[SR-2535] [SwiftPM] Ability to control deployment target

[kevints]

Previous ID	SR-2535
Radar	rdar://problem/28253354
Original Reporter	@kevints
Type	Bug
Status	Resolved
Resolution	Done

Additional Detail from JIRA

Votes	0
Component/s	Package Manager
Labels	Bug
Assignee	None
Priority	Medium

md5: 9a8cd848cb1275b3f7fcb018080fd12e

Issue Description:

On macOS, swift build hardcodes the swiftc flag

-target x86_64-apple-macosx10.10

This means that to write portable (macOS 10.11+ and Linux) code that uses a Foundation API introduced in macOS 10.11 we must convert the following straightforward code (2 module-level URL constants):

import Foundation

let baseURL: URL = ...
let resourceURL = URL(fileURLWithPath: "path", relativeTo: baseURL)

to this

import Foundation

let baseURL: URL = ...
let resourceURL: URL
#if !os(Linux)
    resourceURL = {
        guard #available(macOS 10.11, *) else {
            fatalError("This program requires macOS 10.11 or greater.")
        }
        return URL(fileURLWithPath: "path", relativeTo: baseURL)
    }()
#else
    resourceURL = URL(fileURLWithPath: "path", relativeTo: baseURL)
#endif

Swift packages should be able to specify a minimum target platform version. There's also the problem of the impedance mismatch - if we were allowed to do #if os(Linux) && available(macOS 10.11, *) the resourceURL assignment line would not need to be duplicated in each block.

[belkadan]

The * in #available(macOS 10.11, *) means "all other platforms".

[belkadan]

Arguably Swift packages should still let you set the minimum deployment target on certain platforms, but this limitation isn't it.

[ddunbar]

I'd like to just use this for the ability to control the deployment target, as I'm not sure we have another bug tracking that and it is pretty important.

[belkadan]

Okay, fair enough. Sorry for jumping the gun.

[keith]

You can now pass the target flags mentioned in order to override the hard coded 10.10 value. #715