module api: new region, ibuf, key_def, tuple, Lua/C APIs

[Totktonada]

We have added the bunch of new APIs in order to implement the new tuple-keydef and tuple-merger external modules. It would be good to document the new C structures and functions.

The relevant descriptions may be found in API comments in the header files, see the patchset. It was land to master (future 2.6.1), 2.5 (future 2.5.2), 2.4 (future 2.4.3) and 1.10 (future 1.10.8). Aside of the linked changes luaL_iscallable() was [backported]() to 1.10.

The work was done in the scope of the following issues:

https://github.com/tarantool/tarantool/issues/5273 https://github.com/tarantool/tarantool/issues/5384

BTW, is not it worth to generate the C API documentation from the Doxygen comments in the generated src/module.h? However first we should investigate the difference in the current state of the Doxygen comments and the RST docs.

[NickVolynkin]

BTW, is not it worth to generate the C API documentation from the Doxygen comments in the generated src/module.h?

Yes. We should autogenerate this documentation.

• [ ] Research how to generate documentation from source code
• [ ] Update source code comments with human-written texts
• [ ] Add autogeneration to documentation build pipeline
• [ ] Set up a process for actualizing source code comments

[Totktonada]

Yes. We should autogenerate this documentation.

Is there a related issue?

[Totktonada]

The box region is officially fiber local: https://github.com/tarantool/tarantool/pull/6874.