How to efficiently combine flags and select()s

[nicholasjng]

Hello! I'm currently porting a project from CMake to Bazel, and I'm facing a situation in which I want to pass size optimizations (-Os on clang/gcc, /Os on MSVC) to a target based on the value of a flag which I define.

Before I started implementing this flag, I had a simple select() in my copts supplying the above option for "MVSC or not" based on the current toolchain compiler.

Now, however, I need to also select on the value of the sizeopt flag, and to pass the right one for "MSVC or not". This results in at least 4 config settings (compiler is MSVC, compiler is not MSVC (!!!), sizeopts, no sizeopts. But there's more:

(!!!) Because both select paths have different options, each condition has to be unique, so after introducing the sizeopts flag, I cannot go with "not MSVC" anymore, but have to take in all compiler names, e.g. from @rules_cc//cc/compiler in my case. That technically restricts me from being able to use any compiler before, to only the natively known compilers (gcc, clang, clang-cl, mingw-gcc, msvc-cl).

On top of that, all of these settings clutter my build target - running bazel query "@nanobind//:*" gives me 9 total config settings, but I guess I can make them invisible by changing the package's default visibility (right now, it's //visibility:public).

Question: Is there a better way to handle these flag-guarded options for different compilers at the same time?