CMake: add option to use Google Test already installed on system (abseil#969)

As of this change, you can use `-DABSL_USE_EXTERNAL_GOOGLETEST=ON -DABSL_FIND_GOOGLETEST=ON` to have Abseil use the standard CMake find_package(GTest) mechanism.

Author: florin-crisan

CMake/AbseilHelpers.cmake

@@ -336,8 +336,8 @@ endfunction()
 #     "awesome_test.cc"
 #   DEPS
 #     absl::awesome
-#     gmock
-#     gtest_main
+#     GTest::gmock
+#     GTest::gtest_main
 # )
 function(absl_cc_test)
   if(NOT BUILD_TESTING)

CMake/README.md

@@ -99,3 +99,48 @@ 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`

CMakeLists.txt

@@ -102,9 +102,18 @@ endif()
 ## pthread
 find_package(Threads REQUIRED)
 
+include(CMakeDependentOption)
+
 option(ABSL_USE_EXTERNAL_GOOGLETEST
   "If ON, Abseil will assume that the targets for GoogleTest are already provided by the including project. This makes sense when Abseil is used with add_subproject." OFF)
 
+cmake_dependent_option(ABSL_FIND_GOOGLETEST
+  "If ON, Abseil will use find_package(GTest) rather than assuming that GoogleTest is already provided by the including project."
+  ON
+  "ABSL_USE_EXTERNAL_GOOGLETEST"
+  OFF)
+
+
 option(ABSL_USE_GOOGLETEST_HEAD
   "If ON, abseil will download HEAD from GoogleTest at config time." OFF)
 
@@ -116,7 +125,15 @@ set(ABSL_LOCAL_GOOGLETEST_DIR "/usr/src/googletest" CACHE PATH
 
 if(BUILD_TESTING)
   ## check targets
-  if (NOT ABSL_USE_EXTERNAL_GOOGLETEST)
+  if (ABSL_USE_EXTERNAL_GOOGLETEST)
+    if (ABSL_FIND_GOOGLETEST)
+      find_package(GTest REQUIRED)
+    else()
+      if (NOT TARGET gtest AND NOT TARGET GTest::gtest)
+        message(FATAL_ERROR "ABSL_USE_EXTERNAL_GOOGLETEST is ON and ABSL_FIND_GOOGLETEST is OFF, which means that the top-level project must build the Google Test project. However, the target gtest was not found.")
+      endif()
+    endif()
+  else()
     set(absl_gtest_build_dir ${CMAKE_BINARY_DIR}/googletest-build)
     if(ABSL_USE_GOOGLETEST_HEAD AND ABSL_GOOGLETEST_DOWNLOAD_URL)
       message(FATAL_ERROR "Do not set both ABSL_USE_GOOGLETEST_HEAD and ABSL_GOOGLETEST_DOWNLOAD_URL")
@@ -134,14 +151,22 @@ if(BUILD_TESTING)
     include(CMake/Googletest/DownloadGTest.cmake)
   endif()
 
-  check_target(gtest)
-  check_target(gtest_main)
-  check_target(gmock)
+  if (NOT ABSL_FIND_GOOGLETEST)
+    # When Google Test is included directly rather than through find_package, the aliases are missing.
+    add_library(GTest::gtest_main ALIAS gtest_main)
+    add_library(GTest::gtest ALIAS gtest)
+    add_library(GTest::gmock ALIAS gmock)
+  endif()
+
+  check_target(GTest::gtest)
+  check_target(GTest::gtest_main)
+  check_target(GTest::gmock)
+  check_target(GTest::gmock_main)
 
   list(APPEND ABSL_TEST_COMMON_LIBRARIES
-    gtest_main
-    gtest
-    gmock
+    GTest::gtest_main
+    GTest::gtest
+    GTest::gmock
     ${CMAKE_THREAD_LIBS_INIT}
   )
 endif()

absl/algorithm/CMakeLists.txt

@@ -35,7 +35,7 @@ absl_cc_test(
     ${ABSL_TEST_COPTS}
   DEPS
     absl::algorithm
-    gmock_main
+    GTest::gmock_main
 )
 
 absl_cc_library(
@@ -65,5 +65,5 @@ absl_cc_test(
     absl::core_headers
     absl::memory
     absl::span
-    gmock_main
+    GTest::gmock_main
 )

absl/base/CMakeLists.txt

@@ -230,7 +230,7 @@ absl_cc_library(
     ${ABSL_DEFAULT_COPTS}
   DEPS
     absl::config
-    gtest
+    GTest::gtest
   TESTONLY
 )
 
@@ -259,7 +259,7 @@ absl_cc_library(
     absl::meta
     absl::strings
     absl::utility
-    gtest
+    GTest::gtest
   TESTONLY
 )
 
@@ -273,7 +273,7 @@ absl_cc_test(
   DEPS
     absl::exception_safety_testing
     absl::memory
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_library(
@@ -300,8 +300,8 @@ absl_cc_test(
     absl::atomic_hook_test_helper
     absl::atomic_hook
     absl::core_headers
-    gmock
-    gtest_main
+    GTest::gmock
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -314,7 +314,7 @@ absl_cc_test(
   DEPS
     absl::base
     absl::core_headers
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -327,8 +327,8 @@ absl_cc_test(
   DEPS
     absl::errno_saver
     absl::strerror
-    gmock
-    gtest_main
+    GTest::gmock
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -342,7 +342,7 @@ absl_cc_test(
     absl::base
     absl::config
     absl::throw_delegate
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -357,7 +357,7 @@ absl_cc_test(
     ${ABSL_TEST_COPTS}
   DEPS
     absl::base_internal
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -371,8 +371,8 @@ absl_cc_test(
     absl::base_internal
     absl::memory
     absl::strings
-    gmock
-    gtest_main
+    GTest::gmock
+    GTest::gtest_main
 )
 
 absl_cc_library(
@@ -388,7 +388,7 @@ absl_cc_library(
     absl::base_internal
     absl::core_headers
     absl::synchronization
-    gtest
+    GTest::gtest
   TESTONLY
 )
 
@@ -406,7 +406,7 @@ absl_cc_test(
     absl::config
     absl::core_headers
     absl::synchronization
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_library(
@@ -435,7 +435,7 @@ absl_cc_test(
     absl::base
     absl::config
     absl::endian
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -448,7 +448,7 @@ absl_cc_test(
   DEPS
     absl::config
     absl::synchronization
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -462,7 +462,7 @@ absl_cc_test(
     absl::base
     absl::core_headers
     absl::synchronization
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -475,7 +475,7 @@ absl_cc_test(
   DEPS
     absl::raw_logging_internal
     absl::strings
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -488,7 +488,7 @@ absl_cc_test(
   DEPS
     absl::base
     absl::synchronization
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -516,7 +516,7 @@ absl_cc_test(
     absl::core_headers
     absl::synchronization
     Threads::Threads
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_library(
@@ -543,7 +543,7 @@ absl_cc_test(
   DEPS
     absl::exponential_biased
     absl::strings
-    gmock_main
+    GTest::gmock_main
 )
 
 absl_cc_library(
@@ -570,7 +570,7 @@ absl_cc_test(
   DEPS
     absl::core_headers
     absl::periodic_sampler
-    gmock_main
+    GTest::gmock_main
 )
 
 absl_cc_library(
@@ -596,7 +596,7 @@ absl_cc_test(
     ${ABSL_TEST_COPTS}
   DEPS
     absl::scoped_set_env
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -620,8 +620,8 @@ absl_cc_test(
     absl::flags_marshalling
     absl::log_severity
     absl::strings
-    gmock
-    gtest_main
+    GTest::gmock
+    GTest::gtest_main
 )
 
 absl_cc_library(
@@ -651,8 +651,8 @@ absl_cc_test(
   DEPS
     absl::strerror
     absl::strings
-    gmock
-    gtest_main
+    GTest::gmock
+    GTest::gtest_main
 )
 
 absl_cc_library(
@@ -677,7 +677,7 @@ absl_cc_test(
     ${ABSL_TEST_COPTS}
   DEPS
     absl::fast_type_id
-    gtest_main
+    GTest::gtest_main
 )
 
 absl_cc_test(
@@ -690,5 +690,5 @@ absl_cc_test(
   DEPS
     absl::core_headers
     absl::optional
-    gtest_main
+    GTest::gtest_main
 )

absl/cleanup/CMakeLists.txt

@@ -51,5 +51,5 @@ absl_cc_test(
     absl::cleanup
     absl::config
     absl::utility
-    gmock_main
+    GTest::gmock_main
 )