[CMake] CmakeLists chain cannot find source added with add_custom_command

Eric Noulard eric.noulard at gmail.com
Wed Jul 5 06:34:59 EDT 2017 

OK right.
I missed the proper FAQ entry, thanks Nicholas for pointing it out.

Eric

2017-07-05 12:10 GMT+02:00 Nicholas Devenish <ndevenish at gmail.com>:

> Hi,
>
> It looks like this is the issue covered in
> https://cmake.org/Wiki/CMake_FAQ#How_can_I_add_a_
> dependency_to_a_source_file_which_is_generated_in_a_subdirectory.3F
> and bug https://gitlab.kitware.com/cmake/cmake/issues/14633 ? I
> suppose if you are writing your own systems from scratch it's easy not
> to run into this, but a lot easier when converting existing
> complicated build systems.
>
> I kind of agree that it's easy to miss this constraint reading the
> documentation, but there doesn't seem to be a better suggested
> solution yet.
>
> Nick
>
>
> On Sun, Jul 2, 2017 at 11:57 AM, Eric Noulard <eric.noulard at gmail.com>
> wrote:
> > Ok,
> >
> > I reproduced your issue and I can then confirm it.
> > I tried several thing including:
> >    - generating the file is the buildtree
> >    - refering to the same file with another target in the same dir
> >    - using absolute path in the sub2/add_executable
> >
> > nothing works.
> > it looks like a generated file cannot be referred outside the directory
> > where the custom command generates it ???
> >
> > Here comes an archive with an example similar to the one descrived by J.
> > Decker.
> > If you build it without option it wokrs (because I used an intermediate
> > object lib)
> > If you (try to) build it with
> >
> > cmake -DBROKEN=1
> >
> > then it'll fails with "Cannot find source file..."
> >
> > This is definitely weird and I never encountered this after +10 years of
> > CMake usage!!
> > So I guess I have always used generated file locally to build exe or lib
> and
> > then refer to the lib.
> > If this is the intended behaviour then it should be documented more
> > explicitely.
> >
> > Now re-reading the doc of add_custom_command:
> >
> > "This defines a command to generate specified ``OUTPUT`` file(s).
> > A target created in the same directory (``CMakeLists.txt`` file)
> > that specifies any output of the custom command as a source file
> > is given a rule to generate the file using the command at build time."
> >
> > So the "same directory" should be underlined!! Or may be another sentence
> > saying that in fact you CANNOT refer to outputed files outside the
> > directory...
> >
> > In fact it is possible to have cross-directory reference to generated
> file
> > but this is
> > more like a workaround. You'll have to:
> >
> > define your custom_command and an associated custom target in dir1
> > define your exe/lib in dir2 and explicitely:
> >    - flag the referred cross-dir generated source as GENERATED
> >    - make your exe/lib depend on the cross-dir custom target in order to
> > trigger the file generation.
> >
> >
> > The second zip implement that workaround. This is nasty, I wouldn't do
> that.
> > Shall we open a bug for this misleading behavior or shall we open a bug
> for
> > doc update?
> >
> >
> >
> > 2017-07-02 10:20 GMT+02:00 J Decker <d3ck0r at gmail.com>:
> >>
> >> It is not generated; because it is generated during a the build phase
> not
> >> the generate phase.  So only the logical idea of the file exists.
> >>
> >> On Sun, Jul 2, 2017 at 12:12 AM, Eric Noulard <eric.noulard at gmail.com>
> >> wrote:
> >>>
> >>> Needless to say that your example should work but somehow CMake does
> not
> >>> see that the referred file is GENERATED.
> >>>
> >>> Le 2 juil. 2017 09:11, "Eric Noulard" <eric.noulard at gmail.com> a
> écrit :
> >>>>
> >>>> Is the referred file created?
> >>>> Does your actual command creating the file doing it in the source tree
> >>>> and not in the build tree?
> >>>> Are you building in-source or out of source?
> >>>>
> >>>> Could you give us us a toy example which shows the issue?
> >>>>
> >>>> Le 2 juil. 2017 04:32, "J Decker" <d3ck0r at gmail.com> a écrit :
> >>>>
> >>>> Known issue?  Or just doesn't require a response?
> >>>>
> >>>> On Wed, Jun 28, 2017 at 6:05 AM, J Decker <d3ck0r at gmail.com> wrote:
> >>>>>
> >>>>> I have this chain of makefiles.  It adds a custom rule to build a
> >>>>> source file, and then a subdirectory cannot reference that file.
> >>>>>
> >>>>> The first is added custom rule for M:/tmp/cmake-chain/sub/src/sack.c
> >>>>> and then later cannot find M:/tmp/cmake-chain/sub/src/sack.c
> >>>>> though it's really referencing it as
> >>>>> M:/tmp/cmake-chain/sub/sub2/../src/sack.c
> >>>>>
> >>>>> tested with 3.6.0-rc4 and 3.9.0-rc5
> >>>>>
> >>>>> if the add_custom_rule and add_executable are in the same makefile
> even
> >>>>> if there's a added path to make it not exactly the same source as the
> >>>>> 'referencing source' message logs; it works.
> >>>>>
> >>>>>
> >>>>> --- CMakeLists.txt ---
> >>>>> cmake_minimum_required(VERSION 2.8)
> >>>>>
> >>>>> message( "Adding custom rule for
> >>>>> ${CMAKE_CURRENT_SOURCE_DIR}/src/sack.c" )
> >>>>>   add_custom_command( OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/src/sack.c
> >>>>>   COMMAND cmake -E echo do something to make src/sack.c
> >>>>>   )
> >>>>> add_subdirectory( sub2 )
> >>>>> -------------------------------------
> >>>>>
> >>>>> --- sub2/CmakeLists.txt ---
> >>>>> message( "referencing source ${CMAKE_CURRENT_SOURCE_DIR}/..
> /src/sack.c"
> >>>>> )
> >>>>> add_executable( something ${CMAKE_CURRENT_SOURCE_DIR}/../src/sack.c
> )
> >>>>>
> >>>>> -------------------------------------
> >>>>>
> >>>>> --- Truncated output log ------
> >>>>> Adding custom rule for M:/tmp/cmake-chain/sub/src/sack.c
> >>>>> referencing source M:/tmp/cmake-chain/sub/sub2/../src/sack.c
> >>>>> -- Configuring done
> >>>>> CMake Error at sub2/CMakeLists.txt:3 (add_executable):
> >>>>>   Cannot find source file:
> >>>>>
> >>>>>     M:/tmp/cmake-chain/sub/src/sack.c
> >>>>>
> >>>>>   Tried extensions .c .C .c++ .cc .cpp .cxx .m .M .mm .h .hh .h++ .hm
> >>>>> .hpp
> >>>>>   .hxx .in .txx
> >>>>> --------------------------------------
> >>>>>
> >>>>>
> >>>>> ------ Flat CmakeLists.txt which works ---------------
> >>>>> cmake_minimum_required(VERSION 2.8)
> >>>>>
> >>>>> message( "Adding custom rule for
> >>>>> ${CMAKE_CURRENT_SOURCE_DIR}/src/sack.c" )
> >>>>>   add_custom_command( OUTPUT ${CMAKE_CURRENT_SOURCE_DIR}/src/sack.c
> >>>>> COMMAND cmake -e echo make file.
> >>>>>   )
> >>>>>
> >>>>> message( "referencing source ${CMAKE_CURRENT_SOURCE_DIR}/src/sack.c"
> )
> >>>>> add_executable( something
> >>>>> ${CMAKE_CURRENT_SOURCE_DIR}/sub2/../src/sack.c )
> >>>>> --------------------------------------
> >>>>>
> >>>>> ----- flat cmakelists output.... -----------
> >>>>> Adding custom rule for M:/tmp/cmake-chain-flat/src/sack.c
> >>>>> referencing source M:/tmp/cmake-chain-flat/sub2/../src/sack.c
> >>>>> -- Configuring done
> >>>>> --------------------------------------
> >>>>>
> >>>>
> >>>>
> >>>> --
> >>>>
> >>>> Powered by www.kitware.com
> >>>>
> >>>> Please keep messages on-topic and check the CMake FAQ at:
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> >>>>
> >>
> >>
> >> --
> >>
> >> Powered by www.kitware.com
> >>
> >> Please keep messages on-topic and check the CMake FAQ at:
> >> http://www.cmake.org/Wiki/CMake_FAQ
> >>
> >> Kitware offers various services to support the CMake community. For more
> >> information on each offering, please visit:
> >>
> >> CMake Support: http://cmake.org/cmake/help/support.html
> >> CMake Consulting: http://cmake.org/cmake/help/consulting.html
> >> CMake Training Courses: http://cmake.org/cmake/help/training.html
> >>
> >> Visit other Kitware open-source projects at
> >> http://www.kitware.com/opensource/opensource.html
> >>
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> >> http://public.kitware.com/mailman/listinfo/cmake
> >
> >
> >
> >
> > --
> > Eric
> >
> > --
> >
> > Powered by www.kitware.com
> >
> > Please keep messages on-topic and check the CMake FAQ at:
> > http://www.cmake.org/Wiki/CMake_FAQ
> >
> > Kitware offers various services to support the CMake community. For more
> > information on each offering, please visit:
> >
> > CMake Support: http://cmake.org/cmake/help/support.html
> > CMake Consulting: http://cmake.org/cmake/help/consulting.html
> > CMake Training Courses: http://cmake.org/cmake/help/training.html
> >
> > Visit other Kitware open-source projects at
> > http://www.kitware.com/opensource/opensource.html
> >
> > Follow this link to subscribe/unsubscribe:
> > http://public.kitware.com/mailman/listinfo/cmake
>



-- 
Eric
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