Represent empty Name::slice() using null

Instead of a Name([]) dummy value, that is invalid in other
contexts.

lib/PhpParser/Node/Name.php

@@ -104,15 +104,15 @@ class Name extends NodeAbstract
      * This method returns a new instance of the same type as the original and with the same
      * attributes.
      *
-     * If the slice is empty, a Name with an empty parts array is returned. While this is
+     * If the slice is empty, null is returned. The null value will be correctly handled in
-     * meaningless in itself, it works correctly in conjunction with concat().
+     * concatenations using concat().
      *
      * Offset and length have the same meaning as in array_slice().
      *
      * @param int      $offset Offset to start the slice at (may be negative)
      * @param int|null $length Length of the slice (may be negative)
      *
-     * @return static Sliced name
+     * @return static|null Sliced name
      */
     public function slice($offset, $length = null) {
         $numParts = count($this->parts);
@@ -131,6 +131,11 @@ class Name extends NodeAbstract
             }
         }
 
+        if ($realLength === 0) {
+            // Empty slice is represented as null
+            return null;
+        }
+
         return new static(array_slice($this->parts, $realOffset, $realLength), $this->attributes);
     }
 
@@ -140,16 +145,29 @@ class Name extends NodeAbstract
      * The type of the generated instance depends on which class this method is called on, for
      * example Name\FullyQualified::concat() will yield a Name\FullyQualified instance.
      *
-     * @param string|array|self $name1      The first name
+     * If one of the arguments is null, a new instance of the other name will be returned. If both
-     * @param string|array|self $name2      The second name
+     * arguments are null, null will be returned. As such, writing
-     * @param array             $attributes Attributes to assign to concatenated name
+     *     Name::concat($namespace, $shortName)
+     * where $namespace is a Name node or null will work as expected.
      *
-     * @return static Concatenated name
+     * @param string|array|self|null $name1      The first name
+     * @param string|array|self|null $name2      The second name
+     * @param array                  $attributes Attributes to assign to concatenated name
+     *
+     * @return static|null Concatenated name
      */
     public static function concat($name1, $name2, array $attributes = []) {
-        return new static(
+        if (null === $name1 && null === $name2) {
-            array_merge(self::prepareName($name1), self::prepareName($name2)), $attributes
+            return null;
-        );
+        } elseif (null === $name1) {
+            return new static(self::prepareName($name2), $attributes);
+        } else if (null === $name2) {
+            return new static(self::prepareName($name1), $attributes);
+        } else {
+            return new static(
+                array_merge(self::prepareName($name1), self::prepareName($name2)), $attributes
+            );
+        }
     }
 
     /**

lib/PhpParser/NodeVisitor/NameResolver.php

@@ -195,12 +195,8 @@ class NameResolver extends NodeVisitorAbstract
             return FullyQualified::concat($alias, $name->slice(1), $name->getAttributes());
         }
 
-        if (null !== $this->namespace) {
+        // if no alias exists prepend current namespace
-            // if no alias exists prepend current namespace
+        return FullyQualified::concat($this->namespace, $name, $name->getAttributes());
-            return FullyQualified::concat($this->namespace, $name, $name->getAttributes());
-        }
-
-        return new FullyQualified($name, $name->getAttributes());
     }
 
     protected function resolveOtherName(Name $name, $type) {
@@ -239,19 +235,11 @@ class NameResolver extends NodeVisitorAbstract
             return $name;
         }
 
-        if (null !== $this->namespace) {
+        // if no alias exists prepend current namespace
-            // if no alias exists prepend current namespace
+        return FullyQualified::concat($this->namespace, $name, $name->getAttributes());
-            return FullyQualified::concat($this->namespace, $name, $name->getAttributes());
-        }
-
-        return new FullyQualified($name, $name->getAttributes());
     }
 
     protected function addNamespacedName(Node $node) {
-        if (null !== $this->namespace) {
+        $node->namespacedName = Name::concat($this->namespace, $node->name);
-            $node->namespacedName = Name::concat($this->namespace, $node->name);
-        } else {
-            $node->namespacedName = new Name($node->name);
-        }
     }
 }

test/PhpParser/Node/NameTest.php

@@ -36,16 +36,16 @@ class NameTest extends \PHPUnit_Framework_TestCase
         $name = new Name('foo\bar\baz');
         $this->assertEquals(new Name('foo\bar\baz'), $name->slice(0));
         $this->assertEquals(new Name('bar\baz'), $name->slice(1));
-        $this->assertEquals(new Name([]), $name->slice(3));
+        $this->assertNull($name->slice(3));
         $this->assertEquals(new Name('foo\bar\baz'), $name->slice(-3));
         $this->assertEquals(new Name('bar\baz'), $name->slice(-2));
         $this->assertEquals(new Name('foo\bar'), $name->slice(0, -1));
-        $this->assertEquals(new Name([]), $name->slice(0, -3));
+        $this->assertNull($name->slice(0, -3));
         $this->assertEquals(new Name('bar'), $name->slice(1, -1));
-        $this->assertEquals(new Name([]), $name->slice(1, -2));
+        $this->assertNull($name->slice(1, -2));
         $this->assertEquals(new Name('bar'), $name->slice(-2, 1));
         $this->assertEquals(new Name('bar'), $name->slice(-2, -1));
-        $this->assertEquals(new Name([]), $name->slice(-2, -2));
+        $this->assertNull($name->slice(-2, -2));
     }
 
     /**
@@ -93,8 +93,9 @@ class NameTest extends \PHPUnit_Framework_TestCase
             Name\Relative::concat(new Name\FullyQualified('foo\bar'), 'baz', $attributes)
         );
 
-        $this->assertEquals(new Name('foo'), Name::concat([], 'foo'));
+        $this->assertEquals(new Name('foo'), Name::concat(null, 'foo'));
-        $this->assertEquals(new Name([]), Name::concat([], []));
+        $this->assertEquals(new Name('foo'), Name::concat('foo', null));
+        $this->assertNull(Name::concat(null, null));
     }
 
     public function testIs() {