Update Traits when environment has been changed

documentation/wiki/ChangeWaves.md

@@ -28,10 +28,13 @@ A wave of features is set to "rotate out" (i.e. become standard functionality) t
 - [Warning on serialization custom events by default in .NET framework](https://github.com/dotnet/msbuild/pull/9318)
 - [Cache SDK resolver data process-wide](https://github.com/dotnet/msbuild/pull/9335)
 - [Target parameters will be unquoted](https://github.com/dotnet/msbuild/pull/9452), meaning  the ';' symbol in the parameter target name will always be treated as separator
+- [Add Link metadata to Resources in AssignLinkMetadata target](https://github.com/dotnet/msbuild/pull/9464)
 - [Change Version switch output to finish with a newline](https://github.com/dotnet/msbuild/pull/9485)
 - [Load Microsoft.DotNet.MSBuildSdkResolver into default load context (MSBuild.exe only)](https://github.com/dotnet/msbuild/pull/9439)
 - [Load NuGet.Frameworks into secondary AppDomain (MSBuild.exe only)](https://github.com/dotnet/msbuild/pull/9446)
 - [ResultsCache ignores some of the BuildRequest data, may return incorrect results](https://github.com/dotnet/msbuild/pull/9565)
+- [Update Traits when environment has been changed](https://github.com/dotnet/msbuild/pull/9655)
+
 
 ### 17.8
 - [[RAR] Don't do I/O on SDK-provided references](https://github.com/dotnet/msbuild/pull/8688)

src/Build/BackEnd/Node/InProcNode.cs

@@ -336,18 +336,7 @@ private NodeEngineShutdownReason HandleShutdown(out Exception exception)
                 NativeMethodsShared.SetCurrentDirectory(_savedCurrentDirectory);
 
                 // Restore the original environment.
-                foreach (KeyValuePair<string, string> entry in CommunicationsUtilities.GetEnvironmentVariables())
-                {
-                    if (!_savedEnvironment.ContainsKey(entry.Key))
-                    {
-                        Environment.SetEnvironmentVariable(entry.Key, null);
-                    }
-                }
-
-                foreach (KeyValuePair<string, string> entry in _savedEnvironment)
-                {
-                    Environment.SetEnvironmentVariable(entry.Key, entry.Value);
-                }
+                CommunicationsUtilities.SetEnvironment(_savedEnvironment);
             }
 
             exception = _shutdownException;

src/Build/BackEnd/Node/OutOfProcNode.cs

@@ -476,20 +476,9 @@ private NodeEngineShutdownReason HandleShutdown(out Exception exception)
             // If the node was never configured, this will be null.
             if (_savedEnvironment != null)
             {
-                foreach (KeyValuePair<string, string> entry in CommunicationsUtilities.GetEnvironmentVariables())
-                {
-                    if (!_savedEnvironment.ContainsKey(entry.Key))
-                    {
-                        Environment.SetEnvironmentVariable(entry.Key, null);
-                    }
-                }
-
-                foreach (KeyValuePair<string, string> entry in _savedEnvironment)
-                {
-                    Environment.SetEnvironmentVariable(entry.Key, entry.Value);
-                }
+                CommunicationsUtilities.SetEnvironment(_savedEnvironment);
+                Traits.UpdateFromEnvironment();
             }
-
             try
             {
                 // Shut down logging, which will cause all queued logging messages to be sent.
@@ -722,12 +711,14 @@ private void HandleNodeConfiguration(NodeConfiguration configuration)
                 }
             }
 
-            // Now set the new environment
+            // Now set the new environment and update Traits class accordingly
             foreach (KeyValuePair<string, string> environmentPair in _buildParameters.BuildProcessEnvironment)
             {
                 Environment.SetEnvironmentVariable(environmentPair.Key, environmentPair.Value);
             }
 
+            Traits.UpdateFromEnvironment();
+
             // We want to make sure the global project collection has the toolsets which were defined on the parent
             // so that any custom toolsets defined can be picked up by tasks who may use the global project collection but are
             // executed on the child node.

src/Build/BackEnd/Node/OutOfProcServerNode.cs

@@ -9,6 +9,7 @@
 using Microsoft.Build.BackEnd;
 using Microsoft.Build.BackEnd.Logging;
 using Microsoft.Build.Execution;
+using Microsoft.Build.Framework;
 using Microsoft.Build.Framework.Telemetry;
 using Microsoft.Build.Internal;
 using Microsoft.Build.Shared;
@@ -357,7 +358,10 @@ private void HandleServerNodeBuildCommand(ServerNodeBuildCommand command)
 
             // Set build process context
             Directory.SetCurrentDirectory(command.StartupDirectory);
+
             CommunicationsUtilities.SetEnvironment(command.BuildProcessEnvironment);
+            Traits.UpdateFromEnvironment();
+
             Thread.CurrentThread.CurrentCulture = command.Culture;
             Thread.CurrentThread.CurrentUICulture = command.UICulture;
 

src/Framework/Traits.cs

@@ -13,7 +13,7 @@ namespace Microsoft.Build.Framework
     /// </summary>
     internal class Traits
     {
-        private static readonly Traits _instance = new Traits();
+        private static Traits _instance = new Traits();
         public static Traits Instance
         {
             get
@@ -136,6 +136,15 @@ public Traits()
 
         public readonly bool InProcNodeDisabled = Environment.GetEnvironmentVariable("MSBUILDNOINPROCNODE") == "1";
 
+        public static void UpdateFromEnvironment()
+        {
+            // Re-create Traits instance to update values in Traits according to current environment.
+            if (ChangeWaves.AreFeaturesEnabled(ChangeWaves.Wave17_10))
+            {
+                _instance = new Traits();
+            }
+        }
+
         private static int ParseIntFromEnvironmentVariableOrDefault(string environmentVariable, int defaultValue)
         {
             return int.TryParse(Environment.GetEnvironmentVariable(environmentVariable), out int result)

src/Shared/CommunicationsUtilities.cs

@@ -377,7 +377,7 @@ internal static void SetEnvironment(IDictionary<string, string> newEnvironment)
         {
             if (newEnvironment != null)
             {
-                // First, empty out any new variables
+                // First, empty out any old variables
                 foreach (KeyValuePair<string, string> entry in CommunicationsUtilities.GetEnvironmentVariables())
                 {
                     if (!newEnvironment.ContainsKey(entry.Key))
@@ -386,7 +386,7 @@ internal static void SetEnvironment(IDictionary<string, string> newEnvironment)
                     }
                 }
 
-                // Then, make sure the old ones have their old values.
+                // Then, make sure the new ones have their new values.
                 foreach (KeyValuePair<string, string> entry in newEnvironment)
                 {
                     Environment.SetEnvironmentVariable(entry.Key, entry.Value);