For policy-specific tests, use the version before the policy was
introduced. Otherwise, use 3.5 where possible.
Also, remove `cmake_minimum_required()` and `project()` calls from
individual cases where they are handled by `CMakeLists.txt`.
The OLD behaviors of all policies are deprecated, but only by
documentation. Add an explicit deprecation diagnostic for policies
introduced in CMake 3.12 and below to encourage projects to port
away from setting policies to OLD.
Extend the change made by commit fe4b25ec2f (Teach target_* commands to
set INTERFACE properties of IMPORTED targets, 2017-09-18,
v3.11.0-rc1~433^2~2) to work with imported targets of type `UNKNOWN`.
Fixes: #19434
Note: This still does not link the object-files of the `OBJECT` library
from the right-hand side of `target_link_libraries` to the target on the
left-hand side. (In this particular case of another `OBJECT` library on
the left-hand side this would not make any sense anyway. The target on
the left-hand side has no link-step.)
Issue: #14778
Note: This only allows `OBJECT` libraries to be on the right-hand side
of `target_link_libraries` but still does not link its object-files to
the target on the left-hand side.
Issue: #14778
The proper way to use libraries is now through `target_link_libraries`
for things such as usage requirements, compile definitions, include
directories, etc. To facilitate this, allow `OBJECT` libraries to "link"
to other libraries.
Co-Author: Ben Boeckel <ben.boeckel@kitware.com>
Issue: #14778
Now, several `INTERFACE_*` properties can be set on `IMPORTED` targets,
not only via `set_property` and `set_target_properties` but also via
`target_compile_definitions`, `target_compile_features`,
`target_compile_options`, `target_include_directories`, `target_sources`
and `target_link_libraries`.
Fixes: #15689
Issue: #17197
The `add_library` and `add_executable` commands can now be called with
no source-files and won't generate a warning or error message, as long
as source-files will be added later via the `target_sources` command.
If during the generation step still no sources are associated with
targets created by such calls a useful error message will be generated
and generation fails.
Targets of type `INTERFACE_LIBRARY`, `UTILITY` or `GLOBAL_TARGET` are
excluded from this check because we do not need sources for these target
types during generation.
Fixes: #16872
