How to avoid two packages colliding?

[Julio C. Galindo]

Issue description

I'm adding my dependencies Protobuf and Snappy (both from Google) and they build gmock (other of Google libraries) included and it's built twice, which throws and error. How can I avoid that behavior?

CMakeLists.txt

...
add_package("gh:protocolbuffers/protobuf#main")
add_package("gh:google/snappy#main")
...

Error

CMake Error at C:/Users/jcgal/.cpm/snappy/59b0f9bb82a31b56cf6197fb63af2a03d76f9331/third_party/googletest/googletest/cmake/internal_utils.cmake:150 (add_library):
  add_library cannot create target "gmock" because another target with the
  same name already exists.  The existing target is a static library created
  in source directory
  "C:/Users/jcgal/.cpm/protobuf/29522687be03e21b7683f4277ecb0c4d3bd83954".
  See documentation for policy CMP0002 for more details.
Call Stack (most recent call first):
  C:/Users/jcgal/.cpm/snappy/59b0f9bb82a31b56cf6197fb63af2a03d76f9331/third_party/googletest/googletest/cmake/internal_utils.cmake:206 (cxx_library_with_type)
  C:/Users/jcgal/.cpm/snappy/59b0f9bb82a31b56cf6197fb63af2a03d76f9331/third_party/googletest/googlemock/CMakeLists.txt:101 (cxx_library)


CMake Error at C:/Users/jcgal/.cpm/snappy/59b0f9bb82a31b56cf6197fb63af2a03d76f9331/third_party/googletest/googlemock/CMakeLists.txt:102 (target_link_libraries):
  Attempt to add link library "gtest" to target "gmock" which is not built in
  this directory.

  This is allowed only when policy CMP0079 is set to NEW.


CMake Error at C:/Users/jcgal/.cpm/snappy/59b0f9bb82a31b56cf6197fb63af2a03d76f9331/third_party/googletest/googletest/cmake/internal_utils.cmake:150 (add_library):
  add_library cannot create target "gmock_main" because another target with
  the same name already exists.  The existing target is a static library
  created in source directory
  "C:/Users/jcgal/.cpm/protobuf/29522687be03e21b7683f4277ecb0c4d3bd83954".
  See documentation for policy CMP0002 for more details.
Call Stack (most recent call first):
  C:/Users/jcgal/.cpm/snappy/59b0f9bb82a31b56cf6197fb63af2a03d76f9331/third_party/googletest/googletest/cmake/internal_utils.cmake:206 (cxx_library_with_type)
  C:/Users/jcgal/.cpm/snappy/59b0f9bb82a31b56cf6197fb63af2a03d76f9331/third_party/googletest/googlemock/CMakeLists.txt:104 (cxx_library)


CMake Warning (dev) at C:/Users/jcgal/.cpm/snappy/59b0f9bb82a31b56cf6197fb63af2a03d76f9331/third_party/googletest/googlemock/CMakeLists.txt:105 (target_link_libraries):
  Policy CMP0023 is not set: Plain and keyword target_link_libraries
  signatures cannot be mixed.  Run "cmake --help-policy CMP0023" for policy
  details.  Use the cmake_policy command to set the policy and suppress this
  warning.

  The plain signature for target_link_libraries has already been used with
  the target "gmock_main".  All uses of target_link_libraries with a target
  should be either all-keyword or all-plain.

  The uses of the plain signature are here:

   * C:/Users/jcgal/.cpm/protobuf/29522687be03e21b7683f4277ecb0c4d3bd83954/cmake/gtest.cmake:42 (target_link_libraries)

This warning is for project developers.  Use -Wno-dev to suppress it.

CMake Error at C:/Users/jcgal/.cpm/snappy/59b0f9bb82a31b56cf6197fb63af2a03d76f9331/third_party/googletest/googlemock/CMakeLists.txt:105 (target_link_libraries):
  Attempt to add link library "gmock" to target "gmock_main" which is not
  built in this directory.

  This is allowed only when policy CMP0079 is set to NEW.

[Olivier Le Doeuff]

fix it in your project

You can set SNAPPY_BUILD_TESTS to OFF & protobuf_BUILD_TESTS to OFF

Snappy fix:

Other solution is to wrap:
https://github.com/google/snappy/blob/92f18e66fdf34bdde3d5116ca3fac3910fe14fc5/CMakeLists.txt#L315-L316

In a if(NOT TARGET gtest) in snappy to support super build.

protobuf fix:

In https://github.com/protocolbuffers/protobuf/blob/084d9702d69ab5039af515ab005fcc65cae18da4/cmake/gtest.cmake#L2

They should add a

if(TARGET gtest)
  return()
endif()

[Julio C. Galindo]

Thanks for the quick reply. I'll test it soon and let you know.
I was looking for a more general solution from a CPM angle for avoiding this type of collisions, but seen you even took the time to review my case in particular I asume there is no such approach.

[Olivier Le Doeuff]

No cpm rely on the fact cmakelists are for super build, but often people don't write cmake with that in my mind.
Fix is often easy.

[Julio C. Galindo]

It worked just fine. Thanks a lot!