Which version of CMake and Ninja are you using?
It seems like you are trying to reimplement what has been added in CMake
3.9. Quote from the changelog:
The Ninja generator has loosened the dependencies of object compilation.
Object compilation now depends only on custom targets and custom
commands associated with libraries on which the object’s target depends
and no longer depends on the libraries themselves. Source files in
dependent targets may now compile without waiting for their targets’
dependencies to link.
Have you tried it? It shouldn't need any change in your project, but I'm
not sure how it will behave if you already started to migrate to OBJECT
libraries.
Regards,
Florent
On 14/11/2017 17:48, Bernhard Burgermeister wrote:
Hello,
I'm trying to improve parallelization of a massive parallel
Ninja/icecream build by using object libraries. We are already using
interface include directories extensively.
While moving the compilation to separate object libraries I need to
define the include directories for these object targets. Previously
this simply worked by target_link_library(x PRIVATE a) so that x uses
the public and interface include directories of a. With object
libraries this is not possible, for example
======================================
CMAKE_MINIMUM_REQUIRED(VERSION 3.7)
PROJECT(ObjectLibLink C)
ADD_LIBRARY(a INTERFACE)
TARGET_INCLUDE_DIRECTORIES(a INTERFACE include)
ADD_LIBRARY(b OBJECT b.c)
TARGET_LINK_LIBRARIES(b PRIVATE a)
======================================
gives the error message
Object library target "b" may not link to anything
with CMake 3.7, 3.9 and 3.10rc3. The documentation of the later
version says "OBJECT libraries may not be used in the right hand side
of target_link_libraries()" but does not restrict the left hand side.
I would expect it to build b with include-directory "include" from a.
Currently I'm using a workaround
FOREACH(Lib ${ARG_LINK})
IF(TARGET ${Lib})
TARGET_INCLUDE_DIRECTORIES(MyObjectLib PRIVATE
$<TARGET_PROPERTY:${Lib},INTERFACE_INCLUDE_DIRECTORIES>)
ENDIF()
ENDFOREACH()
but this only works for targets previously defined or only target
libraries may be used. Otherwise the generator fails for file names or
system library names because there is no generator expression to check
for existing targets (see
https://gitlab.kitware.com/cmake/cmake/issues/17123). I want to avoid
explicitly import all these libraries.
Is there an other reliable way to populate include_directories that I
have not yet found? Of course compile_definitions and compile_options
should be added from the other libraries too.
Regards,
Bernhard.
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