Simplify integration with googletest

Firestore/CMakeLists.txt

@@ -28,7 +28,23 @@ set(FIREBASE_INSTALL_DIR ${CMAKE_INSTALL_PREFIX})
 list(INSERT CMAKE_MODULE_PATH 0 ${FIREBASE_SOURCE_DIR}/cmake)
 include(utils)
 
-find_package(GTest REQUIRED)
+# Include GoogleTest directly in the build.
+set(gtest_dir ${FIREBASE_INSTALL_DIR}/external/googletest)
+add_subdirectory(
+  ${gtest_dir}/src/googletest
+  ${gtest_dir}/src/googletest-build
+  EXCLUDE_FROM_ALL
+)
+
+# Set up aliases with the same names as available via FindGTest.
+add_library(
+  GTest::GTest ALIAS gtest
+)
+
+add_library(
+  GTest::Main ALIAS gtest_main
+)
+
 find_package(LevelDB REQUIRED)
 find_package(GRPC REQUIRED)
 

cmake/external/firestore.cmake

@@ -31,7 +31,6 @@ ExternalProject_Add(
   CMAKE_ARGS
     -DCMAKE_BUILD_TYPE:STRING=${CMAKE_BUILD_TYPE}
     -DCMAKE_INSTALL_PREFIX:PATH=${FIREBASE_INSTALL_DIR}
-    ${GTEST_CMAKE_ARGS}
 
   BUILD_ALWAYS ON
 

cmake/external/googletest.cmake

@@ -30,27 +30,9 @@ ExternalProject_Add(
 
   PREFIX ${PROJECT_BINARY_DIR}/external/googletest
 
-  CMAKE_ARGS
-    -DCMAKE_BUILD_TYPE:STRING=${CMAKE_BUILD_TYPE}
-    -DBUILD_SHARED_LIBS:BOOL=OFF
-
+  # Just download the sources without building.
+  CONFIGURE_COMMAND ""
+  BUILD_COMMAND ""
   INSTALL_COMMAND ""
   TEST_COMMAND ""
 )
-
-ExternalProject_Get_Property(
-  googletest
-  SOURCE_DIR BINARY_DIR
-)
-
-# Arguments to pass to another CMake invocation so that it can find googletest
-# without installing it using the standard FindGTest module.
-set(GTEST_INCLUDE_DIR ${SOURCE_DIR}/googletest/include)
-set(GTEST_LIBRARY ${BINARY_DIR}/googlemock/gtest/libgtest.a)
-set(GTEST_MAIN_LIBRARY ${BINARY_DIR}/googlemock/gtest/libgtest_main.a)
-set(
-  GTEST_CMAKE_ARGS
-  -DGTEST_INCLUDE_DIR=${GTEST_INCLUDE_DIR}
-  -DGTEST_LIBRARY=${GTEST_LIBRARY}
-  -DGTEST_MAIN_LIBRARY=${GTEST_MAIN_LIBRARY}
-)