[cmake-developers] ExternalProject: Use native paths as substitute for directory tokens
Kislinskiy, Stefan
s.kislinskiy at Dkfz-Heidelberg.de
Fri Aug 21 03:58:08 EDT 2015
I still disagree on the point that CMake shouldn't be fixed because of possibly erroneous external scripts that are not able to handle paths which were - again possibly - passed to them as parameters in the style of the platform they were written for. This is very hypothetical in my opinion. We should also bring to mind here that CMake as seen as an entity as well as CMake scripts wouldn't be affected by the fix at all regarding backwards compatibility. How can these obviously rare cases - if existent at all - lie in the scope of responsibility of CMake? And how could one justify that everyone (else?) have to continue working around this bug?
Please be aware that I am not asking that EVERYONE should solve a problem which I have encountered and that this is far from "it just works". In fact, James Johnston even ran into trouble with this bug yesterday "coincidentally" and I know at least of colleagues working around this issue for years now. It just doesn't work and there is no way that one could know this without burning lifetime figuring out what's going on and how to work around. Referring to the latest email of James Johnston and your advice not to use directory tokens, you see, that this, on one hand, is not a good option sometimes (and this would ironically create potential to break backwards compatibility as one would need to maintain script that kind of mimics CMake internals). On the other hand it is a little strange as it is rather equivalent to to say not to use the feature for what is solely intended to at all.
Obviously, something has to be done. The question seems to be: What should be done if you still want to keep the erroneous behavior?
- Point out the issue in the documentation (and wish good luck to CMake users for future upgrades of CMake as they are potentially mimicking potentially changing internals instead)? :)
- Adding a CMake policy?
- Adding a new *single* binary option to ExternalProject_* functions in the style of the "BUILD_IN_SOURCE 1" option, e.g. NATIVE_DIR_TOKENS?
- Something else?
I would still prefer to fix the bug directly as the only counter argument until now was about (loosely coupled) backwards compatibility and I hope I could show above that actually the reverse is true, and there is an on-going (loosely coupled) backwards compatibility issue.
Stefan
________________________________________
Von: cmake-developers [cmake-developers-bounces at cmake.org] im Auftrag von David Cole via cmake-developers [cmake-developers at cmake.org]
Gesendet: Donnerstag, 20. August 2015 23:20
An: James Johnston
Cc: cmake-developers at cmake.org
Betreff: Re: [cmake-developers] ExternalProject: Use native paths as substitute for directory tokens
It's exactly what I am concerned about:
You're asking to change the behavior of something for EVERYONE to
solve a problem which you have encountered. If you change it the way
you have proposed, you will cause problems for others. It has worked
the way it is now since ExternalProject_Add was introduced in CMake
2.8. Changing it unconditionally the way you propose is simply not
feasible for backwards compatibility.
I think commands that take native paths ought NOT to use the <*_DIR>
replacement values, and instead, ought to pass in variables that
contain the native paths in the first place.
David C.
On Thu, Aug 20, 2015 at 2:58 PM, James Johnston
<johnstonj.public at codenest.com> wrote:
> Hi,
>
> Funny you are mailing the list about this, since I just ran into this same issue today building something totally different from Boost... In this case it's a build tool that thinks the "/U" in "C:/Users" is a new command line argument, that isn't recognized - and then the subsequent "s" also ends up unrecognized... and it all fails... And it has nothing to do with the working directory, so _Add_Step(WORKING_DIRECTORY) isn't a possible workaround for me.
>
> I think the issue with globally making this change to the existing tokens is that there could be some external tool/program that is EXPECTING to get CMake paths, not native paths. Who knows? I am guessing that is what David Cole was concerned about.
>
> Maybe the right answer is to introduce some NEW tokens while leaving the behavior of the old ones unchanged. E.g. <BINARY_DIR_NATIVE> etc. It would be good if the patch updates the documentation of ExternalProject and clearly states the path format of <BINARY_DIR> vs <BINARY_DIR_NATIVE>. Then the user can pick whichever one suits them best, depending on the tool being invoked.
>
> Furthermore, sometimes <BINARY_DIR_NATIVE> still needs to be replaced with a CMake path, not native path. For example, if the token is being found in a property like WORKING_DIRECTORY that eventually gets passed to add_custom_command(WORKING_DIRECTORY) then I'm guessing still has to be a CMake path. I am guessing this is what David Cole was also concerned about.
>
> I still think your original method of building Boost is a bit unusual and would be better served by _Add_Step with a custom working directory - because that's the publicly documented/standard way of changing the working directory, but that is up to you. :)
>
> Best regards,
>
> James Johnston
>
>
> ---- On Thu, 20 Aug 2015 14:37:08 +0000 Stefan Kislinskiy <s.kislinskiy at Dkfz-Heidelberg.de> wrote ----
>
> > Hi,
> >
> > thank you for our suggestions. I am aware that I can solve my example differently and that it might look not directly connected the proposal, but well, it is an example just to show a single case and why it matters. :) I did not want to discuss the example itself. Working around here would just resolve a symptom.
> >
> > My point is the overall problem that would persist: A big part of ExternalProject is to issue commands for predefined and custom steps. Those commands are supposed to be executed by the shell/command line. According to the documentation and the source code of ExternalProject, directory tokens are mainly supposed to be replaced in commands. It is my understanding, that it is a bug, if CMake isn't able to assemble these commands correctly. This would include usage of the correct path style of the OS for shell/command line commands. As directory tokens are replaced internally right before a shell/command line command is assembled, I can't see why this would be kind of "API-breaking". You cannot interfere in your CMake code with these internal replacements.
> >
> > Therefore I would still prefer my solution as it is pretty simple without adding even more features to ExternalProject and in my opinion without breaking code in the wild. It is a true bug fix instead of a feature request for working directories, which is a different topic that just coincidentally arised because of my specific example I guess. The features you described wouldn't fix the actual bug.
> >
> > As you were not sure if my approach would even fix my problems: It does of course and this is what I am currently doing and what I tested extensively before creating the patch. :) Regarding your quote from the add_custom_command documentation I can tell you that this is how things are currently done in ExternalProject and always were as far as I know, for example (from ExternalProject.cmake):
> >
> > add_custom_command(
> > OUTPUT ${stamp_file}
> > BYPRODUCTS ${byproducts}
> > COMMENT ${comment}
> > COMMAND ${command}
> > COMMAND ${touch}
> > DEPENDS ${depends}
> > WORKING_DIRECTORY ${work_dir}
> > VERBATIM
> > )
> >
> > Best regards,
> > Stefan
> >
> >
> > -----Original Message-----
> > From: cmake-developers [mailto:cmake-developers-bounces at cmake.org] On Behalf Of James Johnston
> > Sent: Donnerstag, 20. August 2015 15:37
> > To: cmake-developers at cmake.org
> > Subject: Re: [cmake-developers] ExternalProject: Use native paths as substitute for directory tokens
> >
> > > -----Original Message-----
> > > From: cmake-developers [mailto:cmake-developers-bounces at cmake.org]
> > > On Behalf Of Kislinskiy, Stefan
> > > Sent: Thursday, August 20, 2015 09:02
> > > To: David Cole
> > > Cc: cmake-developers at cmake.org
> > > Subject: Re: [cmake-developers] ExternalProject: Use native paths as
> > > substitute for directory tokens
> > >
> > > Hi David,
> > >
> > > Example excerpt (it is not possible to change the working directory
> > > for
> > the
> > > CONFIGURE_COMMAND as it is fixed to the BUILD_DIR, which might not be
> > > sufficient):
> >
> > This doesn't really directly have to do with your proposal, but what if an option was added to change the working dir of the CONFIGURE_COMMAND? E.g.
> > WORKING_DIRECTORY_CONFIGURE. And suppose you'd have it recognize the various tags like <SOURCE_DIR>, etc. This might be useful to add to other steps as well, and would be more portable than your solution which is using cmd.exe-specific commands. You'd want to audit for any resulting breakage (e.g. does ExternalProject make assumptions that the working directory of CONFIGURE is always the binary dir? - e.g. a relative path being used somewhere. And probably only allow specification of WORKING_DIRECTORY_CONFIGURE if a CONFIGURE_COMMAND was also specified, as the built-in commands certainly assume the default working dir.)
> >
> > In your situation though, I'm not sure it's strictly needed. From your sample, it looks like you're building boost. In your case what if you:
> >
> > * Use ExternalProject_Add_Step to bootstrap. You can specify a WORKING_DIRECTORY here. Note one problem: you can't do out of source build of b2, which breaks user expectations.
> > * Then use ExternalProject_Add_Step to build Boost.
> >
> > Yes, using _Add_Step is somewhat of a workaround, but in this case, I've found it wasn't much of a burden at all. In fact the only case I can think of where it WOULD be a burden would be if the configure step is CMake. But then you wouldn't need to change the working directory; changing it would break CMake. In practice nobody will want to change WORKING_DIRECTORY unless it's a custom command and then it's easy to use _Add_Step anyway.
> > That said, it might still be considered a little undesired and so maybe my proposal above would be a better way to handle it.
> >
> > Corrections from maintainers and others on the above commentary are welcome...
> >
> > >
> > > set(bootstrap_cmd "<SOURCE_DIR>/bootstrap${shell_ext}"
> > > ${bootstrap_toolset})
> > >
> > > if(WIN32)
> > > set(bootstrap_cmd pushd "<SOURCE_DIR>" COMMAND ${bootstrap_cmd}
> > > COMMAND popd)
> > > endif()
> > >
> > > ExternalProject_Add(Boost
> > > ...
> > > CONFIGURE_COMMAND ${bootstrap_cmd}
> > > ...
> > > )
> >
> > From add_custom_command: "If more than one COMMAND is specified they will be executed in order, but not necessarily composed into a stateful shell or batch script."
> >
> > So I am not sure your approach will work for you even if you fix the issue with path slashes.
> >
> > James
> >
>
> --
>
> 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-developers
--
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-developers
More information about the cmake-developers
mailing list