Thread Safety, closure captures, debug-only FatalErrors, self-self aliasing, misc tweaks

[RamblinWreck77]

Decided to take a crack at fixing #153 and ended up poking around a bit more than I planned. Key points for this PR:

• Move all FatalErrors to #DEBUG only, as it should not be done in release/prod code. Hard crashing like this will, AFAIK, break people's crash reporting/make crashes seem random.

• let self=self aliasing is a compiler bug and will be removed in future swift versions, might as well fix now and use a guard inside weak self closures for cleaning up optional chaining.

• Main thread safety: More enforcement of main thread usage for functions that manipulate UIKit classes. Conversion involved adding asserts, making current functions private and adding a public function that thread casts the private function to main.

• Closure Captures: Generally closures should capture their inputs (especially if they're classes/reference types) to prevent memory/BAD_ACCESS errors when/if things get changed out from under you. ViewControllers are, in my experience, particularly nasty about this so closure captures help a ton.

Thanks again for an awesome library! It looks like all tests are passing and I'll run this fork in through our QA/production and report back over the next week if any unexpected issues occur

[RamblinWreck77]

Hmmm, looks like I introduced a scrolling direction bug. One sec

[RamblinWreck77]

Got it! I used auto-complete which didn't include parameters with default arguments in the main thread cast so direction was defaulting to .forward.

[msaps]

@RamblinWreck77 oh nice! Have you found it's managed to mitigate the internal UIPageViewController crashes? I'll get to reviewing it, thanks! 💯

[uias-bot]

	1 Warning
⚠️	Looks like you changed some source files, should there have been some tests added?

SwiftLint found issues

Warnings

File	Line	Reason
PageboyViewController+Management.swift	13	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	20	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	40	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	54	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	106	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	137	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	160	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	175	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	191	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	193	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	205	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	212	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	234	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	240	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	243	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	253	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	261	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	266	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	270	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	280	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	284	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	295	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	311	Lines should not have trailing whitespace.
PageboyViewController+Management.swift	108	Function parameters should be aligned vertically if they're in multiple lines in a declaration.
PageboyViewController+Management.swift	109	Function parameters should be aligned vertically if they're in multiple lines in a declaration.
PageboyViewController+Management.swift	110	Function parameters should be aligned vertically if they're in multiple lines in a declaration.
PageboyViewController+Management.swift	111	Function parameters should be aligned vertically if they're in multiple lines in a declaration.
PageboyViewController+Management.swift	112	Function parameters should be aligned vertically if they're in multiple lines in a declaration.
PageboyViewController+Management.swift	113	Function parameters should be aligned vertically if they're in multiple lines in a declaration.
PageboyViewController+Management.swift	114	Function parameters should be aligned vertically if they're in multiple lines in a declaration.
PageboyViewController+Management.swift	125	Limit vertical whitespace to a single empty line. Currently 2.
PageboyViewController+Management.swift	41	Line should be 120 characters or less: currently 145 characters
PageboyViewController+Management.swift	146	Line should be 120 characters or less: currently 138 characters
PageboyViewController+Management.swift	148	Line should be 120 characters or less: currently 136 characters
PageboyViewController+Updating.swift	12	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	27	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	35	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	46	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	52	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	65	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	73	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	76	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	79	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	82	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	86	Lines should not have trailing whitespace.
PageboyViewController+Updating.swift	53	Line should be 120 characters or less: currently 167 characters
PageboyViewController.swift	15	Lines should not have trailing whitespace.
PageboyViewController.swift	17	Lines should not have trailing whitespace.
PageboyViewController.swift	22	Lines should not have trailing whitespace.
PageboyViewController.swift	39	Lines should not have trailing whitespace.
PageboyViewController.swift	41	Lines should not have trailing whitespace.
PageboyViewController.swift	56	Lines should not have trailing whitespace.
PageboyViewController.swift	58	Lines should not have trailing whitespace.
PageboyViewController.swift	67	Lines should not have trailing whitespace.
PageboyViewController.swift	68	Lines should not have trailing whitespace.
PageboyViewController.swift	84	Lines should not have trailing whitespace.
PageboyViewController.swift	137	Lines should not have trailing whitespace.
PageboyViewController.swift	142	Lines should not have trailing whitespace.
PageboyViewController.swift	147	Lines should not have trailing whitespace.
PageboyViewController.swift	175	Lines should not have trailing whitespace.
PageboyViewController.swift	178	Lines should not have trailing whitespace.
PageboyViewController.swift	185	Lines should not have trailing whitespace.
PageboyViewController.swift	188	Lines should not have trailing whitespace.
PageboyViewController.swift	201	Lines should not have trailing whitespace.
PageboyViewController.swift	209	Lines should not have trailing whitespace.
PageboyViewController.swift	228	Lines should not have trailing whitespace.
PageboyViewController.swift	230	Lines should not have trailing whitespace.
PageboyViewController.swift	261	Lines should not have trailing whitespace.
PageboyViewController.swift	298	Lines should not have trailing whitespace.
PageboyViewController.swift	325	Lines should not have trailing whitespace.
PageboyViewController.swift	410	Lines should not have trailing whitespace.
PageboyViewController.swift	433	Lines should not have trailing whitespace.
PageboyViewController.swift	439	Lines should not have trailing whitespace.
PageboyViewController.swift	334	Function body should span 40 lines or less excluding comments and whitespace: currently spans 45 lines
PageboyViewController.swift	68	Limit vertical whitespace to a single empty line. Currently 2.
PageboyViewController.swift	19	Line should be 120 characters or less: currently 127 characters
PageboyViewController.swift	69	Line should be 120 characters or less: currently 125 characters
PageboyViewController.swift	77	Line should be 120 characters or less: currently 130 characters
PageboyViewController.swift	78	Line should be 120 characters or less: currently 152 characters
PageboyViewController.swift	148	Line should be 120 characters or less: currently 130 characters
PageboyViewController.swift	349	Line should be 120 characters or less: currently 133 characters
PageboyViewController.swift	360	Line should be 120 characters or less: currently 129 characters
PageboyViewController+Transitioning.swift	13	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	16	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	29	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	34	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	36	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	51	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	53	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	68	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	73	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	75	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	79	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	135	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	143	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	168	Lines should not have trailing whitespace.
PageboyViewController+Transitioning.swift	23	Types should be nested at most 1 level deep
TransitionOperation.swift	12	Lines should not have trailing whitespace.
TransitionOperation.swift	20	Lines should not have trailing whitespace.
TransitionOperation.swift	32	Lines should not have trailing whitespace.
TransitionOperation.swift	34	Lines should not have trailing whitespace.
TransitionOperation.swift	37	Lines should not have trailing whitespace.
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TransitionOperation.swift	44	Lines should not have trailing whitespace.
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TransitionOperation.swift	129	Lines should not have trailing whitespace.
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UIView+AutoLayout.swift	12	Lines should not have trailing whitespace.
UIView+AutoLayout.swift	24	Lines should not have trailing whitespace.
UIView+AutoLayout.swift	34	Lines should not have trailing whitespace.
UIView+AutoLayout.swift	47	Lines should not have trailing whitespace.
UIView+AutoLayout.swift	57	Lines should not have trailing whitespace.
UIView+AutoLayout.swift	70	Lines should not have trailing whitespace.
UIView+AutoLayout.swift	80	Lines should not have trailing whitespace.
UIView+AutoLayout.swift	82	Lines should not have trailing whitespace.
UIView+AutoLayout.swift	87	Lines should not have trailing whitespace.
UIView+AutoLayout.swift	97	Lines should not have trailing whitespace.
UIView+AutoLayout.swift	24	Limit vertical whitespace to a single empty line. Currently 3.
UIView+AutoLayout.swift	89	Line should be 120 characters or less: currently 127 characters
UIView+Localization.swift	12	Lines should not have trailing whitespace.
UIView+Localization.swift	25	Lines should not have trailing whitespace.

Generated by 🚫 Danger

[msaps]

Looks good to me 👍 I'll sort the linter errors 😄

[RamblinWreck77]

@msaps That bug was/is particularly rare in our project, but so far it hasn't happened again in prod with these changes so knock on wood!