How to handle CMake ExternalProject when repo (googletest) has multiple libraries?

Question

How can I add external projects in CMake when the project's repo isn't the root of the library I want to use, but in fact contains two directories which are each root directories of repos that I want to use in my project?

I'm working to set up a framework CMake project that uses Google Test and Mock for testing, however when I try to download the google test repo (https://github.com/google/googletest) with ExternalProject_Add, it complains on build that it can't find the source for the project. Well, that's because Google have merged googletest and googlemock into a single project, except it's now two projects.

Some of the repo's file structure:

googletest-master/
├──[...no CMakeFiles.txt exists here...]
├──googletest/
│  ├──src/
│  └──CMakeFiles.txt
└──googlemock/
   ├──src/
   └──CMakeFiles.txt

When I do the following...

ExternalProject_Add(
    gtest
    GIT_REPOSITORY https://github.com/google/googletest.git
    TIMEOUT 10
    INSTALL_COMMAND ""
    LOG_DOWNLOAD ON
    LOG_CONFIGURE ON
    LOG_BUILD ON
    PREFIX "googletest-master"
)

...it downloads the actual repo to googletest-master/src/gtest because I'm prefixing the repo with "googletest-master" to keep it out of my main source code, and it assumes that I'm downloading a project that is only source and that source is in the root directory.

So I'd like to accomplish two things:

1. Download the repo into the googletest-master directory, exactly as it would be if I cloned the repo there, or downloaded the zip off GitHub and extracted it.
2. Build and include both googletest and googlemock in my CMake project

Answer 1

You need single download step, but two build steps. Different ExternalProject_add command calls cannot share steps, but you can arrange all these steps into different calls with appropriate dependencies between them:

# Single download(git clone)
ExternalProject_Add(
    googletest-master
    DOWNLOAD_DIR "googletest-master/src" # The only dir option which is required
    GIT_REPOSITORY https://github.com/google/googletest.git
    TIMEOUT 10
    LOG_DOWNLOAD ON
    # Disable all other steps
    CONFIGURE_COMMAND ""
    BUILD_COMMAND ""
    INSTALL_COMMAND ""
)

# Build gtest from existing sources
ExternalProject_Add(
    gtest
    DOWNLOAD_COMMAND "" # No download required
    SOURCE_DIR "googletest-master/src/googletest" # Use specific source dir
    PREFIX "googletest-master" # But use prefix for compute other dirs
    INSTALL_COMMAND ""
    LOG_CONFIGURE ON
    LOG_BUILD ON
)

# gtest should be build after being downloaded
add_dependencies(gtest googletest-master)

# Build gmock from existing sources
ExternalProject_Add(
    gmock
    DOWNLOAD_COMMAND "" # No download required
    SOURCE_DIR "googletest-master/src/googlemock" # Use specific source dir
    PREFIX "googletest-master" # But use prefix for compute other dirs
    INSTALL_COMMAND ""
    LOG_CONFIGURE ON
    LOG_BUILD ON
)

# gmock should be build after being downloaded
add_dependencies(gmock googletest-master)