[cmake-developers] why includes the Ninja decency contents sytemheader too?

[Claus Klein]

I’m wondering about the different dependency strategies between ‚Unix Makefiles’ and Nina generator. IMHO: This make ninja slower without much user benefit! -Claus find . -name depend.make | xargs cat # CMAKE generated file: DO NOT EDIT! # Generated by "Unix Makefiles" Generator, CMake Version 3.10 CMakeFiles/BindToDevice.dir/BindToDevice.c.o: ../BindToDevice.c # CMAKE generated file: DO NOT EDIT! # Generated by "Unix Makefiles" Generator, CMake Version 3.10 CMakeFiles/InnerClassIdiom.dir/InnerClassIdiom.cpp.o: ../InnerClassIdiom.cpp # CMAKE generated file: DO NOT EDIT! # Generated by "Unix Makefiles" Generator, CMake Version 3.10 CMakeFiles/testFileAppend.dir/tests/testFileAppend.c.o: ../tests/testFileAppend.c ######################################### Claus-MBP:build clausklein$ ninja -t deps CMakeFiles/testFileAppend.dir/tests/testFileAppend.c.o: #deps 98, deps mtime 1517904010 (VALID)     ../tests/testFileAppend.c     /usr/include/sys/stat.h     /usr/include/sys/_types.h     /usr/include/sys/cdefs.h     /usr/include/sys/_symbol_aliasing.h     /usr/include/sys/_posix_availability.h     /usr/include/machine/_types.h     /usr/include/i386/_types.h     /usr/include/sys/_pthread/_pthread_types.h     /usr/include/Availability.h     /usr/include/AvailabilityInternal.h # …. quote from ninja list: On Thu, Nov 30, 2017 at 12:09:55 -0800, Evan Martin wrote: That CMake change is interesting.  While it's true that it is more correct to check the state of the system headers, it's also true that to be fully correct here you need a completely hermetic build.  If CMake doesn't also check the compiler binary as well as any shared libraries that the compiler binary uses, then I think using this extra flag only serves to make ninja slower without much user benefit. The mentioned issue is here:    https://cmake.org/Bug/view.php?id=14914 It was done for feature parity with the Makefiles generators. They use CMake's scanning logic rather than exact dependencies like Ninja (for various reasons). --Ben

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