ParameterHandler::print_parameters(): Demangle JSON

[mschreter]

In this PR, we propose to demangle the parameters in case of ParameterHandler::OutputStyle::JSON or ParameterHandler::OutputStyle::ShortJSON prior to printing them within ParameterHandler::print_parameters(). Otherwise, the output is not really readable, e.g., for the key-value pair of

"end time": "0.5"

printing the output ends up in

"end_20time": "0.05"

@peterrum @nmuch

[peterrum]

/rebuild

[gassmoeller]

I think this PR is causing some unintended consequences in ASPECT, but I am not sure if it is deal.II's fault or how we use it. Our parameters contain a bunch of keys named "deprecation_status", which are apparently created by the function ParameterHandler::declare_alias. I guess the underscore looks to the function as if it needs to be demangled, but then it fails. @mschreter could you check if this change works with a parameter alias for you?
I was successful reproducing this problem by adding the following line after line 40 of tests/parameter_handler/parameter_handler_write_json.cc:

      prm.declare_alias("double 2", "double 3");

I guess in the end the question is: Are underscores valid characters for parameter names in deal.II? If so, can we change this modification to not accidentally try to demangle these underscores?

[tjhei]

Makes sense. I can take a look this weekend if nobody else beats me to it l.

[mschreter]

@gassmoeller Thanks for your notice. Unfortunately I did not test the behavior in case of an alias parameter. I was able to reproduce your issue and hopefully also already found the problematic line, see this patch. Now, the diff of the test output oftests/parameter_handler/parameter_handler_write_json.cc including your suggested changes looks as follows:

65,69d64
<             },
<             "double 3":
<             {
<                 "alias": "double 2",
<                 "deprecation_status": "false"
89,94c84
<             "double 2": "4.321",
<             "double 3":
<             {
<                 "alias": "double 2",
<                 "deprecation_status": "false"
<             }
---
>             "double 2": "4.321"

If you are happy with that, I'll open a follow-up PR including the fix and also an extension of the test case with alias parameters.

FYI @tjhei

[tjhei]

That looks good! Thank you.

[gassmoeller]

Looks good to me, feel free to open a PR. Thanks for the quick fix! 👍