Adding a private indicator for the activation of the terminal logger (#…

…10423)

Adding a private indicator for the activation of the terminal logger

src/MSBuild/XMake.cs

@@ -2516,6 +2516,11 @@ private static bool ProcessCommandLineSwitches(
 #endif
 
             bool useTerminalLogger = ProcessTerminalLoggerConfiguration(commandLineSwitches, out string aggregatedTerminalLoggerParameters);
+
+            // This is temporary until we can remove the need for the environment variable.
+            // DO NOT use this environment variable for any new features as it will be removed without further notice.
+            Environment.SetEnvironmentVariable("_MSBUILDTLENABLED", useTerminalLogger ? "1" : "0");
+
             DisplayVersionMessageIfNeeded(recursing, useTerminalLogger, commandLineSwitches);
 
             // Idle priority would prevent the build from proceeding as the user does normal actions.

src/UnitTests.Shared/TestEnvironment.cs

@@ -442,6 +442,11 @@ void AssertDictionaryInclusion(IDictionary superset, IDictionary subset, string
             {
                 foreach (var key in subset.Keys)
                 {
+                    if (key is "_MSBUILDTLENABLED")
+                    {
+                        continue;
+                    }
+
                     // workaround for https://github.com/dotnet/msbuild/pull/3866
                     // if the initial environment had empty keys, then MSBuild will accidentally remove them via Environment.SetEnvironmentVariable
                     if (operation != "removed" || !string.IsNullOrEmpty((string)subset[key]))