Re: [CMake] correct dependencies of update-if-different generated files?`
On 2013-07-29 19:02, Matthew Woehlke wrote: Let's say¹ I have a code generation tool, 'gen', that I am naïvely using to build a library, like so: add_custom_command( OUTPUT a.cpp b.cpp COMMAND gen in.xml DEPENDS in.xml ) add_library(foo a.cpp b.cpp) Now let's say that 'gen' is clever and does not overwrite the output files with identical content (sort-of like configure_file). Now, if in.xml is changed, the 'gen' command will run every time because the mtime of in.xml is newer than that of a.cpp and b.cpp. BUT... this "only" affects gmake (at least, it does not affect ninja² and reportedly does not affect VS). Has anyone run into this before, and/or is there a way to express the build rules so that the build will completely converge (will not execute any commands) *without* unnecessarily recompiling the generated source files? And, since I don't believe that there is, how would folks feel about improving add_custom_command to specifically handle this case? I think in pure make it is possible to solve the problem by having the custom command also update a sentinel file on successful completion, and doing like: a.cpp b.cpp: sentinel # No command here! sentinel: in.xml gen in.xml touch sentinel Such an enhancement would also be desirable as it would allow 'automatic' adjusting of the build rules for generators that have the problem with only a minor change to the CMake rules, and without penalizing generators that are more clever. (¹ Original/actual code where I ran into this: https://codereview.qt-project.org/61497) (² Ninja is not affected because it records the last time it updated the output files independent of their mtime.) bump? -- Matthew -- 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://www.cmake.org/mailman/listinfo/cmake
Re: [CMake] correct dependencies of update-if-different generated files?`
On 2013-07-29 19:02, Matthew Woehlke wrote: Let's say¹ I have a code generation tool, 'gen', that I am naïvely using to build a library, like so: add_custom_command( OUTPUT a.cpp b.cpp COMMAND gen in.xml DEPENDS in.xml ) add_library(foo a.cpp b.cpp) Now let's say that 'gen' is clever and does not overwrite the output files with identical content (sort-of like configure_file). Now, if in.xml is changed, the 'gen' command will run every time because the mtime of in.xml is newer than that of a.cpp and b.cpp. BUT... this "only" affects gmake (at least, it does not affect ninja² and reportedly does not affect VS). Has anyone run into this before, and/or is there a way to express the build rules so that the build will completely converge (will not execute any commands) *without* unnecessarily recompiling the generated source files? And, since I don't believe that there is, how would folks feel about improving add_custom_command to specifically handle this case? I think in pure make it is possible to solve the problem by having the custom command also update a sentinel file on successful completion, and doing like: a.cpp b.cpp: sentinel # No command here! sentinel: in.xml gen in.xml touch sentinel Such an enhancement would also be desirable as it would allow 'automatic' adjusting of the build rules for generators that have the problem with only a minor change to the CMake rules, and without penalizing generators that are more clever. (¹ Original/actual code where I ran into this: https://codereview.qt-project.org/61497) (² Ninja is not affected because it records the last time it updated the output files independent of their mtime.) No comments? -- Matthew -- 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://www.cmake.org/mailman/listinfo/cmake
[CMake] correct dependencies of update-if-different generated files?`
Let's say¹ I have a code generation tool, 'gen', that I am naïvely using to build a library, like so: add_custom_command( OUTPUT a.cpp b.cpp COMMAND gen in.xml DEPENDS in.xml ) add_library(foo a.cpp b.cpp) Now let's say that 'gen' is clever and does not overwrite the output files with identical content (sort-of like configure_file). Now, if in.xml is changed, the 'gen' command will run every time because the mtime of in.xml is newer than that of a.cpp and b.cpp. BUT... this "only" affects gmake (at least, it does not affect ninja² and reportedly does not affect VS). Has anyone run into this before, and/or is there a way to express the build rules so that the build will completely converge (will not execute any commands) *without* unnecessarily recompiling the generated source files? And, since I don't believe that there is, how would folks feel about improving add_custom_command to specifically handle this case? I think in pure make it is possible to solve the problem by having the custom command also update a sentinel file on successful completion, and doing like: a.cpp b.cpp: sentinel # No command here! sentinel: in.xml gen in.xml touch sentinel Such an enhancement would also be desirable as it would allow 'automatic' adjusting of the build rules for generators that have the problem with only a minor change to the CMake rules, and without penalizing generators that are more clever. (¹ Original/actual code where I ran into this: https://codereview.qt-project.org/61497) (² Ninja is not affected because it records the last time it updated the output files independent of their mtime.) -- Matthew -- 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://www.cmake.org/mailman/listinfo/cmake
