trail-into-darkness/Packages/com.jovian.inspector-tools/Editor/Attributes/CompactDrawerAttribute.cs

using System;
using System.Collections;
using System.Collections.Generic;
using UnityEngine;
#if UNITY_EDITOR
using System.Text;
using UnityEditor;
#endif

namespace Jovian.InspectorTools {
    public class CompactDrawerAttribute : PropertyAttribute { }
}

#if UNITY_EDITOR
namespace Jovian.InspectorTools.Internal {
    [CustomPropertyDrawer(typeof(CompactDrawerAttribute))]
    public class CompactDrawerAttributeDrawer : PropertyDrawer {
        private static readonly List<SerializedProperty> cacheProperties = new();
        private static readonly StringBuilder stringBuilder = new();

        public override float GetPropertyHeight(SerializedProperty property, GUIContent label) {
            return EditorGUIUtility.singleLineHeight;
        }

        public override void OnGUI(Rect position, SerializedProperty property, GUIContent label) {
            cacheProperties.Clear();
            stringBuilder.Clear();

            EditorGUI.BeginProperty(position, label, property);

            stringBuilder.Append(" (");
            IEnumerator enumerator = property.GetEnumerator();
            while (enumerator.MoveNext()) {
                SerializedProperty childProperty = (SerializedProperty)enumerator.Current;
                cacheProperties.Add(childProperty!.Copy()); // Copy is very important since .Current changes its content while enumerating
                stringBuilder.Append(ObjectNames.NicifyVariableName(childProperty!.name));
                stringBuilder.Append(", ");
            }

            if (cacheProperties.Count > 0) {
                stringBuilder.Remove(stringBuilder.Length - 2, 2);
                stringBuilder.Append(")");
            }
            else {
                stringBuilder.Clear();
            }

            GUIContent newLabel = new($"{label}{stringBuilder}", label.tooltip);

            Rect labelRect = new(position) { height = EditorGUIUtility.singleLineHeight };
            Rect fieldRect = EditorGUI.PrefixLabel(labelRect, newLabel);
            fieldRect.height = EditorGUIUtility.singleLineHeight;

            int childCount = cacheProperties.Count;
            int childIndex = 0;
            float spacing = EditorGUIUtility.standardVerticalSpacing;
            float fullWidth = fieldRect.width / childCount;
            float widthMinusSpacing = fullWidth - spacing * (childCount - 1) / childCount;

            int indentLevel = EditorGUI.indentLevel;
            EditorGUI.indentLevel = 0;

            for (int i = 0, c = cacheProperties.Count; i < c; i++) {
                SerializedProperty childProperty = cacheProperties[i];
                Rect childFieldRect = new(fieldRect) {
                    x = Mathf.CeilToInt(fieldRect.x + fullWidth * childIndex),
                    width = widthMinusSpacing
                };
                EditorGUI.PropertyField(childFieldRect, childProperty, GUIContent.none);
                childIndex++;
            }

            EditorGUI.indentLevel = indentLevel;

            EditorGUI.EndProperty();
        }
    }
}
#endif