StoreStatsV4PeriodViewController stringForValue → EXC_BREAKPOINT: Exception 6, Code 21127904, Subcode 8

[sentry-io]

Sentry Issue: WOOCOMMERCE-IOS-1DAB

EXC_BREAKPOINT: Exception 6, Code 21127904, Subcode 8
  File "StoreStatsV4PeriodViewController.swift", in range
  File "<compiler-generated>", in _ArrayBuffer._checkInoutAndNativeTypeCheckedBounds
  File "<compiler-generated>", in Array._checkSubscript
  File "<compiler-generated>", in Array.subscript.getter
  File "StoreStatsV4PeriodViewController.swift", line 467, in StoreStatsV4PeriodViewController.stringForValue
...
(58 additional frame(s) were not displayed)

[sentry-io]

Sentry issue: WOOCOMMERCE-IOS-1DB1

[shiki]

☝️ @jaclync This still seems to be happening for 8.7. I guess #6343 didn't fix it?

It still looks like this line:

woocommerce-ios/WooCommerce/Classes/ViewRelated/Dashboard/Stats v4/StoreStatsV4PeriodViewController.swift

Line 488 in daba32d

return createOrderStatsIntervalLabels()[Int(value)]

Any advice?

(cc @itsmeichigo)

---

Events: 266
Users: 28

[jaclync]

Hey @shiki, unfortunately the PR didn't fix it. I took a deeper look into the code again but couldn't find anything that could cause orderStatsIntervals: [OrderStatsV4Interval] to be a different size when it's used for chart data and axis label generation now that this variable is only set in one place followed by the update 😞 The x-axis value should be the index based on what we set for the chart data, and I don't see anything obvious that could cause the x-axis value (index) to be out of bound.

We could check the index and return some default value to prevent the app from crashing, but personally I felt like that's just hiding the issue. To help us find out the root cause, I could add some DDLogInfo on the x-axis index/value and the intervals size when it's out of bound so that we can inspect the encrypted logs in future crashes. What do you think? Or maybe someone else can help take a look in case there are som blind spots that I didn't see?

One interesting thing from the crash data is that the surges are around daily savings time change in the US and EU. However, I couldn't reproduce it when I set a device to the same time and region.

[shiki]

Thank you for looking into this!

I could add some DDLogInfo on the x-axis index/value and the intervals size when it's out of bound so that we can inspect the encrypted logs in future crashes.

That sounds reasonable to me!

Or maybe someone else can help take a look in case there are som blind spots that I didn't see?

That's also not a bad idea. If this is a DST issue, then hopefully it'll disappear. If not, then it would be nice if someone's had a chance to take a deeper look. Who else knows this part of the codebase?

[itsmeichigo]

I reviewed Jaclyn's update to this part so I can maybe take a look and hopefully can spot something.

[itsmeichigo]

I haven't found the root cause yet, but I was looking at the legacy code found that we updated the interval labels immediately after setting a new value to the order stats intervals:

woocommerce-ios/WooCommerce/Classes/ViewRelated/Dashboard/Stats v4/OldStoreStatsV4PeriodViewController.swift

Lines 34 to 42 in 9b79910

	private var orderStatsIntervals: [OrderStatsV4Interval] = [] {
	didSet {
	let helper = StoreStatsV4ChartAxisHelper()
	let intervalDates = orderStatsIntervals.map({ $0.dateStart(timeZone: siteTimezone) })
	orderStatsIntervalLabels = helper.generateLabelText(for: intervalDates,
	timeRange: timeRange,
	siteTimezone: siteTimezone)
	}
	}

In our current version, we're calculating the interval labels only when needed. I have no clue why there's a difference in the number of items on the X-axis and the number of intervals - but I think maybe it's safer to keep track of the interval labels like in the previous iteration. WDYT?

[jaclync]

I haven't found the root cause yet, but I was looking at the legacy code found that we updated the interval labels immediately after setting a new value to the order stats intervals:

woocommerce-ios/WooCommerce/Classes/ViewRelated/Dashboard/Stats v4/OldStoreStatsV4PeriodViewController.swift

Lines 34 to 42 in 9b79910

	private var orderStatsIntervals: [OrderStatsV4Interval] = [] {
	didSet {
	let helper = StoreStatsV4ChartAxisHelper()
	let intervalDates = orderStatsIntervals.map({ $0.dateStart(timeZone: siteTimezone) })
	orderStatsIntervalLabels = helper.generateLabelText(for: intervalDates,
	timeRange: timeRange,
	siteTimezone: siteTimezone)
	}
	}

In our current version, we're calculating the interval labels only when needed. I have no clue why there's a difference in the number of items on the X-axis and the number of intervals - but I think maybe it's safer to keep track of the interval labels like in the previous iteration. WDYT?

Good suggestion on reverting to the previous behavior to set the x-axis labels right after the intervals data, I'll make a PR today!

Assuming the Charts framework is working as expected, the x-axis updates are triggered right after the chart data is set:

woocommerce-ios/WooCommerce/Classes/ViewRelated/Dashboard/Stats v4/StoreStatsV4PeriodViewController.swift

Lines 590 to 591 in 7dd74b1

	lineChartView.data = generateChartDataSet()
	lineChartView.notifyDataSetChanged()

Since the source of truth orderStatsIntervals for both data sets is only set in one place in the subscription followed by UI updates, I can't think of reasons how the data could diverge unless the x-axis updates are triggered unexpectedly.

[sentry-io]

Still saw crashes for one user after another attempted fix for release 8.9 in #6551.

Sentry issue: WOOCOMMERCE-IOS-1DC3