[CMake] CmakeLists chain cannot find source added with add_custom_command

Wed Jul 5 06:10:52 EDT 2017

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
>>>>> --------------------------------------
>>>>>
>>>>
>>>>
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>>>>
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>>
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>> Powered by www.kitware.com
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>
>
>
>
> --
> Eric
>
> --
>
> Powered by www.kitware.com
>
> Please keep messages on-topic and check the CMake FAQ at:
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>
> Kitware offers various services to support the CMake community. For more
> information on each offering, please visit:
>
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