[SR-993] Objc class extensions don't support stored type properties, error message is confusing

[an0]

Previous ID	SR-993
Radar	radar://20512544
Original Reporter	@an0
Type	Bug
Status	Resolved
Resolution	Done

Environment

Swift 3 in Xcode 8.0 beta 3

Additional Detail from JIRA

Votes	2
Component/s	Compiler
Labels	Bug, DiagnosticsQoI, StarterBug
Assignee	None
Priority	Medium

md5: d9305dc29182276d2baf4b7f5081f44f

is duplicated by:

• SR-2386 Error when adding static stored properties to Objective-C classes in extensions

Issue Description:

I guess currently ObjC class extensions don't support stored type properties. But the error message is very confusing and without any location information:

a declaration cannot be both 'final' and 'dynamic'

import Foundation

extension Int {
    // Swift extensions support stored type properties.
    static let a = 1
}

class Foo: NSObject {}

extension Foo {
    static let a = 1
}

[an0]

From the release notes of Xcode 8 beta 4 I learned that it is the same bug:

When using static in an extension of an Objective-C class, the compiler may produce the error "a declaration cannot be both 'final' and ‘dynamic'." This error is a consequence of Swift using dynamic to implement members exposed to Objective-C in extensions, and static being equivalent to class final when used within a class or extension of a class. In some cases, this error will not have the correct location information.

Workaround: Use class instead of static (making the method or property non-final) or add @nonobjc (making the method or property non-dynamic and hiding it from Objective-C). (20512544)

Someone please link it to that bug. Thanks.

[DougGregor]

#4874

[DougGregor]

ca59a40