Enable CMake user option BUILD_SHARED_LIB

[Waschina]

Description

The CMake configuration does not respect the user option "-DBUILD_SHARED_LIB=<ON/OFF>". Package managers (and users) commonly use this main configuration option to decide whether to build the project as a shared or static library. Specifically, library build systems for dependencies of R-packages expect the BUILD_SHARED_LIB option: (Windows build system, MacOS build system).

Generally, the BUILD_SHARED_LIB variable directly affects the command add_library() if no type (SHARED or STATIC) is given to the function. Instead of BUILD_SHARED_LIB, libsbml's CMake setup seems to use the non-canonical options LIBSBML_SKIP_SHARED_LIBRARY and LIBSBML_SKIP_STATIC_LIBRARY:

https://github.com/sbmlteam/libsbml/blob/a3e217851f18d3c5e8e2b0082fb98176738491e8/src/CMakeLists.txt#L512C1-L513C2
https://github.com/sbmlteam/libsbml/blob/a3e217851f18d3c5e8e2b0082fb98176738491e8/src/CMakeLists.txt#L462C1-L464C2

Motivation and Context

Although I think the libsbml-specific shared/static build config options (LIBSBML_SKIP_<SHARED/STATIC>_LIBRARY) are totally fine, I would suggest enabling the widespread user option BUILD_SHARED_LIB as well, which would make libsbml also more accessible and easier to implement for developers of packages and toolchains.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Change in documentation

Checklist:

• I have updated all documentation necessary.
• I have checked spelling in (new) comments.

Testing

• Testing is done automatically and codecov shows test coverage
• This cannot be tested automatically
  I tested the new option manually using the CMake GUI in Windows. It worked as expected: Shared library build can be skipped with the new option "-DBUILD_SHARED_LIB=OFF".

[fbergmann]

Thanks for the PR, I agree we should honor the BUILD_SHARED_LIBS option if specified. But we should not set a default. I'll make slight changes so that

• if BUILD_SHARED_LIBS is defined and TRUE, only the shared lib is built,
• if it is defined and FALSE only the static one is built
• if not defined the build behavior is the same as before (building both by default, or honoring LIBSBML_SKIP variables)

that should solve your issue, and not change the behavior for anyone else.