[PATCH] D99005: [clang] Implement P2266 Simpler implicit move

[Arthur O'Dwyer via Phabricator via cfe-commits]

Quuxplusone added a comment.

> I'd like to give some time for other stakeholders to give their opinion if this is not too urgent, specially @Quuxplusone and @rsmith.

I have no strong/well-informed opinions here. I have an idea to offer, //if// there is precedent for it. My idea is, keep it as an error if the rvalue resolution finds nothing, but (1) fall back to an lvalue resolution //for error-recovery purposes//, and (2) suppress the error in system headers. Then, the usage in MSVC STL will keep working but only because it's in a system header. I seem to recall that there is precedent for diagnostics that are "non-downgradable error in user code, yet still suppressed in system headers." If I'm imagining things, then please do not invent such a facility purely for this feature.

My second choice is to do whatever minimalistic hack suffices to satisfy the customer (Aaron etc. in this case), but only with the understanding that we plan to eliminate that hack as soon as MSVC STL gets updated. My third choice is to revert the whole thing and then land a new version of it that always falls back to lvalue resolution, but with an on-by-default //warning// (not error) (so this would probably affect a ton of your test cases); then the user can downgrade that warning as a workaround.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D99005/new/

https://reviews.llvm.org/D99005