How could I link to so file generated by cmake add_subdirectory?

I have seen a similar question but I cannot make sense by that accepted answer.

my project structure is like this

├── CMakeLists.txt
├── main.cpp
└── plugins
    ├── CMakeLists.txt
    ├── plugin.cpp
    └── plugin.h

The content of CMakeLists.txt is like this:

# top-level CMakeLists.txt
CMAKE_MINIMUM_REQUIRED(VERSION 3.22)

PROJECT(example)

add_subdirectory(./plugins/)

add_executable(main main.cpp)
target_include_directories(main PUBLIC ./plugins/)
target_link_libraries(main -lplugin)

CMakeLists.txt in folder of ./plugins/

add_library(plugin SHARED plugin.cpp)

And the code is like this:

// main.cpp
#include <iostream>
#include "plugin.h"


int call() {
    using namespace std;
    cout << "call\n";
    func();
}

int main() {
    call();
    return 0;
}

// plugins/plugin.cpp
#include <iostream>

void func() {
    using namespace std;
    cout << "plugin\n";
}

// plugins/plugin.h
void func();

When I compile this, I got the error that

make[2]: *** No rule to make target 'plugins/libplugin.so', needed by 'main'.  Stop.
make[1]: *** [CMakeFiles/Makefile2:100: CMakeFiles/main.dir/all] Error 2
make: *** [Makefile:91: all] Error 2

Would you please tell me how to make this work?

If you change your target_link_libraries call to the following:

target_link_libraries(main PUBLIC plugin)

CMake will:

1. Add a dependency from the main target to the plugin target.
2. Configure main such that it knows where to find libplugin.so