[Php] Fix filter cache on PolyfillPackagesProvider

phpstan.neon

@@ -534,4 +534,4 @@ parameters:
             message: '#Parameters should use "PhpParser\\Node\\Stmt\\ClassMethod" types as the only types passed to this method#'
 
         # known enum from strings
-        - '#Method Rector\\Core\\Php\\PolyfillPackagesProvider\:\:filterPolyfillPackages\(\) should return array(.*?) but returns array<string, string>#'
+        - '#Method Rector\\Core\\Php\\PolyfillPackagesProvider\:\:filterPolyfillPackages\(\) should return array\<.*\> but returns array<int, non\-falsy\-string>#'

src/Php/PolyfillPackagesProvider.php

@@ -13,12 +13,12 @@
 final class PolyfillPackagesProvider
 {
     /**
-     * @var array<PolyfillPackage::*>
+     * @var null|array<int, PolyfillPackage::*>
      */
-    private array $cachedPolyfillPackages = [];
+    private null|array $cachedPolyfillPackages = null;
 
     /**
-     * @return array<PolyfillPackage::*>
+     * @return array<int, PolyfillPackage::*>
      */
     public function provide(): array
     {
@@ -27,12 +27,14 @@ public function provide(): array
             return SimpleParameterProvider::provideArrayParameter(Option::POLYFILL_PACKAGES);
         }
 
-        $projectComposerJson = getcwd() . '/composer.json';
-        if (! file_exists($projectComposerJson)) {
-            return [];
+        // already cached, even only empty array
+        if ($this->cachedPolyfillPackages !== null) {
+            return $this->cachedPolyfillPackages;
         }
 
-        if ($this->cachedPolyfillPackages !== []) {
+        $projectComposerJson = getcwd() . '/composer.json';
+        if (! file_exists($projectComposerJson)) {
+            $this->cachedPolyfillPackages = [];
             return $this->cachedPolyfillPackages;
         }
 
@@ -46,11 +48,11 @@ public function provide(): array
 
     /**
      * @param array<string, string> $require
-     * @return array<PolyfillPackage::*>
+     * @return array<int, PolyfillPackage::*>
      */
     private function filterPolyfillPackages(array $require): array
     {
-        return array_filter($require, static fn (string $packageName): bool => ! str_starts_with(
+        return array_filter(array_keys($require), static fn (string $packageName): bool => str_starts_with(
             $packageName,
             'symfony/polyfill-'
         ));