Hi, I'm a new user of CMake, but I just want to express my newcomer point of view. Honestly , I can feel the power of CMAKE, but it's a real pain to learn ... I'm using CMAKE for an embedded platform with a non GNU compiler , ant at the end the CMAKE description is longer than the one I built directly in Ninja. I had to write a python script to parse my eclipse project xml to create a list of sources files usable by CMAKE. The first thing I thought was: why this is not a part of cmake ? And the second thing was : why not using the scripting power of an existing language like Python(or other one) and add CMAKE as a framework / library ? Probably a dumb question ! :)
Yann 2016-01-13 10:34 GMT+01:00 Charles Huet <charles.h...@gmail.com>: > Hi, > > > * There is a lot of code out there in the current CMake language so I do > not > think it is realistic to drop it. I'm not proposing that this change. > > I am. (more below) > > > * Many projects build elaborate macro/function systems in the CMake > language > in order to end up with a declarative specification listing the actual > source files, dependencies, and usage requirements. I'd like to offer > an alternative to this. > > In my experience, most of the elaborate macros/functions come either from > a misunderstanding of some of CMake's internals (scope, link debug/release > libs, etc) or to circumvent some shortcoming of the CMake language (e.g. no > return value for functions). > > > I'd like to improve this by *optionally* moving part of the > specification > to a (stateless) declarative format that IDEs can load/edit/save directly > > Split the buildsystem in two different languages ? Would the declarative > part be in a different file ? > Also, the declarative part in my opinion must take advantage of the > language. > For instance, add a source file only for WIN32 systems should be easy in > said declarative format. > Using a custom language (based on JSON for instance) would mean to add > conditionals, which comes back to making a custom language again. > > > To come back to my first point, I understand completely that this would be > a tremendous change, and the transition would be difficult to say the > least. But I think it would be more than worth it in the long term. > > > The moment you make CMake scriptable in more than one language, you are > forcing > > every CMake user to learn that additional language because sooner or > later he > > will step into a third-party that is using that additional language. > > What I have in mind is to deprecate the current CMake language and replace > it with another language. So there would be a transition period, but in the > end there would only be one language again, and a better one. > > If CMake transitioned to python (or Lua, or whatever) newcomers to CMake > would not need learn a new language (or at least learn one that has many > resources, and can be used for other purposes). > Old-timers would have to learn a new language (or maybe not, most > programmers I know have played a bit with python to automate simple tasks), > but this would be easier than learning CMake was, since there are > established rules and a more consistent design to it. > > Of course I'm not saying this should happen overnight, nor am I saying > this *must* happen, but I think discussing it can only be beneficial. > > I've seen lots of people wonder how to make their CMake scripts more > efficient, and currently this is a very difficult thing to do, since there > is no profiling possible. > And who can say they never spent way too much time trying to understand > why a variable was not correctly initialized ? When the configure step > takes about 30 seconds, and all you can do is use MESSAGE() to find what > happens, this is no walk in the park. A real debugger would do a world of > good to CMake. > I have seen some hardly understandable CMake code, and only thanks to the > git history was I able to understand that the person who wrote the script > completely misunderstood the CMake language. > > >As discussed above if some kind of callback or user-coded function needs > to > be included for advanced usage of the declarative spec then we would need > a language for it. The current CMake language is not well suited to that > use case (e.g. no expressions or return values), so an existing alternative > language should be chosen. > > >CMake's current "generator expressions" fill this role somewhat now and > are > essentially a sub-language. As with the main language they grew out of > something not intended to serve their current full role. They could be > superseded by a common alternative generate-time language too. > > These points are part of the reason I think a new language should be used, > if it can cover all of these issues. I'd rather not see a new CMake > declarative language that might itself grow out and become something > difficult to grasp. > Something like generator expressions could be expressed in a language such > as python or lua, by using objects that get resolved at generate time (or > functions, or whatever). > > > Cheers > > Le lun. 11 janv. 2016 à 21:53, Brad King <brad.k...@kitware.com> a écrit : > >> Hi Folks, >> >> I'm replying directly to my previous post in this thread in order to >> consolidate >> responses to related discussion raised in others' responses to it: >> >> >> http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/15339/focus=15383 >> >> http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/15339/focus=15386 >> >> http://thread.gmane.org/gmane.comp.programming.tools.cmake.devel/15339/focus=15389 >> >> General comments: >> >> * There is a lot of code out there in the current CMake language so I do >> not >> think it is realistic to drop it. I'm not proposing that this change. >> >> * CMake's procedural/imperative design is good as the main entry point to >> configuration of a project. It can do system introspection, file >> generation, >> etc. I'm not proposing that this change. >> >> * Many projects build elaborate macro/function systems in the CMake >> language >> in order to end up with a declarative specification listing the actual >> source files, dependencies, and usage requirements. I'd like to offer >> an alternative to this. >> >> * Integration with IDEs is currently based on one-way generation (VS IDE >> projects, Xcode projects, CodeBlocks, etc.). Editing the project build >> specification requires editing CMake code directly because IDEs cannot >> easily pierce CMake's procedural/imperative specification: >> >> https://cmake.org/pipermail/cmake-developers/2016-January/027386.html >> >> I'd like to improve this by *optionally* moving part of the >> specification >> to a (stateless) declarative format that IDEs can load/edit/save >> directly. >> >> Specific responses follow. >> >> >> -------------------------------------------------------------------------------- >> >> On 01/11/2016 12:24 PM, Charles Huet wrote: >> > I think these goals aim towards a faster configure, and the ability to >> > only partly reconfigure, right? >> >> Yes. >> >> > I know I am largely biased by the project I work on, but I do not see >> how >> > parallel evaluation woud be a huge benefit. >> [snip] >> > And how would that work with CMakeLists that affect their parent scope ? >> >> Evaluation of the imperative language is currently serial for reasons like >> this, which is why I said it would take semantic changes to enable >> parallel >> evaluation. This is not the main point of my proposal so I'd rather not >> get bogged down in the details of this part of the discussion. >> >> >> Ideally most of the specification (sources, libraries, executables, >> etc.) >> >> should be in a pure format that can be evaluated without side effects >> (e.g. >> >> declarative or functional). >> > >> > I'm not sure I understand how this could be done without losing a lot of >> > what CMake offers, such as copying or generating files. >> >> I'm not proposing dropping the current imperative capabilities. >> >> > I'm leaning towards a declarative approach as it is quite easy to learn >> > (since you declare objects, and every C++ programmer I know is familiar >> > with those) >> >> Yes. >> >> > It seems you are leaning towards pure functional, but I do not see how >> > this would work with the current way CMake handles variables and scope, >> > could you elaborate ? >> >> While declarative may get us most of the way, advanced users may wish to >> hook in to generation-time evaluation. A clean way to do that would be >> to specify a function within the declared values. It would not have to >> be in a functional language as long as it has no access to anything other >> than the inputs passed to it during evaluation. >> >> I mentioned "functional" mostly as an example of a specification whose >> evaluation is free of side effects. >> >> > To clarify, only the following lines should be considered when looking >> at the POC. >> >> myProject=cmake.Project("MyTestProject") >> >> myProject.targets=[cmake.SharedLibrary("testLibrary",["lib.cxx"])] >> >> Yes, this is the kind of stuff that can be in a declarative format. >> >> > It seems you have in mind to write a new CMake language. >> >> No, at most a new specification format that can be used for IDE >> integration. >> If some kind of user-coded function were included in the specification it >> should certainly be in an existing language. >> >> > Maybe I should take my POC further >> >> I think implementation even of a POC is premature at this point. We >> should explore the design space further. >> >> > CMake's own buildsystem seems like a good testing ground for this, but >> > it is a little too big for a first go, do you know of a small >> CMake-based >> > project that would be better suited ? >> >> Maybe you could find something in our test suite. >> >> > I don't have a clear view of what a pure functional CMake would look >> like, >> > but if you give me some mock code, I could give a try at bringing some >> pure >> > functional language up to the level of my POC and we could use it as a >> more >> > concrete discussion support. >> >> I have no prototype (nor substantial time to spend on design myself) but >> I've imagined a declarative format in a well-known syntax (e.g. JSON or >> one >> of the lightweight human-friendly choices). If generate-time >> functionality >> is needed then code snippets in e.g. Lua could be included. >> >> >> -------------------------------------------------------------------------------- >> >> Petr Kmoch wrote: >> > I'd like to voice my opinion as a somewhat advanced CMake user here. >> >> Thanks for joining the discussion with this point of view. >> >> > For me, one of the strongest points of CMake is the fact that its >> project >> > specification is procedural rather than declarative. >> >> Good. We will not be dropping imperative capabilities. >> >> > end result of our framework is that the CMakeLists consist mostly of >> > declarative commands from our framework >> >> Yes, many projects have such frameworks. Most of them result in a >> declarative spec inside calls to their macros/functions. I'd like to >> formalize such specs in a re-usable way. >> >> > If I understand Brad's suggestion correctly, it would amount to a >> > (possibly empty) procedural step being used to generate a declarative >> > description of the buildsystem. >> >> Not quite. Yes, the procedural/imperative part would still be the entry >> point as it is now. However, the declarative part would also be an >> input, not an output. The procedural part's role would be to compute >> *parameters* to be used for the evaluation of the declarative spec. >> >> For example, imagine the declarative spec somehow encodes that source >> file "foo.c" is optional based on some condition "FOO". The value of >> that condition could be computed by the procedural part of the process >> based on system introspection, command-line options, etc., and then >> provided to CMake for use in the final evaluation. >> >> >> -------------------------------------------------------------------------------- >> >> On 01/11/2016 01:21 PM, Pau Garcia i Quiles wrote: >> > The moment you make CMake scriptable in more than one language, you are >> forcing >> > every CMake user to learn that additional language because sooner or >> later he >> > will step into a third-party that is using that additional language. >> >> I don't think the main "entry point" language should be selectable. >> >> As discussed above if some kind of callback or user-coded function needs >> to >> be included for advanced usage of the declarative spec then we would need >> a language for it. The current CMake language is not well suited to that >> use case (e.g. no expressions or return values), so an existing >> alternative >> language should be chosen. >> >> CMake's current "generator expressions" fill this role somewhat now and >> are >> essentially a sub-language. As with the main language they grew out of >> something not intended to serve their current full role. They could be >> superseded by a common alternative generate-time language too. >> >> > Also, declarative? Why? >> >> See above. >> >> > There are already a few declarative build systems >> >> Yes, and perhaps we can learn from their formats for the proposed >> declarative >> part. >> >> > qbs, one of the reasons for its existence was CMake was not declarative >> >> IIUC that is exactly because of the fact that an imperative spec cannot >> be pierced easily for editing in IDEs. >> >> >> -------------------------------------------------------------------------------- >> >> Thanks all for the discussion so far! >> >> -Brad >> >> -- >> >> 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 >
-- 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
