Fix false positive invariance check for template types with same identity

- TemplateMixedType and TemplateStrictMixedType with same scope+name represent
  the same template parameter but fail equals() due to different concrete classes
- At level 9+ transformCommonType converts TemplateMixedType to
  TemplateStrictMixedType in accepting type but not in accepted closure params
- Added fallback check in isValidVariance() for invariant templates: if both
  sides are TemplateType with matching scope and name, treat as equal
- New regression test in tests/PHPStan/Rules/Classes/data/bug-13440.php

Closes phpstan/phpstan#13440

Author: github-actions[bot]

src/Type/Generic/TemplateTypeVariance.php

@@ -177,6 +177,15 @@ public function isValidVariance(TemplateType $templateType, Type $a, Type $b): I
 
 		if ($this->invariant()) {
 			$result = $a->equals($b);
+			if (
+				!$result
+				&& $a instanceof TemplateType
+				&& $b instanceof TemplateType
+				&& $a->getScope()->equals($b->getScope())
+				&& $a->getName() === $b->getName()
+			) {
+				$result = true;
+			}
 			$reasons = [];
 			if (!$result) {
 				if (

tests/PHPStan/Rules/Classes/InstantiationRuleTest.php

@@ -20,14 +20,16 @@
 class InstantiationRuleTest extends RuleTestCase
 {
 
+	private bool $checkExplicitMixed = false;
+
 	protected function getRule(): Rule
 	{
 		$reflectionProvider = self::createReflectionProvider();
 		$container = self::getContainer();
 		return new InstantiationRule(
 			$container,
 			$reflectionProvider,
-			new FunctionCallParametersCheck(new RuleLevelHelper($reflectionProvider, true, false, true, false, false, false, true), new NullsafeCheck(), new UnresolvableTypeHelper(), new PropertyReflectionFinder(), $reflectionProvider, true, true, true, true),
+			new FunctionCallParametersCheck(new RuleLevelHelper($reflectionProvider, true, false, true, $this->checkExplicitMixed, false, false, true), new NullsafeCheck(), new UnresolvableTypeHelper(), new PropertyReflectionFinder(), $reflectionProvider, true, true, true, true),
 			new ClassNameCheck(
 				new ClassCaseSensitivityCheck($reflectionProvider, true),
 				new ClassForbiddenNameCheck($container),
@@ -570,6 +572,13 @@ public function testBug14097(): void
 		$this->analyse([__DIR__ . '/data/bug-14097.php'], []);
 	}
 
+	#[RequiresPhp('>= 8.0')]
+	public function testBug13440(): void
+	{
+		$this->checkExplicitMixed = true;
+		$this->analyse([__DIR__ . '/data/bug-13440.php'], []);
+	}
+
 	public function testNewStaticWithConsistentConstructor(): void
 	{
 		$this->analyse([__DIR__ . '/data/instantiation-new-static-consistent-constructor.php'], [

tests/PHPStan/Rules/Classes/data/bug-13440.php

@@ -0,0 +1,37 @@
+<?php // lint >= 8.0
+
+declare(strict_types = 1);
+
+namespace Bug13440;
+
+use Closure;
+
+/** @template T */
+interface Foo {}
+
+/**
+ * @template TVal
+ * @template TReturn
+ */
+class Box
+{
+    /**
+     * @param TVal $val
+     * @param Closure(Foo<TVal>): TReturn $cb
+     */
+    public function __construct(
+        private mixed $val,
+        private Closure $cb,
+    ) {
+    }
+
+    /**
+     * @template TNewReturn
+     * @param Closure(Foo<TVal>): TNewReturn $cb
+     * @return self<TVal, TNewReturn>
+     */
+    public function test(Closure $cb): self
+    {
+        return new self($this->val, $cb);
+    }
+}