Protectt double inclusion of CMakeLists.txt

CMakeLists.txt

@@ -1,32 +1,37 @@
-cmake_minimum_required(VERSION 3.12)
+cmake_minimum_required(VERSION 3.13)
 
-# Pull in PICO SDK (must be before project)
-include(pico_sdk_import.cmake)
+if (NOT TARGET _pico_extras_inclusion_marker)
+    add_library(_pico_extras_inclusion_marker INTERFACE)
 
-project(pico_extras C CXX)
+    # Pull in PICO SDK (must be before project)
+    include(pico_sdk_import.cmake)
 
-set(CMAKE_C_STANDARD 11)
-set(CMAKE_CXX_STANDARD 17)
+    project(pico_extras C CXX)
 
-# Initialize the SDK
-pico_sdk_init()
+    set(CMAKE_C_STANDARD 11)
+    set(CMAKE_CXX_STANDARD 17)
 
-pico_is_top_level_project(PICO_EXTRAS_TOP_LEVEL_PROJECT)
+    # Initialize the SDK
+    pico_sdk_init()
 
-add_library(pico_extras_included INTERFACE)
-target_compile_definitions(pico_extras_included INTERFACE
-        -DPICO_EXTRAS=1
-)
+    pico_is_top_level_project(PICO_EXTRAS_TOP_LEVEL_PROJECT)
 
-pico_add_platform_library(pico_extras_included)
+    add_library(pico_extras_included INTERFACE)
+    target_compile_definitions(pico_extras_included INTERFACE
+            -DPICO_EXTRAS=1
+    )
 
-if (NOT PICO_EXTRAS_PATH)
-    set(PICO_EXTRAS_PATH ${CMAKE_CURRENT_LIST_DIR})
-endif()
-set(PICO_EXTRAS_PATH "${PICO_EXTRAS_PATH}" CACHE PATH "Path to Pico Extras")
+    pico_add_platform_library(pico_extras_included)
 
-add_subdirectory(src)
+    if (NOT PICO_EXTRAS_PATH)
+        set(PICO_EXTRAS_PATH ${CMAKE_CURRENT_LIST_DIR})
+    endif()
+    set(PICO_EXTRAS_PATH "${PICO_EXTRAS_PATH}" CACHE PATH "Path to Pico Extras")
 
-if (PICO_EXTRAS_TESTS_ENABLED OR PICO_EXTRAS_TOP_LEVEL_PROJECT)
-    add_subdirectory(test)
-endif ()
+    add_subdirectory(src)
+
+    if (PICO_EXTRAS_TESTS_ENABLED OR PICO_EXTRAS_TOP_LEVEL_PROJECT)
+        add_subdirectory(test)
+    endif ()
+
+endif()