STABLE clang planned update MFC path (3.4.1 STABLE, 3.7.0, CURRENT)

[Dimitry Andric]

On 11 Oct 2015, at 14:05, Piotr Kubaj <pkubaj at riseup.net> wrote:
> 
> AFAIK if there had been such plans, they were dropped long ago. The
> reasoning it can't be done (at least for now) is that versions 3.5.0+
> require C++11-capable stack and that would break upgrades from 9-STABLE
> (if the user still uses GCC, as is by default). So, LLVM in stable/10
> will probably be upgraded when stable/9 goes EOL.

If stable/10 had clang 3.5 or higher, you could still upgrade from
stable/9.  It would only require you to do the upgrade in two steps:

* Rebuild and reinstall your stable/9 world using WITH_CLANG,
  WITH_CLANG_IS_CC, and WITH_LIBCPLUSPLUS.  This will install clang
  3.4.1 and libc++, and make clang the default compiler.
* Checkout stable/10 (or even head), and build/install it in the regular
  fashion.

I am personally not against merging newer llvm/clang versions into
stable/10.  But the "silent agreement" has always been that you could
upgrade easily from the latest stable/X to stable/X+1, and the above
two-step process breaks that, or at least makes it more complicated.

Last but not least, note that this would only apply to the architectures
that *can* actually build clang 3.4.1 and libc++ on stable/9.  This is
currently limited to x86, little-endian arm and powerpc (64 bit, I'm
unsure about 32 bit).

-Dimitry

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