refactor: harden browser page host view transfers

Author: yonaries

ora/Core/BrowserEngine/BrowserPageView.swift

@@ -25,23 +25,29 @@ final class BrowserPageHostView: NSView {
 
         let shouldRestoreFirstResponder = shouldTransferFirstResponder(from: previousContentView)
 
-        previousContentView?.removeFromSuperview()
-        hostedContentView = nil
+        if isSameContentView {
+            hostedContentView = nil
+        } else {
+            detachHostedContentView()
+        }
 
         guard let newContentView else {
-            needsLayout = true
-            layoutSubtreeIfNeeded()
-            displayIfNeeded()
+            refreshHostingLayout()
             return
         }
 
         configure(contentView: newContentView)
 
+        if let previousHost = newContentView.superview as? BrowserPageHostView,
+           previousHost !== self
+        {
+            previousHost.releaseHostedContentView(newContentView)
+        }
+
         if newContentView.superview !== self {
-            if let previousHost = newContentView.superview as? BrowserPageHostView {
-                previousHost.hostedContentView = nil
+            if newContentView.superview != nil {
+                newContentView.removeFromSuperview()
             }
-            newContentView.removeFromSuperview()
             addSubview(newContentView)
         }
 
@@ -72,6 +78,33 @@ final class BrowserPageHostView: NSView {
         contentView.layer?.drawsAsynchronously = true
     }
 
+    private func detachHostedContentView() {
+        guard let hostedContentView else {
+            return
+        }
+
+        if hostedContentView.superview === self {
+            hostedContentView.removeFromSuperview()
+        }
+
+        self.hostedContentView = nil
+    }
+
+    private func releaseHostedContentView(_ contentView: NSView) {
+        guard hostedContentView === contentView else {
+            return
+        }
+
+        detachHostedContentView()
+        refreshHostingLayout()
+    }
+
+    private func refreshHostingLayout() {
+        needsLayout = true
+        layoutSubtreeIfNeeded()
+        displayIfNeeded()
+    }
+
     private func shouldTransferFirstResponder(from previousContentView: NSView?) -> Bool {
         guard let previousContentView,
               let firstResponder = window?.firstResponder as? NSView

ora/Features/Tabs/Switcher/FloatingTabSwitcher.swift

@@ -99,12 +99,12 @@ struct FloatingTabSwitcher: View {
                 }
             }
         }
-        .padding(.horizontal, 28)
-        .padding(.vertical, 20)
+        .padding(.horizontal, 20)
+        .padding(.vertical, 18)
         .background(BlurEffectView(material: .popover, blendingMode: .withinWindow))
         .background(theme.background.opacity(0.3))
         .cornerRadius(Constants.containerCornerRadius)
-        .shadow(color: .blue.opacity(0.07), radius: 16, x: 0, y: 12)
+        .shadow(color: theme.primary.opacity(0.07), radius: 16, x: 0, y: 12)
         .background(keyboardHandler)
         .overlay(containerBorder)
     }

oraTests/BrowserPageHostViewTests.swift

@@ -71,6 +71,28 @@ struct BrowserPageHostViewTests {
         #expect(secondHost.subviews.first === contentView)
         #expect(secondHost.hostedContentView === contentView)
         #expect(contentView.superview === secondHost)
+        #expect(contentView.removeFromSuperviewCalls == 1)
+    }
+
+    @Test func switchingToAStaleSubviewAlreadyAttachedToTheSameHostDoesNotReparentIt() {
+        let host = makeHost()
+        let firstContentView = TrackingContentView()
+        let staleContentView = TrackingContentView()
+
+        host.host(contentView: firstContentView)
+        host.addSubview(staleContentView)
+
+        let staleSuperviewTransitions = staleContentView.superviewTransitions
+
+        host.host(contentView: staleContentView)
+
+        #expect(host.subviews.count == 1)
+        #expect(host.subviews.first === staleContentView)
+        #expect(host.hostedContentView === staleContentView)
+        #expect(firstContentView.superview == nil)
+        #expect(staleContentView.superview === host)
+        #expect(staleContentView.superviewTransitions == staleSuperviewTransitions)
+        #expect(staleContentView.removeFromSuperviewCalls == 0)
     }
 
     private func makeHost() -> BrowserPageHostView {
@@ -80,6 +102,12 @@ struct BrowserPageHostViewTests {
 
 private final class TrackingContentView: NSView {
     var superviewTransitions = 0
+    var removeFromSuperviewCalls = 0
+
+    override func removeFromSuperview() {
+        removeFromSuperviewCalls += 1
+        super.removeFromSuperview()
+    }
 
     override func viewWillMove(toSuperview newSuperview: NSView?) {
         superviewTransitions += 1