Remove ambiguating constraint priorities, avoid removing and recreating the same constraints

Closes #407

Tusker/Screens/Notifications/ActionNotificationGroupCollectionViewCell.swift

@@ -48,11 +48,7 @@ class ActionNotificationGroupCollectionViewCell: UICollectionViewListCell {
         $0.axis = .horizontal
         $0.alignment = .fill
         $0.spacing = 8
-        let heightConstraint = $0.heightAnchor.constraint(equalToConstant: 30)
+        $0.heightAnchor.constraint(equalToConstant: 30).isActive = true
-        // the collection view cell imposes a height constraint before it's calculated the actual height
-        // so let this constraint be broken temporarily to avoid unsatisfiable constraints log spam
-        heightConstraint.priority = .init(999)
-        heightConstraint.isActive = true
     }
     
     private lazy var actionLabel = MultiSourceEmojiLabel().configure {

Tusker/Screens/Notifications/FollowNotificationGroupCollectionViewCell.swift

@@ -45,9 +45,7 @@ class FollowNotificationGroupCollectionViewCell: UICollectionViewListCell {
     ]).configure {
         $0.axis = .horizontal
         $0.alignment = .fill
-        let heightConstraint = $0.heightAnchor.constraint(equalToConstant: 30)
+        $0.heightAnchor.constraint(equalToConstant: 30).isActive = true
-        heightConstraint.priority = .init(999)
-        heightConstraint.isActive = true
     }
     
     private lazy var actionLabel = MultiSourceEmojiLabel().configure {

Tusker/Screens/Notifications/FollowRequestNotificationCollectionViewCell.swift

@@ -48,9 +48,7 @@ class FollowRequestNotificationCollectionViewCell: UICollectionViewListCell {
     ]).configure {
         $0.axis = .horizontal
         $0.alignment = .fill
-        let heightConstraint = $0.heightAnchor.constraint(equalToConstant: 30)
+        $0.heightAnchor.constraint(equalToConstant: 30).isActive = true
-        heightConstraint.priority = .init(999)
-        heightConstraint.isActive = true
     }
     
     private lazy var actionLabel = EmojiLabel().configure {

Tusker/Screens/Notifications/PollFinishedNotificationCollectionViewCell.swift

@@ -91,9 +91,6 @@ class PollFinishedNotificationCollectionViewCell: UICollectionViewListCell {
         contentView.addSubview(iconView)
         vStack.translatesAutoresizingMaskIntoConstraints = false
         contentView.addSubview(vStack)
-        let vStackBottomConstraint = vStack.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -8)
-        // need something to break during intermediate layouts when the cell imposes a 44pt height :S
-        vStackBottomConstraint.priority = .init(999)
         NSLayoutConstraint.activate([
             iconView.topAnchor.constraint(equalTo: vStack.topAnchor),
             iconView.trailingAnchor.constraint(equalTo: contentView.leadingAnchor, constant: 16 + 50),
@@ -101,7 +98,7 @@ class PollFinishedNotificationCollectionViewCell: UICollectionViewListCell {
             vStack.leadingAnchor.constraint(equalTo: iconView.trailingAnchor, constant: 8),
             vStack.trailingAnchor.constraint(equalTo: contentView.trailingAnchor, constant: -16),
             vStack.topAnchor.constraint(equalTo: contentView.topAnchor, constant: 8),
-            vStackBottomConstraint,
+            vStack.bottomAnchor.constraint(equalTo: contentView.bottomAnchor, constant: -8),
         ])
         
         NotificationCenter.default.addObserver(self, selector: #selector(updateUIForPreferences), name: .preferencesChanged, object: nil)

Tusker/Views/Poll/PollOptionView.swift

@@ -56,13 +56,8 @@ class PollOptionView: UIView {
         percentLabel.setContentHuggingPriority(.required, for: .horizontal)
         addSubview(percentLabel)
         
-        let minHeightConstraint = heightAnchor.constraint(greaterThanOrEqualToConstant: PollOptionView.minHeight)
-        // on the first layout, something is weird and this becomes ambiguous even though it's fine on subsequent layouts
-        // this keeps autolayout from complaining
-        minHeightConstraint.priority = .required - 1
-
         NSLayoutConstraint.activate([
-            minHeightConstraint,
+            heightAnchor.constraint(greaterThanOrEqualToConstant: PollOptionView.minHeight),
 
             label.topAnchor.constraint(equalTo: topAnchor, constant: 4),
             label.bottomAnchor.constraint(equalTo: bottomAnchor, constant: -4),

Tusker/Views/Status/StatusContentContainer.swift

@@ -50,8 +50,9 @@ class StatusContentContainer<ContentView: ContentTextView, PollView: StatusConte
     
     private var isHiddenObservations: [NSKeyValueObservation] = []
     
+    private var visibleSubviews = IndexSet()
     private var verticalConstraints: [NSLayoutConstraint] = []
-    private var lastSubviewBottomConstraint: NSLayoutConstraint?
+    private var lastSubviewBottomConstraint: (UIView, NSLayoutConstraint)?
     private var zeroHeightConstraint: NSLayoutConstraint!
     
     private var isCollapsed = false
@@ -93,31 +94,35 @@ class StatusContentContainer<ContentView: ContentTextView, PollView: StatusConte
     }
     
     override func updateConstraints() {
-        NSLayoutConstraint.deactivate(verticalConstraints)
+        let visibleSubviews = IndexSet(arrangedSubviews.indices.filter { !arrangedSubviews[$0].isHidden })
-        verticalConstraints = []
+        if self.visibleSubviews != visibleSubviews {
-        var lastVisibleSubview: UIView?
+            self.visibleSubviews = visibleSubviews
+            NSLayoutConstraint.deactivate(verticalConstraints)
+            verticalConstraints = []
+            var lastVisibleSubview: UIView?
             
-        for subview in arrangedSubviews {
+            for subviewIndex in visibleSubviews {
-            guard !subview.isHidden else {
+                let subview = arrangedSubviews[subviewIndex]
-                continue
+                if let lastVisibleSubview {
+                    verticalConstraints.append(subview.topAnchor.constraint(equalTo: lastVisibleSubview.bottomAnchor, constant: 4))
+                } else {
+                    verticalConstraints.append(subview.topAnchor.constraint(equalTo: topAnchor))
+                }
+                lastVisibleSubview = subview
             }
             
-            if let lastVisibleSubview {
+            NSLayoutConstraint.activate(verticalConstraints)
-                verticalConstraints.append(subview.topAnchor.constraint(equalTo: lastVisibleSubview.bottomAnchor, constant: 4))
-            } else {
-                verticalConstraints.append(subview.topAnchor.constraint(equalTo: topAnchor))
-            }
-            
-            lastVisibleSubview = subview
         }
             
-        NSLayoutConstraint.activate(verticalConstraints)
+        if lastSubviewBottomConstraint == nil || arrangedSubviews[visibleSubviews.last!] !== lastSubviewBottomConstraint?.0 {
-        
+            lastSubviewBottomConstraint?.1.isActive = false
-        lastSubviewBottomConstraint?.isActive = false
+            // this constraint needs to have low priority so that during the collapse/expand animation, the content container is the view that shrinks/expands
-        // this constraint needs to have low priority so that during the collapse/expand animation, the content container is the view that shrinks/expands
+            let lastVisibleSubview = arrangedSubviews[visibleSubviews.last!]
-        lastSubviewBottomConstraint = subviews.last(where: { !$0.isHidden })!.bottomAnchor.constraint(equalTo: bottomAnchor)
+            let constraint = lastVisibleSubview.bottomAnchor.constraint(equalTo: bottomAnchor)
-        lastSubviewBottomConstraint!.isActive = !isCollapsed
+            constraint.isActive = !isCollapsed
-        lastSubviewBottomConstraint!.priority = .defaultLow
+            constraint.priority = .defaultLow
+            lastSubviewBottomConstraint = (lastVisibleSubview, constraint)
+        }
         
         zeroHeightConstraint.isActive = isCollapsed
         
@@ -133,7 +138,7 @@ class StatusContentContainer<ContentView: ContentTextView, PollView: StatusConte
         // don't call setNeedsUpdateConstraints b/c that destroys/recreates a bunch of other constraints
         // if there is no lastSubviewBottomConstraint, then we already need a constraint update, so we don't need to do anything here
         if let lastSubviewBottomConstraint {
-            lastSubviewBottomConstraint.isActive = !collapsed
+            lastSubviewBottomConstraint.1.isActive = !collapsed
             zeroHeightConstraint.isActive = collapsed
         }
     }

Tusker/Views/Status/TimelineStatusCollectionViewCell.swift

@@ -35,9 +35,11 @@ class TimelineStatusCollectionViewCell: UICollectionViewListCell, StatusCollecti
         $0.layer.masksToBounds = true
         $0.layer.cornerCurve = .continuous
         $0.tintColor = .secondaryLabel
+        let heightConstraint = $0.heightAnchor.constraint(equalToConstant: TimelineStatusCollectionViewCell.timelineReasonIconSize)
+        heightConstraint.identifier = "TimelineReason-Height"
         NSLayoutConstraint.activate([
             // this needs to be lessThanOrEqualTo not just equalTo b/c otherwise intermediate layouts are broken
-            $0.heightAnchor.constraint(lessThanOrEqualToConstant: TimelineStatusCollectionViewCell.timelineReasonIconSize),
+            heightConstraint,
             $0.widthAnchor.constraint(equalTo: $0.heightAnchor),
         ])
     }
@@ -60,16 +62,20 @@ class TimelineStatusCollectionViewCell: UICollectionViewListCell, StatusCollecti
         $0.addSubview(contentVStack)
         metaIndicatorsView.translatesAutoresizingMaskIntoConstraints = false
         $0.addSubview(metaIndicatorsView)
+        let avatarTopConstraint = avatarImageView.topAnchor.constraint(equalTo: $0.topAnchor)
+        avatarTopConstraint.identifier = "Avatar-Top"
+        let metaIndicatorsTopConstraint = metaIndicatorsView.topAnchor.constraint(equalTo: avatarImageView.bottomAnchor, constant: 4)
+        metaIndicatorsTopConstraint.identifier = "MetaIndicators-Top"
         NSLayoutConstraint.activate([
             avatarImageView.leadingAnchor.constraint(equalTo: $0.leadingAnchor),
-            avatarImageView.topAnchor.constraint(equalTo: $0.topAnchor),
+            avatarTopConstraint,
             contentVStack.leadingAnchor.constraint(equalTo: avatarImageView.trailingAnchor, constant: 8),
             contentVStack.trailingAnchor.constraint(equalTo: $0.trailingAnchor),
             contentVStack.topAnchor.constraint(equalTo: $0.topAnchor),
             contentVStack.bottomAnchor.constraint(equalTo: $0.bottomAnchor),
             metaIndicatorsView.leadingAnchor.constraint(greaterThanOrEqualTo: $0.leadingAnchor),
             metaIndicatorsView.trailingAnchor.constraint(equalTo: avatarImageView.trailingAnchor),
-            metaIndicatorsView.topAnchor.constraint(equalTo: avatarImageView.bottomAnchor, constant: 4),
+            metaIndicatorsTopConstraint,
         ])
     }
     
@@ -177,6 +183,7 @@ class TimelineStatusCollectionViewCell: UICollectionViewListCell, StatusCollecti
         $0.tintAdjustmentMode = .normal
         $0.setContentHuggingPriority(.defaultHigh, for: .vertical)
         $0.addTarget(self, action: #selector(collapseButtonPressed), for: .touchUpInside)
+        $0.setContentCompressionResistancePriority(.required, for: .vertical)
     }
     
     let contentContainer = StatusContentContainer<StatusContentTextView, StatusPollView>(useTopSpacer: false).configure {
@@ -316,17 +323,12 @@ class TimelineStatusCollectionViewCell: UICollectionViewListCell, StatusCollecti
         }
         
         mainContainerTopToReblogLabelConstraint = mainContainer.topAnchor.constraint(equalTo: timelineReasonHStack.bottomAnchor, constant: 4)
+        mainContainerTopToReblogLabelConstraint.identifier = "MainContainerTopToReblog"
         mainContainerTopToSelfConstraint = mainContainer.topAnchor.constraint(equalTo: statusContainer.topAnchor, constant: 8)
-        // when flipping between topToReblog and topToSelf constraints, the framework sometimes thinks both of them should be active simultaneously
+        mainContainerTopToSelfConstraint.identifier = "MainContainerTopToSelf"
-        // even though the code never does that; so let this one get broken temporarily
-        mainContainerTopToSelfConstraint.priority = .init(999)
         mainContainerBottomToActionsConstraint = mainContainer.bottomAnchor.constraint(equalTo: actionsContainer.topAnchor, constant: -4)
         mainContainerBottomToSelfConstraint = mainContainer.bottomAnchor.constraint(equalTo: statusContainer.bottomAnchor, constant: -6)
         
-        let metaIndicatorsBottomConstraint = metaIndicatorsView.bottomAnchor.constraint(lessThanOrEqualTo: statusContainer.bottomAnchor, constant: -6)
-        // sometimes during intermediate layouts, there are conflicting constraints, so let this one get broken temporarily, to avoid a bunch of printing
-        metaIndicatorsBottomConstraint.priority = .init(999)
-        
         NSLayoutConstraint.activate([
             // why is this 4 but the mainContainerTopSelfConstraint constant 8? because this looks more balanced
             timelineReasonHStack.topAnchor.constraint(equalTo: statusContainer.topAnchor, constant: 4),
@@ -335,13 +337,14 @@ class TimelineStatusCollectionViewCell: UICollectionViewListCell, StatusCollecti
             
             mainContainer.leadingAnchor.constraint(equalTo: statusContainer.leadingAnchor, constant: 16),
             mainContainer.trailingAnchor.constraint(equalTo: statusContainer.trailingAnchor, constant: -16),
+            mainContainerBottomToActionsConstraint,
             
             actionsContainer.leadingAnchor.constraint(equalTo: statusContainer.leadingAnchor, constant: 16),
             actionsContainer.trailingAnchor.constraint(equalTo: statusContainer.trailingAnchor, constant: -16),
             // yes, this is deliberately 6. 4 looks to cramped, 8 looks uneven
             actionsContainer.bottomAnchor.constraint(equalTo: statusContainer.bottomAnchor, constant: -6),
             
-            metaIndicatorsBottomConstraint,
+            metaIndicatorsView.bottomAnchor.constraint(lessThanOrEqualTo: statusContainer.bottomAnchor, constant: -6),
         ])
         
         updateActionsVisibility()
@@ -590,8 +593,14 @@ class TimelineStatusCollectionViewCell: UICollectionViewListCell, StatusCollecti
         }
         
         timelineReasonHStack.isHidden = hideTimelineReason
-        mainContainerTopToReblogLabelConstraint.isActive = !hideTimelineReason
+        // do this to make sure the currently active constraint is deactivated first
-        mainContainerTopToSelfConstraint.isActive = hideTimelineReason
+        if hideTimelineReason {
+            mainContainerTopToReblogLabelConstraint.isActive = false
+            mainContainerTopToSelfConstraint.isActive = true
+        } else {
+            mainContainerTopToSelfConstraint.isActive = false
+            mainContainerTopToReblogLabelConstraint.isActive = true
+        }
         
         doUpdateUI(status: status, precomputedContent: precomputedContent)
         
@@ -690,11 +699,11 @@ class TimelineStatusCollectionViewCell: UICollectionViewListCell, StatusCollecti
     }
     
     private func updateActionsVisibility() {
-        if Preferences.shared.hideActionsInTimeline {
+        if Preferences.shared.hideActionsInTimeline && !actionsContainer.isHidden {
             actionsContainer.isHidden = true
-            mainContainerBottomToSelfConstraint.isActive = true
             mainContainerBottomToActionsConstraint.isActive = false
-        } else {
+            mainContainerBottomToSelfConstraint.isActive = true
+        } else if !Preferences.shared.hideActionsInTimeline && actionsContainer.isHidden {
             actionsContainer.isHidden = false
             mainContainerBottomToSelfConstraint.isActive = false
             mainContainerBottomToActionsConstraint.isActive = true