disable-shared-library-for-platform.md

How do I disable building of a shared library variant for a platform/compiler?

My ideal solution would be to disable libs{hello} for Windows, log a warning and continue building only liba{hello}. At consumer side, access it as lib{hello} and get liba{hello} on Windows, on all other platforms, get what is set by the user. If the consumer forces config.bin.lib=shared then error out on Windows.

Firstly, this is not an ideal arrangement since it doesn't fit well into build2's library model. Ideally, a project should either provide only liba{} or libs{} or provide lib{} and let the user decide which variant(s) they want.

But if there is no other choice, you can achieve this by overriding bin.lib in your build/root.build. For example, add something along these lines after loading the cxx module (adjust the code accordingly if you are using c):

if ($cxx.target.class == 'windows')
{
  assert ($bin.lib != 'shared') 'only static variant can be built on Windows'
  bin.lib = static
}

For completeness you will also want to disable importing of the shared variant by modifying your build/export.build along these lines:

$out_root/
{
  include libhello/
}

if ($($out_root/libhello/ cxx.target.class) == 'windows')
  assert ($import.target != libs{hello}) "only static variant can be imported on Windows"

export $out_root/libhello/$import.target

I wouldn't recommend issuing a warning (there is nothing the user of your library can do about it), but if you want, you can modify the above code in build/root.build along these lines:

if ($cxx.target.class == 'windows')
{
  switch $bin.lib
  {
    case 'shared'
      fail 'only static variant can be built on Windows'
    case 'both'
    {
      warn 'only static variant will be built on Windows'
      bin.lib = static
    }
  }
}