Src folder without CMakeLists.txt - cmake

Question

I'm starting with cmake I'm following a tutorial that has as an example the following structure:
$ tree -L 2 ExampleProject/
ExampleProject/
|-- build/
|-- CMakeLists.txt
|-- inc/
| |-- Formula.h
|-- src/
| |-- CMakeLists.txt
| |-- Formula.cpp
| |-- main.cpp
To include the header files that are in the inc folder I just have to include_directories inside CMakeLists.txt in the src folder. However, I would not want to put CMakeLists files in the source folder, because I think that in this folder should be only source files. I don't like to mix build files with application source files. So my idea is to use only top level CMakeLists, ie:
$ tree -L 2 ExampleProject/
ExampleProject/
|-- build/
|-- CMakeLists.txt
|-- inc/
| |-- Formula.h
|-- src/
| |-- Formula.cpp
| |-- main.cpp
That is, I don't want to treat the src folder as a subdirectory.
It is possible? Is there something like source_directories?
Here is how far I managed to get:
cmake_minimum_required(VERSION 3.10)
project(ExampleProject)
set(CMAKE_CXX_STANDARD 14)
include_directories(inc)
set(BINARY ${CMAKE_PROJECT_NAME})
file(GLOB_RECURSE SOURCES LIST_DIRECTORIES true *.h)
set(SOURCES ${SOURCES})
add_executable(${BINARY}_run ${SOURCES})
But it would not work because it has to include the .cpp files.

Answer 1

You can add executable from top level CMakelists.txt file. With add_executable(target src/main.cpp). You can try something like this:
add_executable(output src/main.cpp)
add_library(formula src/Formula.cpp)
target_include_directories(formula PUBLIC inc)
target_link_libraries(output PUBLIC formula)