Merge pull request #18263 from dotnet/revert-18081-revert-17916-rokon…

…ec/msbuild-server-v1

Re-Revert "MSBuild server V1"

src/Cli/Microsoft.DotNet.Cli.Utils/MSBuildForwardingAppWithoutLogging.cs

@@ -16,6 +16,7 @@ namespace Microsoft.DotNet.Cli.Utils
     internal class MSBuildForwardingAppWithoutLogging
     {
         private static readonly bool AlwaysExecuteMSBuildOutOfProc = Env.GetEnvironmentVariableAsBool("DOTNET_CLI_RUN_MSBUILD_OUTOFPROC");
+        private static readonly bool DoNotUseMSBUILDNOINPROCNODE = Env.GetEnvironmentVariableAsBool("DOTNET_CLI_DO_NOT_USE_MSBUILDNOINPROCNODE");
 
         private const string MSBuildExeName = "MSBuild.dll";
 
@@ -53,6 +54,13 @@ public MSBuildForwardingAppWithoutLogging(IEnumerable<string> argsToForward, str
             _argsToForward = argsToForward;
             MSBuildPath = msbuildPath ?? defaultMSBuildPath;
 
+            if (!DoNotUseMSBUILDNOINPROCNODE)
+            {
+                // Force MSBuild to use external working node long living process for building projects
+                // We also refers to this as MSBuild Server V1 as entry process forwards most of the work to it.
+                EnvironmentVariable("MSBUILDNOINPROCNODE", "1");
+            }
+
             // If DOTNET_CLI_RUN_MSBUILD_OUTOFPROC is set or we're asked to execute a non-default binary, call MSBuild out-of-proc.
             if (AlwaysExecuteMSBuildOutOfProc || !string.Equals(MSBuildPath, defaultMSBuildPath, StringComparison.OrdinalIgnoreCase))
             {
@@ -92,6 +100,8 @@ public void EnvironmentVariable(string name, string value)
 
             if (value == string.Empty || value == "\0")
             {
+                // Do not allow MSBuild NOIPROCNODE as null env vars are not properly transferred to build nodes
+                _msbuildRequiredEnvironmentVariables["MSBUILDNOINPROCNODE"] = "0";
                 // Unlike ProcessStartInfo.EnvironmentVariables, Environment.SetEnvironmentVariable can't set a variable
                 // to an empty value, so we just fall back to calling MSBuild out-of-proc if we encounter this case.
                 // https://github.com/dotnet/runtime/issues/50554