDynamicReturnType.php');
 	}
 
 	/**

tests/PHPStan/Analyser/data/DatePeriodGetEndDateDynamicReturnType.php

@@ -0,0 +1,13 @@
+<?php declare(strict_types=1);
+
+use function PHPStan\Testing\assertType;
+
+$start = new DateTime('2012-07-01');
+$interval = new DateInterval('P7D');
+$end = new DateTime('2012-07-31');
+$recurrences = 4;
+$iso = 'R4/2012-07-01T00:00:00Z/P7D';
+
+assertType('null', (new DatePeriod($start, $interval, $recurrences))->getEndDate());
+assertType(\DateTimeInterface::class, (new DatePeriod($start, $interval, $end))->getEndDate());
+assertType('null', (new DatePeriod($iso))->getEndDate());