build: Improve googletest handling

Behavior is largely unchanged except that specifying BUILD_TESTS=ON
with googletest not present no longer quietly skips building the tests.

- Make inclusion of external directory unconditional.  We may someday
  put something there is not related to testing.
- Make default for BUILD_TEST dependent on googletest presence.
- Remove if() around entire contents of tests CMake file.
- Add CMake messaging to clarify googletest activity.
- Throw a CMake error if googletest not present and BUILD_TESTS=ON

1 files changed, 23 insertions, 16 deletions

diff --git a/external/CMakeLists.txt b/external/CMakeLists.txt
index d0fc32afa..91cfe7e0f 100644
--- a/external/CMakeLists.txt
+++ b/external/CMakeLists.txt
@@ -1,19 +1,26 @@
-# googletest is an external dependency for the tests in the ValidationLayers
-# repo. Check for its presence before trying to build tests.
+if(BUILD_TESTS)
+    # googletest is an external dependency for the tests in the ValidationLayers
+    # repo. Add googletest to the project if present and not already defined.
 
-# Suppress all warnings from external projects.
-set_property(DIRECTORY APPEND PROPERTY COMPILE_OPTIONS -w)
+    # Suppress all warnings from external projects.
+    set_property(DIRECTORY APPEND PROPERTY COMPILE_OPTIONS -w)
 
-if(TARGET gtest_main)
-    message(STATUS "Google Test (googletest) already configured - use it")
-elseif(IS_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/googletest)
-    SET(BUILD_GTEST ON CACHE BOOL "Builds the googletest subproject")
-    SET(BUILD_GMOCK OFF CACHE BOOL "Builds the googlemock subproject")
-    SET(gtest_force_shared_crt ON CACHE BOOL "Link gtest runtimes dynamically")
-    SET(BUILD_SHARED_LIBS ON CACHE BOOL "Build shared libraries")
-    # EXCLUDE_FROM_ALL keeps the install target from installing GTEST files.
-    add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/googletest EXCLUDE_FROM_ALL)
-else()
-    message(STATUS
-        "Google Test was not found - tests based on that will not build")
+    if(TARGET gtest_main)
+        # It is possible that a project enclosing this one has defined the gtest target
+        message(STATUS "Vulkan-ValidationLayers/external: "
+            "Google Test (googletest) already configured - use it")
+    elseif(IS_DIRECTORY ${CMAKE_CURRENT_SOURCE_DIR}/googletest)
+        message(STATUS "Vulkan-ValidationLayers/external: "
+            "googletests found - configuring it for tests")
+        SET(BUILD_GTEST ON CACHE BOOL "Builds the googletest subproject")
+        SET(BUILD_GMOCK OFF CACHE BOOL "Builds the googlemock subproject")
+        SET(gtest_force_shared_crt ON CACHE BOOL "Link gtest runtimes dynamically")
+        SET(BUILD_SHARED_LIBS ON CACHE BOOL "Build shared libraries")
+        # EXCLUDE_FROM_ALL keeps the install target from installing GTEST files.
+        add_subdirectory(${CMAKE_CURRENT_SOURCE_DIR}/googletest EXCLUDE_FROM_ALL)
+    else()
+        message(SEND_ERROR
+            "Vulkan-ValidationLayers/external: Google Test was not found.  "
+            "Provide Google Test in external/googletest or set BUILD_TESTS=OFF")
+    endif()
 endif()