[swift-dev] Default deployment target for swiftc

[Chris Lattner]

+1

-Chris

> On Nov 28, 2017, at 10:36 AM, Tony Allevato via swift-dev <swift-dev at swift.org> wrote:
> 
> I agree, the currently running OS seems like the right default here. Progressive disclosure and ease of prototyping are good motivations here. If I just want to quickly prototype something, I'm not going to be thinking about choosing a minimum OS; I'm just going to write something using the APIs that are available on my current one. If I decide to distribute that later, *that's* when I'm going to start thinking about minimums (and adding availability directives, if needed).
> 
> On Mon, Nov 27, 2017 at 4:53 PM William Dillon via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
> It would be my assumption that it would build for the currently running OS.  It would be very confusing to me to have availability checks failing for an OS version lower that what I'm using.  I'm sure that I would be swearing for a few hours before I finally found the obscure documentation that said that it would compile for the oldest OS swift supports.
> 
> Thanks for asking us! :)
> 
> - Will
> 
> 
>> On Nov 27, 2017, at 4:44 PM, Jordan Rose via swift-dev <swift-dev at swift.org <mailto:swift-dev at swift.org>> wrote:
>> 
>> Hi, all. Consider the following command, as run on a Mac with an up-to-date Xcode installed:
>> 
>> xcrun swiftc foo.swift
>> 
>> The question: should this build for the current running OS, or the oldest macOS Swift supports (10.9)? You can always specify the deployment target OS version explicitly with the -target option, but what should the default behavior be?
>> 
>> Some points to consider:
>> - The deployment OS affects availability checks, which means that the command might succeed on one host but fail on another.
>> - …but we already changed the default for the interpreter (`xcrun swift`) to be the current running OS in Swift 3.1 (Xcode 8.3, last spring).
>> - Clang defaults to the current running OS (as of a few Xcodes ago, IIRC).
>> 
>> Given these points, I'm inclined to change swiftc to default to building for the current running OS when no target is specified, but what do other people think?
>> 
>> Note that this doesn't apply to projects built with either Xcode or the Swift Package Manager, both of which always explicitly provide a deployment target. Invoking swiftc directly and not providing -target means (1) you are definitely compiling for Mac (when run on a Mac), and (2) there's a good chance you don't plan to distribute what you just built, because until Swift lives in the OS, it has dependencies on your installed Swift toolchain (currently messily resolved with absolute rpaths). If you avoid this with -static-stdlib, you're giving up the ability to have dynamic libraries, because we didn't implement that properly.
>> 
>> Thanks for your feedback!
>> Jordan
>> 
>> P.S. For Apple folks, this is rdar://problem/29948658 <>.
>> 
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