PSR2/ClassDeclaration: prevent fixer conflict with itself [2]

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

This led to a fixer conflict within the sniff, where the sniff would first add a newline between the `namespace` keyword and the namespace separator (`InterfaceSameLine` fixer) and in a subsequent loop would remove that same new line 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 `implements` check.

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

@@ -314,12 +314,14 @@ public function processOpen(File $phpcsFile, $stackPtr)
  if ($checkingImplements === true
  && $multiLineImplements === true
  && ($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))
  ) {
  $prev = $phpcsFile->findPrevious(
  [
  T_NS_SEPARATOR,
  T_WHITESPACE,
+ T_NAMESPACE,
  ],
  ($className - 1),
  $implements,

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

@@ -287,3 +287,9 @@ readonly
 interface FooBar extends namespace\BarFoo
 {
 }
+
+// Safeguard against fixer conflict when there are namespace relative interface names in a multi-line implements.
+class BarFoo implements
+ namespace\BarFoo
+{
+}

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

@@ -275,3 +275,9 @@ readonly
 interface FooBar extends namespace\BarFoo
 {
 }
+
+// Safeguard against fixer conflict when there are namespace relative interface names in a multi-line implements.
+class BarFoo implements
+ namespace\BarFoo
+{
+}