Why is include folder empty after make install using cmake? - c++

Question

I am trying to create a lib and include for my project so that others can use my project.
So I have my project structured as
├── mlce
   ├── CMakeLists.txt
   ├── README.txt
   ├── include
   ├── lib
   └── src
   ├── io
   │   └── IO.h
   └── mesh
   ├── Mesh.cpp
   └── Mesh.h
Currenly include and lib are empty. I created them manually so that latter on when I make install those will get filled.
My CMakeLists.txt looks like
cmake_minimum_required(VERSION 3.0.2)
project(mlcelib)
set (SOURCE
${SOURCE}
${CMAKE_CURRENT_SOURCE_DIR}/src/mesh/Mesh.cpp
)
set (HEADER
${HEADER}
${CMAKE_CURRENT_SOURCE_DIR}/src/mesh/Mesh.h
${CMAKE_CURRENT_SOURCE_DIR}/src/io/IO.h
)
find_package (Eigen3 3.3 REQUIRED NO_MODULE)
add_library(${PROJECT_NAME} SHARED ${SOURCE})
target_include_directories(${PROJECT_NAME} PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/src)
target_link_libraries (${PROJECT_NAME} Eigen3::Eigen)
message(${CMAKE_INSTALL_INCLUDEDIR})
install(TARGETS ${PROJECT_NAME}
LIBRARY DESTINATION ${CMAKE_INSTALL_LIBDIR}
PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}) # <--- I was hoping
# this "PUBLIC_HEADER DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}" would place all the header file of my project inside include folder.
# But apparently it is not doing that. The include folder is empty.
Then what I do is :
mkdir build
cd build
cmake -DCMAKE_INSTALL_LIBDIR=/path/to/mlce/lib -DCMAKE_INSTALL_INCLUDEDIR=/path/to/mlce/include ..
make
make install
So when I do make install only the lib is filled by the shared lib but the install is not.
├── include
├── lib
│   └── libmlcelib.dylib
I was expecting include would contain mesh/Mesh.h and IO/IO.h