C++11

[Stephan Bergmann]

As discussed previously (ESC meeting minutes 
<http://lists.freedesktop.org/archives/libreoffice/2014-May/061146.html> 
and 
<http://lists.freedesktop.org/archives/libreoffice/2014-May/061294.html>), 
we intended to start using at least some C++11 features unconditionally 
on master towards LO 4.4.

That implies new minimum requirements for the various toolchains, and we 
piggybacked on the research done by the LLVM team on this and settled on

   Clang 3.1
   GCC 4.7
   MSVC 2012

intended to offer a good subset of C++11, bringing both core and library 
improvements.

For the "official" TDF Linux baseline builds (CentOS 5, GCC 4.1) this 
requires building against the <http://people.centos.org/tru/devtools-2/> 
toolchain (GCC 4.8).  Christian already took care of that.

For Mac OS X, this is achieved by abandoning the deprecated 32-bit 
builds requiring OS X 10.6 at a minimum (as announced at 
<https://wiki.documentfoundation.org/ReleaseNotes/4.3#Mac>) and only 
supporting 64-bit builds requiring OS X 10.8.  (For C++11, it would 
suffice to require only 10.7, but there were other reasons that made us 
pick 10.8 as the minimum requirement for the 64-bit builds.)

Technically, our configure.ac currently still allows some GCC < 4.7, and 
some tinderboxes still make use of that (esp. the logerrit buildbot 
Linux machines), but I urge all tinderbox owners to upgrade to the above 
minimum compiler versions as soon as possible.  (I disabled Markus' 
Linux-with-check at 50 tinderbox until he is back from vacation, it is 
based on an old SUSE release with a too-old GCC rejected by configure.ac 
now.)

Two commits went into master over the last few days, 
<http://cgit.freedesktop.org/libreoffice/core/commit/?id=fcf015832466f4d902e8aeb1466309a1bc230475> 
"(Rudimentary) C++11 support is a hard requirement now" to require a 
compiler supporting C++11 (at least to some degree) in configure.ac, and 
<http://cgit.freedesktop.org/libreoffice/core/commit/?id=ea733ab5b632109d28bb8f1dc37116340b26229b> 
"Turn SfxItemState into a C++11 scoped enumeration" as a test balloon to 
actually unconditionally use a C++11 feature (scoped enumerations) in 
the code.  Both of them pass the logerrit buildbots and the tinderboxes.

But, unfortunately, the minimum compiler versions still do not support 
the full C++11 Standard. 
<http://wiki.apache.org/stdcxx/C++0xCompilerSupport> gives a somewhat 
useful overview of what features (concentrating on core language, not 
standard library, though) are available in which compiler release (for 
MSVC, 11.0 means 2012), but at least the claim made there that MSVC 2012 
supports variadic templates appears to be false.

So, when intending to use a new C++11 feature in our code base, check 
first whether it is actually supported by the various toolchains (by 
e.g. running it past the logerrit buildbots), and be prepared to fix up 
any tinderbox breakage it might cause.

And check out Scott Meyers' helpful "Effective Modern C++," 
<http://shop.oreilly.com/product/0636920033707.do>, if only to make you 
realize that C++ is still a baroque pile of gotchas.

Happy coding,
Stephan