This tracking was added during the development of commit 042ecf04
(Add API to calculate link-interface-dependent bool properties
or error., 2013-01-06), but was never used.
It was not necessary to use the content because what is really
useful in that logic is to determine if a property has been implied
to be null by appearing in a LINK_LIBRARIES genex.
I think the motivating usecase for developing the feature of
keeping track of the targets relevant to a property was that I
thought it would make it possible to allow requiring granular
compatibility of interface properties only for targets which
depended on the interface property. Eg:
add_library(foo ...)
add_library(bar ...)
add_executable(user ...)
# Read the INTERFACE_POSITION_INDEPENDENT_CODE from bar, but not
# from foo:
target_link_libraries(user foo $<$<TARGET_PROPERTY:POSTITION_INDEPENDENT_CODE>:bar>)
This obviously doesn't make sense. We require that INTERFACE
properties are consistent across all linked targets instead.
We need to make sure expressions which evaluate TARGET_PROPERTY:TYPE
multiple times for example get the correct result each time, and
not an empty string instead.
Generator expressions whose output depends on the configuration
now record that fact. The GetIncludeDirectories method can use
that result to cache the include directories for later calls.
GetIncludeDirectories is called multiple times for a target
for each configuration, so this should restore performance for
multi-config generators.
While porting boost to use these features, the generation step took
too long (several minutes before I stopped it). The reason was that
the boost libraries form a large interdependent mesh. The libraries
list their dependencies in their INTERFACE such as:
$<LINKED:boost::core>;$<LINKED:boost::config>;$<LINKED:boost::mpl>
As boost::core already depends on the boost::config libraries, that
expression has no impact on the end-content, as it is removed after
the generation step. There is no DAG issue though, so the generator
expression evaluation would fully evaluate them. In the case of the
config library, it also depends on the core library, so all depends
are followed through that again, despite the fact that they've just
been evaluated. After this patch, the evaluation skips libraries if
they have already been seen via depends or directly in the content.
This patch keeps track of targets whose INTERFACE has been consumed
already. The INCLUDE_DIRECTORIES and COMPILE_DEFINITIONS properties
are whitelisted because repeated content will be stripped out later
during generation. For other properties now and in the future, that
may not be the case.
This is both a short form of using a TARGET_DEFINED expression
together with a TARGET_PROPERTY definition, and a way to strip
non-target content from interface properties when exporting.
This new expression allows checking how a policy was set when a target
was created. That information is only recorded for a subset of policies,
so a whitelist is used.
894f52f Handle INTERFACE properties transitively for includes and defines.
f5b1980 Populate the ExportedTargets member early in GenerateMainFile
c67b812 Make cycles in target properties ignored, not an error.
d0f950f Use mapped config properties to evaluate $<CONFIG>
26def17 Make all relevant targets available in the genex context.
0c657dc Add API to populate INTERFACE properties in exported targets.
e04f737 Add API to extract target names from a genex string.
b0c8f73 Add the TARGET_NAME generator expression.
77475fe Allow generator expressions to require literals.
b2f1700 GenEx: Add expressions to specify build- or install-only values
Constructs such as these are an error as they are direct self-references:
set_property(TARGET foo APPEND PROPERTY
INCLUDE_DIRECTORIES $<TARGET_PROPERTY:foo,INCLUDE_DIRECTORIES>)
set_property(TARGET foo APPEND PROPERTY
INCLUDE_DIRECTORIES $<TARGET_PROPERTY:INCLUDE_DIRECTORIES>)
However, this is an indirect self-reference in a cycle, and not an error:
set_property(TARGET foo APPEND PROPERTY
INCLUDE_DIRECTORIES $<TARGET_PROPERTY:bar,INCLUDE_DIRECTORIES>)
set_property(TARGET bar APPEND PROPERTY
INCLUDE_DIRECTORIES $<TARGET_PROPERTY:foo,INCLUDE_DIRECTORIES>)
This is for specifying INCLUDE_DIRECTORIES relevant to the build-location
or the install location for example:
set_property(TARGET foo PROPERTY
INTERFACE_INCLUDE_DIRECTORIES
"$<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
"$<TARGET_PROPERTY:foo,INTERFACE_INCLUDE_DIRECTORIES>"
)
and it will work whether foo is in the same project, or an imported target
from an installation location, or an imported target from a build location
generated by the export() command.
Because the generator expressions are only evaluated at build-time, these
new expressions are equivalent to the ZeroNode and OneNode.
The GeneratorExpression test is split into parts. Some shells can't run
the custom command as it is getting too long.
Following from the discussion here:
http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/3615/focus=5170
(Re: Generator expressisons in target properties, 26 Oct 12:10)
we can't split cmTarget API for linking into cmGeneratorTarget. In
the future we will probably also need to move the include and compile
definitions API back to cmTarget so that it can be used by export().
083de7e Process generator expressions in the COMPILE_DEFINITIONS target property.
08cb4fa Process generator expressions in the INCLUDE_DIRECTORIES property.
0ef091d Early return if there is no target.
eb250cd Add a self-reference check for target properties.
7e80747 Add API to check that dependent target properties form a DAG.
239ac84 Add a generator expression for target properties.
e028381 Extend the generator expression language with more logic.
b8e61d6 Refactor GetCompileDefinitions a bit.
2c2b25b Return a std::string from GetCompileDefinitions.
b7e48e0 Add an AppendDefines std::string overload.
9a16087 Convert paths in INCLUDE_DIRECTORIES property to Unix slashes.
4557c8d Don't prepend a path before generator expressions in include_directories.
c6abc41 Add include guard for cmGeneratorExpression.
0ff4e3f Port remaining code to GetCompileDefinitions().
f178d53 Fix indentation in the code blocks generator.
Prevent constructs like:
... INCLUDE_DIRECTORIES "$<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