[SR-1226] Marking a method as unavailable in iOS Extensions should allow me to use APIs unsafe for extensions

[swift-ci]

Previous ID	SR-1226
Radar	rdar://problem/34949130
Original Reporter	kaybutter (JIRA User)
Type	Bug

Environment

Xcode 7.3 with Swift 2.2

Additional Detail from JIRA

Votes	10
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 51ba9fd65347cc3638554b002b1937f1

Issue Description:

I am writing a dynamic framework used both by an iOS application target and an iOS extension target. The framework is marked with the "allow app extension API only" flag.

The following swift code from the framework will fail to compile:

@available(iOSApplicationExtension, unavailable)
func test() {
    _ = UIApplication.sharedApplication()
}

The Objective-C version, using NS_EXTENSION_UNAVAILABLE will compile:

- (void)test NS_EXTENSION_UNAVAILABLE("don't use this in extensions") {
    [UIApplication sharedApplication];
}

Expected Behavior:
@available(iOSApplicationExtension, unavailable) should behave like NS_EXTENSION_UNAVAILABLE. Methods or classes marked as available in extensions should be allowed to use APIs not available for extensions.

[swift-ci]

Comment by Scott Berrevoets (JIRA)

I'm running into this same problem (Xcode 8.3/Swift 3.1). Are there any known workarounds?

[tjw]

We're hitting this as well when working on app extensions that use our existing frameworks. Those frameworks have been marked as being annotated for reviewing extension unsafe API in the ObjC parts, but doing so for the Swift parts doesn't work. This makes Swift difficult/impossible to use for frameworks where some pieces of the framework might need to be called from app extensions.

Also, comically, if I add an explicit availability check:

class Example {
    @available(iOSApplicationExtension, unavailable)
    func x() {
        if #available(iOSApplicationExtension 11, *) {
            _ = UIApplication.shared
        }
    }
}

then I get a warning "unnecessary check for 'iOSApplicationExtension'; enclosing scope ensures guard will always be true" ... so at some level it seems the compiler is tracking the needed state to make the feature work correctly.

[tjw]

Logged as Radar 34949130 (Annotating Swift framework code for app-extension safe API doesn't work)

[tjw]

Here is a possible fix <tjw@6e57b861d37eab8cf5ccf888865bdad5019227b9\> , which seems reasonable to me. Right above this is a less permissive early-out for "same unavailability" checks that could maybe be removed.

[tjw]

Also submitted as a pull request. #12410

[BasThomas]

It looks like this has been fixed and the pull request has been merged. Should the state of this issue reflect that?

[swift-ci]

Comment by Daniel Jalkut (JIRA)

I came across this bug while searching for a solution to the original problem. I am happy to say the
@available(iOSApplicationExtension, unavailable)
Annotation seems to work as expected in Xcode 12 with Swift 5.4.