trail-into-darkness/Packages/com.jovian.inspector-tools/Editor/Tools/RequiredUtil.cs

using UnityEngine;

#if UNITY_EDITOR
using UnityEditor;
namespace Jovian.InspectorTools.Internal {

    public static class RequiredUtil {
        private const float ICON_X_OFFSET = 15f;
        private const float ICON_SIZE = 18f;
        private static Color ErrorColor = new(1f, 0.5f, 0.5f, 1f);
        private static GUIContent errorIcon;
        private static GUIStyle errorStyle;
        
        public static void LayoutRequired(ref Rect position, string tooltip, bool indent = true) {
            if (indent) {
                position.x += ICON_SIZE;
                position.width -= ICON_SIZE;
            }
        }

        public static void DrawRequired(ref Rect position, string tooltip, bool indent = true) {
            if(errorIcon == null || errorStyle == null) {
                errorIcon = new GUIContent(EditorGUIUtility.IconContent("console.erroricon.sml").image);
                errorStyle = new GUIStyle(GUI.skin.label) {
                    padding = new RectOffset(0, 0, 0, 0),
                    imagePosition = ImagePosition.ImageOnly
                };
            }

            errorIcon.tooltip = tooltip;

            Rect errorIconRect = new Rect(position.x - ICON_X_OFFSET, position.y + 1, ICON_SIZE, EditorGUIUtility.singleLineHeight);
            GUI.Label(errorIconRect, errorIcon, errorStyle);
            GUI.color = ErrorColor;
            
            if (indent) {
                position.x += ICON_SIZE;
                position.width -= ICON_SIZE;
            }
        }
    }
}
#endif