[C++17] Add compile-time reflection for fields. (#6324)
* [C++17] Add compile-time reflection for fields.
Included in this commit is the following:
- The C++ generator has been modified so that,
when in C++17 mode, it will emit Table and
Struct field traits that can be used at com-
pile time as a form of static reflection. This
includes field types, field names, and a tuple
of field getter results.
- Diffs to the cpp17 generated files. No other
generated files are affected.
- A unit test that also serves as an example. It
demonstrates how to use the full power of this
reflection to implement a full recursive
JSON-like stringifier for Flatbuffers types,
but without needing any runtime access to the
*.fbs definition files; the computation is
done using only static reflection.
Tested on Linux with gcc 10.2.0.
Fixes #6285.
* Fix int-conversion warning on MSVC.
* Try to fix std::to_string ambiguity on MSVC.
* Fix clang-format diffs.
* Fix more clang-format diffs.
* Fix last clang-format diff.
* Enable C++17 build/test for VC 19 platform in CI.
* Forgot to add value to cmake command line variable.
* Various fixes/changes in response to @vglavnyy's feedback.
* Replace "fields pack" with index-based getters.
* Fix MSVC error.
* Fix clang-format diffs.
* getter_for method returns result instead of address-of-getter.
* Next round of reviewer suggestions.
* Use type instead of hardcoded struct name.
* Fix clang-format diff.
* Add test for FieldType since it is not used in the stringify test.
* Add fields_number field to Traits struct.
* Add --cpp-static-reflection flag and put those features behind it.
* Fix clang-format diffs.
* Remove <tuple> include.