[cfe-dev] Recent failing tests in libc++

[JF Bastien via cfe-dev]

Thanks for tracking this Marshall!

> On May 28, 2018, at 5:01 PM, Marshall Clow via cfe-dev <cfe-dev at lists.llvm.org> wrote:
> 
> On Mon, May 28, 2018 at 2:29 PM, Richard Smith <richard at metafoo.co.uk <mailto:richard at metafoo.co.uk>> wrote:
> Clang 5 implemented the originally adopted proposal. The behaviour you're referring to was introduced by P0620R0, which I think was not implemented until Clang 6.
> 
> That would explain what I'm seeing.
>  
> Perhaps we should bump the deduction guides feature test macro version for that paper?
> 
> I don't see any mention of feature macros in P0620R0 :-(
> Besides, I don't see how it will help now that clang 6 is out there.

Ouch yeah, fixing the deduction guides would have been nice.

Looks like latest changes for this came in late 2017 from:
https://reviews.llvm.org/rL320401 <https://reviews.llvm.org/rL320401>
https://reviews.llvm.org/rL316292 <https://reviews.llvm.org/rL316292>

Was the green dragon bot passing? It’s down now for maintenance, but I expect some of the tests should have been failing before your change.


> -- Marshall
> 
> 
> 
> 
> On 28 May 2018 14:10, "Marshall Clow via cfe-dev" <cfe-dev at lists.llvm.org <mailto:cfe-dev at lists.llvm.org>> wrote:
> On Mon, May 28, 2018 at 12:51 PM, Marshall Clow <mclow.lists at gmail.com <mailto:mclow.lists at gmail.com>> wrote:
> This past week, I checked in a bunch of code (and tests) having to do with the deduction guides features of C++17 - adding support for many of the standard library types. Some of the tests started failing - mostly (but not exclusively) on ARM. JF tried to fix some of the tests on Friday, but was not completely successful.
> 
> Today, I took a fresh look at the failures, and realized that all but one of them were on bots that were running clang-5.  It appears that clang-5 has a bug where it mis-deduces the template arguments when it is handed something that looks like a copy constructor. (Alternately, it implicitly generates an incorrect template deduction guide and uses that.)
> 
> Another possible diagnosis is that clang-5 generates no implicit deduction guides - and only uses the explicitly provided ones.
> 
> -- Marshall
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