perf: fast-path for default Composer namespaces loading in Autoloader

When Config\Modules::$composerPackages has no filters defined (the default
behavior in almost all applications), all PSR-4 prefixes from Composer
belong to installed packages.

Skip the expensive InstalledVersions::getAllRawData() scanning, versions
array_merge, and triple-nested str_starts_with matching loop when neither
'only' nor 'exclude' is configured. When package filtering is configured,
the original full validation logic is preserved with zero BC breaks.

Author: gr8man

system/Autoloader/Autoloader.php

@@ -404,13 +404,37 @@ private function loadComposerNamespaces(ClassLoader $composer, array $composerPa
             }
         }
 
+        // Check config for $composerPackages.
+        $only    = $composerPackages['only'] ?? [];
+        $exclude = $composerPackages['exclude'] ?? [];
+
+        if ($only !== [] && $exclude !== []) {
+            throw new ConfigException('Cannot use "only" and "exclude" at the same time in "Config\Modules::$composerPackages".');
+        }
+
+        // When no package filtering is configured (the default), all PSR-4 prefixes
+        // from Composer can be added directly without expensive InstalledVersions scanning.
+        if ($only === [] && $exclude === []) {
+            $newPaths = [];
+
+            foreach ($namespacePaths as $namespace => $srcPaths) {
+                // Composer stores namespaces with trailing slash. We don't.
+                $newPaths[rtrim($namespace, '\\ ')] = $srcPaths;
+            }
+
+            $this->addNamespace($newPaths);
+
+            return;
+        }
+
         if (! method_exists(InstalledVersions::class, 'getAllRawData')) { // @phpstan-ignore function.alreadyNarrowedType
             throw new RuntimeException(
                 'Your Composer version is too old.'
                 . ' Please update Composer (run `composer self-update`) to v2.0.14 or later'
                 . ' and remove your vendor/ directory, and run `composer update`.',
             );
         }
+
         // This method requires Composer 2.0.14 or later.
         $allData     = InstalledVersions::getAllRawData();
         $packageList = [];
@@ -419,15 +443,9 @@ private function loadComposerNamespaces(ClassLoader $composer, array $composerPa
             $packageList = array_merge($packageList, $list['versions']);
         }
 
-        // Check config for $composerPackages.
-        $only    = $composerPackages['only'] ?? [];
-        $exclude = $composerPackages['exclude'] ?? [];
-        if ($only !== [] && $exclude !== []) {
-            throw new ConfigException('Cannot use "only" and "exclude" at the same time in "Config\Modules::$composerPackages".');
-        }
-
         // Get install paths of packages to add namespace for auto-discovery.
         $installPaths = [];
+
         if ($only !== []) {
             foreach ($packageList as $packageName => $data) {
                 if (in_array($packageName, $only, true) && isset($data['install_path'])) {

tests/system/Autoloader/AutoloaderTest.php

@@ -417,6 +417,26 @@ public function testFindsComposerRoutesWithComposerPathNotFound(): void
         $this->assertArrayNotHasKey('Laminas\\Escaper', $namespaces);
     }
 
+    public function testComposerPackagesDefaultLoadsAllNamespacesDirectly(): void
+    {
+        $config                      = new Autoload();
+        $config->psr4                = [];
+        $modules                     = new Modules();
+        $modules->discoverInComposer = true;
+        $modules->composerPackages   = [];
+
+        $loader = new Autoloader();
+        $loader->initialize($config, $modules);
+
+        $namespaces = $loader->getNamespace();
+
+        $this->assertArrayHasKey('Laminas\Escaper', $namespaces);
+        $this->assertArrayHasKey('Psr\Log', $namespaces);
+        $this->assertArrayNotHasKey('CodeIgniter', $namespaces);
+        $this->assertArrayNotHasKey(APP_NAMESPACE, $namespaces);
+        $this->assertArrayNotHasKey('Config', $namespaces);
+    }
+
     public function testAutoloaderLoadsNonClassFiles(): void
     {
         $config          = new Autoload();