JonathanHenson
commented
4 years ago Okay, so I've been wanting to ditch EXTERNAL_PROJECT_ADD for a while and this finally convinced me to actually do it.
So the idea is,
each aws-c- lib will be able to build in source (this takes work and I'm doing it now), or via traditional find_package. then the aws-crt-cpp package will use git submodules to each aws-c- lib it needs with the new flag IN_SOURCE_BUILD=ON
the crt will just use add_subdirectory.
We'll do the same thing for the iot sdk at that point as well. This way the cmake build problems with caching, needing a network during build, and the numerous flag passing bugs just go away.
This does mean however, users migrating from the current version to the next version will need to remember to do git clone --recursive to build. I think this is a fair tradeoff though.
Thoughts on this approach?
EeroKurimo
massi-ang
I cannot run cmake configure as instructed in README.md for aws-iot-device-sdk-cpp-v2 with the tag v1.4.3 (or older) using Visual Studio 2019 and Cmake 3.15.2 with the command
cmake -DCMAKE_INSTALL_PREFIX="c:/data/aws-iot-device-sdk-cpp-v2-install" -DBUILD_DEPS=ON c:/data/aws-iot-device-sdk-cpp-v2, because the cmake configure step fails while building aws-crt-cpp with a number of errors like:However, if manually clone and cmake configure aws-crt-cpp independently, it works fine!
Comparing the build directories of the manually configured aws-crt-cpp and the failing aws-crt-cpp automatically configured by the sdk v2 depencency chain, in their CMakeCache.txt files I can see that the manually configured aws-crt-cpp has the env variable
CMAKE_CXX_FLAGS:STRING=/DWIN32 /D_WINDOWS /W3 /GR /EHsc, but in the dependency chain configured CMakeCache.txt the variable instead is an empty stringCMAKE_CXX_FLAGS:STRING=.Unless I'm doing something horribly wrong, I suspect the problem is that aws-iot-device-sdk-cpp-v2/CMakeLists.txt on line 71 (just before mixing tabs and spaces for indentation!) uses execute_process() to run cmake configure for aws-crt-cpp with the option
-DCMAKE_CXX_FLAGS=${CMAKE_CXX_FLAGS}, which sets the value of CMAKE_CXX_FLAGS of aws-crt-cpp to be an empty string instead undefined, and apparently if it's undefined it eventually gets replaced with the cmake default values.Removing the option
-DCMAKE_CXX_FLAGS=${CMAKE_CXX_FLAGS}from the aws-iot-device-sdk-cpp-v2/CMakeLists.txt fixes the cmake configure step errors, at least for me.As for a good solution, I'm not sure what would be a good way pass cmake env variables but only when defined. One option might be the the new FetchContent() (https://cmake.org/cmake/help/latest/module/FetchContent.html) cmake command, which might be a good way to pass all env variables automatically instead of manually passing command line strings with execute_process().
P.S. I believe that when @kankri in https://github.com/awslabs/aws-c-mqtt/pull/116 mentioned that his build of sdk-cpp-v2 fails on windows, he referred to this issue, as he was also having this same build issue before the christmas holidays.