[BUG] Certain quantifier regex patterns erroneously fail to compile

[kuhushukla]

Describe the bug
A recent change in cudf regex parser return error for invalid quantifier per 575e944f777df0b904be0a8f1a9722ded0c045a6 fails some patterns that passed earlier that seem reasonable to pass in the first place.

Steps/Code to reproduce bug
Following tests fail :

 TEST_F(StringsContainsTests, custom_anynl)
    {
        std::string medium_regex = "(.|\\n)*";

        std::vector<const char*> h_strings{
            "hello"
        };
        cudf::test::strings_column_wrapper strings( h_strings.begin(), h_strings.end(),
            thrust::make_transform_iterator( h_strings.begin(), [] (auto str) { return str!=nullptr; }));

        auto strings_view = cudf::strings_column_view(strings);
        {
            auto results = cudf::strings::matches_re(strings_view, medium_regex);
            cudf::experimental::bool8 h_expected[] = {true};
            cudf::test::fixed_width_column_wrapper<cudf::experimental::bool8> expected( h_expected, h_expected+h_strings.size(),
                thrust::make_transform_iterator( h_strings.begin(), [] (auto str) { return str!=nullptr; }));
            cudf::test::expect_columns_equal(*results,expected);
        }
    }

    TEST_F(StringsContainsTests, dotStarWithBraces)
        {
            std::string medium_regex = "(.)*";

            std::vector<const char*> h_strings{
                "hello"
            };
            cudf::test::strings_column_wrapper strings( h_strings.begin(), h_strings.end(),
                thrust::make_transform_iterator( h_strings.begin(), [] (auto str) { return str!=nullptr; }));

            auto strings_view = cudf::strings_column_view(strings);
            {
                auto results = cudf::strings::matches_re(strings_view, medium_regex);
                cudf::experimental::bool8 h_expected[] = {true};
                cudf::test::fixed_width_column_wrapper<cudf::experimental::bool8> expected( h_expected, h_expected+h_strings.size(),
                    thrust::make_transform_iterator( h_strings.begin(), [] (auto str) { return str!=nullptr; }));
                cudf::test::expect_columns_equal(*results,expected);
            }
        }

they thorw

C++ exception with description "cuDF failure at: /home/kuhus/Reps/cudf/cpp/src/strings/regex/regcomp.cpp:504: invalid regex pattern: nothing to repeat at position 6" thrown in the test body.

and,

C++ exception with description "cuDF failure at: /home/kuhus/Reps/cudf/cpp/src/strings/regex/regcomp.cpp:504: invalid regex pattern: nothing to repeat at position 3" thrown in the test body.

respectively.
Expected behavior
These tests above passed before the change.

Environment overview (please complete the following information)
cudf 0.14 on Ubuntu 18.04

[davidwendt]

Another example with the same error and conditions:

>>> s = cudf.Series(["0.0.0.0", "5.79.97.178"])
>>> reg=r"^(100\.(6[4-9]|[7-9][0-9]|1([0-1][0-9]|2[0-7]))\.([0-9]|[1-9][0-9]|1([0-9][0-9])|2([0-4][0-9]|5[0-5]))\.([0-9]|[1-9][0-9]|1([0-9][0-9])|2([0-4][0-9]|5[0-5]))$)"
>>> s.str.match(reg)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/conda/envs/cudf/lib/python3.7/site-packages/cudf/core/column/string.py", line 1736, in match
    cpp_match_re(self._column, pat), **kwargs
  File "cudf/_libxx/strings/contains.pyx", line 67, in cudf._libxx.strings.contains.match_re
RuntimeError: cuDF failure at: /cudf/cpp/src/strings/regex/regcomp.cpp:504: invalid regex pattern: nothing to repeat at position 80

Also, I was able to reproduce with the minimal pattern of `r"(9)|2" so it looks like the ")" plus quantifier is causing the problem.