Fix phpstan/phpstan#10076: Union of string literal and class-string<T> loses literal members

- GenericClassStringType::isSuperTypeOf() returned Yes for non-class-string
  constants when the generic type was MixedType (including TemplateMixedType)
- This caused TypeCombinator::union to absorb string literals like 'object'
  and 'array' into class-string<T>, losing them from the union
- Added a check: when generic type is MixedType but the constant string is
  not a class-string, return Maybe instead of Yes
- New regression test in tests/PHPStan/Rules/Functions/data/bug-10076.php

Author: github-actions[bot]

src/Type/Generic/GenericClassStringType.php

@@ -94,6 +94,9 @@ public function isSuperTypeOf(Type $type): IsSuperTypeOfResult
 		if ($type instanceof ConstantStringType) {
 			$genericType = $this->type;
 			if ($genericType instanceof MixedType) {
+				if (!$type->isClassString()->yes()) {
+					return IsSuperTypeOfResult::createMaybe();
+				}
 				return IsSuperTypeOfResult::createYes();
 			}
 

tests/PHPStan/Rules/Functions/CallToFunctionParametersRuleTest.php

@@ -2817,4 +2817,9 @@ public function testBug14312b(): void
 		$this->analyse([__DIR__ . '/data/bug-14312b.php'], []);
 	}
 
+	public function testBug10076(): void
+	{
+		$this->analyse([__DIR__ . '/data/bug-10076.php'], []);
+	}
+
 }

tests/PHPStan/Rules/Functions/data/bug-10076.php

@@ -0,0 +1,20 @@
+<?php
+
+namespace Bug10076;
+
+/**
+ * @template T
+ *
+ * @param 'object'|'array'|class-string<T> $type
+ *
+ * @return list<mixed>
+ */
+function result($type = 'object'): array
+{
+	return [];
+}
+
+result();
+result('object');
+result('array');
+result(\DateTime::class);