Notify MSBuild TerminalLogger of project cache plugin starting

src/MSBuild/Resources/Strings.resx

@@ -1184,6 +1184,12 @@
   <data name="PossiblyOmittedMaxCPUSwitch" xml:space="preserve">
     <value>Building the projects in this solution one at a time. To enable parallel build, please add the "-m" switch.</value>
   </data>
+  <data name="ProjectCacheHitWithOutputs" xml:space="preserve">
+    <value>{0} -> Cache Hit</value>
+    <comment>
+      {StrBegin="{0} -> "}LOCALIZATION: This string is used to indicate progress and matches the format for a log message from Microsoft.Common.CurrentVersion.targets. {0} is a project name.
+    </comment>
+  </data>
   <data name="ProjectSchemaErrorHalt" xml:space="preserve">
     <value>MSBUILD : MSB1045: Stopping because of syntax errors in project file.</value>
     <comment>{StrBegin="MSBUILD : MSB1045: "}</comment>

src/MSBuild/TerminalLogger/Project.cs

@@ -51,6 +51,11 @@ public Project(string? targetFramework, StopwatchAbstraction? stopwatch)
     /// </summary>
     public bool IsTestProject { get; set; }
 
+    /// <summary>
+    /// True when the project has run target with name "_CachePluginRunStart" defined in <see cref="TerminalLogger._cachePluginStartTarget"/>.
+    /// </summary>
+    public bool IsCachePluginProject { get; set; }
+
     /// <summary>
     /// A lazily initialized list of build messages/warnings/errors raised during the build.
     /// </summary>

src/MSBuild/TerminalLogger/TerminalLogger.cs

@@ -35,6 +35,7 @@ namespace Microsoft.Build.Logging.TerminalLogger;
 internal sealed partial class TerminalLogger : INodeLogger
 {
     private const string FilePathPattern = " -> ";
+    private const string MSBuildSenderName = "MSBuild";
 
 #if NET7_0_OR_GREATER
     [StringSyntax(StringSyntaxAttribute.Regex)]
@@ -200,6 +201,16 @@ public ProjectContext(BuildEventContext context)
     /// </summary>
     private DateTime? _testEndTime;
 
+    /// <summary>
+    /// Name of target that identifies the project cache plugin run has just started.
+    /// </summary>
+    private static string _cachePluginStartTarget = "_CachePluginRunStart";
+
+    /// <summary>
+    /// Whether to show high-priority messages corresponding to the cache plugin.
+    /// </summary>
+    private bool _cachePluginStarted = false;
+
     /// <summary>
     /// Whether to show TaskCommandLineEventArgs high-priority messages. 
     /// </summary>
@@ -637,6 +648,19 @@ private void ProjectFinished(object sender, ProjectFinishedEventArgs e)
                         {
                             Terminal.WriteLine(string.Empty);
                         }
+
+                        if (!_cachePluginStarted && project.IsCachePluginProject)
+                        {
+                            // First non-traversal project results in cache miss
+                            _cachePluginStarted = true;
+                        }
+                    }
+                    else if (!_cachePluginStarted && project.IsCachePluginProject)
+                    {
+                        // First non-traversal project results in cache hit
+                        Terminal.WriteLine(ResourceUtilities.FormatResourceStringIgnoreCodeAndKeyword("ProjectCacheHitWithOutputs",
+                            projectFile));
+                        _cachePluginStarted = true;
                     }
 
                     // Print diagnostic output under the Project -> Output line.
@@ -673,12 +697,16 @@ private void TargetStarted(object sender, TargetStartedEventArgs e)
 
             string projectFile = Path.GetFileNameWithoutExtension(e.ProjectFile);
 
+            string targetName = e.TargetName;
+            if (targetName == "GetTargetPath" || targetName == _cachePluginStartTarget) // TODO: Change to _cachePluginStartTarget (from "GetTargetPath" for testing cache hit scenario)
+            {
+                project.IsCachePluginProject = true;
+            }
 
-            var isTestTarget = e.TargetName == _testStartTarget;
-
-            var targetName = isTestTarget ? "Testing" : e.TargetName;
-            if (isTestTarget)
+            if (targetName == _testStartTarget)
             {
+                targetName = "Testing";
+
                 // Use the minimal start time, so if we run tests in parallel, we can calculate duration
                 // as this start time, minus time when tests finished.
                 _testStartTime = _testStartTime == null
@@ -778,6 +806,15 @@ private void MessageRaised(object sender, BuildMessageEventArgs e)
                 }
             }
 
+            if (_cachePluginStarted)
+            {
+                if (e.SenderName is not null and MSBuildSenderName)
+                {
+                    RenderImmediateMessage(message);
+                    return;
+                }
+            }
+
             if (hasProject && project!.IsTestProject)
             {
                 var node = _nodes[NodeIndexForContext(buildEventContext)];
@@ -931,7 +968,7 @@ private void ErrorRaised(object sender, BuildErrorEventArgs e)
         }
     }
 
-    #endregion
+#endregion
 
     #region Refresher thread implementation