PSR2/ClassDeclaration: prevent fixer conflict with itself [1]

While the `PSR2.Classes.ClassDeclaration` sniff did take partially/fully qualified names into account for interfaces being extended, it did not take _namespace relative_ interface name into account.

This led to a fixer conflict within the sniff, where the sniff would first add a space between the `namespace` keyword and the namespace separator (`SpaceBeforeName` fixer) and in a subsequent loop would remove that same space again as it would think it was a space before a comma (`SpaceBeforeComma` fixer).

Fixed now by adding support for namespace relative interface names in the `extends` checks.

Includes unit test.

Related to 152

Note: at a glance, this sniff could probably do with a more thorough review and more defensive token walking/more precise checking, but that's outside the scope of this PR.

src/Standards/PSR2/Sniffs/Classes/ClassDeclarationSniff.php

@@ -397,9 +397,10 @@ public function processOpen(File $phpcsFile, $stackPtr)
  }
  }//end if
  } else if ($tokens[($className - 1)]['code'] !== T_NS_SEPARATOR
- || $tokens[($className - 2)]['code'] !== T_STRING
+ || ($tokens[($className - 2)]['code'] !== T_STRING
+ && $tokens[($className - 2)]['code'] !== T_NAMESPACE)
  ) {
- // Not part of a longer fully qualified class name.
+ // Not part of a longer fully qualified or namespace relative class name.
  if ($tokens[($className - 1)]['code'] === T_COMMA
  || ($tokens[($className - 1)]['code'] === T_NS_SEPARATOR
  && $tokens[($className - 2)]['code'] === T_COMMA)

src/Standards/PSR2/Tests/Classes/ClassDeclarationUnitTest.inc

@@ -282,3 +282,8 @@ readonly
  class ReadonlyClassWithComment
  {
  }
+
+// Safeguard against fixer conflict when there are namespace relative interface names in extends.
+interface FooBar extends namespace\BarFoo
+{
+}

src/Standards/PSR2/Tests/Classes/ClassDeclarationUnitTest.inc.fixed

@@ -270,3 +270,8 @@ readonly
  class ReadonlyClassWithComment
  {
  }
+
+// Safeguard against fixer conflict when there are namespace relative interface names in extends.
+interface FooBar extends namespace\BarFoo
+{
+}