[cfe-dev] [libc++] Guarantee that TUs built with different versions of libc++ can be linked together

[Reid Kleckner via cfe-dev]

I 100% support not providing this guarantee by default. It always seemed a
bit too heroic to me for libc++ to try to provide this support.

I think most people with standard library version skew typically only have
skew between separate DSOs.

On Tue, Aug 14, 2018 at 6:49 AM Louis Dionne via cfe-dev <
cfe-dev at lists.llvm.org> wrote:

> Hi,
>
> libc++ currently allows TUs that were built using different versions of
> libc++ to be linked together. Roughly speaking, this is achieved by making
> sure that anything not ABI-stable is local to each TU. This also allows
> distributing a static archive without caring too much about the version of
> libc++ it was compiled with, at least in principle. Supporting this use
> case creates code bloat for all users of libc++, since private functions
> are duplicated in each TU.
>
> I posit that few clients actually care about this, yet everybody is paying
> for it in terms of executable size. Hence, I would like to change the
> default guarantee offered by libc++ from "this use case is supported" to
> "this use case is not supported". The use case would still be supported by
> defining a macro for those that need it.
>
> Does anybody have objections to this change?
>
> Louis
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