Open Radar

 
Summary:
When using a UITextField whose inputAssistantItem won't contain any autocorrection suggestions (either it's a secure text field or it's autocorrectionType is set to UIAutoCorrectionTypeNo) it breaks auto-layout constraints after entering the background then entering the foreground again (hitting the home button and re-launching the application)

Steps to Reproduce:
* Run the sample app (single view application with one textfield) on an iPad.
* Hit the home button.
* Launch the sample app again.

Sample project is a vanilla single view app with one IBOutlet UITextField, this code is in the ViewController:

- (void)viewDidLoad {
    [super viewDidLoad];
    self.aTextField.autocorrectionType = UITextAutocorrectionTypeNo;
}

- (void)viewDidAppear:(BOOL)animated {
    [super viewDidAppear:animated];
    [self.aTextField becomeFirstResponder];
}



Expected Results:
No breaking of auto-layout constraints associated with the UIButtonBarStackView in the inputAssistantItem.

Observed Results:
Breaking of auto-layout constraint associated with the UIButtonBarStackView in the inputAssistantItem with the following log:

TestKeyboardAssistant[37264:1029080] [LayoutConstraints] Unable to simultaneously satisfy constraints.
	Probably at least one of the constraints in the following list is one you don't want. 
	Try this: 
		(1) look at each constraint and try to figure out which you don't expect; 
		(2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<NSLayoutConstraint:0x618000092980 _UIButtonBarStackView:0x7fcf05c0af40.width <= 0   (active)>",
    "<NSLayoutConstraint:0x6180000924d0 'UIView-leftMargin-guide-constraint' H:|-(15)-[UILayoutGuide:0x618000195470'UIViewLayoutMarginsGuide'](LTR)   (active, names: '|':_UIButtonBarStackView:0x7fcf05c0af40 )>",
    "<NSLayoutConstraint:0x618000092570 'UIView-rightMargin-guide-constraint' H:[UILayoutGuide:0x618000195470'UIViewLayoutMarginsGuide']-(15)-|(LTR)   (active, names: '|':_UIButtonBarStackView:0x7fcf05c0af40 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x618000092570 'UIView-rightMargin-guide-constraint' H:[UILayoutGuide:0x618000195470'UIViewLayoutMarginsGuide']-(15)-|(LTR)   (active, names: '|':_UIButtonBarStackView:0x7fcf05c0af40 )>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.
2017-05-23 13:37:20.184961-0400 TestKeyboardAssistant[37264:1029080] [LayoutConstraints] Unable to simultaneously satisfy constraints.
	Probably at least one of the constraints in the following list is one you don't want. 
	Try this: 
		(1) look at each constraint and try to figure out which you don't expect; 
		(2) find the code that added the unwanted constraint or constraints and fix it. 
(
    "<NSLayoutConstraint:0x6180000929d0 _UIButtonBarStackView:0x7fcf05c0a780.width <= 0   (active)>",
    "<NSLayoutConstraint:0x6180000917b0 'UIView-leftMargin-guide-constraint' H:|-(15)-[UILayoutGuide:0x618000195af0'UIViewLayoutMarginsGuide'](LTR)   (active, names: '|':_UIButtonBarStackView:0x7fcf05c0a780 )>",
    "<NSLayoutConstraint:0x6180000918f0 'UIView-rightMargin-guide-constraint' H:[UILayoutGuide:0x618000195af0'UIViewLayoutMarginsGuide']-(15)-|(LTR)   (active, names: '|':_UIButtonBarStackView:0x7fcf05c0a780 )>"
)

Will attempt to recover by breaking constraint 
<NSLayoutConstraint:0x6180000918f0 'UIView-rightMargin-guide-constraint' H:[UILayoutGuide:0x618000195af0'UIViewLayoutMarginsGuide']-(15)-|(LTR)   (active, names: '|':_UIButtonBarStackView:0x7fcf05c0a780 )>

Make a symbolic breakpoint at UIViewAlertForUnsatisfiableConstraints to catch this in the debugger.
The methods in the UIConstraintBasedLayoutDebugging category on UIView listed in <UIKit/UIView.h> may also be helpful.

Notes:
This open radar could be related: https://openradar.appspot.com/25825137

Configuration:
This occurs in 2 scenarios:

1.  The textfield has it's autocorrectionType set to UITextAutoCorrectionTypeNo.
2.  The textfield is a Secure TextField.

In both cases the center UIButtonBarStackView would be empty (contain no autocorrect suggestions).  I suspect this may be the cause of the auto-layout issues.

The issue isn't present when you either disable the inputAssistantItem by setting the leading/trailing BarButtonGroups to an empty array or use a textfield with auto-correction enabled.