Force find_package to fail if required library type (shared vs. static) is not found

Usage
1

Note: a similar issue is described in Choose between shared/static library after find_package() but the answer is inadequate for some scenarios in my opinion.

Near trivial task: I want to link a shared library against dependencies installed on the system.

Now, to my understanding, CMake target_link_libraries does not support linking a shared library against static dependencies (at least I got linker errors when I last tried).

So - I want find_package to fail if the installed dependency is a static library, when BUILD_SHARED_LIBS=ON.

Edit: The solution should also work for MinGW where it appears shared libraries are split into a .dll and a .dll.a file. I would expect find_package to find the shared library so that I can perform a get_target_property for TYPE on the found package and the result is SHARED_LIBRARY

How would I best accomplish that?

2

This is not the meaning of this variable. It just defines shared/static for libraries that your project builds (if not set to a fixed type)

Linking to static libraries is definitely supported. However, you also have to know all transitive libraries or use something like pkg-config or cmake config files.

On some environments, you cannot always easily tell if the lib is shared or static and the property might be UNKNOWN.

3

Linking to static libraries is definitely supported. However, you also have to know all transitive libraries or use something like pkg-config or cmake config files.

That’s not my definition of “supported” - if I have to do a lot of workarounds myself in order to accomplish what normally is done with a single line target_link_libraries, then it’s not supported by cmake to link a shared library against static dependencies.

This is what I am asking: How do I ensure a controlled error when the user sets BUILD_SHARED_LIBS=ON, but the local system has at least one dependency only as a STATIC_LIBRARY?

The controlled error will look much cleaner than tons of linker errors during the build stage as it happened last time I had this scenario.