[SR-3667] Crash in CharacterSet

[swift-ci]

Previous ID	SR-3667
Radar	None
Original Reporter	aamctustwo (JIRA User)
Type	Bug

Attachment: Download

Environment

Xcode 8.2
macOS 10.12.2

Additional Detail from JIRA

Votes	1
Component/s	Foundation
Labels	Bug, RunTimeCrash
Assignee	None
Priority	Medium

md5: 6883edae0bb5e9e44b987df04957b303

Issue Description:

There is a crash in the CharacterSet implementation. See the example below. I've attached a Playground with this issue and a screenshot of the error.

import Foundation

extension CharacterSet {
    func isSuperset(ofCharactersIn string: String) -> Bool {
        let otherSet = CharacterSet(charactersIn: string)
        return isSuperset(of: otherSet)
    }
}

let foo = "_"

let bar = CharacterSet.alphanumerics.union(CharacterSet(charactersIn: foo))

print(bar.isSuperset(ofCharactersIn: foo))

[swift-ci]

Comment by Nathaniel Bomberger (JIRA)

Some observations that may be helpful: I was able to reproduce this bug intermittently. For example, it seemed if I restarted playground and enterered in your code, it would occur. If I changed the characters, it might crash at first, then it would work, however, then it would seem to work correctly after deleting some text in playground. It felt very racy.. or perhaps some underlying memory mishandle?

it should be noted I am on the Xcode 8.3.2, Swift 3.1. Sierra 10.12.5, and it still exists.

[swift-ci]

Comment by Nathaniel Bomberger (JIRA)

Possibly related to SR-3485, SR-2510, SR-2509

[CharlesJS]

I'm thinking it's a memory error, because I intermittently get either crashes or incorrect results with the following code, but it reliably crashes once I turn Guard Malloc on:

{code:none}import Foundation

let charset1 = CharacterSet(charactersIn: "abc")
let charset2 = CharacterSet(charactersIn: "a")

// returns 'false' with Guard Malloc off, crashes with Guard Malloc on
print(charset1.isSuperset(of: charset2))

[CharlesJS]

Also, this workaround seems to work: copy the charsets so that they become good old C/ObjC __NSCFCharacterSets instead of _SwiftNSCharacterSet, and then use CoreFoundation to prevent the bridge from bringing things back:

import Foundation

let charset1 = (CharacterSet(charactersIn: "abc") as NSCharacterSet).copy() as! CFCharacterSet
let charset2 = (CharacterSet(charactersIn: "a") as NSCharacterSet).copy() as! CFCharacterSet

print(CFCharacterSetIsSupersetOfSet(charset1, charset2)) // true