cache NuGetEnvironment.GetFolderPath values (#6874)

Author: zivkan

src/NuGet.Core/NuGet.Common/PathUtil/NuGetEnvironment.cs

@@ -5,6 +5,7 @@
 #nullable disable
 
 using System;
+using System.Collections.Concurrent;
 using System.Globalization;
 using System.IO;
 using System.Runtime.InteropServices;
@@ -26,6 +27,9 @@ public static class NuGetEnvironment
         private static readonly Lazy<string> _getHome = new Lazy<string>(() => GetHome());
 
         private static string _nuGetTempDirectory = null;
+
+        private static readonly ConcurrentDictionary<NuGetFolderPath, string> Cache = new ConcurrentDictionary<NuGetFolderPath, string>();
+
         internal static string NuGetTempDirectory
         {
             get { return _nuGetTempDirectory ??= GetNuGetTempDirectory(); }
@@ -65,6 +69,12 @@ private static string GetNuGetTempDirectory()
         }
 
         public static string GetFolderPath(NuGetFolderPath folder)
+        {
+            string path = Cache.GetOrAdd(folder, CalculateFolderPath);
+            return path;
+        }
+
+        private static string CalculateFolderPath(NuGetFolderPath folder)
         {
             switch (folder)
             {

test/NuGet.Core.Tests/NuGet.Common.Test/NuGetEnvironmentTests.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System.Collections.Generic;
 using NuGet.Common.Migrations;
 using NuGet.Test.Utility;
 using Xunit;
@@ -15,5 +16,27 @@ public void GetFolderPath_Temp_Success()
             var nuGetTempDirectory = NuGetEnvironment.GetFolderPath(NuGetFolderPath.Temp);
             Assert.Equal("700", Migration1.GetPermissions(nuGetTempDirectory).ToString());
         }
+
+        public static IEnumerable<object[]> AllNuGetFolderPaths()
+        {
+            foreach (NuGetFolderPath folderPath in (NuGetFolderPath[])System.Enum.GetValues(typeof(NuGetFolderPath)))
+            {
+                if (folderPath == NuGetFolderPath.DefaultMsBuildPath)
+                {
+                    // Skip DefaultMsBuildPath as it throws on Mac and Linux
+                    continue;
+                }
+                yield return new object[] { folderPath };
+            }
+        }
+
+        [Theory]
+        [MemberData(nameof(AllNuGetFolderPaths))]
+        public void GetFolderPath_MultipleCalls_ReturnsCachedInstance(NuGetFolderPath folder)
+        {
+            var firstCall = NuGetEnvironment.GetFolderPath(folder);
+            var secondCall = NuGetEnvironment.GetFolderPath(folder);
+            Assert.Same(firstCall, secondCall);
+        }
     }
 }