1 files changed, 101 insertions, 0 deletions
diff --git a/third_party/abseil-cpp/CMake/README.md b/third_party/abseil-cpp/CMake/README.md
new file mode 100644
index 0000000000..04d5df3ab0
--- /dev/null
+++ b/third_party/abseil-cpp/CMake/README.md
@@ -0,0 +1,101 @@
+# Abseil CMake Build Instructions
+
+Abseil comes with a CMake build script ([CMakeLists.txt](../CMakeLists.txt))
+that can be used on a wide range of platforms ("C" stands for cross-platform.).
+If you don't have CMake installed already, you can download it for free from
+<https://www.cmake.org/>.
+
+CMake works by generating native makefiles or build projects that can
+be used in the compiler environment of your choice.
+
+For API/ABI compatibility reasons, we strongly recommend building Abseil in a
+subdirectory of your project or as an embedded dependency.
+
+## Incorporating Abseil Into a CMake Project
+
+The recommendations below are similar to those for using CMake within the
+googletest framework
+(<https://github.com/google/googletest/blob/master/googletest/README.md#incorporating-into-an-existing-cmake-project>)
+
+### Step-by-Step Instructions
+
+1. If you want to build the Abseil tests, integrate the Abseil dependency
+[Google Test](https://github.com/google/googletest) into your CMake project. To disable Abseil tests, you have to pass
+`-DBUILD_TESTING=OFF` when configuring your project with CMake.
+
+2. Download Abseil and copy it into a subdirectory in your CMake project or add
+Abseil as a [git submodule](https://git-scm.com/docs/git-submodule) in your
+CMake project.
+
+3. You can then use the CMake command
+[`add_subdirectory()`](https://cmake.org/cmake/help/latest/command/add_subdirectory.html)
+to include Abseil directly in your CMake project.
+
+4. Add the **absl::** target you wish to use to the
+[`target_link_libraries()`](https://cmake.org/cmake/help/latest/command/target_link_libraries.html)
+section of your executable or of your library.<br>
+Here is a short CMakeLists.txt example of a project file using Abseil.
+
+```cmake
+cmake_minimum_required(VERSION 3.5)
+project(my_project)
+
+# Pick the C++ standard to compile with.
+# Abseil currently supports C++11, C++14, and C++17.
+set(CMAKE_CXX_STANDARD 11)
+
+add_subdirectory(abseil-cpp)
+
+add_executable(my_exe source.cpp)
+target_link_libraries(my_exe absl::base absl::synchronization absl::strings)
+```
+
+### Running Abseil Tests with CMake
+
+Use the `-DABSL_RUN_TESTS=ON` flag to run Abseil tests.  Note that if the `-DBUILD_TESTING=OFF` flag is passed then Abseil tests will not be run.
+
+You will need to provide Abseil with a Googletest dependency.  There are two
+options for how to do this:
+
+* Use `-DABSL_USE_GOOGLETEST_HEAD`.  This will automatically download the latest
+Googletest source into the build directory at configure time.  Googletest will
+then be compiled directly alongside Abseil's tests.
+* Manually integrate Googletest with your build.  See
+https://github.com/google/googletest/blob/master/googletest/README.md#using-cmake
+for more information on using Googletest in a CMake project.
+
+For example, to run just the Abseil tests, you could use this script:
+
+```
+cd path/to/abseil-cpp
+mkdir build
+cd build
+cmake -DABSL_USE_GOOGLETEST_HEAD=ON -DABSL_RUN_TESTS=ON ..
+make -j
+ctest
+```
+
+Currently, we only run our tests with CMake in a Linux environment, but we are
+working on the rest of our supported platforms. See
+https://github.com/abseil/abseil-cpp/projects/1 and
+https://github.com/abseil/abseil-cpp/issues/109 for more information.
+
+### Available Abseil CMake Public Targets
+
+Here's a non-exhaustive list of Abseil CMake public targets:
+
+```cmake
+absl::algorithm
+absl::base
+absl::debugging
+absl::flat_hash_map
+absl::flags
+absl::memory
+absl::meta
+absl::numeric
+absl::random
+absl::strings
+absl::synchronization
+absl::time
+absl::utility
+```