cmake: allow users to define CMAKE_FIND_ROOT_PATH_MODE_XXX

[theodelrieu]

Hello,

I'm opening this PR to solve an issue I have with my setup, here is a short summary:

I'm using Conan at work to manage C++ dependencies, and we are trying to cross-build to WebAssembly with Emscripten. To do so, I created a "Toolchain package" which sets correct flags automatically for consumers of this package.

For CMake builds, I simply exposed the CMAKE_TOOLCHAIN_FILE to point to Emscripten.cmake.

The thing is find_package now fails to find any dependency, due to the CMAKE_FIND_ROOT_PATH_MODE_PACKAGE set to ONLY.

While this is a valid behavior for regular CMake use-case, it is quite inconvenient for us, since Conan packages are all located in different folders, but are still found easily with CMAKE_PREFIX_PATH being set with all the package folders' paths. However, ONLY prevents it from working, and I'd like to set every MODE_XXX setting to BOTH.

So I simply mimicked what's done in the Android NDK's toolchain file and added some if/endif guards around each set(). It allows users to specify a different value if they need. This works great for us when cross-building to Android with Conan.

Note:

I first tried to simply include Emscripten's Toolchain from a custom toolchain file, and reset those variables. However, the CMakeSystemSpecificInformation.cmake includes Emscripten.cmake right before processing the customer CMakeLists.txt and thus the variables are overriden with the default values.

[gabrielcuvillier]

Did you try to update the CMAKE_FIND_ROOT_PATH with your own paths ?
eg. list(APPEND CMAKE_FIND_ROOT_PATH <path_to_conan_root>)

It could possibly work. At least, I am solving a similar issue like this...

[traversaro]

Did you try to update the CMAKE_FIND_ROOT_PATH with your own paths ?
eg. list(APPEND CMAKE_FIND_ROOT_PATH <path_to_conan_root>)

It could possibly work. At least, I am solving a similar issue like this...

We are experiencing a similar issue in vcpkg (see microsoft/vcpkg#11323 (comment)) and, unless we are doing something wrong, appending the desired root to CMAKE_FIND_ROOT_PATH is not sufficient.

[traversaro]

Did you try to update the CMAKE_FIND_ROOT_PATH with your own paths ?
eg. list(APPEND CMAKE_FIND_ROOT_PATH <path_to_conan_root>)
It could possibly work. At least, I am solving a similar issue like this...

We are experiencing a similar issue in vcpkg (see microsoft/vcpkg#11323 (comment)) and, unless we are doing something wrong, appending the desired root to CMAKE_FIND_ROOT_PATH is not sufficient.

It turns out that solution was working, but it is also necessary to add / to the CMAKE_PREFIX_PATH, see microsoft/vcpkg#11323 (comment) .

[stale]

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