Show tool tip when label is truncated.

Packages/MacUI/Sources/ControlUI/FilenameTextField.swift

@@ -38,6 +38,22 @@ public final class FilenameTextField: NSTextField {
     }
 
 
+    public override var stringValue: String {
+
+        didSet {
+            self.invalidateToolTip()
+        }
+    }
+
+
+    public override func setFrameSize(_ newSize: NSSize) {
+
+        super.setFrameSize(newSize)
+
+        self.invalidateToolTip()
+    }
+
+
     public override func mouseDown(with event: NSEvent) {
 
         super.mouseDown(with: event)
@@ -56,6 +72,18 @@ public final class FilenameTextField: NSTextField {
 
         return true
     }
+
+
+    /// Invalidates whether showing the tool tip if the label is truncated.
+    private func invalidateToolTip() {
+
+        guard let cell else { return }
+
+        let expansionFrame = cell.expansionFrame(withFrame: self.frame, in: self)
+        let isTruncated = !expansionFrame.isEmpty
+
+        self.toolTip = isTruncated ? self.stringValue : nil
+    }
 }