[CMake] FetchContent and find_package

[Saad Khattak]

Hi,

My project is setup in such a way that I perform a FetchContent 'only if'
my find_package fails.

This works very well until I start building different configurations. Let's
say I generate and build Debug for my project. My project tries to
find_package(LibA QUIET) and cannot find it. So, it performs a
FetchContent(...) step, builds the dependency and my library and installs
everything. This works flawlessly.

Now I start building a Release version with different build and install
folders. Unfortunately, find_package(LibA QUIET) finds the Debug libraries
and does not perform a FetchContent(...) step and in turn doesn't build the
Release version of the dependent library. Consequently, the linking step
fails.

Is there an easy way around this issue?

I say 'easy' because I could write some CMake scripts to search for the
libraries after a successful find_package(...) and if it only finds
libraries for Debug when it really wants Release, it performs a
FetchContent(...). However, this could be quite fragile.

It would be nice if CMake has a way of knowing if an installed library,
found through find_package(...) is Debug, Release, RelWithDebInfo etc.

- Saad
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