[BUGFIX] Replace STL regex with Boost for MinGW bug

[andrjohns]

Submission Checklist

• Run unit tests: ./runTests.py src/test/unit
• Run cpplint: make cpplint
• Declare copyright holder and open-source license: see below

Summary

Depending on the user's locale, using std::regex with the MinGW GCC in RTools will result in a memory leak and the program hangs.

This has previously been reported as bug to MinGW here, but it is still an issue.

For Stan, this can cause a hang when parsing JSON data (seen recently as the cause of this downstream issue). We can instead use the Boost Regex headers as a drop-in replacement, which I've verified resolve the issue.

Intended Effect

Avoid hanging under certain locales

How to Verify

Side Effects

N/A

Documentation

N/A

Copyright and Licensing

Please list the copyright holder for the work you are submitting (this will be you or your assignee, such as a university or company): Andrew Johnson

By submitting this pull request, the copyright holder is agreeing to license the submitted work under the following licenses:

• Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
• Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

[andrjohns]

GCC bug listing here as well: https://gcc.gnu.org/bugzilla/show_bug.cgi?id=98723

[WardBrian]

I think we would be fine to include this in a 2.34.1 if we end up needing one, so it should be good to merge now.

Thanks!

[andrjohns]

Awkward, but it looks like I don't have permissions for stan:

Can I get a grown-up to merge this for me?

[syclik]

@andrjohns, merged! That looks like an oversight.

@WardBrian, can we give @andrjohns permissions?

[WardBrian]

So far as I can tell he has them:

Maybe it was a github hiccup?

[syclik]

Thanks for checking! I hope it was. @andrjohns please let people know if it happens again!