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 >
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