We should also check whether the INTERFACE_ variant of a property
is being read, and in the case of the compile definitions, we should
test the _<CONFIG> suffixed variants. That is already available
through the use of the methods.
This way, we use the ALREADY_SEEN optimization when evaluating
the includes of a target in 'external' generator expressions, ie, those
used in a add_custom_command invokation, as opposed to evaluating the
INCLUDE_DIRECTORIES of a target itself via GetIncludeDirectories.
This means that we can use expressions of the form
$<TARGET_PROPERTY:foo,INTERFACE_INCLUDE_DIRECTORIES>
to get a list of the interface include directories of foo, including
those coming from dependencies.
We can't have a test of a target which has a single include directory in
its INCLUDE_DIRECTORIES because the shell on the MSYS platforms transforms
a single include directory to include a prefix, which is not what the test
expects. We test a target with two directories instead as a means to
test a target with no link dependencies.
This is for specifying INCLUDE_DIRECTORIES relevant to the build-location
or the install location for example:
set_property(TARGET foo PROPERTY
INTERFACE_INCLUDE_DIRECTORIES
"$<BUILD_INTERFACE:${CMAKE_CURRENT_BINARY_DIR};${CMAKE_CURRENT_SOURCE_DIR}>"
"$<INSTALL_INTERFACE:${CMAKE_INSTALL_PREFIX}/include>"
)
A 'bar' target can then use:
set_property(TARGET bar PROPERTY
INCLUDE_DIRECTORIES
"$<TARGET_PROPERTY:foo,INTERFACE_INCLUDE_DIRECTORIES>"
)
and it will work whether foo is in the same project, or an imported target
from an installation location, or an imported target from a build location
generated by the export() command.
Because the generator expressions are only evaluated at build-time, these
new expressions are equivalent to the ZeroNode and OneNode.
The GeneratorExpression test is split into parts. Some shells can't run
the custom command as it is getting too long.
Stephen Kelly