[clang] [clang] Implement P2582R1: CTAD from inherited constructors (PR #98788)

[Haojian Wu via cfe-commits]

hokein wrote:

> Thanks for the reviews!
> 
> > ```
> > * can you give a description  if what needs to be done in subsequent PRs? (maybe cxx_status.html should say "partial"
> > ```
> 
> The remaining tasks are:
> 
> * Supporting dependent using-declarators such as `using Derived::Base::Base`. These are somewhat annoying to deal with, there isn't much of an existing mechanism (that I could find, at least) to look up the base type from the raw dependent identifier.

Although there are FIXMEs in the code, could you also file a GitHub issue for better tracking?

> * Supporting deduction guides that are declared after the first lookup of deduction guides on the derived class. This is unimplemented due to a similar issue in alias template deduction that needs to be resolved first.
> 
> I have updated the cxx_status to partial, and added a note about the unsupported depdendent using-declarators. This aligns with the status for alias template deduction, which is partial due to the feature macro not being set. I presume the issue of deduction guides declared after the first lookup of deduction guides would be fixed in both features at the same time, either in this patch set if it is fixed in upstream first, or after this patch set as a followup.

Yes, the missing-after-first-lookup issue is already tracked in #103016, and it also affects alias template deduction (it’s the only blocker remaining to mark alias template deduction as a completed feature).

We can address this as a follow-up, and I think we should resolve it before the next Clang 20 release.


https://github.com/llvm/llvm-project/pull/98788