cmake mutliple targets - one header only target and another an executable - c++

Question

Based on this stackoverflow answer to a similar question (Cmake include header only target from header only target), I am creating a header only library and trying to use it in an executable.
My folder structure is below:
├── CMakeLists.txt // root folder CMake file
├── srcs // this is the hdr only library
│   ├── src1.hpp
│   ├── CMakeLists.txt
│   ├── src2.hpp
│   └── src3.hpp
│   └── ...
└── test // this is the executable project
├── CMakeLists.txt
└── main.cpp
Root level CMakeLists.txt
cmake_minimum_required(VERSION 3.13)
project (MyProj CXX)
add_subdirectory(srcs)
add_subdirectory(test)
src level CMakeLists.txt (for header only library)
add_library(MyLib INTERFACE)
target_sources(MyLib INTERFACE
"${CMAKE_CURRENT_SOURCE_DIR}/src1.hpp"
"${CMAKE_CURRENT_SOURCE_DIR}/src2.hpp"
"${CMAKE_CURRENT_SOURCE_DIR}/src3.hpp"
)
target_include_directories(MyLib
INTERFACE ${CMAKE_CURRENT_BINARY_DIR})
add_subdirectory(plugins)
CMake file for executable test project
add_executable(MyTest main.cpp)
target_sources(MyTest
PRIVATE main.cpp
)
target_include_directories(MyTest PUBLIC
$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>)
target_link_libraries(MyTest PUBLIC MyLib)
Though this configures cmake without warnings/error, running the make fails, indicating that the executable project is unable to find the header file(s) from library.
/.../nettu2/test/main.cpp:6:10: fatal error: src1.hpp: No such
file or directory #include "src1.hpp"
^~~~~~~~~~~~~~~~ compilation terminated. test/CMakeFiles/MyTest.dir/build.make:62: recipe for target
'test/CMakeFiles/MyTest.dir/main.cpp.o' failed make[2]: *
[test/CMakeFiles/MyTest.dir/main.cpp.o] Error 1
CMakeFiles/Makefile2:126: recipe for target
'test/CMakeFiles/MyTest.dir/all' failed make[1]: *
[test/CMakeFiles/MyTest.dir/all] Error 2 Makefile:129: recipe for
target 'all' failed make: *** [all] Error 2
I am sure that I am missing some crucial but trivial thing here, but yet unable to figure out, what is going wrong here. How can I get this build working?

Answer 1

You have a minor mistake in this line:
target_include_directories(MyLib
INTERFACE ${CMAKE_CURRENT_BINARY_DIR})
The include directory you specify for MyLib expands to the build directory corresponding to srcs, i.e. it results in an invocation like
clang++ /path/to/build/test/test.cpp -I /path/to/build/srcs ...
but you want to pass the actual source directory to the preprocessor. To fix this, try
target_include_directories(MyLib
INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})