From a198a599168f120337baf4140b669b763c10356f Mon Sep 17 00:00:00 2001
From: Tom Longhurst <30480171+thomhurst@users.noreply.github.com>
Date: Thu, 28 May 2026 21:05:57 +0100
Subject: [PATCH] perf: dedupe GetSimpleTypeName into shared TypeNameFormatter

Extract the duplicated runtime GetSimpleTypeName logic from
TestDataFormatter and DisplayNameBuilder into a single internal
TypeNameFormatter helper in TUnit.Core.Helpers.

The shared implementation builds the entire recursive name with one
pooled StringBuilder, allocating only the final string instead of a
new string[] + string.Join per generic level. Output is byte-identical
to both previous call sites.

Closes #6039
---
 TUnit.Core/DataSources/TestDataFormatter.cs | 28 +-------
 TUnit.Core/Helpers/TypeNameFormatter.cs     | 71 +++++++++++++++++++++
 TUnit.Engine/Helpers/DisplayNameBuilder.cs  | 27 +-------
 3 files changed, 73 insertions(+), 53 deletions(-)
 create mode 100644 TUnit.Core/Helpers/TypeNameFormatter.cs

diff --git a/TUnit.Core/DataSources/TestDataFormatter.cs b/TUnit.Core/DataSources/TestDataFormatter.cs
index b1cd16f0aa..1ef3428883 100644
--- a/TUnit.Core/DataSources/TestDataFormatter.cs
+++ b/TUnit.Core/DataSources/TestDataFormatter.cs
@@ -86,7 +86,7 @@ public static string CreateGenericDisplayName(TestMetadata metadata, Type[] gene
             var genericTypeNames = new string[genericTypes.Length];
             for (var i = 0; i < genericTypes.Length; i++)
             {
-                genericTypeNames[i] = GetSimpleTypeName(genericTypes[i]);
+                genericTypeNames[i] = TypeNameFormatter.GetSimpleTypeName(genericTypes[i]);
             }
             var genericPart = string.Join(", ", genericTypeNames);
             testName = $"{testName}<{genericPart}>";
@@ -100,30 +100,4 @@ public static string CreateGenericDisplayName(TestMetadata metadata, Type[] gene
         var argumentsText = FormatArguments(arguments);
         return $"{testName}({argumentsText})";
     }
-
-    private static string GetSimpleTypeName(Type type)
-    {
-        if (!type.IsGenericType)
-        {
-            return type.Name;
-        }
-
-        var genericTypeName = type.GetGenericTypeDefinition().Name;
-        var index = genericTypeName.IndexOf('`');
-        if (index > 0)
-        {
-            genericTypeName = genericTypeName.Substring(0, index);
-        }
-
-        var genericArgs = type.GetGenericArguments();
-        var genericArgNames = new string[genericArgs.Length];
-        for (var i = 0; i < genericArgs.Length; i++)
-        {
-            genericArgNames[i] = GetSimpleTypeName(genericArgs[i]);
-        }
-        var genericArgsText = string.Join(", ", genericArgNames);
-
-        return $"{genericTypeName}<{genericArgsText}>";
-    }
-
 }
diff --git a/TUnit.Core/Helpers/TypeNameFormatter.cs b/TUnit.Core/Helpers/TypeNameFormatter.cs
new file mode 100644
index 0000000000..d14548b66a
--- /dev/null
+++ b/TUnit.Core/Helpers/TypeNameFormatter.cs
@@ -0,0 +1,71 @@
+using System.Text;
+
+namespace TUnit.Core.Helpers;
+
+/// <summary>
+/// Formats <see cref="Type"/> instances into simple, human-readable names for display purposes.
+/// </summary>
+internal static class TypeNameFormatter
+{
+    /// <summary>
+    /// Builds a simple type name, recursively expanding generic arguments
+    /// (e.g. <c>Dictionary&lt;String, List&lt;Int32&gt;&gt;</c>).
+    /// </summary>
+    /// <remarks>
+    /// Uses a single pooled <see cref="StringBuilder"/> for the entire recursive build,
+    /// allocating only the final string rather than one string per generic level.
+    /// </remarks>
+    public static string GetSimpleTypeName(Type type)
+    {
+        if (!type.IsGenericType)
+        {
+            return type.Name;
+        }
+
+        var builder = StringBuilderPool.Get();
+        try
+        {
+            AppendSimpleTypeName(builder, type);
+            return builder.ToString();
+        }
+        finally
+        {
+            StringBuilderPool.Return(builder);
+        }
+    }
+
+    private static void AppendSimpleTypeName(StringBuilder builder, Type type)
+    {
+        if (!type.IsGenericType)
+        {
+            builder.Append(type.Name);
+            return;
+        }
+
+        var genericTypeName = type.GetGenericTypeDefinition().Name;
+        var index = genericTypeName.IndexOf('`');
+        if (index > 0)
+        {
+            builder.Append(genericTypeName, 0, index);
+        }
+        else
+        {
+            builder.Append(genericTypeName);
+        }
+
+        builder.Append('<');
+
+        var genericArgs = type.GetGenericArguments();
+        for (var i = 0; i < genericArgs.Length; i++)
+        {
+            if (i > 0)
+            {
+                builder.Append(", ");
+            }
+
+            AppendSimpleTypeName(builder, genericArgs[i]);
+        }
+
+        builder.Append('>');
+    }
+}
diff --git a/TUnit.Engine/Helpers/DisplayNameBuilder.cs b/TUnit.Engine/Helpers/DisplayNameBuilder.cs
index 512236d892..d5e60c6696 100644
--- a/TUnit.Engine/Helpers/DisplayNameBuilder.cs
+++ b/TUnit.Engine/Helpers/DisplayNameBuilder.cs
@@ -110,7 +110,7 @@ public static string BuildGenericDisplayName(TestMetadata metadata, Type[] gener
             var genericTypeNames = new string[genericTypes.Length];
             for (var i = 0; i < genericTypes.Length; i++)
             {
-                genericTypeNames[i] = GetSimpleTypeName(genericTypes[i]);
+                genericTypeNames[i] = TypeNameFormatter.GetSimpleTypeName(genericTypes[i]);
             }
             var genericPart = string.Join(", ", genericTypeNames);
             testName = $"{testName}<{genericPart}>";
@@ -125,31 +125,6 @@ public static string BuildGenericDisplayName(TestMetadata metadata, Type[] gener
         return $"{testName}({argumentsText})";
     }
 
-    private static string GetSimpleTypeName(Type type)
-    {
-        if (!type.IsGenericType)
-        {
-            return type.Name;
-        }
-
-        var genericTypeName = type.GetGenericTypeDefinition().Name;
-        var index = genericTypeName.IndexOf('`');
-        if (index > 0)
-        {
-            genericTypeName = genericTypeName.Substring(0, index);
-        }
-
-        var genericArgs = type.GetGenericArguments();
-        var genericArgNames = new string[genericArgs.Length];
-        for (var i = 0; i < genericArgs.Length; i++)
-        {
-            genericArgNames[i] = GetSimpleTypeName(genericArgs[i]);
-        }
-        var genericArgsText = string.Join(", ", genericArgNames);
-
-        return $"{genericTypeName}<{genericArgsText}>";
-    }
-
     /// <summary>
     /// Resolves the actual value from a data source factory result
     /// </summary>