module-inspector/Editor/Predrawers/FieldLabelFromArrayIndexAttributeDrawer.cs

using System.Text;
using UnityEditor;
using UnityEngine;

namespace Module.Inspector.Editor
{
    [CustomPropertyDrawer(typeof(FieldLabelFromArrayIndexAttribute))]
    internal sealed class FieldLabelFroArrayIndexAttributeDrawer : PredrawerModifierPropertyDrawer
    {
        public override void Modify(PredrawerModifierPropertyAttribute attribute, SerializedProperty property, GUIContent label)
        {
            var att = (FieldLabelFromArrayIndexAttribute)attribute;
            var spParent = property.GetParent();

            if (spParent == null || !spParent.isArray)
                return;
            
            var index = spParent.IndexOfProperty(property);

            if (index == -1)
                return;

            var builder = new StringBuilder();

            if (!string.IsNullOrEmpty(att.prefix))
                builder.Append(att.prefix);

            builder.Append(index);
            
            if (!string.IsNullOrEmpty(att.postfix))
                builder.Append(att.postfix);
            
            label.text = builder.ToString();
        }
    }
}