CMake: Error out if source directory if src/ instead of top-level dir

CMakeLists.txt

@@ -221,7 +221,7 @@ if(NOT EMU_BUILD_NUM)
     set(EMU_BUILD_NUM 0)
 endif()
 if(NOT EMU_COPYRIGHT_YEAR)
-    set(EMU_COPYRIGHT_YEAR 2024)
+    set(EMU_COPYRIGHT_YEAR 2025)
 endif()
 
 # Libasan
@@ -230,4 +230,6 @@ if(LIBASAN)
     add_link_options(-fsanitize=address)
 endif()
 
+set(CMAKE_TOP_LEVEL_PROCESSED TRUE)
+
 add_subdirectory(src)

src/CMakeLists.txt

@@ -16,6 +16,10 @@
 #          Copyright 2024      Jasmine Iwanek.
 #
 
+if(NOT CMAKE_TOP_LEVEL_PROCESSED)
+    message(FATAL_ERROR "Incorrect source directory specified. Delete your build directory and retry with the top-level directory instead")
+endif()
+
 if(APPLE)
     set(CMAKE_INSTALL_RPATH_USE_LINK_PATH TRUE)
 endif()