[swift-evolution] [Proposal] Linux specific Package.swift file

[rintaro ishizaki]

Hi Said,

Since `Package.targets` is a mutable public property,
https://github.com/apple/swift-package-manager/blob/master/Sources/PackageDescription/Package.swift#L60-L67
you can freely mutate it later, as documented in
https://github.com/apple/swift-package-manager/blob/master/Documentation/Reference.md#customizing-builds


2016-11-22 4:21 GMT+09:00 Said Sikira via swift-evolution <
swift-evolution at swift.org>:

> Hello everyone,
>
> Currently, we use Package.swift manifest file when defining our packages.
> Within the manifest file you define your targets, dependencies, excluded
> folders etc. This works fairly well while you’re using frameworks that
> exist on all supported platforms (ex. Foundation).
>
> The main problem starts if you want to use code that exists only on macOS
> platform, for example, if you want to use Objective C runtime calls or
> UIKit. Then, you need to use bunch of #if os(Linux) to define what’s
> available on Linux and what’s available on macOS. While this approach can
> be non problematic for simple projects, it can introduce unnecessary
> complexity if you have a large target and dependency graph.
>
> One way people tackle this problem is writing something like this:
>
> #if os(Linux)
> let macOnlyTargets = []
> #else
> let macOnlyTargets = [
>     .Target(name: "SomeMacOSTarget")
> ]
> #end
>
> This structure looks even worse if you need to define more complex
> behaviors. For example, look at the RxSwift Package.swift
> <https://github.com/ReactiveX/RxSwift/blob/master/Package.swift> file. In
> my case, I try to write #if os(Linux) as little as possible which leads
> me to writing my packages like:
>
> #if os(Linux)
>     // Define full Linux package
>     let package = Package(...)
> #else
>     // Define full macOS package
>     let package = Package(..)
> #end
>
> Proposal
>
> I propose that we support using different file for writing Linux package
> manifests. This file could be named:
>
>    - PackageLinux.swift
>    - Package.Linux.swift
>    - Package.linux.swift
>
> Inside this file you would be able to define your package only for Linux
> in the same way you’re defining one in regular Package.swift. The defined
> behaviors of building a package would be:
>
>    1. If building on Linux and PackageLinux.swift is present, use that
>    file when building the package.
>    2. If building on Linux and PackageLinux.swift is not present, use
>    regular Package.swift manifest.
>    3. If building on macOS always use Package.swift manifest.
>
> Possible problems
>
> This behavior would only introduce problems when SPM gains support for new
> platforms, but then again, you would need to use new #if os(somethingNew)
> checks.
> Compatibility with current packages
>
> This would be only a additive feature for Swift Package Manager and
> backwards compatibility will be maintained.
>
> _______________________________________________
> swift-evolution mailing list
> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
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