[PATCH] D135341: [clang] adds `__reference_constructs_from_temporary`

Tue Feb 7 20:26:30 PST 2023

cjdb added a comment.

In D135341#4111673 <https://reviews.llvm.org/D135341#4111673>, @ldionne wrote:

> I've been looking at implementing `reference_constructs_from_temporary` & friends and this would be sweet to have. Is this blocked on something specific?

This trait should be ready to go, pending an LGTM. `__reference_converts_from_temporary` is a different story, and someone else might need to do this one if you need it in a timely fashion (but I'll be happy to review it).

================
Comment at: clang/include/clang/Basic/DiagnosticCommonKinds.td:397
+def err_reserved_identifier_for_future_use : Error<
+  "%0 is a compiler-reserved identifier for a future feature">;
 }
----------------
ldionne wrote:
> cjdb wrote:
> > erichkeane wrote:
> > > I don't think we should diagnose this for individual identifiers, I don't think this adds much value, and the identifier is already reserved for implementation use.  This implies we are going to diagnose ALL future reserved things, which we have no intention of doing.
> > The motivation for this error is to ensure that standard library implementations don't take this name (`__remove_cvref` and `__is_null_pointer` had to get names that weren't a 1:1 mapping to their library counterparts as a result).
> Oh, just ask and we can rename ours! What do you want us to rename?
Much appreciated! I think `__remove_cvref` had a libc++ conflict and `__is_null_pointer` had a libstdc++ conflict, so it's not specific to one library. I figured that it would be easier for backwards-compatibility reasons to just rename them to something slightly more awkward, so that previous versions of the stdlib don't spontaneously break for more recent compilers. This is more of an issue when you're dealing with package managers like apt, where some things depend on libc++-v$OLD, but there aren't any restrictions on Clang's version (for example, I use nightly Clang on Ubuntu, but apt notes that the Discord app has an older libc++ dependency).

After having let this sit for a few months, I don't really have strong opinions on reserving `__std_trait` anymore, so I'll touch this up in the morning.

Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D135341/new/

https://reviews.llvm.org/D135341