Add code causing the error

CMakeLists.txt

@@ -1,6 +1,7 @@
-cmake_minimum_required(VERSION 3.22)
+cmake_minimum_required(VERSION 3.18)
 
 project(proj)
 
 add_subdirectory(src)
+add_subdirectory(external)
 add_subdirectory(example)

example/CMakeLists.txt

@@ -1,6 +1,2 @@
-cmake_minimum_required(VERSION 3.22)
-
-project(example)
-
 add_executable(example example.cpp)
-target_link_libraries(example lib)
+target_link_libraries(example ${PROJECT_NAME})

example/example.cpp

@@ -1,8 +1,8 @@
-#include <lib.h>
+#include "../include/SomeClass.h"
 
 int main()
 {
-	Test t;
+	SomeClass t;
 	t.func();
 
 	return 0;

external/CMakeLists.txt

@@ -0,0 +1,2 @@
+add_subdirectory(scapix)
+# Other libs here

external/scapix/CMakeLists.txt

@@ -0,0 +1,11 @@
+include(FetchContent)
+FetchContent_Declare(
+        cmodule
+        URL "https://github.com/scapix-com/cmodule/archive/refs/tags/v1.0.33.tar.gz"
+        URL_HASH SHA256=b56bf2f3b5acb979f1242757976eaf525caeea70714caa6e19571f65e0b60727
+)
+FetchContent_MakeAvailable(cmodule)
+
+find_package(Scapix REQUIRED)
+
+scapix_bridge_headers(${PROJECT_NAME} "com.example.lib" ${CMAKE_SOURCE_DIR}/include/SomeClass.h)

include/SomeClass.h

@@ -0,0 +1,6 @@
+#include <scapix/bridge/object.h>
+
+class SomeClass : public scapix::bridge::object<SomeClass> {
+ public:
+    void func();
+};

src/CMakeLists.txt

@@ -1,18 +1,5 @@
-cmake_minimum_required(VERSION 3.22)
+set(SOURCE_FILES SomeClass.cpp)
 
-project(lib)
+add_library(${PROJECT_NAME} SHARED ${SOURCE_FILES} ${CMAKE_SOURCE_DIR}/include/SomeClass.h)
 
-add_library(lib lib.cpp lib.h)
-target_include_directories(lib PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
-
-include(FetchContent)
-FetchContent_Declare(
-  cmodule
-  URL "https://github.com/scapix-com/cmodule/archive/refs/tags/v1.0.32.tar.gz"
-  URL_HASH SHA256=e6937c95d73188a5add846b27cd00160fe4f6ea31af33be417d2ab7ac19bd8d2
-)
-FetchContent_MakeAvailable(cmodule)
-
-find_package(Scapix REQUIRED)
-
-scapix_bridge_headers(lib "com.example.lib" ${CMAKE_CURRENT_SOURCE_DIR}/lib.h)
+target_include_directories(${PROJECT_NAME} PUBLIC ${CMAKE_SOURCE_DIR}/include)

src/SomeClass.cpp

@@ -0,0 +1,3 @@
+#include "../include/SomeClass.h"
+
+void SomeClass::func() {}