Fix phpstan/phpstan#9045: Narrowed template on interface ignored when generics not specified

- When a child interface narrows a template bound (e.g. `@template T of SpecificType`)
  and passes it to a parent via `@extends Parent<T>`, using the child without specifying
  generics now correctly resolves to the narrowed bound instead of the parent's wider bound
- Added `getActiveTemplateTypeMapForAncestorResolution()` in ClassReflection that resolves
  ErrorType entries to template bounds when the bound is not mixed
- Applied this resolution in both `getImmediateInterfaces()` and `getParentClass()`
- Updated bug-2676 test expectation: Collection's TKey now correctly resolves to
  `(int|string)` (array-key bound) instead of `mixed` when not explicitly specified
- New regression test in tests/PHPStan/Analyser/nsrt/bug-9045.php

Author: github-actions[bot]

src/Reflection/ClassReflection.php

@@ -48,6 +48,7 @@
 use PHPStan\Type\Generic\TemplateTypeVariance;
 use PHPStan\Type\Generic\TemplateTypeVarianceMap;
 use PHPStan\Type\Generic\TypeProjectionHelper;
+use PHPStan\Type\MixedType;
 use PHPStan\Type\ObjectType;
 use PHPStan\Type\Type;
 use PHPStan\Type\TypeAlias;
@@ -237,7 +238,7 @@ public function getParentClass(): ?ClassReflection
 			if ($this->isGeneric()) {
 				$extendedType = TemplateTypeHelper::resolveTemplateTypes(
 					$extendedType,
-					$this->getPossiblyIncompleteActiveTemplateTypeMap(),
+					$this->getActiveTemplateTypeMapForAncestorResolution(),
 					$this->getCallSiteVarianceMap(),
 					TemplateTypeVariance::createStatic(),
 				);
@@ -1164,7 +1165,7 @@ public function getImmediateInterfaces(): array
 				if ($this->isGeneric()) {
 					$implementedType = TemplateTypeHelper::resolveTemplateTypes(
 						$implementedType,
-						$this->getPossiblyIncompleteActiveTemplateTypeMap(),
+						$this->getActiveTemplateTypeMapForAncestorResolution(),
 						$this->getCallSiteVarianceMap(),
 						TemplateTypeVariance::createStatic(),
 						true,
@@ -1686,6 +1687,37 @@ public function getPossiblyIncompleteActiveTemplateTypeMap(): TemplateTypeMap
 		return $this->resolvedTemplateTypeMap ?? $this->getTemplateTypeMap();
 	}
 
+	/**
+	 * Returns a template type map for resolving ancestor type declarations (@extends, @implements).
+	 * Like getPossiblyIncompleteActiveTemplateTypeMap(), but resolves ErrorType entries
+	 * to their template bounds when the bound is not mixed. This ensures that when a child
+	 * class narrows a template bound (e.g. `@template T of SpecificType`), the narrowed bound
+	 * is propagated to ancestor declarations instead of being lost as ErrorType.
+	 */
+	private function getActiveTemplateTypeMapForAncestorResolution(): TemplateTypeMap
+	{
+		$map = $this->getPossiblyIncompleteActiveTemplateTypeMap();
+		$templateTypeMap = $this->getTemplateTypeMap();
+
+		return $map->map(static function (string $name, Type $type) use ($templateTypeMap): Type {
+			if (!$type instanceof ErrorType) {
+				return $type;
+			}
+
+			$templateType = $templateTypeMap->getType($name);
+			if (!$templateType instanceof TemplateType) {
+				return $type;
+			}
+
+			$bound = $templateType->getBound();
+			if ($bound instanceof MixedType) {
+				return $type;
+			}
+
+			return TemplateTypeHelper::resolveToDefaults($templateType);
+		});
+	}
+
 	private function getDefaultCallSiteVarianceMap(): TemplateTypeVarianceMap
 	{
 		if ($this->defaultCallSiteVarianceMap !== null) {

tests/PHPStan/Analyser/nsrt/bug-2676.php

@@ -39,7 +39,7 @@ function (Wallet $wallet): void
 	assertType('DoctrineIntersectionTypeIsSupertypeOf\Collection&iterable<Bug2676\BankAccount>', $bankAccounts);
 
 	foreach ($bankAccounts as $key => $bankAccount) {
-		assertType('mixed', $key);
+		assertType('(int|string)', $key);
 		assertType('Bug2676\BankAccount', $bankAccount);
 	}
 };

tests/PHPStan/Analyser/nsrt/bug-9045.php

@@ -0,0 +1,32 @@
+<?php declare(strict_types = 1);
+
+namespace Bug9045;
+
+use function PHPStan\Testing\assertType;
+
+interface TranslationInterface {}
+interface TransportTranslationInterface extends TranslationInterface {
+    public function getAdditionalInformation(): ?string;
+}
+
+/**
+ * @template T of TransportTranslationInterface
+ * @extends TranslatableInterface<T>
+ */
+interface TransportInterface extends TranslatableInterface {}
+
+/**
+ * @template T of TranslationInterface
+ */
+interface TranslatableInterface
+{
+    /** @phpstan-return T */
+    public function getTranslation(): TranslationInterface;
+}
+
+class Foo {
+	public function bar(TransportInterface $transport): void {
+		assertType('Bug9045\TransportTranslationInterface', $transport->getTranslation());
+		$transport->getTranslation()->getAdditionalInformation();
+	}
+}