[cmake-developers] Source file dependencies

[Wouter Klouwen]

Hi Craig,

thanks for the tip.

My use case is specifically with external projects producing files that I don't know about in advance, so I thought OBJECT_DEPENDS wouldn't really work. But then I realised that if I can extract the name of the "done" stamp, this would do the trick.

So I end up with an external project declaration something like this:

ExternalProject_Add(foo URL foo.tgz
	BUILD_COMMAND make -C <SOURCE_DIR> all
	INSTALL_COMMAND make -C <SOURCE_DIR> install
)

_ep_get_step_stampfile(foo "done" foo_done_stamp_file)
add_library(libfoo INTERFACE IMPORTED)
add_dependencies(libfoo foo)
set_target_properties(libfoo PROPERTIES
	INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_INSTALL_PREFIX}/include)

And then simply a project declaration like this:

project(bar)

set_source_files_properties(bar.c OBJECT_DEPENDS ${foo_done_stamp_file})
add_executable(bar bar.c)
target_link_libraries(bar libfoo)

And very happily, it doesn't try to compile bar.c until the "foo" external project has been installed. It's unfortunate to have to use an internal ExternalProject function but AFAICT this is the best way without repeating logic to get the complete filepath of the stamp.

Thanks again,
    W
________________________________________
From: Craig Scott [craig.scott at crascit.com]
Sent: 07 December 2017 19:50
To: Wouter Klouwen
Cc: CMake Developers
Subject: Re: [cmake-developers] Source file dependencies

[External email]

Have a look at the documentation for the OBJECT_DEPENDS source property<https://cmake.org/cmake/help/latest/prop_sf/OBJECT_DEPENDS.html>, which explains some options that may be relevant for your question.

On Fri, Dec 8, 2017 at 5:08 AM, Wouter Klouwen <wouter.klouwen at youview.com<mailto:wouter.klouwen at youview.com>> wrote:
Hi all,

In trying to improve our build rules, one of the problems I encountered
is that I effectively have some source files that cannot be compiled
unless certain targets are run.

I noticed that cmSourceFile has the AddDepend() method, which looks to
do the kind of thing that I want to do.
cmFlTKWrapUICommand and cmCPluginAPI are the only users of this, with
there being no way of setting this from a CMakeLists.txt.
The former seems to do exactly the kind of think that I need, which is
to set up some code generation.

It would be nice if I could add items to this list, perhaps through
setting a property on the source files themselves, e.g this rather
contrived short example:

add_custom_command(OUTPUT bar.h COMMAND touch bar.h)
add_custom_target(bar DEPENDS generate_bar bar.h)
set_source_files_properties(foo.cpp PROPERTIES DEPENDS bar)

Is this a bad idea? Would there be a better way?

Thanks,
    W
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Craig Scott
Melbourne, Australia
https://crascit.com


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