[CMake] Dependency cycle - why?

[Bill Somerville]

Hi folks,

I am struggling to understand what the problem is with this:

find_program (GO go)
set (GOPATH "${CMAKE_CURRENT_BINARY_DIR}/go")
file (MAKE_DIRECTORY ${GOPATH})

set (sources ${CMAKE_CURRENT_SOURCE_DIR}/callback_generator.go)
set (build_command ${GO} build)
set (output callback_generator${CMAKE_EXECUTABLE_SUFFIX})
add_custom_command (OUTPUT ${output}
   COMMAND ${CMAKE_COMMAND} -E env GOPATH=${GOPATH} CGO_CFLAGS=${CMAKE_CGO_CFLAGS} ${build_command} -o ${output} ${CMAKE_GO_FLAGS} ${sources}
   DEPENDS ${sources}
   VERBATIM)
add_custom_target (callback_generator_target DEPENDS ${CMAKE_CURRENT_BINARY_DIR}/${output})
add_executable (callback_generator IMPORTED)
set_target_properties (callback_generator
   PROPERTIES
   IMPORTED_LOCATION ${CMAKE_CURRENT_BINARY_DIR}/${output}
   )
add_dependencies (callback_generator callback_generator_target)

add_custom_target (server ALL DEPENDS callback_generator)

which gives this error:

>cmake --version
cmake --version
cmake version 3.14.3

>cmake -G "MinGW Makefiles" ..\..
cmake -G "MinGW Makefiles" ..\..
-- Configuring done
CMake Error: The inter-target dependency graph contains the following strongly connected component (cycle):
   "callback_generator_target" of type UTILITY
     depends on "callback_generator_target" (strong)
The component contains at least one cycle consisting of strong dependencies (created by add_dependencies) that cannot be broken.

The set_target_properties () call seems to be part of the problem but I 
don't understand why.

Regards
Bill Somerville.

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