Add check for leading backslash in Name ctor

Fixes #523.

CHANGELOG.md

@@ -8,6 +8,11 @@ Version 4.0.4-dev
   * `useConst()`
   * `var()`
   * `propertyFetch()`
+  
+### Changed
+
+* Passing a string with a leading backslash to the `Name` constructor will now throw an exception.
+  Most likely a use of `Name\FullyQualified` was intended.
 
 Version 4.0.3 (2018-07-15)
 --------------------------

lib/PhpParser/Node/Name.php

@@ -222,6 +222,10 @@ class Name extends NodeAbstract
                 throw new \InvalidArgumentException('Name cannot be empty');
             }
 
+            if ('\\' === $name[0]) {
+                throw new \InvalidArgumentException('Name cannot start with backslash. Did you mean to use Name\FullyQualified?');
+            }
+
             return explode('\\', $name);
         } elseif (\is_array($name)) {
             if (empty($name)) {

test/PhpParser/Node/NameTest.php

@@ -155,6 +155,14 @@ class NameTest extends TestCase
         new Name([]);
     }
 
+    /**
+     * @expectedException \InvalidArgumentException
+     * @expectedExceptionMessage Name cannot start with backslash. Did you mean to use Name\FullyQualified?
+     */
+    public function testInvalidLeadingBackslash() {
+        new Name('\Foo');
+    }
+
     /** @dataProvider provideTestIsSpecialClassName */
     public function testIsSpecialClassName($name, $expected) {
         $name = new Name($name);