[bug] Crash: FormViewController attempts to remove rows from empty section

[ctr119]

Hi 👋🏻

While working on a Client's App, Firebase reported a weird crash that is caused by FormViewController trying to remove some rows from a section that does contain anything, when actually it says the opposite.

The trace starts here in the Client's app code:

            if !self.feedSection.isEmpty {
                self.feedSection.removeAll()
            }

where feedSection is Eureka.Section.

The .isEmpty property states that the section is not empty, so the App proceeds to remove the content. Then, it crashes at FormViewController.rowsHaveBeenRemoved(_:at:) with the following message:

attempt to delete row 4 from section 0 which only contains 0 rows before the update

Here you go the stack trace I got from Firebase:

          Fatal Exception: NSInternalInconsistencyException
0  CoreFoundation                 0x827cc __exceptionPreprocess
1  libobjc.A.dylib                0x172e4 objc_exception_throw
2  Foundation                     0x80f8d8 _userInfoForFileAndLine
3  UIKitCore                      0x354630 -[UITableView _endCellAnimationsWithContext:]
4  UIKitCore                      0x388f78 -[UITableView endUpdatesWithContext:]
5  Pan                            0x51de70 FormViewController.rowsHaveBeenRemoved(_:at:) + 733 (Core.swift:733)
6  Pan                            0x55ed00 specialized Section.KVOWrapper.observeValue(forKeyPath:of:change:context:) + 94 (Section.swift:94)
7  Pan                            0x555dd8 @objc Section.KVOWrapper.observeValue(forKeyPath:of:change:context:) (<compiler-generated>)
8  Foundation                     0x1a72c NSKeyValueNotifyObserver
9  Foundation                     0x1a420 NSKeyValueDidChange
10 Foundation                     0x11d17c -[NSObject(NSKeyValueObservingPrivate) _changeValueForKeys:count:maybeOldValuesDict:maybeNewValuesDict:usingBlock:]
11 Foundation                     0x11cd98 -[NSObject(NSKeyValueObservingPrivate) _changeValueForKey:key:key:usingBlock:]
12 Foundation                     0x11c22c _NSSetObjectValueAndNotify
13 Pan                            0x55f784 specialized Section.removeAll(keepingCapacity:) + 78 (Section.swift:78)

Steps To Reproduce

Sadly, I was not able to reproduce it myself 😞 but it is constantly crashing according to Firebase: 207 crash events affecting 206 users in the last week since today.

Expected behavior

I would have expected the .isEmpty function to work as intended, so the App does not tries to remove rows if the section is already empty. Also, I would have expected the SDK to check the section's content before updating it.

Having a look, I have seen that there are no checks done before the Form updates the TableView in FormViewController.rowsHaveBeenRemoved(_:at:).

Versions

• Device: iPhone 13
• OS: iOS 18.1.1
• Eureka Version: 5.5.0
• Xcode version: 15.4

Additional context

Just in case it helps, the % of free RAM according to Firebase is 160.43 MB.