We should fail to compile if _Py_TAIL_CALL_INTERP is set but `preserve_none` and `musttail` do not exist.

[Fidget-Spinner]

Bug report

Bug description:

The code should look something like this:

#if _Py_TAIL_CALL_INTERP && (defined(__clang__) || defined(__GNUC__))
# if !_Py__has_attribute(preserve_none) || !!_Py__has_attribute(musttail)
# error "This compiler does not have support for efficient tail calling."
# endif
#endif

CPython versions tested on:

CPython main branch, 3.15, 3.14

Operating systems tested on:

No response

Linked PRs

• gh-140513: Fail to compile if _Py_TAIL_CALL_INTERP is set but preserve_none and musttail do not exist. #140548
• [3.14] gh-140513: Fail to compile if _Py_TAIL_CALL_INTERP is set but preserve_none and musttail do not exist (GH-140548) #140923

[XChaitanyaX]

Can I have a pr for this?

!!_Py__has_attribute(musttail)

double exclamation !! mark?? Shouldn't it be single?

[chris-eibl]

Maybe we can already handle that "earlier" in configure?

[Fidget-Spinner]

Maybe we can already handle that "earlier" in configure?

This works too but I'd rather bloat up our C code rather than the configure code. The configure script is already pretty complex so I don't like adding more to it.

[chris-eibl]

Yeah, and we could handle MSVC (#139962) here then in a similar way, too.

E.g. include a check for _MSC_VER like #if defined(_MSC_VER) && (_MSC_VER < 1950)?

[Fidget-Spinner]

We missed the train for 3.14. Backporting now would break GCC 15.