RFR: 8314488: Compile the JDK as C++17 [v5]

[Kim Barrett]

On Thu, 11 Jan 2024 08:04:40 GMT, Julian Waters <jwaters at openjdk.org> wrote:

> > Hi Martin, probably we can update our devkit if really needed. But https://clang.llvm.org/cxx_status.html states that c++17 is supported for a very long time, so probably clang 13.1 is sufficient too (or is there a real showstopper known with this release of clang) .
> 
> I was hoping to avoid 13.x since there seems to be a noexcept bug in that release series, though some other testing seems to suggest this is transient (and also I wanted to align with what Oracle uses, which is 14.x). I guess I can roll back to 13.x if that is really needed

See https://bugs.openjdk.org/browse/JDK-8255082, comments in 12/2023.

> > P0283R2: Ignoring unsupported non-standard attributes
> 
> It's probably important to note that MSVC takes this to mean that unknown attributes don't have an effect, and still warns for them when warning C5030 is enabled (which is by default in our make system): https://developercommunity.visualstudio.com/t/c-warning-c5030-generated-for-attribute-within-a-n/138429

So VS doesn't have a mechanism for disabling warnings about just scoped attributes it doesn't recognize.  (gcc has
-Wno-attributes=_vendor_:: for this.)  That's unfortunate.

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PR Comment: https://git.openjdk.org/jdk/pull/14988#issuecomment-1886727940