I’m new to CMake and I found this file.

set( EXAMPLE_DEMO_TARGET demo )

set ( USH_TARGET ush_demo )
build_ush ( ${USH_TARGET}
    ${CMAKE_CURRENT_SOURCE_DIR}
)
target_compile_definitions(
    ${USH_TARGET}
    PUBLIC
    USH_CONFIG_PLATFORM_POSIX
)

add_executable(
    ${EXAMPLE_DEMO_TARGET}
    ${CMAKE_CURRENT_SOURCE_DIR}/demo.c
    ${CMAKE_CURRENT_SOURCE_DIR}/interface.c
    ${CMAKE_CURRENT_SOURCE_DIR}/commands.c
    ${CMAKE_CURRENT_SOURCE_DIR}/terminal.c
    ${CMAKE_CURRENT_SOURCE_DIR}/shell.c
    ${CMAKE_CURRENT_SOURCE_DIR}/fs/fs.c
    ${CMAKE_CURRENT_SOURCE_DIR}/fs/path/root.c
    ${CMAKE_CURRENT_SOURCE_DIR}/fs/path/etc.c
    ${CMAKE_CURRENT_SOURCE_DIR}/fs/path/dev.c
    ${CMAKE_CURRENT_SOURCE_DIR}/fs/path/bin.c
)
target_link_libraries( ${EXAMPLE_DEMO_TARGET} PUBLIC ${USH_TARGET})
target_compile_options( ${EXAMPLE_DEMO_TARGET} PRIVATE -Werror -Wall -Wextra  -g -O0)

Mostly my problem is with USH_TARGET/ush_demo. The first part that I don’t understand is this. Is it a function or something else and what does it do? I can see that it is not just another CMake command.

build_ush ( ${USH_TARGET}
    ${CMAKE_CURRENT_SOURCE_DIR}
)

This is other line that confused me because now it looks like ush_demo is a library.

target_link_libraries( ${EXAMPLE_DEMO_TARGET} PUBLIC ${USH_TARGET})

In the generated Makefile I found this and now I don’t know what is the difference between demo and ush_demo.

# Target rules for targets named ush_demo

# Build rule for target.
ush_demo: cmake_check_build_system
    $(MAKE) $(MAKESILENT) -f CMakeFiles/Makefile2 ush_demo
.PHONY : ush_demo

# fast build rule for target.
ush_demo/fast:
    $(MAKE) $(MAKESILENT) -f examples/demo_linux/CMakeFiles/ush_demo.dir/build.make examples/demo_linux/CMakeFiles/ush_demo.dir/build
.PHONY : ush_demo/fast

#=============================================================================
# Target rules for targets named demo

# Build rule for target.
demo: cmake_check_build_system
    $(MAKE) $(MAKESILENT) -f CMakeFiles/Makefile2 demo
.PHONY : demo

# fast build rule for target.
demo/fast:
    $(MAKE) $(MAKESILENT) -f examples/demo_linux/CMakeFiles/demo.dir/build.make examples/demo_linux/CMakeFiles/demo.dir/build
.PHONY : demo/fast

At what point does ush_demo become a target and what is the difference between it and demo?

The full project is here.