[cmake-developers] find_package with NO_MODULE while cross-compiling

[Julien Schueller]

Hi, 

When using find_package (<name> NO_MODULE) while cross-compiling, 
cmake may find an existing <name>Config.cmake in the host root path if <name>Config.cmake is not available in the target root path. 

For example let's say that I have Qt5 project in my host Linux box, which provides a /usr/lib/cmake/.../Qt5WidgetsConfig.cmake. 
In my cmake project I use: find_package (Qt5Widgets NO_MODULE), everything goes as planned. 
Now I want to cross-compile using MinGW-w64, I install qt5 in my mingw target root, so I have a /usr/i686-w64-mingw32/lib/cmake/.../Qt5WidgetsConfig.cmake 
I set CMAKE_FIND_ROOT_PATH to /usr/i686-w64-mingw32 and stuff via a toolchain file, and everything goes fine too. 
No if I remove the qt5 target package for mingw, or it is unavailable in the first place, cmake prefers the host qt5 config file, and the compilation fails. 

I found a workaround, which is to not let cmake use host rules to find <name>Config.cmake in the case of cross-compiling: 
if (CMAKE_CROSSCOMPILING) 
set (NO_MODULE_ARGS NO_MODULE NO_SYSTEM_ENVIRONMENT_PATH NO_CMAKE_SYSTEM_PATH) 
endif () 
find_package (Qt5Widgets ${NO_MODULE_ARGS}) 
Would there be a smarter way to do this instead of invading each CMakeLists that uses a find_package relying on package-provided cmake configs ? 


-- 
Julien Schueller 
Phimeca Engineering 
www.phimeca.com 
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