What does output_required_files() [0] do, and is it applicable here? [0] https://cmake.org/cmake/help/v3.4/command/output_required_files.html
On Mon, Nov 30, 2015 at 2:09 AM, Petr Kmoch <petr.km...@gmail.com> wrote: > Hi Dan, > > you could look into the IMPLICIT_DEPENDS argument of add_custom_command: > https://cmake.org/cmake/help/latest/command/add_custom_command.html > > I don't have direct experience with it, but it looks like it could do what > you're looking for. > > Petr > > On Sun, Nov 29, 2015 at 10:47 AM, Dan Liew <d...@su-root.co.uk> wrote: >> >> Hi, >> >> # TL;DR >> >> I need a way of determining the header file dependencies of a source >> file and inform CMake about them. CMake doesn't do this automatically >> because I'm using custom commands for the compilation step so CMake >> doesn't do it's usual magic of automatically inferring source file >> header dependencies. This is because this part of the compilation step >> requires a separate C++ compiler (completely independent from the one >> that CMake detects at configure time). >> >> Is there a way of doing this that will also regenerate the >> dependencies if the source file changes? >> >> # Long version >> >> A C++ project that I work on [1] is (amongst other things) a compiler. >> In order to compile applications it needs to link in a supporting >> runtime that is compiled to LLVM bitcode which is linked into the >> applications it compiles. >> >> The supporting runtime is written in C++ and compiled with Clang. The >> compilation of the runtime is currently achieved using >> ``add_custom_command()`` and so I am not using CMake's in built >> support for detecting header file dependencies. The reason for doing >> it this way is because the LLVM bitcode compiler (i.e. Clang) **is >> not** the same compiler as the host C++ compiler for the project. For >> example the host code might be built with MSVC but the supporting >> runtime is **always** built with Clang. >> >> To see this concretely take a look at [2]. >> >> The build works correctly if you build from a clean build directory. >> It does not work correctly if you perform a rebuild and change one of >> the header files that the supporting runtime depends on. This is >> because CMake doesn't know that the runtime source files depend on the >> header files and so doesn't rebuild the relevant source files. >> >> I can obviously tell CMake about these manually (adding more entries >> under ``DEPENDS`` in the ``add_custom_command()`` invocation) but this >> is very cumbersome. >> >> What I really need is a way to >> >> * Automatically infer the dependencies of a source file and tell CMake >> about them >> * Have the dependencies automatically regenerated if the source file >> changes (someone could add or remove a header file include). >> >> In a simple Makefile build system this typically achieved by doing >> something like this: >> >> ``` >> all:: $(SRCS:.cpp:.o) >> >> SRCS := foo.cpp bar.cpp >> >> # Include SRC file dependencies generated by the compiler if they exist >> -include $(SRCs:.cpp=.d) >> >> %.o : %.cpp >> $(CXX) -c $< -o $@ -MP -MMD -MF $*.d >> ``` >> >> Note the ``-M*`` flags get the compiler when it runs to generate >> additional makefile rules that will get included next time a build >> happens. >> >> I don't really know how to do the same thing with CMake. One idea is >> at configure time invoke Clang with the ``-MP -MMD -MF`` flags on each >> runtime source file, extract the dependencies then pass them to >> ``DEPENDS`` in ``add_custom_command()``. If I wanted the dependencies >> regenerated if the runtime source file changes then I would need to >> somehow get CMake to reconfigure every time this happens. >> >> I don't like this idea very much due to >> >> * Having to invoke Clang manually to determine the dependencies. CMake >> already knows how to determine source file dependencies, but this >> functionality (AFAIK) isn't exposed to me. >> >> * Reconfiguring every time one of the runtime source file changes is >> annoying (configuring can be slow sometimes). >> >> Does anyone have any other ideas? CMake obviously knows how to do all >> this stuff already for source files being compiled for the detected >> host C++ compiler, I just don't know how to get at this logic for >> source files that need to be built with a second independent C++ >> compiler. >> >> [1] https://github.com/halide/Halide >> [2] https://github.com/halide/Halide/blob/master/src/CMakeLists.txt#L140 >> >> Thanks, >> Dan. >> -- >> >> Powered by www.kitware.com >> >> Please keep messages on-topic and check the CMake FAQ at: >> http://www.cmake.org/Wiki/CMake_FAQ >> >> Kitware offers various services to support the CMake community. For more >> information on each offering, please visit: >> >> CMake Support: http://cmake.org/cmake/help/support.html >> CMake Consulting: http://cmake.org/cmake/help/consulting.html >> CMake Training Courses: http://cmake.org/cmake/help/training.html >> >> Visit other Kitware open-source projects at >> http://www.kitware.com/opensource/opensource.html >> >> Follow this link to subscribe/unsubscribe: >> http://public.kitware.com/mailman/listinfo/cmake-developers > > > > -- > > Powered by www.kitware.com > > Please keep messages on-topic and check the CMake FAQ at: > http://www.cmake.org/Wiki/CMake_FAQ > > Kitware offers various services to support the CMake community. For more > information on each offering, please visit: > > CMake Support: http://cmake.org/cmake/help/support.html > CMake Consulting: http://cmake.org/cmake/help/consulting.html > CMake Training Courses: http://cmake.org/cmake/help/training.html > > Visit other Kitware open-source projects at > http://www.kitware.com/opensource/opensource.html > > Follow this link to subscribe/unsubscribe: > http://public.kitware.com/mailman/listinfo/cmake -- Powered by www.kitware.com Please keep messages on-topic and check the CMake FAQ at: http://www.cmake.org/Wiki/CMake_FAQ Kitware offers various services to support the CMake community. For more information on each offering, please visit: CMake Support: http://cmake.org/cmake/help/support.html CMake Consulting: http://cmake.org/cmake/help/consulting.html CMake Training Courses: http://cmake.org/cmake/help/training.html Visit other Kitware open-source projects at http://www.kitware.com/opensource/opensource.html Follow this link to subscribe/unsubscribe: http://public.kitware.com/mailman/listinfo/cmake
