UI ScrollRect mask not hiding Input Field Caret and Highlight

Seems that the issue is still not fixed in Unity 5.5. Issue Tracker says that it is in 5.5.0 but I just checked Unity 5.5.0f3, and the bug is still here. Maybe it's fixed in patch releases, I don't know. But anyway, there may be people who can't upgrade to latest version, so, here is a workaround I found.

 using UnityEngine;
 using UnityEngine.UI;
 
 [RequireComponent(typeof(InputField))]
 public class FixInputSelectionMasking : MonoBehaviour {
     InputField _inputField;
     Transform _caret;
 
     public void Awake() {
         _inputField = GetComponent<InputField>();
     }
 
     public void Update() {
         if (!_caret) {
             _caret = _inputField.transform.Find(_inputField.transform.name + " Input Caret");
             if (_caret) {
                 var graphic = _caret.GetComponent<Graphic>();
                 if (!graphic)
                     _caret.gameObject.AddComponent<Image>();
             }
         }
     }
 }

Put this script on an InputField and the selection should be masked as expected:

I've tested it in 5.4.4f1 and 5.5.0f3.

Some explanations

InputField on the fly creates a GameObject to render the selection and the caret. This object has a CanvasRenderer component and renders its geometry directly. I think that the issue is caused by that CanvasRenderer by itself doesn't know anything about masking. It doesn't update shader properties, related to masking (_ClipRect for Mask Rect 2D and _Stencil* for Mask).

The script that is shown above adds a dummy Image component to the GameObject which renders the selection. Image is a Graphic and it knows how to deal with the masking. I'm not sure, that this fix will work in all cases, I haven't dug too much into implementation details of Image and InputField. I suppose that theoretically Image may override the selection geometry generated by InputField but, as I understand it, InputField regenerates the selection geometry each frame (in CanvasUpdate.LatePreRender handler).