Validators: allow pipe character inside a pattern: regular expression

[dualfroz]

Problem

Validators::is() crashes on a valid pattern that contains a pipe:

Validators::is('a', 'pattern:(a|b)');
// Nette\Utils\RegexpException: Compilation failed: missing closing parenthesis
// at offset 4 in pattern: |^(a$|D

The call should simply return true. This has been reported and confirmed valid
in #206.

Root cause (two intertwined parsing bugs)

src/Utils/Validators.php, method is():

1. Spec splitting (was line ~140): explode('|', $expected) splits the whole
   expression on every |. It is meant to separate combined validators
   (int|string), but it also tears a regular expression apart, so
   pattern:(a|b) becomes the two tokens pattern:(a and b).

2. PCRE delimiter collision (was line ~164):
   Strings::match($value, '|^' . $pattern . '$|D') uses | as the PCRE
   delimiter. Even without bug 1, any | in the user pattern would prematurely
   close the delimiter and produce an invalid regex.

Together they turn a valid pattern into |^(a$|D, which fails to compile and
throws RegexpException.

Fix

• A pattern: argument now consumes the remaining part of the expression, so the
  pipes it contains are no longer treated as the validator separator. Combined
  forms such as int|pattern:(a|b) keep working because the pipe-as-OR semantics
  are preserved for every non-pattern validator.
• The PCRE delimiter is changed from | to ~, which does not collide with the
  common alternation metacharacter. The pattern is additionally wrapped in a
  non-capturing group ^(?:...)$ so a bare alternation (pattern:a|b) is
  anchored as a whole instead of being read as (^a)|(b$).

The int|string, pattern:\d+ and empty pattern cases are unchanged.