DateTimeImmutable removed from DateTimeInterface results in DateTime

src/Type/TypeCombinator.php

@@ -120,7 +120,17 @@ public static function remove(Type $fromType, Type $typeToRemove): Type
 			if ($typeToRemove instanceof AccessoryNonEmptyStringType) {
 				return new ConstantStringType('');
 			}
-		} elseif ($fromType instanceof SubtractableType) {
+		} elseif ($fromType instanceof ObjectType && $fromType->getClassName() === \DateTimeInterface::class) {
+			if ($typeToRemove instanceof ObjectType && $typeToRemove->getClassName() === \DateTimeImmutable::class) {
+				return new ObjectType(\DateTime::class);
+			}
+
+			if ($typeToRemove instanceof ObjectType && $typeToRemove->getClassName() === \DateTime::class) {
+				return new ObjectType(\DateTimeImmutable::class);
+			}
+		}
+
+		if ($fromType instanceof SubtractableType) {
 			$typeToSubtractFrom = $fromType;
 			if ($fromType instanceof TemplateType) {
 				$typeToSubtractFrom = $fromType->getBound();

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -440,6 +440,7 @@ public function dataFileAsserts(): iterable
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/generic-object-lower-bound.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/class-reflection-interfaces.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/../Rules/Methods/data/bug-4415.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-5259.php');
 	}
 
 	/**

tests/PHPStan/Analyser/data/bug-5259.php

@@ -0,0 +1,30 @@
+<?php
+
+namespace Bug5259Types;
+
+use DateTime;
+use DateTimeImmutable;
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+
+	public function doFoo(\DateTimeInterface $dtin): void
+	{
+		if ($dtin instanceof \DateTimeImmutable) {
+			return;
+		}
+
+		assertType(DateTime::class, $dtin);
+	}
+
+	public function doBar(\DateTimeInterface $dtin): void
+	{
+		if ($dtin instanceof \DateTime) {
+			return;
+		}
+
+		assertType(DateTimeImmutable::class, $dtin);
+	}
+
+}

tests/PHPStan/Analyser/data/native-types.php

@@ -159,7 +159,7 @@ public function doIfElse(\DateTimeInterface $date): void
 			assertNativeType(\DateTimeImmutable::class, $date);
 		} else {
 			assertType('*NEVER*', $date);
-			assertNativeType('DateTimeInterface~DateTimeImmutable', $date);
+			assertNativeType('DateTime', $date);
 		}
 
 		assertType(\DateTimeImmutable::class, $date);

tests/PHPStan/Rules/Methods/CallStaticMethodsRuleTest.php

@@ -435,4 +435,10 @@ public function testBug1971(): void
 		]);
 	}
 
+	public function testBug5259(): void
+	{
+		$this->checkThisOnly = false;
+		$this->analyse([__DIR__ . '/data/bug-5259.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Methods/data/bug-5259.php

@@ -0,0 +1,15 @@
+<?php
+
+namespace Bug5259;
+
+class HelloWorld
+{
+
+	/** @var \DateTimeImmutable  */
+	private $date;
+
+	public function __construct(\DateTimeInterface $date)
+	{
+		$this->date = $date instanceof \DateTimeImmutable ? $date : \DateTimeImmutable::createFromMutable($date);
+	}
+}