FIX: Implement caching for InputControlPath display name

Packages/com.unity.inputsystem/CHANGELOG.md

@@ -17,6 +17,7 @@ however, it has to be formatted properly to pass verification tests.
 
 ### Fixed
 
+- Fixed caching for InputControlPath display name.
 - Fixed the `Auto-Save` toggle button with some extra pixels to align the text in the window better.
 - Align title font size with toolbar style in `Input Action` window.
 - Updated Action Properties headers to use colors consistent with GameObject component headers.

Packages/com.unity.inputsystem/InputSystem/Editor/ControlPicker/InputControlPathEditor.cs

@@ -123,8 +123,22 @@ public void OnGUI(Rect rect, GUIContent label = null, SerializedProperty propert
                 return;
             }
 
-            ////TODO: this should be cached; generates needless GC churn
-            var displayName = InputControlPath.ToHumanReadableString(path);
+            // Cache the display name per path value and only recompute when the string actually changes.
+            if (!string.Equals(path, m_CachedPath, StringComparison.Ordinal))
+            {
+                m_CachedPath = path;
+
+                if (string.IsNullOrEmpty(path))
+                {
+                    m_CachedDisplayName = string.Empty;
+                }
+                else
+                {
+                    m_CachedDisplayName = InputControlPath.ToHumanReadableString(path);
+                }
+            }
+
+            var displayName = m_CachedDisplayName;
 
             // Either show dropdown control that opens path picker or show path directly as
             // text, if manual path editing is toggled on.
@@ -209,6 +223,9 @@ private void SetExpectedControlLayoutFromAttribute(SerializedProperty property)
         private string m_ExpectedControlLayout;
         private string[] m_ControlPathsToMatch;
 
+        private string m_CachedPath;
+        private string m_CachedDisplayName;
+
         private InputControlPickerDropdown m_PickerDropdown;
         private readonly InputControlPickerState m_PickerState;