Crash in String+ListItemFormatter.swift

[liamnichols]

Our crash reports don't log the exact locale being used when formatting strings however I do know that it was in an Arabic speaking region but not completely sure if language is playing a part to this.

Crashed: com.apple.main-thread
0  ListItemFormatter              0x10371fe14 closure #1 in String.init(format:locale:ranges:arguments:) (String+ListItemFormatter.swift:76)
1  ListItemFormatter              0x103720f1c partial apply for closure #1 in String.init(format:locale:ranges:arguments:) (<compiler-generated>)
2  ListItemFormatter              0x103720f4c partial apply for thunk for @callee_guaranteed (@guaranteed NSTextCheckingResult?, @unowned NSMatchingFlags, @unowned UnsafeMutablePointer<ObjCBool>) -> () (<compiler-generated>)
3  ListItemFormatter              0x10371fe68 thunk for @escaping @callee_guaranteed (@guaranteed NSTextCheckingResult?, @unowned NSMatchingFlags, @unowned UnsafeMutablePointer<ObjCBool>) -> () (<compiler-generated>)
4  Foundation                     0x18252bd24 -[NSRegularExpression(NSMatching) enumerateMatchesInString:options:range:usingBlock:] + 1380
5  ListItemFormatter              0x103720e00 specialized String.init(format:locale:ranges:arguments:) (String+ListItemFormatter.swift:49)
6  ListItemFormatter              0x10371c324 ListPatternBuilder.listByUsingStartMiddleAndEndFormat(between:) (ListPatternBuilder.swift)
7  ListItemFormatter              0x10371bde4 ListPatternBuilder.build(from:) (ListPatternBuilder.swift:57)
8  ListItemFormatter              0x10371af30 ListItemFormatter.attributedString(for:withDefaultAttributes:) (ListItemFormatter.swift:190)
9  ListItemFormatter              0x10371b568 @objc ListItemFormatter.attributedString(for:withDefaultAttributes:) (<compiler-generated>)
10 ListItemFormatter              0x10371ac30 ListItemFormatter.string(for:) (ListItemFormatter.swift:179)
11 ListItemFormatter              0x10371ad0c @objc ListItemFormatter.string(for:) (<compiler-generated>)
12 Global                         0x102b253b8 InboxItem.sendersText(with:) (InboxItem+Localization.swift:43)
13 Global                         0x102b25ce4 InboxItem.messageToDisplay(for:with:) (InboxItem+Localization.swift:106)
14 Global                         0x102b2683c InboxItem.attributedMessageToDisplay(for:with:) (InboxItem+Localization.swift:137)
15 Global                         0x102ccfadc InboxCollectionViewCell.configureWithInboxItem(_:session:formatter:) (InboxCollectionViewCell.swift:163)
16 Global                         0x102453d14 specialized InboxViewController.collectionView(_:layout:sizeForItemAt:) (InboxViewController.swift:209)
17 Global                         0x102450830 @objc InboxViewController.collectionView(_:layout:sizeForItemAt:) (<compiler-generated>)
18 UIKit                          0x18b8f5ee4 -[UICollectionViewFlowLayout _getSizingInfosWithExistingSizingDictionary:] + 2972
19 UIKit                          0x18b8f5008 -[UICollectionViewFlowLayout _fetchItemsInfoForRect:] + 144
20 UIKit                          0x18b8f4f5c -[UICollectionViewFlowLayout prepareLayout] + 224
21 UIKit                          0x18b8f4e3c -[UICollectionViewData _prepareToLoadData] + 160
22 UIKit                          0x18b8f4484 -[UICollectionViewData validateLayoutInRect:] + 104
23 UIKit                          0x18b8f36b4 -[UICollectionView layoutSubviews] + 248
24 UIKit                          0x18b7c26f4 -[UIView(CALayerDelegate) layoutSublayersOfLayer:] + 1420
25 QuartzCore                     0x185d37e54 -[CALayer layoutSublayers] + 184
26 QuartzCore                     0x185d3bfe4 CA::Layer::layout_if_needed(CA::Transaction*) + 324
27 QuartzCore                     0x185ca86c8 CA::Context::commit_transaction(CA::Transaction*) + 320
28 QuartzCore                     0x185cd01b0 CA::Transaction::commit() + 580
29 QuartzCore                     0x185cd1030 CA::Transaction::observer_callback(__CFRunLoopObserver*, unsigned long, void*) + 92
30 CoreFoundation                 0x181b56910 __CFRUNLOOP_IS_CALLING_OUT_TO_AN_OBSERVER_CALLBACK_FUNCTION__ + 32
31 CoreFoundation                 0x181b54238 __CFRunLoopDoObservers + 412
32 CoreFoundation                 0x181b54884 __CFRunLoopRun + 1436
33 CoreFoundation                 0x181a74da8 CFRunLoopRunSpecific + 552
34 GraphicsServices               0x183a5a020 GSEventRunModal + 100
35 UIKit                          0x18ba94758 UIApplicationMain + 236
36 Global                         0x1022fde50 main (main.swift:19)
37 libdyld.dylib                  0x181505fc0 start + 4

This part of the code in theory was working fine since there is test coverage but I guess the first place to start is by adding some more robust tests to see if the issue can be reproduced.

[liamnichols]

I've finally managed to reproduce this with the following data:

let json = #"["roro(همسات المستقبل)","َمنار منار، Alwahabi Alwahabi، و10 آخرين"]"#
let data = try XCTUnwrap(json.data(using: .utf8))
let array = try JSONDecoder().decode([String].self, from: data)

var ranges: [Range<String.Index>] = []
let output = String(format: "{0}، {1}", ranges: &ranges, array.first!, array.last!) // crashes

I think its partially related to deserialising via JSONDecoder (NSJSONSerialization) since the strings are actually bridged from NSString and have some kind of different memory layout that messes with the ranges

[liamnichols]

Ok so the bottom line is that this issue crops up when there is a combining character in one of the strings.. If a lone combining character was placed at the start of a string then it can combine with whatever string it is joined with causing the range calculation to be off which then results in a crash 😕

I'll try and simplify the replication steps

[liamnichols]

Fixed in 0.1.0