CMake cannot detect symbol conflicts in different static libraries - c++

Question

I created a simple cmake project to reproduct it.
├── CMakeLists.txt
├── lib1
│   ├── CMakeLists.txt
│   ├── lib1.cpp
│   └── lib1.h
├── lib2
│   ├── CMakeLists.txt
│   ├── lib2.cpp
│   └── lib2.h
└── main.cpp
lib1/CMakeLists.txt:
add_library(lib1 "")
target_include_directories(lib1
PUBLIC
${CMAKE_CURRENT_LIST_DIR}
)
target_sources(lib1
PRIVATE
lib1.cpp
lib1.h
)
In lib1.cpp, there is a function "void say()":
#include <stdio.h>
void say()
{
printf("hello from lib1\n");
}
lib2/CMakeLists.txt:
add_library(lib2 "")
target_include_directories(lib2
PUBLIC
${CMAKE_CURRENT_LIST_DIR}
)
target_sources(lib2
PRIVATE
lib2.cpp
lib2.h
)
And in lib2/lib2.cpp, there is a function of the same signature:
#include <stdio.h>
void say()
{
printf("hello from lib2\n");
}
CMakeLists.txt:
cmake_minimum_required(VERSION 3.16)
project(shell LANGUAGES CXX)
add_subdirectory(lib1)
add_subdirectory(lib2)
add_executable(test2
main.cpp
)
target_link_libraries(test2
PRIVATE
lib1
lib2
)
Here is the main.cpp:
void say();
int main()
{
say();
return 0;
}
The output:
hello from lib1
There is no compile or link error, not even a warning.
The linker just picked one and symply ignored the other one.
I'm using cmake 3.16, and tested it with msvc 2017/2019 and g++ 7.5.
How to make the linker prompts errors when there are symbol conflicts in static libraries?
Thanks!

Answer 1

How to make the linker prompts errors when there are symbol conflicts in static libraries?
With gcc use the --whole-archive option to include every object file in the archive rather then search the archives for the required symbol.
As there is no cmake support that I know of, I find it's typically done when linking the executable:
target_link_libraries(test2 PRIVATE
-Wl,--whole-archive
lib1
lib2
-Wl,--no-whole-archive
)
"Symbol conflicts" is rather vague term. This will only detect multiple symbol definitions. Types of symbols are not stored anywhere after compilation.