Crash I cannot resolve since a long time - ios

Question

This is what appear in crash log for crashlytics:
Crashed: com.apple.main-thread
0 FieldService 0x665cc specialized MonthNameFormater.stringForValue(_:axis:) + 4304774604 (GraphViewController.swift:4304774604)
1 FieldService 0x5fd74 #objc MonthNameFormater.stringForValue(_:axis:) + 4304747892 (:4304747892)
2 Charts 0xcc4c AxisBase.getFormattedLabel(_:) + 149 (AxisBase.swift:149)
3 Charts 0xcaa8 AxisBase.getLongestLabel() + 138 (AxisBase.swift:138)
4 Charts 0xb0c78 XAxisRenderer.computeSize() + 158 (XAxisRenderer.swift:158)
5 Charts 0xb0b3c XAxisRenderer.computeAxisValues(min:max:) + 154 (XAxisRenderer.swift:154)
6 Charts 0x1cb9c BarLineChartViewBase.notifyDataSetChanged() + 592 (:592)
7 Charts 0x57ee8 ChartViewBase.data.didset + 656 (:656)
8 Charts 0x54750 ChartViewBase.data.setter + 84 (:84)
9 FieldService 0x62368 GraphViewController.updateGraph() + 4304757608 (:4304757608)
10 FieldService 0x610e0 closure #1 in closure #1 in GraphViewController.viewDidLoad() + 4304752864
11 FieldService 0xb2000 thunk for #escaping #callee_guaranteed () -> () + 4305084416 (:4305084416)
12 libdispatch.dylib 0x1e6c _dispatch_call_block_and_release + 32
13 libdispatch.dylib 0x3a30 _dispatch_client_callout + 20
14 libdispatch.dylib 0x11f48 _dispatch_main_queue_drain + 928
15 libdispatch.dylib 0x11b98 _dispatch_main_queue_callback_4CF + 44
16 CoreFoundation 0x51800 __CFRUNLOOP_IS_SERVICING_THE_MAIN_DISPATCH_QUEUE__ + 16
17 CoreFoundation 0xb704 __CFRunLoopRun + 2532
18 CoreFoundation 0x1ebc8 CFRunLoopRunSpecific + 600
19 GraphicsServices 0x1374 GSEventRunModal + 164
20 UIKitCore 0x514b58 -[UIApplication _run] + 1100
21 UIKitCore 0x296098 UIApplicationMain + 364
22 FieldService 0x6b74 main + 20 (AppDelegate.swift:20)
23 ??? 0x1018a9da4 (Missing)
As you can see, a lot of users is impacted with it.
And this is my class called MonthNameFormatter. What and where is the issue?
import Charts
import CoreData
class MonthNameFormater: IndexAxisValueFormatter {
override func stringForValue(_ value: Double, axis: AxisBase?) -> String {
let symbols = Calendar.localizedCurrent.shortMonthSymbols
let index = min(Options.shared.isTheocraticYearEnabled ? (Int(value) + 8) % 12 : Int(value), 11)
guard symbols.count == 12 else {
return "-"
}
return symbols[index]
}
}
Where do I use it in code?
private let chartView: LineChartView = {
let view = LineChartView()
view.xAxis.labelPosition = .bottom
view.rightAxis.enabled = false
view.borderLineWidth = 0
view.xAxis.valueFormatter = MonthNameFormater()
view.xAxis.granularity = 1
view.isUserInteractionEnabled = false
return view
}()
This is an info from Xcode
Thread 0 name:
Thread 0 Crashed:
0 FieldService 0x0000000104f665cc Swift runtime failure: Index out of range + 0 (:0)
1 FieldService 0x0000000104f665cc specialized _ArrayBuffer._checkInoutAndNativeTypeCheckedBounds(_:wasNativeTypeChecked:) + 0 (:0)
2 FieldService 0x0000000104f665cc specialized Array._checkSubscript(_:wasNativeTypeChecked:) + 0 (GraphViewController.swift:0)
3 FieldService 0x0000000104f665cc specialized Array.subscript.getter + 0 (GraphViewController.swift:17)
4 FieldService 0x0000000104f665cc specialized MonthNameFormater.stringForValue(_:axis:) + 744
5 FieldService 0x0000000104f66498 specialized MonthNameFormater.stringForValue(_:axis:) + 436 (:0)
6 FieldService 0x0000000104f5fd74 MonthNameFormater.stringForValue(_:axis:) + 4 (:0)
7 FieldService 0x0000000104f5fd74 #objc MonthNameFormater.stringForValue(_:axis:) + 16
8 Charts 0x0000000106b88c4c AxisBase.getFormattedLabel(_:) + 160 (AxisBase.swift:149)
9 Charts 0x0000000106b88aa8 implicit closure #2 in implicit closure #1 in AxisBase.getLongestLabel() + 8 (AxisBase.swift:138)
10 Charts 0x0000000106b88aa8 thunk for #escaping #callee_guaranteed (#unowned Int) -> (#owned String) + 8 (:0)
11 Charts 0x0000000106b88aa8 specialized Optional.map(_:) + 8 (:0)
12 Charts 0x0000000106b88aa8 specialized LazyMapSequence.Iterator.next() + 8 (:0)
13 Charts 0x0000000106b88aa8 specialized protocol witness for IteratorProtocol.next() in conformance LazyMapSequence.Iterator + 8 (:0)
I am not sure if it is exactly the same bug, but it is also related to MonthNameFormater.

Answer 1

Given
Swift runtime failure: Index out of range + 0 (:0)
I suspect the crash happens at return symbols[index] - make sure index is in fact a valid index in symbols.