[llvm-dev] [RFC] migrating past C++11

via llvm-dev llvm-dev at lists.llvm.org
Thu Jan 24 10:29:16 PST 2019

*Sigh*  Mine was in response to Mehdi, who says he mis-typed his post, and so my last is (by construction) completely irrelevant to the policy and the CMake implementation of the warning/error.  Go for it.

Regarding bot protection from people being too ambitious with their feature set, there's already a separate thread:
"Buildbot for minimum supported GCC version? (seeing local build failures)"
Follow up there, please.

From: jfbastien at apple.com [mailto:jfbastien at apple.com]
Sent: Thursday, January 24, 2019 1:15 PM
To: Robinson, Paul
Cc: joker.eph at gmail.com; llvm-dev at lists.llvm.org
Subject: Re: [llvm-dev] [RFC] migrating past C++11

On Jan 23, 2019, at 4:15 PM, via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:

If we claim to support a Thing, then we should accept patches to fix when the Thing breaks.  Whether a bot verifies that the Thing works, is not really relevant; "support" means "we say this works and will fix it when it breaks."

A bot is a service to the community in that it can tell you more-or-less promptly when you have broken a Thing. It is not the only way to determine that you have broken a Thing.  However, it does tell you that you have broken a Thing that somebody thinks is worth putting up a bot to verify that it stays not-broken.
Given the number of times lately that newcomers have had difficulty getting started (because some Thing we claim works, actually doesn't), I think it would be valuable to the ongoing health of the project to have bots verifying the particular Thing that is the minimum supported compiler versions.  This doesn't mean I'm volunteering to provide that resource; neither does it mean I refuse to provide that resource. I am pointing out that it would be valuable generally, and as part of this longer-term goal to specify minimum compiler versions, it would be a Good Thing™ to be able to tell promptly when we've accidentally broken that, so that newcomers don't beat their head against a wall and go away disgusted with an open-source project that lies to them about supported configurations.

I agree that what you describe would be good. I don’t see why it’s relevant to this discussion: we’re talking about changing the minimum toolchain version. Whether there are bots running the minimum toolchain version today is a fact disassociated from any proposed minimum change. Indeed, the policy we just adopted (and which I’m following) doesn’t mention bots.

For sure if someone has a bot running older toolchains we want them to upgrade to the new minimum, so this RFC and soft-error will give them proper heads up. I hope they’ll chime in if they have concerns or suggestions.

I therefore think that you want to fork this discussion point into a separate email thread, since it’ll help it move this RFC forward without distraction.


From: Mehdi AMINI [mailto:joker.eph at gmail.com]
Sent: Wednesday, January 23, 2019 6:19 PM
To: Robinson, Paul
Cc: James Y Knight; Krzysztof Parzyszek; llvm-dev
Subject: Re: [llvm-dev] [RFC] migrating past C++11

On Wed, Jan 23, 2019 at 9:37 AM via llvm-dev <llvm-dev at lists.llvm.org<mailto:llvm-dev at lists.llvm.org>> wrote:
Please include MSVC in the table. While the picture on Windows is way less complicated than for *nix, it's still a platform and toolchain that matter to a number of us in the community.

Separately, there was talk of needing to have bots that specifically use the oldest supported toolchains, otherwise we can't genuinely promise that they are really supported (don't want feature dependencies creeping in by accident).

IMHO the difference between "supported" and having a bot validating the configuration is whether we accept patches to fix issues on this particular platform.

Otherwise, I believe historically it has been up to the users that care about a platform to provide CI ressources for it. Do we have an alternative plan?


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