Feature/3161 parse tuples json

[mitzimorris]

Submission Checklist

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

Summary

Updates json parser and data handler to allow tuples, including tuples of tuples, arrays of tuples, tuples of arrays of tuples, etc.

Intended Effect

Allow users to supply init files of JSON data corresponding to Stan program tuple variables.

How to Verify

Unit tests.

Side Effects

Parser allows nested objects.

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): Columbia University

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/)

[mitzimorris]

re-review?

[mitzimorris]

I broke the unit tests for ill-formed JSON which the handler should detect and report into from file "json_data_test.cpp" into a new test file, "ill_formed_json_test.cpp", and then added more tests for redefining tuple and array of tuple vars.

[WardBrian]

The latest changes seemed to have introduced a regression, which suggests a new case to test against! (tuple-of-array-of-tuple seems to not trigger the array-of-tuple logic)

And a few more concrete failure tests I'd like to see

[mitzimorris]

Added logic to ignore top-level entries with names that aren't legal Stan varnames and corresponding unit tests.
Ready for re-review.

[WardBrian]

Thanks for all the work on this! I think it's ready to merge

[WardBrian]

[Comment] I think this is very nice that we can have this kind of thing now

[WardBrian]

[Comment] This is probably a problem for the documentation later, but part of me does worry someone will try to write something like this and it will be silently ignored.
Making it always issue a warning is too much (and I don't think we have an ostream laying around to push warnings to), so I don't think we should do anything, just wanted to flag it as a concern