WL#8896: Enable use of C++11 in MySQL server

Affects: Server-8.0   —   Status: Complete   —   Priority: Medium

The aim of this worklog is to enable the use of C++11 in the 8.0 version of
MySQL server.

C++11 has a number of new features, especially related to concurrency, that are
of interest. For arguments of why using standard C++ library features is a good
idea.

GCC support for C++11:
https://gcc.gnu.org/projects/cxx0x.html
Clang support for C++11:
http://clang.llvm.org/cxx_status.html
Visual Studio support for C++11:
https://msdn.microsoft.com/en-us/library/hh567368.aspx
Solaris Studio support for C++11:
https://docs.oracle.com/cd/E37069_01/html/E37071/gndfg.html


Here is what you need to know:

1) New compiler version requirements
====================================
After the WL push, the minimum version requirements of different
compilers will be raised as follows:
  GCC: 4.8 or above
  Clang: 3.4 or above (XCode 7 on OS X)
  Solaris Studio: 12.4 or above (Solaris client build only)
This is done to get a good level of C++11 support across all supported
platforms. Minimum version of Visual Studio is still at 2013, but will
be raised to 2015 soon.

If you use older compilers than this, please upgrade ASAP.


2) Trunk Pushbuild trees will have to be updated
================================================
Once this WL is pushed, existing trunk-based pushbuild trees will have
to be reconfigured due to changes to supported platforms. mysql-trunk,
daily-trunk and weekly-trunk will be updated by RE right away. Other
trunk branches will be updated by RE in the following days. Expect some
red columns until all trunk branches have been synced.


3) Which C++11 feature can I use?
=================================
The supported C++11 features for our compilers are documented here:
https://gcc.gnu.org/projects/cxx0x.html
http://clang.llvm.org/cxx_status.html
https://msdn.microsoft.com/en-us/library/hh567368.aspx
https://docs.oracle.com/cd/E37069_01/html/E37071/gndfg.html

GCC and Clang claim full support. We know from our testing that
there are some small holes (e.g. not all type traits are implemented
in GCC 4.8), but I don't expect this to be an issue in practice.
Visual Studio 2013 misses a few important things (e.g. constexpr),
but this is fixed in Visual Studio 2015. Solaris Studio does not document C++11
support in detail. Note that Solaris Studio in C++11 mode uses the g++ 4.8.2
runtime library, so C++11 library support is as for GCC.

NF-1: No changes in behavior or performance regressions should be introduced by
this WL.
Steps needed to enable C++11
============================

Development changes required:
- Write patch which turns on C++11 support when building and fixes new
  compilation errors [DONE]
- Write patch which uses C++11 features (including library) for testing
  purposes [DONE]
- Fix build issues on Solaris (OOM compiling GIS) [DONE]
- Figure out how the client library should be handled. Solaris Studio 12.4
  supports C++11, so this should not be a problem [DONE]

Packaging changes required:
- Adapt RPMS spec to use non-standard GCC location on EL6 [DONE]
- Remove platforms (EL5) which becomes unsupported in RPMS spec files [DONE]

Release engineering changes required:
- Update pushbuild based on new supported platforms list. Includes using
  Software Collections for RH6/EL6. [DONE]
- Move Generic Linux builds to EL6. [DONE]

Testing required:
- Identify problematic platforms from the current list of 5.7 supported
  platforms [DONE - EL5+Ubuntu 12.04]
- Test using Software Collections for EL6 to get new enough GCC [DONE]
- Verify mysql_config, pkg-config and client library still works for non C++11
applications [DONE]
- Check than no new runtime dependencies are introduced [DONE]

Documentation required:
- Update "Installing MySQL from Source" (2.8) in ref. manual


The issue of GCC C++ ABI version
================================

Currently the server hardcodes the use of version 2 of the GCC C++ ABI.
This is done in cmake/build_configurations/compiler_options.cmake
GCC documentation:
https://gcc.gnu.org/onlinedocs/gcc/C_002b_002b-Dialect-Options.html

The problem is that this version is quite old and that newer versions
contains several bug fixes that are relevant for C++11.

Two alternative approaches for moving to a newer version:

1) Hardcode the newest version of the GCC C++ ABI that is supported by the
oldest version of GCC we will be using. Currently this looks like 4.8 => ver 7.
+ Similar to the current approach.
- Ties us to version 7 even if we move to newer compilers.
- What if Linux distros want to use an older/newer version?

2) Remove hardcoding of ABI version from server sources. Leave it up to Linux
distros to decide which version to use. For our own packages, use whatever is
the default version for the given distro.
+ Linux distros will be more free to use the version they want.
+ Easier to start using newer versions.
+ In line with other applications on that platform
- Different builds can use different versions. Implications for test coverage?

Based on the above +/- points, we have chosen approach 2)
The patch for this WL should:
- Turn on the -std=c++11 compiler flag for G++, Clang++ and Solaris Studio
- Remove -std=c++11 from the mysql_config output except for Solaris Studio
  where it is needed to get the correct C++ libraries.
- Add "-lstdc++ -lgcc_s -lCrunG3" to mysql_config output when using Solaris
  Studio as required by the Solaris Studio documentation.
- Remove all usage and references to stlport for Solaris. With C++11 Solaris
  Studio will automatically use the g++ runtime library.
- Update compiler version checks to the following minium versions:
  GCC 4.8, Clang 3.4, Solaris Studio 12.4. As per 5.8 platform draft linked
  in HLD.
- Remove preparatory C++11 compiler warnings
(-Wc++11-compat-reserved-user-defined-literal and -Wc++11-extra-semi)
- Downgrade new compilation errors about deprecated features to warnings (e.g.
std::auto_ptr). It should be up to individual teams to fix this later.
- Add an unit test using new C++11 library features.
- Add an UDF using new C++11 library features.
- Remove explicit setting of GCC ABI version (see above)