refactor: extract shared mergeTwo() to eliminate duplication

- Make ProviderConfig::mergeTwo() public static so ConfigFactory can use it
- Remove duplicate mergeTwo() implementation from ConfigFactory (32 lines)
- Add test verifying mergeTwo() works as public API
- Update docblocks to reflect the shared architecture

Both classes now use identical merge semantics from a single source of truth.

Author: binaryfire

src/config/src/ConfigFactory.php

@@ -26,7 +26,7 @@ public function __invoke(ContainerInterface $container)
         $allConfigs = [ProviderConfig::load(), $rootConfig, ...$autoloadConfig];
         $merged = array_reduce(
             array_slice($allConfigs, 1),
-            [$this, 'mergeTwo'],
+            ProviderConfig::mergeTwo(...),
             $allConfigs[0]
         );
 
@@ -63,37 +63,4 @@ private function readPaths(array $paths, array $excludes = []): array
 
         return $configs;
     }
-
-    /**
-     * Merge two config arrays.
-     *
-     * Correctly handles:
-     * - Pure lists (numeric keys): appends values with deduplication
-     * - Associative arrays (string keys): recursively merges, later wins for scalars
-     * - Mixed arrays (e.g. listeners with priorities): appends numeric, merges string keys
-     */
-    private function mergeTwo(array $base, array $override): array
-    {
-        $result = $base;
-
-        foreach ($override as $key => $value) {
-            if (is_int($key)) {
-                // Numeric key - append if not already present (deduplicate)
-                if (! in_array($value, $result, true)) {
-                    $result[] = $value;
-                }
-            } elseif (! array_key_exists($key, $result)) {
-                // New string key - just add it
-                $result[$key] = $value;
-            } elseif (is_array($value) && is_array($result[$key])) {
-                // Both are arrays - recursively merge
-                $result[$key] = $this->mergeTwo($result[$key], $value);
-            } else {
-                // Scalar or mixed types - override wins
-                $result[$key] = $value;
-            }
-        }
-
-        return $result;
-    }
 }

src/config/src/ProviderConfig.php

@@ -132,8 +132,17 @@ protected static function merge(...$arrays): array
 
     /**
      * Merge two config arrays.
+     *
+     * Correctly handles:
+     * - Pure lists (numeric keys): appends values with deduplication
+     * - Associative arrays (string keys): recursively merges, later wins for scalars
+     * - Mixed arrays (e.g. listeners with priorities): appends numeric, merges string keys
+     *
+     * This method is public so ConfigFactory can use the same merge semantics.
+     *
+     * @return array<string, mixed>
      */
-    private static function mergeTwo(array $base, array $override): array
+    public static function mergeTwo(array $base, array $override): array
     {
         $result = $base;
 

tests/Config/ConfigFactoryTest.php

@@ -177,10 +177,11 @@ public function testMergeMultipleConfigArrays(): void
     }
 
     /**
-     * Use ProviderConfig::merge() since ConfigFactory uses the same merge logic.
+     * Simulate ConfigFactory's merge behavior using ProviderConfig::merge().
      *
-     * Both ConfigFactory and ProviderConfig need identical merge semantics,
-     * so we test the shared behavior via ProviderConfig's merge method.
+     * ConfigFactory uses ProviderConfig::mergeTwo() directly for merging.
+     * We test via ProviderConfig::merge() which uses the same mergeTwo() method
+     * internally, ensuring identical merge semantics.
      */
     private function mergeConfigs(array ...$configs): array
     {

tests/Config/ProviderConfigTest.php

@@ -710,6 +710,50 @@ public function testMergeMixedDependencies(): void
         $this->assertSame('SmtpMailer', $result['dependencies']['MailerInterface']);
     }
 
+    /**
+     * Test that mergeTwo() is callable as a public static method.
+     *
+     * This method is public so ConfigFactory can use the same merge semantics
+     * without duplicating the implementation.
+     */
+    public function testMergeTwoIsPublicAndWorksDirectly(): void
+    {
+        $base = [
+            'commands' => ['CommandA', 'CommandB'],
+            'database' => [
+                'default' => 'sqlite',
+                'connections' => [
+                    'sqlite' => ['driver' => 'sqlite'],
+                ],
+            ],
+        ];
+
+        $override = [
+            'commands' => ['CommandC'],
+            'database' => [
+                'default' => 'pgsql',
+                'connections' => [
+                    'pgsql' => ['driver' => 'pgsql', 'host' => 'localhost'],
+                ],
+            ],
+        ];
+
+        // Call directly without reflection - this verifies it's public
+        $result = ProviderConfig::mergeTwo($base, $override);
+
+        // Numeric arrays are combined
+        $this->assertSame(['CommandA', 'CommandB', 'CommandC'], $result['commands']);
+
+        // Scalar values are overridden
+        $this->assertSame('pgsql', $result['database']['default']);
+
+        // Nested arrays are merged recursively
+        $this->assertArrayHasKey('sqlite', $result['database']['connections']);
+        $this->assertArrayHasKey('pgsql', $result['database']['connections']);
+        $this->assertSame('sqlite', $result['database']['connections']['sqlite']['driver']);
+        $this->assertSame('pgsql', $result['database']['connections']['pgsql']['driver']);
+    }
+
     /**
      * Call the protected merge method via reflection.
      */