[llvm-dev] [cfe-dev] LLVM C++14/C++17 BoF - Summary

[Keane, Erich via llvm-dev]

Thanks for the update Zachary!
I indeed missed the LLVM-Dev meeting, so this is a welcome bit of news for me!

I’m glad we decided to go with the cmake-warning mechanism.  Was there ever any discussion about a rolling warning system as I proposed here? https://reviews.llvm.org/D47073

It had received positive feedback on the mailing list, though Chandler had/has some reservations.  IMO, it is a way of going about this that prevents this discussion from being so contentious in the future.

-Erich

From: cfe-dev [mailto:cfe-dev-bounces at lists.llvm.org] On Behalf Of Zachary Turner via cfe-dev
Sent: Friday, October 19, 2018 9:58 AM
To: llvm-dev <llvm-dev at lists.llvm.org>; Clang Dev <cfe-dev at lists.llvm.org>
Subject: [cfe-dev] LLVM C++14/C++17 BoF - Summary

For those of you who were not able to attend the LLVM Developer Meeting (and as a recap for those who were), we had a productive BoF about enabling C++14 or C++17 in LLVM.  The outcome of this can be generally summarized as:

* There were no major objections to moving to C++14 / C++17 "as soon as possible"
* "As soon as possible" is not immediately, but we are currently targeting March of 2019 due to some downstream contributors' needing to resolve some blockages before it can be possible.
* There did not seem to be a strong sentiment that we should only move to C++14, so for the sake of this discussion we're assuming 17 unless someone presents a strong argument why 17 is *less* desirable than 14.

Minimum Compiler Versions for "Reasonable C++17 Support" (Mostly everything minus CTAD)
GCC - Version 7 [1]  (Version 8 for CTAD)
Clang - Version 4 [2]  (Version 5 for CTAD)
MSVC - 2017 Update 5 [3] (Update 7 for CTAD)

We plan to add a CMake warning if your compiler version is below these versions soon.  Around January, we will promote this to a CMake error which you must manually override by passing -DCMAKE_ALLLOW_DEPRECATED_COMPILER.

If I'm forgetting anything or misrepresenting anything that was said at the BoF please feel free to correct me.

[1] - https://www.gnu.org/software/gcc/projects/cxx-status.html
[2] - https://clang.llvm.org/cxx_status.html
[3] - https://docs.microsoft.com/en-us/cpp/visual-cpp-language-conformance?view=vs-2017
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