Openenclave: find_package(openenclave) fails the second time

[letmaik]

CMake Error at /opt/openenclave/lib/openenclave/cmake/openenclave-config.cmake:50 (add_executable):
  add_executable cannot create imported target "openenclave::oeedger8r"
  because another target with the same name already exists

Repro:

find_package(openenclave)
find_package(openenclave)

[johnkord]

@andschwa Andy, is this expected? I've hit this before as well

[andschwa]

I don't think you're generally supposed to be able to run find_package twice because they add targets.

[letmaik]

@andschwa I disagree, this is a common scenario, especially when consuming other projects directly via add_subdirectory, which is what FetchContent was invented for. And in that case it is totally reasonable that two unrelated projects each call find_package on the same dependency. So, this should never ever fail and typically there are checks in place to see whether the target is already defined etc. See e.g. https://github.com/Kitware/CMake/blob/4ccf40e61e02cffb28b549a3de6f4794ea3e3d92/Modules/FindZLIB.cmake#L125.

[andschwa]

Ah we can do that.

[andschwa]

@aserdean This should probably just check if the target is defined before making it in the CMake package.

[letmaik]

Why was this closed? There is no test in the PR and it's still broken.

CMake Error at /.../openenclave/cmake/openenclave-config.cmake:49 (add_library):
  add_library cannot create imported target "crypto" because another target
  with the same name already exists.

[johnkord]

Thanks @letmaik I'll reopen this! Looks like the PR that auto-closed this issue solved the problem for the openenclave:: namespaced targets, but not for the crypto/dl imported targets.

Edit: Looks like the crypto/dl imported targets didn't exist at the time! We added those later. @EmilAlexandruStoica Interested in looking at this problem? :)

[EmilAlexandruStoica]

@johnkord I'll try to solve this as soon as posible.