Add C++ version for bazel

[dnmiller]

Description

When adding Catch2 to the bazel workspace, the bazel build of the static libraries will fail if the C++ version of the project is less than C++14 due to use of std::enable_if_t. This calls out the C++ version explicitly in the compilation.

GitHub Issues

Sort of related to #2462 if you're using bazel to manage dependencies instead of a package manager.

[codecov]

Codecov Report

Merging #2525 (fbf8a65) into devel (359542d) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##            devel    #2525   +/-   ##
=======================================
  Coverage   91.54%   91.54%           
=======================================
  Files         183      183           
  Lines        7562     7562           
=======================================
  Hits         6922     6922           
  Misses        640      640           

[horenmar]

How does Bazel handle it if the user wants to use C++17?

[dnmiller]

How does Bazel handle it if the user wants to use C++17?

This actually only applies to the library binaries - the user can still use C++17 for their own targets.

[Vertexwahn]

Adding copts = ["-std=c++14"] does not make sense. Since GCC and Visual Studio handle it in a different way, we have configs for this. See .bazelrc.

bazel build --config=gcc9 //... will add -std=c++2a - if you need -std=c++14 than add a config to bazel.rc e.g. build:my_config --cxxopt=-std=c++14. You can then use bazel build --config=my_config //.... copts = ["-std=c++14"] will lead to compiler warnings on Visual Studio.

[horenmar]

This should be no longer needed.

[dnmiller]

So I have a use case where the bazel config strategy doesn't work - an old embedded compiler that doesn't know -std=c++14, but unit tests that run on a PC with gcc-10.

Maybe this is more of a bazel deficiency. In the meanwhile I can patch BUILD.bazel in my WORKSPACE file.