[swift-dev] [swift-lldb-dev] Switching swift to C++14

Tue Jan 2 13:33:38 CST 2018

On Wed, Dec 20, 2017 at 4:26 PM, Ted Kremenek <kremenek at apple.com> wrote:

>
> On Dec 19, 2017, 8:33 PM -0800, Ted Kremenek via swift-dev <
> swift-dev at swift.org>, wrote:
>
>
>
> On Dec 19, 2017, at 5:08 PM, Saleem Abdulrasool <compnerd at compnerd.org>
> wrote:
>
>
>
> On Dec 19, 2017, at 3:59 PM, Ted Kremenek <kremenek at apple.com> wrote:
>
>
>
> On Dec 19, 2017, at 2:31 PM, Daniel Dunbar <daniel_dunbar at apple.com>
> wrote:
>
>
>
> On Dec 19, 2017, at 2:27 PM, Ted Kremenek <kremenek at apple.com> wrote:
>
> Fair enough.
>
> We care about swiftc and llbuild building a variety of platforms today —
> FreeBSD, Rasberry Pi, etc.  My impression is that C++14 is generally
> supported by both (a) the mininum versions of the distributions we support
> today and (b) the current versions of the platforms we’d like to expand
> Swift to in the future.  Does that sound right?  I suspect you went through
> the same kind of reasoning with llbuild.
>
>
> It sounds reasonable, but to be honest I never did an audit of what
> platforms supported C++14.
>
>
> Interesting.  Was that not a concern when that choice was made for
> llbuild, or was the context different?
>
>
> I do think that we could always use the Clang++ we build as part of Swift
> to build Swift itself. By that logic, it seems reasonable to expect we
> could always have C++14 support, although it does mean that porters would
> need modern Clang to support their platform. However, that is likely
> largely a prerequisite for Swift to work as well.
>
>
> That’s a significant change to make just to get C++14 support guaranteed,
> and (I believe) would have a non-trivial impact on those using development
> environments that expect to use the Clang bundled with them to build
> projects.
>
>
> Agreed.  However, the current supported platforms already support this
> minimum.  I think that future platforms will need to provide that anyways.
> If the system doesn’t have a modern toolchain available, I suspect that it
> already would not have C++11 available either.  In such a scenario, they
> need to provide a newer toolchain, and so the difference there is minimal
> as we already require C++11.
>
>
> OK, I’m convinced.
>
> I want to hold off for a tiny bit just to see if anyone else has any
> commentary on this thread before we make a change.
>
>
> We’d also need to make this change on the LLDB side, and I realize now
> that a few people I’d like to weigh in are on vacation until the holidays.
> How about we pick this up immediately in the new year once it’s clear
> everyone that should weigh in has had a chance to do so.
>

Just a post-holiday bump to bring this back up :-).  I'd like to get this
merged so that the other Windows stuff is unblocked.

>
>
>
>
>  - Daniel
>
>
> On Dec 19, 2017, 2:23 PM -0800, Daniel Dunbar <daniel_dunbar at apple.com>,
> wrote:
>
> It wasn’t changed, it has *always* been C++14 since the day we open
> sourced it. I only investigated the platforms we officially support (Ubuntu
> 14.04/15.10 at the time, and macOS 10.10+ IIRC).
>
> - Daniel
>
> On Dec 19, 2017, at 2:21 PM, Ted Kremenek <kremenek at apple.com> wrote:
>
> Daniel,
>
> When you changed llbuild to require C++14, what platforms did you take
> into account with that change? If you have already done the assessment here
> it could speed a resolution of a decision.
>
> Thanks,
> Ted
>
> On Dec 13, 2017, at 3:19 PM, Daniel Dunbar via swift-lldb-dev <
> swift-lldb-dev at swift.org> wrote:
>
> FWIW, llbuild requires C++14.
>
> We have to do some minor shenanigans to workaround bugs in libstdc++ on
> 14.04, and our use is probably minimal, but just throwing that out there.
>
> - Daniel
>
> On Dec 13, 2017, at 1:45 PM, Jordan Rose via swift-lldb-dev <
> swift-lldb-dev at swift.org> wrote:
>
> No one else has commented on this yet today, so I'll put in that I don't
> have any objections to this and don't foresee any major problems. The one
> place where we'd need to be careful is with LLDB, which imports Swift
> headers; if Swift is going to move to C++14, then Swift-LLDB probably has
> to as well. LLDB folks, what do you think?
>
> The other thing to check is if our minimum Clang or libstdc++ requirements
> on Linux didn't support C++14. It looks like our README is vague on that,
> but LLDB already suggests a minimum requirement of Clang 3.5, which is new
> enough. I suspect we're okay here.
>
> Jordan
>
>
> On Dec 13, 2017, at 10:36, Saleem Abdulrasool via swift-dev <
> swift-dev at swift.org> wrote:
>
> Hi,
>
> The newer Windows SDK requires the use of C++14 (the SDK headers use
> `auto` return types without trailing type information). Joe mentioned that
> there was some interest in switching the rest of swift to C++14 as well. I
> figured that I would just start a thread here to determine if this is okay
> to do globally rather than just specifically for the Windows builds to
> ensure that we can build the Windows components.
>
> Thanks.
>
> --
> Saleem Abdulrasool
> compnerd (at) compnerd (dot) org
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-- 
Saleem Abdulrasool
compnerd (at) compnerd (dot) org
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