dawn-cmake/third_party/abseil-cpp/CMake/README.md

Abseil CMake Build Instructions

Abseil comes with a CMake build script (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 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 in your CMake project.

3. You can then use the CMake command add_subdirectory() to include Abseil directly in your CMake project.

4. Add the absl:: target you wish to use to the target_link_libraries() section of your executable or of your library.
   Here is a short CMakeLists.txt example of an application project using Abseil.

cmake_minimum_required(VERSION 3.8.2)
project(my_app_project)

# Pick the C++ standard to compile with.
# Abseil currently supports C++11, C++14, and C++17.
set(CMAKE_CXX_STANDARD 11)
set(CMAKE_CXX_STANDARD_REQUIRED ON)

add_subdirectory(abseil-cpp)

add_executable(my_exe source.cpp)
target_link_libraries(my_exe absl::base absl::synchronization absl::strings)

Note that if you are developing a library designed for use by other clients, you should instead leave CMAKE_CXX_STANDARD unset (or only set if being built as the current top-level CMake project) and configure the minimum required C++ standard at the target level. If you require a later minimum C++ standard than Abseil does, it's a good idea to also enforce that CMAKE_CXX_STANDARD (which will control Abseil library targets) is set to at least that minimum. For example:

cmake_minimum_required(VERSION 3.8.2)
project(my_lib_project)

# Leave C++ standard up to the root application, so set it only if this is the
# current top-level CMake project.
if(CMAKE_SOURCE_DIR STREQUAL my_lib_project_SOURCE_DIR)
  set(CMAKE_CXX_STANDARD 17)
  set(CMAKE_CXX_STANDARD_REQUIRED ON)
endif()

add_subdirectory(abseil-cpp)

add_library(my_lib source.cpp)
target_link_libraries(my_lib absl::base absl::synchronization absl::strings)

# Enforce that my_lib requires C++17. Important to document for clients that they
# must set CMAKE_CXX_STANDARD to 17 or higher for proper Abseil ABI compatibility
# (since otherwise, Abseil library targets could be compiled with a lower C++
# standard than my_lib).
target_compile_features(my_lib PUBLIC cxx_std_17)
if(CMAKE_CXX_STANDARD LESS 17)
  message(FATAL_ERROR
      "my_lib_project requires CMAKE_CXX_STANDARD >= 17 (got: ${CMAKE_CXX_STANDARD})")
endif()

Then the top-level application project that uses your library is responsible for setting a consistent CMAKE_CXX_STANDARD that is sufficiently high.

Running Abseil Tests with CMake

Use the -DBUILD_TESTING=ON flag to run Abseil tests.

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 -DBUILD_TESTING=ON -DABSL_USE_GOOGLETEST_HEAD=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:

absl::algorithm
absl::base
absl::debugging
absl::flat_hash_map
absl::flags
absl::memory
absl::meta
absl::numeric
absl::random_random
absl::strings
absl::synchronization
absl::time
absl::utility

Traditional CMake Set-Up

For larger projects, it may make sense to use the traditional CMake set-up where you build and install projects separately.

First, you'd need to build and install Google Test:

cmake -S /source/googletest -B /build/googletest -DCMAKE_BUILD_TYPE=Release -DCMAKE_INSTALL_PREFIX=/installation/dir -DBUILD_GMOCK=ON
cmake --build /build/googletest --target install

Then you need to configure and build Abseil. Make sure you enable ABSL_USE_EXTERNAL_GOOGLETEST and ABSL_FIND_GOOGLETEST. You also need to enable ABSL_ENABLE_INSTALL so that you can install Abseil itself.

cmake -S /source/abseil-cpp -B /build/abseil-cpp -DCMAKE_PREFIX_PATH=/installation/dir -DCMAKE_INSTALL_PREFIX=/installation/dir -DABSL_ENABLE_INSTALL=ON -DABSL_USE_EXTERNAL_GOOGLETEST=ON -DABSL_FIND_GOOGLETEST=ON
cmake --build /temporary/build/abseil-cpp

(CMAKE_PREFIX_PATH is where you already have Google Test installed; CMAKE_INSTALL_PREFIX is where you want to have Abseil installed; they can be different.)

Run the tests:

ctest --test-dir /temporary/build/abseil-cpp

And finally install:

cmake --build /temporary/build/abseil-cpp --target install

CMake Option Synposis

Enable Standard CMake Installation

-DABSL_ENABLE_INSTALL=ON

Google Test Options

-DBUILD_TESTING=ON must be set to enable testing

• Have Abseil download and build Google Test for you: -DABSL_USE_EXTERNAL_GOOGLETEST=OFF (default)
  • Download and build latest Google Test: -DABSL_USE_GOOGLETEST_HEAD=ON
  • Download specific Google Test version (ZIP archive): -DABSL_GOOGLETEST_DOWNLOAD_URL=https://.../version.zip
  • Use Google Test from specific local directory: -DABSL_LOCAL_GOOGLETEST_DIR=/path/to/googletest
• Use Google Test included elsewhere in your project: -DABSL_USE_EXTERNAL_GOOGLETEST=ON
• Use standard CMake find_package(CTest) to find installed Google Test: -DABSL_USE_EXTERNAL_GOOGLETEST=ON -DABSL_FIND_GOOGLETEST=ON