[swift-build-dev] Feature request: Scripting support for Swift

[Keith Smiley]

A related issue that's worth mentioning is the overhead of running a
Swift script in general. Here's the simplest of examples of Swift vs
Python:

```
$ cat helloworld
print("Hello World")

Cold:

$ time swift helloworld
Hello World
swift helloworld  0.06s user 0.44s system 67% cpu 0.746 total
$ time python helloworld
Hello World
python helloworld  0.01s user 0.01s system 22% cpu 0.095 total

Warm:

$ time swift helloworld
Hello World
swift helloworld  0.04s user 0.01s system 22% cpu 0.212 total
$ time python helloworld
Hello World
python helloworld  0.02s user 0.01s system 84% cpu 0.035 total
```

While we're thinking about this for scripting, I think it's tangentially
related that the repl has a similar difference in overhead:

```
$ time swift <<< ":quit"
Welcome to Apple Swift version 3.0.2 (swiftlang-800.0.63 clang-800.0.42.1). Type :help for assistance.
swift <<< ":quit"  1.88s user 0.23s system 86% cpu 2.459 total

$ time python <<< "quit()"
python <<< "quit()"  0.01s user 0.01s system 81% cpu 0.030 total
```


--
Keith Smiley

On 02/19, Jason Dusek via swift-build-dev wrote:
> One issue with compiling the dependencies is that script startup would be
> slow. Maybe there should be a per-user or system level cache? System level
> is better from a disk usage perspective but some thought must be given to
> security.
>
> With Ruby and Python, it is not expected that a script's dependencies are
> installed when it is run but rather they have already been installed via
> the package manager, although it does seem useful for single files to
> contain all the relevant information.
>
> Here is another idea: a Swift script can be run from a project directory
> with Sources/, Packages/, &c. In that environment, build products are
> already cached. If the script is symlinked into /usr/local/bin/ it will be
> on the path but xcrun will still be able to find the project. It is kind of
> like a source-level .app bundle.
>
> Maxim Veksler via swift-build-dev <swift-build-dev at swift.org> schrieb am
> Sa. 18. Feb. 2017 um 11:28:
>
> > Hi,
> >
> > Ayaka Nonaka gave a talk[1] about basic scripting[2] support in Swift.
> >
> > The gist of the idea is to use #!/usr/bin/env xcrun swift
> >
> > Therefor it seems the basic building blocks for allowing a swift file to
> > "execute itself" are always laid out and proved to be applicable.
> >
> > What's missing IMHO is a better support for dependencies, the suggested
> > solutions in the talk are using the -F for including frameworks that were
> > built using Carthage or CocoaPods. That's not idle because a script I think
> > should be self contained, meaning that you can "just run it" and it works.
> >
> > So, I'm wondering what if it was possible to include the dependencies
> > inside the swift file itself? Probably using the same format as the
> > Package.swift syntax. The the swift binary would "detect" that it's a self
> > contained file, it could make this distinction because import
> > PackageDescription is defined by the user.
> >
> > Then it would follow a 3 step process:
> > 1. It should download and build the dependencies
> > 2. then compile the code inside the file
> > 3. and then run it.
> >
> > Having everything happening behind the scenes, so the "script user" simply
> > calls ./MyScript.swift or swift MyScript.swift and it "just works".
> >
> > Wondering what the community thinks.
> >
> > [1] https://realm.io/news/swift-scripting/
> > [2] https://github.com/ayanonagon/talks/tree/master/2015-swiftsummit/2
> > _______________________________________________
> > swift-build-dev mailing list
> > swift-build-dev at swift.org
> > https://lists.swift.org/mailman/listinfo/swift-build-dev
> >

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