set CMAKE_BUILD_TYPE only in top-level project (#3480)

Author: double-fault

CMakeLists.txt

@@ -19,7 +19,11 @@ include(GNUInstallDirs)
 # Set default build to release
 # ---------------------------------------------------------------------------------------
 if(NOT CMAKE_BUILD_TYPE AND NOT CMAKE_CONFIGURATION_TYPES)
-    set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Choose Release or Debug" FORCE)
+    # Set CMAKE_BUILD_TYPE only if this project is top-level
+    if((DEFINED PROJECT_IS_TOP_LEVEL AND PROJECT_IS_TOP_LEVEL)
+        OR (NOT DEFINED PROJECT_IS_TOP_LEVEL AND CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR))
+        set(CMAKE_BUILD_TYPE "Release" CACHE STRING "Choose Release or Debug" FORCE)
+    endif()
 endif()
 
 # ---------------------------------------------------------------------------------------