Support testing with a local googletest checkout

Add a new variable, `ABSL_LOCAL_GOOGLETEST_DIR`, that points to a local
checkout of googletest. Building with `-DABSL_RUN_TESTS=ON
-DABSL_USE_GOOGLETEST_HEAD=OFF` will then use that directory rather than
cloning the googletest repo from GitHub.

3 files changed, 34 insertions, 16 deletions

diff --git a/CMake/Googletest/CMakeLists.txt.in b/CMake/Googletest/CMakeLists.txt.in
index 72a7131..0c64218 100644
--- a/CMake/Googletest/CMakeLists.txt.in
+++ b/CMake/Googletest/CMakeLists.txt.in
@@ -3,13 +3,24 @@ cmake_minimum_required(VERSION 2.8.2)
 project(googletest-download NONE)
 
 include(ExternalProject)
-ExternalProject_Add(googletest
-  GIT_REPOSITORY    https://github.com/google/googletest.git
-  GIT_TAG           master
-  SOURCE_DIR        "${absl_gtest_src_dir}"
-  BINARY_DIR        "${absl_gtest_build_dir}"
-  CONFIGURE_COMMAND ""
-  BUILD_COMMAND     ""
-  INSTALL_COMMAND   ""
-  TEST_COMMAND      ""
-)
\ No newline at end of file
+if(${ABSL_USE_GOOGLETEST_HEAD})
+  ExternalProject_Add(googletest
+    GIT_REPOSITORY    https://github.com/google/googletest.git
+    GIT_TAG           master
+    SOURCE_DIR        "${absl_gtest_src_dir}"
+    BINARY_DIR        "${absl_gtest_build_dir}"
+    CONFIGURE_COMMAND ""
+    BUILD_COMMAND     ""
+    INSTALL_COMMAND   ""
+    TEST_COMMAND      ""
+  )
+else()
+  ExternalProject_Add(googletest
+    SOURCE_DIR        "${absl_gtest_src_dir}"
+    BINARY_DIR        "${absl_gtest_build_dir}"
+    CONFIGURE_COMMAND ""
+    BUILD_COMMAND     ""
+    INSTALL_COMMAND   ""
+    TEST_COMMAND      ""
+  )
+endif()
\ No newline at end of file
diff --git a/CMake/Googletest/DownloadGTest.cmake b/CMake/Googletest/DownloadGTest.cmake
index d616fe2..9b4f62b 100644
--- a/CMake/Googletest/DownloadGTest.cmake
+++ b/CMake/Googletest/DownloadGTest.cmake
@@ -1,7 +1,8 @@
-# Downloads and unpacks googletest at configure time.  Based on the instructions
-# at https://github.com/google/googletest/tree/master/googletest#incorporating-into-an-existing-cmake-project
+# Integrates googletest at configure time.  Based on the instructions at
+# https://github.com/google/googletest/tree/master/googletest#incorporating-into-an-existing-cmake-project
 
-# Download the latest googletest from Github master
+# Set up the external googletest project, downloading the latest from Github
+# master if requested.
 configure_file(
   ${CMAKE_CURRENT_LIST_DIR}/CMakeLists.txt.in
   ${CMAKE_BINARY_DIR}/googletest-download/CMakeLists.txt
@@ -14,7 +15,7 @@ if (BUILD_SHARED_LIBS)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DGTEST_CREATE_SHARED_LIBRARY=1")
 endif()
 
-# Configure and build the downloaded googletest source
+# Configure and build the googletest source.
 execute_process(COMMAND ${CMAKE_COMMAND} -G "${CMAKE_GENERATOR}" .
   RESULT_VARIABLE result
   WORKING_DIRECTORY ${CMAKE_BINARY_DIR}/googletest-download )
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 26cd2d0..74b5cd9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -84,6 +84,10 @@ find_package(Threads REQUIRED)
 option(ABSL_USE_GOOGLETEST_HEAD
   "If ON, abseil will download HEAD from googletest at config time." OFF)
 
+set(ABSL_LOCAL_GOOGLETEST_DIR "/usr/src/googletest" CACHE PATH
+  "If ABSL_USE_GOOGLETEST_HEAD is OFF, specifies the directory of a local googletest checkout."
+  )
+
 option(ABSL_RUN_TESTS "If ON, Abseil tests will be run." OFF)
 
 if(${ABSL_RUN_TESTS})
@@ -96,11 +100,13 @@ endif()
 ## check targets
 if(BUILD_TESTING)
 
+  set(absl_gtest_build_dir ${CMAKE_BINARY_DIR}/googletest-build)
   if(${ABSL_USE_GOOGLETEST_HEAD})
     set(absl_gtest_src_dir ${CMAKE_BINARY_DIR}/googletest-src)
-    set(absl_gtest_build_dir ${CMAKE_BINARY_DIR}/googletest-build)
-    include(CMake/Googletest/DownloadGTest.cmake)
+  else()
+    set(absl_gtest_src_dir ${ABSL_LOCAL_GOOGLETEST_DIR})
   endif()
+  include(CMake/Googletest/DownloadGTest.cmake)
 
   check_target(gtest)
   check_target(gtest_main)