Fix phpstan/phpstan#11073: Nullsafe operator chaining false positive

- Fixed DateTimeModifyReturnTypeExtension to strip null from callee type
  before returning it as the method's return type
- The extension was returning $scope->getType($methodCall->var) which
  includes null from the nullsafe operator, causing "Cannot call method
  on DateTimeImmutable|null" false positive for chained calls like
  $date?->modify('+1 year')->setTime(23, 59, 59)
- Updated existing date-format.php test assertion (null was incorrectly
  expected in modify() return type)
- Added regression tests for the nullsafe chaining scenario

Author: VincentLanglet

src/Type/Php/DateTimeModifyReturnTypeExtension.php

@@ -77,7 +77,11 @@ public function getTypeFromMethodCall(MethodReflection $methodReflection, Method
 
 			return null;
 		} elseif ($hasDateTime) {
-			return $scope->getType($methodCall->var);
+			$callerType = $scope->getType($methodCall->var);
+			if (TypeCombinator::containsNull($callerType)) {
+				$callerType = TypeCombinator::removeNull($callerType);
+			}
+			return $callerType;
 		}
 
 		if ($this->phpVersion->hasDateTimeExceptions()) {

tests/PHPStan/Analyser/nsrt/bug-11073.php

@@ -0,0 +1,16 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug11073Nsrt;
+
+use DateTimeImmutable;
+use function PHPStan\Testing\assertType;
+
+class HelloWorld
+{
+	public function sayHello(?DateTimeImmutable $date): void
+	{
+		assertType('DateTimeImmutable|null', $date?->modify('+1 year')->setTime(23, 59, 59));
+	}
+}

tests/PHPStan/Analyser/nsrt/date-format.php

@@ -45,5 +45,5 @@ function (\DateTimeImmutable $dt, string $s): void {
 };
 
 function (?\DateTimeImmutable $d): void {
-	assertType('DateTimeImmutable|null', $d->modify('+1 day'));
+	assertType('DateTimeImmutable', $d->modify('+1 day'));
 };

tests/PHPStan/Rules/Methods/CallMethodsRuleTest.php

@@ -3962,4 +3962,13 @@ public function testBug11463(): void
 		]);
 	}
 
+	#[RequiresPhp('>= 8.0')]
+	public function testBug11073(): void
+	{
+		$this->checkThisOnly = false;
+		$this->checkNullables = true;
+		$this->checkUnionTypes = true;
+		$this->analyse([__DIR__ . '/data/bug-11073.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Methods/data/bug-11073.php

@@ -0,0 +1,15 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug11073;
+
+use DateTimeImmutable;
+
+class HelloWorld
+{
+	public function sayHello(?DateTimeImmutable $date): ?DateTimeImmutable
+	{
+		return $date?->modify('+1 year')->setTime(23, 59, 59);
+	}
+}