Add STTextFinderBarContainer to handle text finder bar

Move responsibility for managing the text finder bar from STTextView to a
new STTextFinderBarContainer class that implements NSTextFinderBarContainer.
This allows properly positioning the gutter view below the find bar when it
is shown/hidden.

Update STTextView to:
- Create the text finder client, bar container and finder in init
- Connect the text finder client and bar container
- Remove code to set up the text finder when moving to a window
- Scope some enclosing scroll view accesses

Author: krzyzanowskim

Sources/STTextViewAppKit/STTextFinderBarContainer.swift

@@ -0,0 +1,43 @@
+import AppKit
+
+final class STTextFinderBarContainer: NSObject, NSTextFinderBarContainer {
+
+    // Forward NSTextFinderBarContainer to enclosing NSScrollView (for now at least)
+    weak var client: STTextView?
+
+    var findBarView: NSView? {
+        get {
+            client?.scrollView?.findBarView
+        }
+
+        set {
+            client?.scrollView?.findBarView = newValue
+
+            // Rearrange gutter view position in NSScrollView hierarchy
+            Task { @MainActor in
+                if let scrollView = client?.scrollView, let gutterView = client?.gutterView {
+                    gutterView.removeFromSuperviewWithoutNeedingDisplay()
+                    scrollView.addSubview(gutterView, positioned: .below, relativeTo: scrollView.findBarView)
+                }
+            }
+        }
+    }
+
+    var isFindBarVisible: Bool {
+        get {
+            client?.scrollView?.isFindBarVisible ?? false
+        }
+
+        set {
+            client?.scrollView?.isFindBarVisible = newValue
+        }
+    }
+
+    func contentView() -> NSView? {
+        client?.contentView
+    }
+
+    func findBarViewDidChangeHeight() {
+        client?.scrollView?.findBarViewDidChangeHeight()
+    }
+}

Sources/STTextViewAppKit/STTextView+Gutter.swift

@@ -21,8 +21,8 @@ extension STTextView {
                 gutterView.selectedLineTextColor = textColor
                 gutterView.highlightSelectedLine = highlightSelectedLine
                 gutterView.selectedLineHighlightColor = selectedLineHighlightColor
-                if let scrollView = enclosingScrollView {
-                    scrollView.addSubview(gutterView, positioned: .below, relativeTo: scrollView.findBarView)
+                if let scrollView {
+                    scrollView.addSubview(gutterView)
                 }
                 self.gutterView = gutterView
                 needsLayout = true

Sources/STTextViewAppKit/STTextView.swift

@@ -457,6 +457,8 @@ import AVFoundation
     /// NSTextFinderClient
     internal let textFinderClient: STTextFinderClient
 
+    internal let textFinderBarContainer: STTextFinderBarContainer
+
     internal var textCheckingController: NSTextCheckingController!
 
     /// A Boolean value that indicates whether the receiver has continuous spell checking enabled.
@@ -592,9 +594,10 @@ import AVFoundation
         allowsUndo = true
         _undoManager = CoalescingUndoManager()
 
-
-        textFinder = NSTextFinder()
         textFinderClient = STTextFinderClient()
+        textFinderBarContainer = STTextFinderBarContainer()
+        textFinder = NSTextFinder()
+        textFinder.client = textFinderClient
 
         _defaultTypingAttributes = [
             .paragraphStyle: NSParagraphStyle.default,
@@ -606,6 +609,9 @@ import AVFoundation
 
         super.init(frame: frameRect)
 
+        textFinderBarContainer.client = self
+        textFinder.findBarContainer = textFinderBarContainer
+
         setSelectedTextRange(NSTextRange(location: textLayoutManager.documentRange.location), updateLayout: false)
 
         textLayoutManager.delegate = self
@@ -724,25 +730,23 @@ import AVFoundation
     open override func viewDidMoveToSuperview() {
         super.viewDidMoveToSuperview()
 
-        NotificationCenter.default.addObserver(
-            self,
-            selector: #selector(enclosingClipViewBoundsDidChange(_:)),
-            name: NSClipView.boundsDidChangeNotification,
-            object: scrollView?.contentView
-        )
+        if let scrollView {
+            NotificationCenter.default.addObserver(
+                self,
+                selector: #selector(enclosingClipViewBoundsDidChange(_:)),
+                name: NSClipView.boundsDidChangeNotification,
+                object: scrollView.contentView
+            )
+        }
     }
 
     open override func viewDidMoveToWindow() {
         super.viewDidMoveToWindow()
 
         if self.window != nil {
-            textFinder.client = textFinderClient
-            textFinder.findBarContainer = enclosingScrollView
-
             // setup registerd plugins
             setupPlugins()
         }
-
     }
 
     open override func hitTest(_ point: NSPoint) -> NSView? {