Fix calling method statically on string

src/Analyser/MutatingScope.php

@@ -2235,10 +2235,21 @@ private function resolveType(Expr $node): Type
 				if ($node->class instanceof Name) {
 					$staticMethodCalledOnType = $this->resolveTypeByName($node->class);
 				} else {
-					$staticMethodCalledOnType = $this->getType($node->class);
-					if ($staticMethodCalledOnType instanceof GenericClassStringType) {
-						$staticMethodCalledOnType = $staticMethodCalledOnType->getGenericType();
-					}
+					$staticMethodCalledOnType = TypeTraverser::map($this->getType($node->class), static function (Type $type, callable $traverse): Type {
+						if ($type instanceof UnionType) {
+							return $traverse($type);
+						}
+
+						if ($type instanceof GenericClassStringType) {
+							return $type->getGenericType();
+						}
+
+						if ($type instanceof ConstantStringType && $type->isClassString()) {
+							return new ObjectType($type->getValue());
+						}
+
+						return $type;
+					});
 				}
 
 				$returnType = $this->methodCallReturnType(

tests/PHPStan/Analyser/NodeScopeResolverTest.php

@@ -609,6 +609,7 @@ public function dataFileAsserts(): iterable
 
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/weird-array_key_exists-issue.php');
 		yield from $this->gatherAssertTypes(__DIR__ . '/data/equal.php');
+		yield from $this->gatherAssertTypes(__DIR__ . '/data/bug-6404.php');
 	}
 
 	/**

tests/PHPStan/Analyser/data/bug-6404.php

@@ -0,0 +1,85 @@
+<?php
+
+namespace Bug6404;
+
+
+use function PHPStan\Testing\assertType;
+
+class Foo
+{
+	public static function getCode(): int
+	{
+		return 1;
+	}
+}
+
+class Bar
+{
+	private const FOOS = [
+		Foo::class,
+	];
+
+	/**
+	 * @var array<int, bool>
+	 */
+	private array $someMap = [];
+
+	public function build(): void
+	{
+		foreach (self::FOOS as $fooClass) {
+			if (is_a($fooClass, Foo::class, true)) {
+				assertType("'Bug6404\\\\Foo'", $fooClass);
+				assertType('int', $fooClass::getCode());
+				$this->someMap[$fooClass::getCode()] = true;
+			}
+		}
+	}
+
+	/**
+	 * @param object[] $objects
+	 * @return void
+	 */
+	public function build2(array $objects): void
+	{
+		foreach ($objects as $fooClass) {
+			if (is_a($fooClass, Foo::class)) {
+				assertType(Foo::class, $fooClass);
+				assertType('int', $fooClass::getCode());
+				$this->someMap[$fooClass::getCode()] = true;
+			}
+		}
+	}
+
+	/**
+	 * @param mixed[] $mixeds
+	 * @return void
+	 */
+	public function build3(array $mixeds): void
+	{
+		foreach ($mixeds as $fooClass) {
+			if (is_a($fooClass, Foo::class, true)) {
+				assertType('Bug6404\\Foo|class-string<Bug6404\\Foo>', $fooClass);
+				assertType('int', $fooClass::getCode());
+				$this->someMap[$fooClass::getCode()] = true;
+			}
+		}
+	}
+
+	/**
+	 * @param class-string<Foo> $classString
+	 * @return void
+	 */
+	public function doBar(string $classString): void
+	{
+		assertType("class-string<" . Foo::class . ">", $classString);
+		assertType('int', $classString::getCode());
+	}
+
+	/**
+	 * @return array<int, bool>
+	 */
+	public function getAll(): array
+	{
+		return $this->someMap;
+	}
+}