re.error in raw escape string marked succeed

[sarnold]

This is "new" behavior as of py311, possibly earlier. Behavior is the same with built-in re.

$ python
Python 3.11.9 (main, May 26 2024, 09:54:30) [GCC 13.2.1 20240503] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> import re2 as re
>>> obj = re.compile(r'(?<!\\\):(.*?)(?<!\\\):')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "compile.pxi", line 6, in re2.compile
  File "compile.pxi", line 96, in re2._compile
  File "pattern.pxi", line 607, in re2.PythonRePattern.__init__
  File "/usr/lib/python3.11/re/__init__.py", line 227, in compile
    return _compile(pattern, flags)
           ^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/re/__init__.py", line 294, in _compile
    p = _compiler.compile(pattern, flags)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/re/_compiler.py", line 745, in compile
    p = _parser.parse(p, flags)
        ^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/re/_parser.py", line 989, in parse
    p = _parse_sub(source, state, flags & SRE_FLAG_VERBOSE, 0)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/re/_parser.py", line 464, in _parse_sub
    itemsappend(_parse(source, state, verbose, nested + 1,
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/re/_parser.py", line 779, in _parse
    p = _parse_sub(source, state, verbose, nested + 1)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/re/_parser.py", line 464, in _parse_sub
    itemsappend(_parse(source, state, verbose, nested + 1,
                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/lib/python3.11/re/_parser.py", line 784, in _parse
    raise source.error("missing ), unterminated subpattern",
re.error: missing ), unterminated subpattern at position 14
>>> obj = re.compile(r'(?<!\\):(.*?)(?<!\\):')
>>>