What's CMake doing with Ninja in Android 7 build system?

From the information I got, in the Android 7 build system :

The Go provides a build support for the Soong.
The Soong, instead of using make, loads the .bp/.mk files, and outputs .ninja files.
The Ninja loads the .ninja files and builds the source code.

And I also found in the help page that CMake includes a Ninja generator.

EDIT :

CMake is included in the platform/prebuilts, but not included in the Android 7 manifests

But I checked the android code again , there being so many CMakeLists.txt and CMake being called in some scripts under /external.

    ./external/clang/CMakeLists.txt:686:  get_cmake_property(variableNames VARIABLES)
    ./external/clang/CMakeLists.txt:711:    ${cmake_3_1_EXCLUDE_FROM_ALL}
    ./external/clang/CMakeLists.txt:725:    ${cmake_3_4_USES_TERMINAL_OPTIONS}
    ./external/clang/CMakeLists.txt:734:    ${cmake_3_4_USES_TERMINAL}
    ./external/clang/CMakeLists.txt:750:      ${cmake_3_4_USES_TERMINAL}
    ./external/clang/runtime/CMakeLists.txt:28:    set(cmake_3_4_USES_TERMINAL_OPTIONS
    ./external/clang/runtime/CMakeLists.txt:49:  get_cmake_property(variableNames VARIABLES)
    ./external/clang/runtime/CMakeLists.txt:78:    ${cmake_3_4_USES_TERMINAL_OPTIONS}
    ./external/dbus/cmake/cross-compile.sh
    ./external/compiler-rt/lib/tsan/check_cmake.sh
    ./external/opencv3/platforms/scripts/cmake_android_mips.sh
    ./external/opencv3/platforms/scripts/cmake_arm_gnueabi_softfp.sh
    ./external/opencv3/platforms/scripts/cmake_carma.sh
    ./external/opencv3/platforms/scripts/cmake_android_x86.sh
    ./external/opencv3/platforms/scripts/cmake_android_arm.sh
    ./external/opencv3/platforms/scripts/cmake_arm_gnueabi_hardfp.sh
    ./external/opencv3/platforms/scripts/cmake_android_service.sh
    ./external/opencv3/samples/android/hello-android/cmake_android.sh

Also, CMake exist under folder

    butter@server131:~/code/AOSP/N$ find ./ -name "cmake"
    ./prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/lib/cmake
    ./prebuilts/gcc/linux-x86/host/x86_64-linux-glibc2.15-4.8/sysroot/usr/lib32/cmake
    ./external/dbus/cmake
    ./external/llvm/cmake
    ./external/compiler-rt/cmake
    ./external/deqp/framework/delibs/cmake
    ./external/eigen/cmake
    ./external/eigen/bench/btl/cmake
    ./external/ceres-solver/cmake
    ./external/google-benchmark/cmake
    ./external/libcxx/cmake
    ./external/libcxxabi/cmake
    ./external/opencv3/platforms/ios/cmake
    ./external/opencv3/cmake
    ./external/clang/cmake
    ./external/google-breakpad/src/testing/gtest/cmake
    ./external/libunwind_llvm/cmake
    ./external/pcre/dist/cmake

So if the Soong could generate .ninja files , what is CMake's role in the Android 7 build system? Just an alternative choice or just not fully replaced by the Soong yet?

Solution

Starting in 2.2, Android Studio on 64 bit OS, supports building C/C++ via CMake and ndk-build through stable gradle.

In both cases, Gradle is configured to point at the external build system. It interrogates the external build system to determine a list of all C/C++ sources that are being built in the project and uses this list to populate the Studio project, enabling editing and debugging inside Studio while still using the external build system to compile and link the C/C++ sources.

There is a set of maintained CMake NDK samples here.

ref: http://tools.android.com/tech-docs/external-c-builds

See: Build Android NDK project with Cmake