[SR-9541] Swift incorrectly fills in ivar attribute for static properties in categories

[swift-ci]

Previous ID	SR-9541
Radar	rdar://problem/46830117
Original Reporter	fclout (JIRA User)
Type	Bug
Status	Closed
Resolution	Done

Environment

Tested on Swift 4.2, will try on a nightly shortly.

Additional Detail from JIRA

Votes	0
Component/s	Compiler
Labels	Bug, IRGen
Assignee	fclout (JIRA)
Priority	Medium

md5: a58e6adb86c07765d89d9b61a502e5d3

Issue Description:

Objective-C does not support ivars on classes, and does not support adding ivars in categories. You can then imagine my surprise when I found programs that claim that they have class properties, defined in categories, that are backed by ivars.

The Swift compiler appears to co-opt the ivar field to put the name of the variable that holds the value of a static property, even though that variable is not an ivar.

Build this:

import Foundation

@objc public extension Formatter {
    @objc static var iso8601: Int = 0
}

then inspect it with your favorite disassembler. You can see that the NSFormatter (test) category defines an "iso8601" class property with the type string "Tq,N,Viso8601" (data type signed long long, nonatomic, backed by ivar called iso8601).

[belkadan]

Whoops! This probably fell out of adding support for ObjC class properties.

[swift-ci]

Comment by Félix Cloutier (JIRA)

Created a PR (which is not yet ready to merge): #21435

[swift-ci]

Comment by Félix Cloutier (JIRA)

Fixed in #21435.

[belkadan]

5.0: #21481