Fix PHPStan issues

Changed:
- `AbstractConfig::__construct()` to merge Traversable rather than ConfigInterface
- Rewrite exception message thrown by `AbstractConfig::__construct()`
- Update unit tests to validate support for Traversable objects

Fixed:
- Parameter comments for `AbstractConfig::__construct()`
- Parameter comments for `AbstractConfig::merge()`

src/Charcoal/Config/AbstractConfig.php

@@ -43,8 +43,9 @@ abstract class AbstractConfig extends AbstractEntity implements
     /**
      * Create the configuration.
      *
-     * @param  mixed             $data      Initial data. Either a filepath, a datamap, or a Config object.
-     * @param  ConfigInterface[] $delegates An array of delegates (config) to set.
+     * @param  mixed             $data      Initial data. Either a filepath,
+     *     an associative array, or an {@see Traversable iterable object}.
+     * @param  EntityInterface[] $delegates An array of delegates (config) to set.
      * @throws InvalidArgumentException If $data is invalid.
      */
     final public function __construct($data = null, array $delegates = null)
@@ -69,12 +70,12 @@ final public function __construct($data = null, array $delegates = null)
             $this->addFile($data);
         } elseif (is_array($data)) {
             $this->merge($data);
-        } elseif ($data instanceof ConfigInterface) {
+        } elseif ($data instanceof Traversable) {
             $this->merge($data);
         } else {
             throw new InvalidArgumentException(sprintf(
-                'Data must be an associative array, a file path, or an instance of %s',
-                ConfigInterface::class
+                'Data must be a config file, an associative array, or an object implementing %s',
+                Traversable::class
             ));
         }
     }
@@ -96,11 +97,10 @@ public function defaults()
     /**
      * Adds new data, replacing / merging existing data with the same key.
      *
-     * The provided `$data` can be a simple array or an object which implements `Traversable`
-     * (such as a `ConfigInterface` instance).
-     *
      * @uses   self::offsetReplace()
-     * @param  array|Traversable|ConfigInterface $data Key-value array of data to merge.
+     * @param  array|Traversable $data Key-value dataset to merge.
+     *     Either an associative array or an {@see Traversable iterable object}
+     *     (such as {@see ConfigInterface}).
      * @return self
      */
     public function merge($data)

tests/Charcoal/Config/ConfigTest.php

@@ -3,7 +3,7 @@
 namespace Charcoal\Tests\Config;
 
 use StdClass;
-use Iterator;
+use ArrayIterator;
 use IteratorAggregate;
 use InvalidArgumentException;
 
@@ -65,7 +65,7 @@ public function testPsr11()
     public function testIteratorAggregate()
     {
         $this->assertInstanceOf(IteratorAggregate::class, $this->cfg);
-        $this->assertInstanceOf(Iterator::class, $this->cfg->getIterator());
+        $this->assertInstanceOf(ArrayIterator::class, $this->cfg->getIterator());
     }
 
     /**
@@ -92,10 +92,24 @@ public function testConstructWithConfigInstance()
         $this->assertEquals('garply', $cfg['baz']);
     }
 
+    /**
+     * @covers ::__construct
+     * @covers ::merge
+     * @return void
+     */
+    public function testConstructWithTraversableInstance()
+    {
+        $iter = new ArrayIterator([
+            'name' => 'Charcoal'
+        ]);
+        $cfg  = $this->mockConfig($iter);
+        $this->assertEquals('Charcoal', $cfg['name']);
+    }
+
     /**
      * @expectedException        InvalidArgumentException
-     * @expectedExceptionMessage Data must be an associative array, a file path,
-     *     or an instance of Charcoal\Config\ConfigInterface
+     * @expectedExceptionMessage Data must be a config file, an associative array,
+     *     or an object implementing Traversable
      *
      * @covers ::__construct
      * @covers ::merge