Regression: link to user profile in comments block fails due to double URI encoding

There was a bug fix in MDL-28952 that was reintroduced by MDL-38431.

The comments block was outputting a double encoded URI for user's profile, which meant that the query parameters where ignored by profile.php, denying access to the resource.

The change in MDL-38431 seems as if it is intended to encode the URL safely by calling moodle_url->out(true). The problem occurs that later in the execution, html_writer::link() is called, which appears to encode the query parameters a second time.

The method where the second encoding occurs seems to be in outputcomponenets.php:

    public static function attribute($name, $value) {

        if ($value instanceof moodle_url) {

            return ' ' . $name . '="' . $value->out() . '"';

        }

        // special case, we do not want these in output

        if ($value === null) {

            return '';

        }

        // no sloppy trimming here!

        return ' ' . $name . '="' . s($value) . '"';

    }

If there is a string, the function s() is called, which calls htmlspecialchars(), which will encode the ampersand into &

function s($var) {

    if ($var === false) {

        return '0';

    }

    // When we move to PHP 5.4 as a minimum version, change ENT_QUOTES on the

    // next line to ENT_QUOTES | ENT_HTML5 | ENT_SUBSTITUTE, and remove the

    // 'UTF-8' argument. Both bring a speed-increase.

    return preg_replace('/&#(\d+|x[0-9a-f]+);/i', '&#$1;', htmlspecialchars($var, ENT_QUOTES, 'UTF-8'));

}

Passing in an object will cause html_writer::attribute() to call moodle_url->out(), which is how I fix this issue in my patch.