cmake issues

[sezero]

In SDL_mixer, we submodule'd opus and opusfile through our forks
and attempted cmake build relying on the submodules. Issues we had:

• The git tree, obviously, is missing a package_version file. We
  added to both opus and opusfile. However:

• If everything fails opusfile cmake'ry sets OPUSFILE_PROJECT_VERSION
  to 0, as in integer:
  https://github.com/xiph/opusfile/blob/master/cmake/OpusFilePackageVersion.cmake#L63
  ... But the caller expects a version instead, and fails:
  https://github.com/xiph/opusfile/blob/master/CMakeLists.txt#L6-L9
  Should you change the fallback OPUSFILE_PROJECT_VERSION to 0.0
  instead? (Same is true in Opus project.)

• Opusfile cmake'ry doesn't look for package_version file if it
  finds git, because the package_version case is an elseif case
  which seems wrong:
  https://github.com/xiph/opusfile/blob/master/cmake/OpusFilePackageVersion.cmake#L31
  Finalizing the git case with an endif changing package_version
  case to an if fixes things for us.

• Opus: Going from v1.3.1 to git master, the issue described above is
  present in opus too:
  https://github.com/xiph/opus/blob/master/cmake/OpusPackageVersion.cmake#L31
  The 1.3.1 release was good:
  https://github.com/xiph/opus/blob/e85ed7726db5d677c9c0677298ea0cb9c65bdd23/opus_functions.cmake#L45
  (Note that get_package_version used to return only if git case succeeded.)
  So the same suggestion as in the opusfile case above.

[sezero]

Any comments please?

[sezero]

PING - anyone?

[xnorpx]

@sezero Hi, I am not so good with all the version stuff. But can you check if this change would fix the issues you have for opus?

xnorpx/opus@093b8da

[sezero]

@madebr: cmake is your language, can you have a look?
Reference issue: libsdl-org/SDL_mixer#386 (comment)
Related commits:
libsdl-org@264fc0d
libsdl-org@9ba5cc3

[daddesio]

I like @sezero's idea of using "if" instead of "else if". That way if decoding the package_version fails, it tries again from git. Like this:

if(NOT OPUS_PACKAGE_VERSION){ try getting it from package_version file }
if(NOT OPUS_PACKAGE_VERSION){ try getting it from git }
if(NOT OPUS_PACKAGE_VERSION){ print warning and set to 0.0 }

Side note, I think it would be useful to keep a basic "version" file maintained in-repo so we don't need to fallback to 0.0. (e.g. ogg keeps the version in the configure.ac file in the repo, but opus/opusfile currently do not.) In that case, we'd still need to get the commit id from git if available (and only if the git tag matches the version file). @mark4o thoughts?