LLVM will "soon" require C++14 / C++17

[cuviper]

This is another discussion I noted from the LLVM Dev Meeting, although I was elsewhere during this BoF.

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

For Rust, I think this will mostly just be an issue of updating our various src/ci containers with newer GCC/Clang builds, and maybe the Windows infrastructure will need to be updated too. We already build custom GCC on many targets to get newer toolchains while keeping ABI compatibility. I don’t think we’ll have to increase our ABI baseline for this (currently ~RHEL5-ish for Linux x86), but that’s something to be careful about too.

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attn @alexcrichton, since you often deal with those CI images.

[alexcrichton]

Thanks for the heads up! I think you’re right in that we should be set for i686/x86_64 Linux as they’re compiling I think Clang 6 or 7 in the container to compile LLVM with. We may have to raise the baseline compatibility of other architectures though as I think they’re all using some voodoo to compile custom compilers which may be hard to modify.

In any case, we can probably cross this bridge when we get there!

[cuviper]

We may have to raise the baseline compatibility of other architectures though as I think they’re all using some voodoo to compile custom compilers which may be hard to modify.

Yes, I’m responsible for some of that voodoo.

I’m willing to help out when we get around to updating this, and definitely please do involve me if the baseline is about to move on the linux-gnu targets!

[alexcrichton]

Of course, will do!

[cuviper]

“The patch is about ready to land” to make old compilers a soft error, and they’re planning to apply that on the 8.x branch too. That won’t directly affect rust until we rebase rust-lang/llvm-project with that change, and even then we can set LLVM_TEMPORARILY_ALLOW_OLD_TOOLCHAIN in the short term.

Users of Rust with external LLVM 8+ will have to deal with this in their own way, of course.