Tracking Issue for `extended_varargs_abi_support`

[Soveu]

This is a tracking issue for extending available ABIs for var-args functions.
The feature gate for the issue is #![feature(extended_varargs_abi_support)].

About tracking issues

Tracking issues are used to record the overall progress of implementation.
They are also used as hubs connecting to other relevant issues, e.g., bugs or open design questions.
A tracking issue is however not meant for large scale discussion, questions, or bug reports about a feature.
Instead, open a dedicated issue for the specific matter and add the relevant feature gate label.

Steps

• Implementation - Enable varargs support for calling conventions other than C or cdecl  #97971
• Adjust documentation (see instructions on rustc-dev-guide)
• Stabilization PR
  • Stabilize extended_varargs_abi_support #116161 reverted by Revert "Stabilize extended_varargs_abi_support" #136897

Implementation history

• Enable varargs support for calling conventions other than C or cdecl  #97971
• Enable varargs support for AAPCS calling convention #115860
• Stabilize extended_varargs_abi_support #116161
• Varargs support for system ABI #119587 note¹

Unresolved Questions

• should extern "system" be included? the original feature only described itself as applying to extern "efiapi", extern "sysv64", and extern "win64", and later the feature described itself as applying to extern "aapcs", but the only case where extern "system" is meaningfully distinct is a case where it cannot be a vararg ABI. while MSVC sometimes translates __stdcall to be identical to the C ABI, we have previously rejected implementing MSVC's oddities:
  • Tracking issue for future-incompatibility lint unsupported_calling_conventions #87678

Footnotes

1. this was not recorded as part of the impl history until after it was discovered this feature was initially stabilized without an FCP. ↩