Following from the discussion here:
http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/3615/focus=5170
(Re: Generator expressisons in target properties, 26 Oct 12:10)
we can't split cmTarget API for linking into cmGeneratorTarget. In
the future we will probably also need to move the include and compile
definitions API back to cmTarget so that it can be used by export().
083de7e Process generator expressions in the COMPILE_DEFINITIONS target property.
08cb4fa Process generator expressions in the INCLUDE_DIRECTORIES property.
0ef091d Early return if there is no target.
eb250cd Add a self-reference check for target properties.
7e80747 Add API to check that dependent target properties form a DAG.
239ac84 Add a generator expression for target properties.
e028381 Extend the generator expression language with more logic.
b8e61d6 Refactor GetCompileDefinitions a bit.
2c2b25b Return a std::string from GetCompileDefinitions.
b7e48e0 Add an AppendDefines std::string overload.
9a16087 Convert paths in INCLUDE_DIRECTORIES property to Unix slashes.
4557c8d Don't prepend a path before generator expressions in include_directories.
c6abc41 Add include guard for cmGeneratorExpression.
0ff4e3f Port remaining code to GetCompileDefinitions().
f178d53 Fix indentation in the code blocks generator.
Prevent constructs like:
... INCLUDE_DIRECTORIES "$<TARGET_PROPERTY:INCLUDE_DIRECTORIES>"
Indirect self-references (cycles) are also prevented here, but
indirect generator expression references of any kind are not
possible yet anyway.
There are two overloads, so that it can use the operational
target when a target property is being evaluated, and a target
can alternatively be specified by name.
At this point, the generators don't chain. That comes later.
Generator expressions for comparing strings, evaluating
strings as booleans, and for creating literal right-angle-brackets
and commas are added. Those may be needed in some cases
where they appear in literals.
The expressions may be parsed and then cached and evaluated multiple
times. They are evaluated lazily so that literals such as ',' can be
treated as universal parameter separators, and can be processed from
results without appearing literally, and without interfering with the
parsing/evaluation of the entire expression.
Stephen Kelly
Brad King