[R-pkg-devel] Frictionless alternative for `-Wstrict-prototypes`

[Lionel Henry]

Davis Vaughan and I were looking into the `-Wstrict-prototypes`
warnings for C code that were recently added to the R-devel checks. We
did a little research and found that these warnings are intended to
catch old-style definitions and declarations that were deprecated a
long time ago. This includes:

1. Unspecified types like `void fn(x, y);`
2. Unspecified parameter lists like `void fn();`.

We also found:

- That only unspecified types (case 1) will become defunct. For
  unspecified parameter lists (case 2), it was announced recently that
  the C standard committee has decided to simply change the meaning to
  "no arguments" in C23. This aligns with what most people think it
  means, and is what C++ does. See item 13 of page 130 in the C23
  working draft at https://open-std.org/JTC1/SC22/WG14/www/docs/n3054.pdf.

- The new `-Wdeprecated-non-prototype` option for clang-15 does not
  warn for empty parameter lists, allowing for a smooth transition
  that allows this widespread usage.

Since the no arguments case is both incredibly common and will become
fully legal C syntax in a close future, it seems it might not be worth
it to require all packages to update their code to an intermediary
form that reads less well, is not as intuitive to most people (and so
might crop up back in further updates), and will become standard in
the future anyway.

Perhaps a good course of action would be:

- Using `-Wno-strict-prototypes` to disable the stringent checks.

- Enabling the new `-Wdeprecated-non-prototype` in clang to catch
  old-style definitions and declarations.

This way CRAN would be able to catch deprecated syntax while allowing
the soon-to-be-legal syntax of empty parameter lists. We hope that
this would mean less code churn on CRAN, which means less work for the
CRAN maintainers as well as for the maintainers of CRAN packages.

Best,
Lionel & Davis