[cmake-developers] ExternalProject: Use native paths as substitute for directory tokens
David Cole
DLRdave at aol.com
Thu Aug 20 17:20:42 EDT 2015
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
> >
>
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