[swift-build-dev] [swiftpm] Add proposal for C language support

Tue Jan 5 12:30:33 CST 2016

Great, glad we could all get on the same page!

I agree these are essentially two unrelated problems and we will end up
with two features to support them. Both will have pros and cons and we
should definitely shoot for both being "excellent"!

Thanks for the PR I'll take a look when I am back at a computer.

 - Daniel

On Tuesday, January 5, 2016, Drew Crawford via swift-build-dev <
swift-build-dev at swift.org> wrote:

> I think I understand better what you are trying to accomplish.  It is not
> a bad way to go about it, and I think my comments were not as constructive
> as they should have been.
>
> I sent a PR that may clarify your motivation so as to head off objections
> like mine.  I think my reaction to the document was largely based around a
> misunderstanding about the motivation.  The title is "Package Manager C
> Language Target Support", and so that *sounds* like it is a proposal
> about C language support as a whole, which immediately raises questions
> about whether Foundation et al can be someday made to fit in its box (e.g.
> via extending it etc.)  Whereas if we are clearer that this is *merely
> one path to C language support, and this is the first one on the whiteboard* then
> I think it is a lot stronger.  It does solve a problem, I have a better
> idea of what that problem is, and the fact that it doesn't map well onto my
> problems is no longer troubling.
>
> I think your language is more polarizing than is due here, and I would
> encourage focusing on a technical argument rather than a judgement like
> "the entire value is debatable".
>
>
> I apologize for that.
>
> For background, when the topic of native C support vs external build
> systems has come up in the past, there's been an implicit value judgment
> that building C with swiftPM is the "preferred" way, and using an external
> build system is the "compromise" way, and when we set up that value
> hierarchy it is necessarily the case that the two ideas are in conflict.
>
> I'm coming around to the idea that actually these are totally unrelated
> problems, they only looked similar at first glance, that neither is any
> better or worse than the other, that we need to support both, and so we
> should just give both of them permission to be excellent in their own way,
> and that we should not try to shoehorn one of them into the problems that
> the other one is better at.
>
> Your proposal is clearly going to be better at the "few files of C code"
> problem, it was a bad idea for me to overcomplicate it with the problems of
> established C projects when they can be better served by handling them with
> an entirely separate solution.
>
> On Jan 4, 2016, at 6:48 PM, Daniel Dunbar <daniel_dunbar at apple.com
> <javascript:_e(%7B%7D,'cvml','daniel_dunbar at apple.com');>> wrote:
>
> Hi Drew,
>
> First off, I believe that the right way to handle something like libsodium
> is to have support for building targets using an external build system. I
> see that as a separate and independent feature from this proposal though.
> If you are interested in working on that feature I would love to discuss it
> more on a separate thread (I already mentioned it explicitly on another
> thread I am unable to find right now) -- it is a feature I would really
> like to see us have but don't have the bandwidth to tackle at the moment.
>
> This proposal is very specifically targeting the desire to be able to
> write and build new C code as part of Swift packages, it is not designed to
> support importing large existing projects. While I do hope that it will
> feature creep over time to allow more and more C projects to fit within the
> supported conventions, I also expect that to be a long incremental process.
>
> At this stage of the project, I would encourage looking at new proposals
> and features from a perspective of "does this add a useful new capability"
> and "is this in line with our goals" rather than "does this solve my
> immediate need X".
>
> More comments in line...
>
> On Jan 3, 2016, at 12:17 AM, Drew Crawford via swift-build-dev <
> swift-build-dev at swift.org
> <javascript:_e(%7B%7D,'cvml','swift-build-dev at swift.org');>> wrote:
>
> You keep referring to "'real' projects" as a proxy for the individual
> project you want support for; while there's a lot to be said for real-world
> use cases, I don't think this proposal's direction should be dictated by
> just libsodium.
>
>
> Nothing about this is reductive or specific to libsodium.
>
> * libdispatch has a build manual
> <https://github.com/apple/swift-corelibs-libdispatch/blob/master/INSTALL> that
> runs over 100 lines and involves checking out *7* other repos.
> * Foundation (incl CoreFoundation) has a python-based build
> <https://github.com/apple/swift-corelibs-foundation/tree/master/lib> system
> that runs to 1900 lines
> * libjpeg is "the" example of a C dependency in our documentation, and its
> build system includes such goodies as choosing a memory manager
> <http://libjpeg.cvs.sourceforge.net/viewvc/libjpeg/libjpeg/configure.ac?view=markup> or
> configuring libpng.
>
> And these are just the projects that *we* are associated with!
>
>
> These are projects I would expect to be tackled with an "external build
> system" feature, not this proposal.
>
> There are C projects that would benefit from modularization, header
> auditing, and cleanups that Swift and swiftpm would bring to it.
>
>
> Swift and swiftpm don't do anything of the kind.  C developers do.  All we
> can do is try to impose new requirements on C developers.  And who is
> volunteering to implement those requirements?
>
> It seems to me that if our new requirements are so amazing, it should be
> easy to convince a few projects to sign on to repackage.  libdispatch and
> Foundation are *our* projects; the bar is so low we're practically
> cheating.  Are they going to switch to this as their build system?  I don't
> know who makes this decision, but it seems like an important question to
> ask.
>
>
> While I think that "support libdispatch and Foundation" are good long term
> goals and useful reference points for what features are still needed to get
> there, it isn't the immediate goal here.
>
> No Swift project could be built with swiftpm when it was introduced
> without repackaging. I don't see why C support should be held to a
> different standard.
>
>
> Because we're designing a package manager for the Swift language, not the
> C language.  C has had build systems for decades.  We're not going to just
> waltz in with a new standard for a 44-year-old language and everybody
> switches the next day.  This is https://xkcd.com/927/.
>
>
> We can all dream, right? :)
>
> On Jan 2, 2016, at 8:11 PM, Zach Waldowski via swift-build-dev <
> swift-build-dev at swift.org
> <javascript:_e(%7B%7D,'cvml','swift-build-dev at swift.org');>> wrote:
>
> *I think an important feature of any C target proposal is that there will
> actually exist C targets which can be built under the proposal*.  Until
> there are C people coming out of the woodwork saying "sure, I will
> repackage my software this way" I think the entire value is debatable.
>
>
> I almost couldn't disagree more. No Swift project could be built with
> swiftpm when it was introduced without repackaging. I don't see why C
> support should be held to a different standard.
>
>
> I agree with Zach here. The purpose of the proposal is to add support for
> new code written in C designed to integrate with other Swift code. The
> merits of the conventions should be weighed about how easy it is to write
> that code, and what the implications for maintenance (on both the package
> manager and the code itself) are.
>
>
> And I do not see realistically how we are ever going to support a project
> like libsodium, except calling out to automake.
>
>
> A potential solution (one of many possible) would look a lot like how
> people generate Xcode projects for C build systems today; hand-tuning
> config.h headers and such. I know many people who will go to ungodly
> lengths to avoid the inevitable nightmare automake causes in a
> source-distributed dependency.
>
>
> IMO something like that is a much, much better direction in the
> short-term, and once we have done the first step of "packaging" those
> software via automake we will have "real" C projects in our package manager
> and we can design our C support around the concerns of real projects
> instead of imaginary ones.
>
>
> There are C projects that would benefit from modularization, header
> auditing, and cleanups that Swift and swiftpm would bring to it. C projects
> are massively disorganized because build systems are a ridiculous
> hodgepodge; we didn't be subject to that long tail of good and bad
> decisions.
>
> I don't think automake support would be a silver bullet at all, and
> contradict with many goals of swiftpm and llbuild to boot. Even targeting a
> really small subset of automake projects what liberties would unnecessarily
> complicate the project, and then there'd be the projects it doesn't
> support.  (Oh? Wait? What version of the tools? Oh, from trunk? Oh, does
> the project take any liberties with its own organization? God help us when
> we start talking about C++…)
>
> "imaginary" is a reductive way of phrasing the problem space. You keep
> referring to "'real' projects" as a proxy for the individual project you
> want support for; while there's a lot to be said for real-world use cases,
> I don't think this proposal's direction should be dictated by just
> libsodium.
>
> Zachary
>
> On Sat, Jan 2, 2016, at 04:57 PM, Drew Crawford via swift-build-dev wrote:
>
> Thanks for directing me to this, I missed it.
>
>
> Most projects will not conform to these conventions.
>
>
> Giggle.  Kind of an understatement, no?
>
> Like, okay.  Here is a project I'd like to package.  (Read: I do package
> it, with features not in mainline swiftPM.)
> https://github.com/jedisct1/libsodium
>
> Let's take a look at how this package realistically builds:
>
>
> Here is how I would expect these things to be tackled:
>
>
> * It has tests ("make check")
>
>
> I don't have any particular plan for this one.
>
> * It has various --enable-foo flags
>
>
> I expect that eventually the package manager will grow some level of
> support for this kind of thing (similar to Cargo's "features" --
> http://doc.crates.io/manifest.html#the-[features]-section).
>
> * It swaps in special implementations depending on if you have AMD64
> <https://github.com/jedisct1/libsodium/blob/master/src/libsodium/Makefile.am#L162>
>  or AVX instructions
> <https://github.com/jedisct1/libsodium/blob/master/src/libsodium/Makefile.am#L145>
>  or SSE2
> <https://github.com/jedisct1/libsodium/blob/master/src/libsodium/Makefile.am#L229>
>  etc.
> * The optimization level is tuned on a per-architecture basis
> <https://github.com/jedisct1/libsodium/blob/master/dist-build/android-armv7-a.sh#L3>
>
>
> I expect that both of these would become possible with small enhancements
> to allow customization via the manifest file. Again, this is just the
> initial feature.
>
> * They build (also) on Windows.  They're not changing how they're packaged
> for "SwiftPM, the Mac/Linux build system".
>
>
> I anticipate that we will eventually support alternative source layouts
> via customization in the manifest file (mostly to change where the sources
> are found, and the way headers are located and treated).
>
> * Oh and this is cryptography code.  Do you *really* want to touch it?
>
>
> It is a non-goal of this proposal to support projects which "I don't want
> to touch".
>
>
> *I think an important feature of any C target proposal is that there will
> actually exist C targets which can be built under the proposal*.  Until
> there are C people coming out of the woodwork saying "sure, I will
> repackage my software this way" I think the entire value is debatable.
>
>
> I think your language is more polarizing than is due here, and I would
> encourage focusing on a technical argument rather than a judgement like
> "the entire value is debatable". This proposal will clearly allow packages
> to add small bits of C code which are used by other targets. Unless you
> believe that is incorrect (and if so, please present a technical argument
> for it), then to me that is a valuable capability (and if you disagree,
> then please present a technical argument for it).
>
>  - Daniel
>
>
> Getting signoff from libdispatch/CoreFoundation is necessary but not
> sufficient to clear that hurdle.  I would think getting the other C deps in
> our own project family to repackage would be "table stakes" for any new C
> build system.  The real test are projects that are third-party and less
> friendly.
>
> And I do not see realistically how we are ever going to support a project
> like libsodium, except calling out to automake.  An automake solution
> coincidentally supports both libdispatch and CoreFoundation right now.  IMO
> something like that is a much, much better direction in the short-term, and
> once we have done the first step of "packaging" those software via automake
> we will have "real" C projects in our package manager and we can design our
> C support around the concerns of real projects instead of imaginary ones.
>
>
> On Jan 2, 2016, at 11:00 AM, Daniel Dunbar via swift-build-dev <
> swift-build-dev at swift.org
> <javascript:_e(%7B%7D,'cvml','swift-build-dev at swift.org');>> wrote:
>
> Happy 2016!
>
> I am working on an initial proposal for adding support for C language
> targets to the Swift package manager, and am interested in feedback:
>
> https://github.com/ddunbar/swift-evolution/blob/master/proposals/NNNN-swiftpm-c-language-targets.md
>
> Some TL;DR:
> - The proposal defines a basic convention for pure C language targets (no
> Swift/C mix and match, but other Swift targets can use the C targets).
> - This is just intended to be the minimal initial feature, there will be a
> lot of add on work which I expect should be tackled in follow on
> PRs/proposals.
> - The proposal doesn't try and outline every single nitty detail (e.g.,
> exactly what C++ standard we will compile with). My intention is to pick a
> sensible default at implementation time and refine incrementally.
>
> Unless there are serious objections, I am hoping to hope to land this
> proposal soon and start work on the feature shortly after.
>
> Cheers,
> - Daniel
>
>
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