Fix issue with unset base dir variable

src/Index.cmake

@@ -2,7 +2,21 @@ cmake_minimum_required (VERSION 3.20 FATAL_ERROR)
 
 include_guard ()
 
-set(IHTA_CMAKE_COMMON_BASE_DIR ${CMAKE_CURRENT_LIST_DIR})
+#[=======================================================================[.rst:
+..command:: set_ihta_common_base_dir
+
+	Set the base dir for the library to reference bundled files.
+
+	::
+
+		set_ihta_common_base_dir()
+
+#]=======================================================================]
+macro (set_ihta_common_base_dir)
+	get_directory_property (LISTFILE_STACK LISTFILE_STACK)
+	list (POP_BACK LISTFILE_STACK _LIST_FILE)
+	cmake_path (GET _LIST_FILE PARENT_PATH IHTA_CMAKE_COMMON_BASE_DIR)
+endmacro ()
 
 include (${CMAKE_CURRENT_LIST_DIR}/InitProject.cmake)
 

src/UseSharedConfigs.cmake

@@ -10,6 +10,8 @@ include_guard ()
 	- `.cmake-format`
 	are supported.
 
+	This should be called after `project` so that `PROJECT_SOURCE_DIR` is set.
+
 	::
 
 		use_shared_configs(TRUE TRUE FALSE)
@@ -28,6 +30,8 @@ include_guard ()
 
 #]=======================================================================]
 macro (use_shared_configs SHARED_CLANG_FORMAT SHARED_CMAKE_FORMAT SHARED_CLANG_TIDY)
+	set_ihta_common_base_dir ()
+
 	if (${SHARED_CLANG_TIDY})
 		file (COPY_FILE ${IHTA_CMAKE_COMMON_BASE_DIR}/resources/.clang-tidy ${PROJECT_SOURCE_DIR}/.clang-tidy
 			  ONLY_IF_DIFFERENT