[CMake] DEPENDS fails on a target created by add_custom_target

[Giampiero Salvi]

Dear list,
I am a bit confused on the use of add_custom_target, I hope someone can 
help me.

Here is what I am trying to do:
I have a number of subdirectories that build libraries, and then I build 
the final executable with a custom command (I am wrapping all the 
libraries in a tclkit executable). Some libraries consist of c++ code, 
others of just tcl code (I just need to copy the tcl files at 
compilation time).

Here is how I tried to do it:
- In case of c++ libraries I use add_library,
- in case of pure tcl libraries I use add_custom_command and 
add_custom_target to copy the files (I do not use configure_file because 
I want to copy the files at build time and not configuration time).
- In the main CMakeLists.txt I use add_custom_command and 
add_custom_target to wrap the libraries into an tclkit executable.

Here is the problem:
when I use DEPENDS in the main add_custom_command, it finds the targets 
generated by add_library, but it complains about the ones generated by 
add_custom_target with a "No rule to make target" even though the 
targets are built ("[ 82%] Built target targetB")

Here is a simplified example (in case the above didn't make too much sense):

main_dir/CMakeLists.txt: --------------------
PROJECT(main)
subdirs(dirA dirB)
ADD_CUSTOM_COMMAND(
   OUTPUT ${EXECUTABLE_OUTPUT_PATH}/main_custom${CMAKE_EXECUTABLE_SUFFIX}
   COMMAND wrap_libs_to_tclkit_exe
   DEPENDS targetA targetB
)
ADD_CUSTOM_TARGET(main_custom ALL
   DEPENDS ${EXECUTABLE_OUTPUT_PATH}/main_custom${CMAKE_EXECUTABLE_SUFFIX}
)

main_dir/dirA/CMakeLists.txt: -----------------
PROJECT(targetA)
ADD_LIBRARY(${PROJECT_NAME} SHARED file1.cxx file2.cxx file3.cxx)
TARGET_LINK_LIBRARIES(${PROJECT_NAME} blabla)

main_dir/dirB/CMakeLists.txt: -----------------
PROJECT(targetB)
SET(TCL_FILES file1.tcl file2.tcl file3.tcl)
ADD_CUSTOM_TARGET(${PROJECT_NAME} ALL)
FOREACH(file ${TCL_FILES})
   GET_FILENAME_COMPONENT(name ${file} NAME)
   SET(tgt ${LIBRARY_OUTPUT_PATH}/${name})
   SET(src ${file})
   ADD_CUSTOM_COMMAND(
     TARGET ${PROJECT_NAME}
     COMMAND ${CMAKE_COMMAND}
     ARGS -E copy_if_different ${src} ${tgt}
     DEPENDS ${src}
     COMMENT "copying file: ${src} ${tgt}"
     )
ENDFOREACH(file)

The result is that both targetA and targetB are built, but when building 
main_custom I get the "No rule to make target `targetB'" problem. I 
don't get any error with only targets on the same type as targetA.

What am I doing wrong?

Thank you!
Giampiero