正则表达式：选择内的反向引用

Question

I'm using TDD and I have to pass a set of tests to implement a new library:

public function providerEdgesParser()
{
    return array(
        array('.edges=(user)', false), // 0
        array('edges=test', false),
        array('another:chars', false),
        array('pl-ouf', false),
        array('test', array('test')),
        array('lang,lang', array('lang', 'lang')), // 5
        array('quest,ans', array('quest', 'ans')),
        array('q.edges=(a)', array('q' => array('a'))),
        array('e.edges=(lang,et.edges=(lang)),ans', array('e' => array('lang', 'et' => array('lang')), 'ans')),
    );
}

This is a PHPUnit provider. In each array, first element is the parameter of my function, second element is what my function must return. Here is this function I've come up with:

public function edgesParser($urlEdges)
{
      // Check if edges syntax is valid
      if (!preg_match('#^((?:(?:[a-z]+(?:\.edges\=\(\1\))?)\,?)+)$#ui', $urlEdges)) {
            throw new \Exception('Edges syntax is wrong');
      }

      // Then, use a recursive function to build the array
      // ...
      // ...
}

The only purpose of that regular expression is to detect bad syntax in the $urlEdges string, as it is an end user input. Only after, I will build the right array to return.

However, this regex doesn't seems to work the way I want: the two lastest tests throw an Exception. They should not.

I have been searching for a solution for a long time, but I just can't see where the regular expression is wrong. Here is a graphical representation of the regex . Could it back reference don't work when it's inside the referred group? Or did I make a trivial error that my tired eyes can't see?

Answer 1

@HamZa brought the answer.

\\1 back reference matchs what was matched in group 1.

(?1) recursive mask executes the pattern from group 1.

The second option is what I needed. So, a suitable regex could be: #^((?:(?:[az]+(?:\\.edges\\=\\((?1)\\))?)\\,?)+)$#ui (split up here ).