BUILD_BYPRODUCTS and dependency cycle for cmake + ninja + googletest + ExternalProject_Add - cmake

Question

Attempting to use external project to build google test like so.
# Add googletest
ExternalProject_Add( googletest
GIT_REPOSITORY https://github.com/google/googletest.git
# We don't need to run update command. Takes time
# and the version we initially d/l will shoudl be fine
CMAKE_ARGS = "-Dgtest_disable_pthreads=1"
# Don't run update
UPDATE_COMMAND ""
# Disable install step
INSTALL_COMMAND ""
# BUILD_BYPRODUCTS googletest-prefix/src/googletest-stamp/googletest-gitinfo.txt
# BUILD_BYPRODUCTS googletest-prefix/tmp/googletest-cfgcmd.txt
BUILD_BYPRODUCTS "googletest-prefix/src/googletest-build/googlemock/libgmock_main.a"
)
# Get include dirs for googletest framework
ExternalProject_Get_Property(googletest source_dir)
set(GTEST_INCLUDE_DIRS
${source_dir}/googlemock/include
${source_dir}/googletest/include
)
# Create library target for gmock main, which is used to create
# test executables
ExternalProject_Get_Property(googletest binary_dir)
set(GTEST_LIBRARY_PATH ${binary_dir}/googlemock/libgmock_main.a)
set(GTEST_LIBRARY gmock_main)
add_library(${GTEST_LIBRARY} UNKNOWN IMPORTED)
set_property(TARGET ${GTEST_LIBRARY} PROPERTY IMPORTED_LOCATION ${GTEST_LIBRARY_PATH})
add_dependencies(${GTEST_LIBRARY} googletest)
With the ninja generator I get the below warning.
Policy CMP0058 is not set: Ninja requires custom command byproducts to be
explicit. Run "cmake --help-policy CMP0058" for policy details. Use the
cmake_policy command to set the policy and suppress this warning.
This project specifies custom command DEPENDS on files in the build tree
that are not specified as the OUTPUT or BYPRODUCTS of any
add_custom_command or add_custom_target:
googletest-prefix/src/googletest-stamp/googletest-gitinfo.txt
googletest-prefix/tmp/googletest-cfgcmd.txt
For compatibility with versions of CMake that did not have the BYPRODUCTS
option, CMake is generating phony rules for such files to convince 'ninja'
to build.
Project authors should add the missing BYPRODUCTS or OUTPUT options to the
custom commands that produce these files.
If I oblige the request of the cmake error by uncommenting the build byproducts lines in my external project command, I get a cyclical dependency error. However, if I leave the build byproducts out of it, the project seems to build just fine.
$ ninja
ninja: error: dependency cycle: googletest-prefix/src/googletest-stamp/googletest-configure -> googletest-prefix/tmp/googletest-cfgcmd.txt -> googletest-prefix/src/googletest-stamp/googletest-configure
I'm using cmake 3.4, ninja 1.6, and running on Windows using MSYS2 package.

Answer 1

I added cmake_policy(SET CMP0058 NEW) to my toplevel CMakeLists.txt file as the --help-policy text explains to. It no longer generates the warnings afterwards. I guess those files aren't needed. Not sure how they're getting picked up as dependencies.

Answer 2

Try to use something like in ExternalProject_Add function:
set(GMOCK_FILE_DIR "gmock-${GMOCK_VERSION}/src/googletest_github-build/googlemock/")
BUILD_BYPRODUCTS "${GMOCK_FILE_DIR}gtest/libgtest_main.a"
BUILD_BYPRODUCTS "${GMOCK_FILE_DIR}gtest/libgtest.a"
BUILD_BYPRODUCTS "${GMOCK_FILE_DIR}libgmock_main.a"
BUILD_BYPRODUCTS "${GMOCK_FILE_DIR}libgmock.a"