[swift-evolution] pitch: Unified libc import (again)

Xiaodi Wu xiaodi.wu at gmail.com
Thu Aug 17 18:13:51 CDT 2017

IMO, you’re touching on at least three or four separate topics here. Daniel
touched on several, but just some comments/questions:

* Standard error output is something that’s been discussed here previously.
I believe the last pitch had something like StandardError being added to
the standard library as a TextOutputStream.

* Foundation is supposed to be the core library that provides file system
access facilities. What’s missing, and can we add it to Foundation?

On Thu, Aug 17, 2017 at 17:50 Taylor Swift via swift-evolution <
swift-evolution at swift.org> wrote:

> Python’s os.path <https://docs.python.org/2/library/os.path.html> is a
> nice abstract model for doing path manipulations. Maybe Swift could get a
> struct like `Filepath` or something on which these operations could be done.
> On Thu, Aug 17, 2017 at 6:47 PM, Taylor Swift <kelvin13ma at gmail.com>
> wrote:
>> On Thu, Aug 17, 2017 at 3:50 PM, Daniel Dunbar <daniel_dunbar at apple.com>
>> wrote:
>>> > On Aug 17, 2017, at 9:26 AM, Taylor Swift via swift-evolution <
>>> swift-evolution at swift.org> wrote:
>>> >
>>> > I know this has come up before without any action, but having the
>>> standard C library be packaged under `Darwin` on OSX and `Glibc` under
>>> Linux is something that’s really becoming an issue as the Swift package
>>> ecosystem matures. Right now a lot of packages are a lot less portable than
>>> they could be because somewhere along the dependency line, there is a
>>> package that only imports the C library for one platform. Unifying it under
>>> one import would allow people to write packages that are portable by
>>> default.
>>> What we (SwiftPM) have done for now is use a `libc` target to start by
>>> normalizing the name:
>>> https://github.com/apple/swift-package-manager/tree/master/Sources/libc
>>> (and in the past, when we find missing things in Glibc getting them
>>> added to the compiler). Also, this name is technically a misnomer, but we
>>> couldn’t think of a better one (“os” might have been a good one).
>>> Unfortunately, I think this change alone is really only the tip of the
>>> iceberg. It would be nice to not have it the difference, but we found we
>>> very quickly needed several other layers on top to get to having a
>>> relatively stable cross-platform base:
>>> https://github.com/apple/swift-package-manager/tree/master/Sources/POSIX
>>> https://github.com/apple/swift-package-manager/tree/master/Sources/Basic
>>> My hope is that one minimal improvement we can get soon is multi-package
>>> repo support in SwiftPM, which will at least allow us to share those
>>> targets & functionality with other packages.
>>> > Since I think this got hung up in the past over “what constitutes” a
>>> universal libc, I propose a unified package should just consist of the
>>> functionality that is common between Darwin and Glibc right now, since
>>> those are the only two supported platforms anyway.
>>> What would the concrete proposal be? It isn’t trivial to determine that
>>> subset and make it well-defined what the exact API is. Is the proposal to
>>> just to pick a standard name, and reexport Darwin and Glibc from it?
>> I don’t know if it’s actually this simple, but could it just be the
>> symbols that are defined in both modules?
>>> > Alternatively, Swift could make it a priority to get basic
>>> functionality like file IO and math functions shipped with the compiler,
>>> which would probably cover 98% of cases where people currently import
>>> Darwin/Glibc. A large portion of the standard C libraries are redundant to
>>> the Swift standard library anyway.
>>> I’m not sure I agree with these statements about the percentages. For
>>> some clients (I’m biased, the areas I work in tend to be in this boat),
>>> what we largely need is good platform-agnostic access to the POSIX APIs.
>>> This is a hard problem to make a good cross-platform API for (esp. if
>>> Windows support is in your head), and which many projects struggle with
>>> (Netscape :: NSPR, LLVM :: libSupport, many many more).
>>> The sticking point I see is this: if the proposal is just to unify the
>>> name & that doesn’t actually buy us all that much (still need standard
>>> layers on top), then have we really solved enough of a problem to be worth
>>> standardizing on?
>>> +1 in general agreement with the meta-issue being an important one to
>>> discuss.
>> There probably is an XY issue at play here; what we *really* need is a
>> way to access the file system built into the standard library. (Math
>> functions are a separate, beleaguered topic for a different thread.) Having
>> support for outputting to `stderr` is also something I’d really like. Going
>> through Glibc/Darwin is just one way to solve this.
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