Simpler fix for FUTD check of copy items when building for debug

src/Microsoft.VisualStudio.ProjectSystem.Managed.VS/ProjectSystem/VS/UpToDate/UpToDateCheckBuildEventNotifier.cs

@@ -151,12 +151,13 @@ private static bool IsBuild(uint options, out bool isRebuild)
             return null;
         }
 
-        int IVsUpdateSolutionEvents.UpdateSolution_StartUpdate(ref int pfCancelUpdate)
+        int IVsUpdateSolutionEvents.UpdateSolution_Begin(ref int pfCancelUpdate)
         {
             _solutionBuildEventListener.NotifySolutionBuildStarting();
 
             return HResult.OK;
         }
+
         int IVsUpdateSolutionEvents.UpdateSolution_Done(int fSucceeded, int fModified, int fCancelCommand)
         {
             _solutionBuildEventListener.NotifySolutionBuildCompleted(cancelled: false);
@@ -174,7 +175,7 @@ int IVsUpdateSolutionEvents.UpdateSolution_Cancel()
         #region IVsUpdateSolutionEvents stubs
 
         int IVsUpdateSolutionEvents.OnActiveProjectCfgChange(IVsHierarchy pIVsHierarchy) => HResult.OK;
-        int IVsUpdateSolutionEvents.UpdateSolution_Begin(ref int pfCancelUpdate) => HResult.OK;
+        int IVsUpdateSolutionEvents.UpdateSolution_StartUpdate(ref int pfCancelUpdate) => HResult.OK;
 
         int IVsUpdateSolutionEvents2.OnActiveProjectCfgChange(IVsHierarchy pIVsHierarchy) => HResult.OK;
         int IVsUpdateSolutionEvents2.UpdateSolution_Begin(ref int pfCancelUpdate) => HResult.OK;

src/Microsoft.VisualStudio.ProjectSystem.Managed/ProjectSystem/UpToDate/BuildUpToDateCheck.TimestampCache.cs

@@ -6,7 +6,7 @@ namespace Microsoft.VisualStudio.ProjectSystem.UpToDate
 {
     internal sealed partial class BuildUpToDateCheck
     {
-        internal readonly struct TimestampCache
+        internal readonly struct TimestampCache : ITimestampCache
         {
             private readonly Dictionary<string, DateTime> _timestampCache = new(StringComparers.Paths);
             private readonly IFileSystem _fileSystem;
@@ -42,6 +42,12 @@ public TimestampCache(IFileSystem fileSystem)
 
                 return time;
             }
+
+            public void ClearTimestamps(IEnumerable<string> paths)
+            {
+                // This should never be called.
+                throw new NotImplementedException();
+            }
         }
     }
 }

src/Microsoft.VisualStudio.ProjectSystem.Managed/ProjectSystem/UpToDate/BuildUpToDateCheck.cs

@@ -722,12 +722,8 @@ private bool CheckBuiltFromInputFiles(Log log, in TimestampCache timestampCache,
             return true;
         }
 
-        private bool CheckCopyToOutputDirectoryItems(Log log, UpToDateCheckImplicitConfiguredInput state, IEnumerable<(string Path, ImmutableArray<CopyItem> CopyItems)> copyItemsByProject, ConfiguredFileSystemOperationAggregator fileSystemAggregator, bool? isBuildAccelerationEnabled, CancellationToken token)
+        private bool CheckCopyToOutputDirectoryItems(Log log, UpToDateCheckImplicitConfiguredInput state, IEnumerable<(string Path, ImmutableArray<CopyItem> CopyItems)> copyItemsByProject, ConfiguredFileSystemOperationAggregator fileSystemAggregator, ITimestampCache copyItemTimestampCache, bool? isBuildAccelerationEnabled, CancellationToken token)
         {
-            ITimestampCache? timestampCache = _solutionBuildContextProvider.CurrentSolutionBuildContext?.CopyItemTimestamps;
-
-            Assumes.NotNull(timestampCache);
-
             string outputFullPath = Path.Combine(state.MSBuildProjectDirectory, state.OutputRelativeOrFullPath);
 
             Log.Scope? scope1 = null;
@@ -771,7 +767,7 @@ private bool CheckCopyToOutputDirectoryItems(Log log, UpToDateCheckImplicitConfi
 
                     log.Verbose(nameof(Resources.FUTD_CheckingCopyToOutputDirectoryItem_1), copyType.ToString());
 
-                    DateTime? sourceTime = timestampCache.GetTimestampUtc(sourcePath);
+                    DateTime? sourceTime = copyItemTimestampCache.GetTimestampUtc(sourcePath);
 
                     if (sourceTime is null)
                     {
@@ -784,7 +780,7 @@ private bool CheckCopyToOutputDirectoryItems(Log log, UpToDateCheckImplicitConfi
 
                     log.Verbose(nameof(Resources.FUTD_SourceFileTimeAndPath_2), sourceTime, sourcePath);
 
-                    DateTime? destinationTime = timestampCache.GetTimestampUtc(destinationPath);
+                    DateTime? destinationTime = copyItemTimestampCache.GetTimestampUtc(destinationPath);
 
                     if (destinationTime is null)
                     {
@@ -958,26 +954,15 @@ private async Task<bool> IsUpToDateInternalAsync(
                 token.ThrowIfCancellationRequested();
 
                 // Short-lived cache of timestamp by path
-                var timestampCache = new TimestampCache(_fileSystem);
+                TimestampCache timestampCache = new(_fileSystem);
 
-                // Ensure we have a context object for the current solution build.
-                //
-                // Ordinarily, this is created when the SBM calls ISolutionBuildEventListener.NotifySolutionBuildStarting,
-                // and cleared again later when the SBM calls ISolutionBuildEventListener.NotifySolutionBuildCompleted.
-                //
-                // However there are two cases where it may be null here:
-                //
-                // 1. When performing a validation run that continues after the solution build completed, or
-                // 2. When the build occurs in response to debugging (e.g. F5) in which case the SBM calls the
-                //    FUTDC *before* it invokes any solution build events.
-                //
-                // In either case, we construct an event here lazily so that we can correctly test for the
-                // existence of copy items in CheckCopyToOutputDirectoryItems.
-                if (_solutionBuildContextProvider.CurrentSolutionBuildContext is null)
-                {
-                    _solutionBuildEventListener.NotifySolutionBuildStarting();
-                    Assumes.NotNull(_solutionBuildContextProvider.CurrentSolutionBuildContext);
-                }
+                // For copy items, we share a timestamp cache across the solution build.
+                // It's constructed when the SBM calls IVsUpdateSolutionEvents.UpdateSolution_Begin,
+                // and cleared when the SBM calls IVsUpdateSolutionEvents.UpdateSolution_Done.
+                // If the FUTDC is called outside those events, the CurrentSolutionBuildContext will
+                // be null, so we share the same short-lived cache. This can happen when performing
+                // validation runs, which can occur after the solution build has completed.
+                ITimestampCache copyItemTimestampCache = _solutionBuildContextProvider.CurrentSolutionBuildContext?.CopyItemTimestamps ?? timestampCache;
 
                 globalProperties.TryGetValue(FastUpToDateCheckIgnoresKindsGlobalPropertyName, out string? ignoreKindsString);
 
@@ -1083,7 +1068,7 @@ private async Task<bool> IsUpToDateInternalAsync(
                             !CheckInputsAndOutputs(logger, lastSuccessfulBuildStartTimeUtc, timestampCache, implicitState, ignoreKinds, token) ||
                             !CheckBuiltFromInputFiles(logger, timestampCache, implicitState, token) ||
                             !CheckMarkers(logger, timestampCache, implicitState, isBuildAccelerationEnabled, fileSystemOperations) ||
-                            !CheckCopyToOutputDirectoryItems(logger, implicitState, copyInfo.ItemsByProject, configuredFileSystemOperations, isBuildAccelerationEnabled, token))
+                            !CheckCopyToOutputDirectoryItems(logger, implicitState, copyInfo.ItemsByProject, configuredFileSystemOperations, copyItemTimestampCache, isBuildAccelerationEnabled, token))
                         {
                             return (false, checkedConfigurations);
                         }

src/Microsoft.VisualStudio.ProjectSystem.Managed/ProjectSystem/UpToDate/SolutionBuildContext.cs

@@ -10,7 +10,6 @@ namespace Microsoft.VisualStudio.ProjectSystem.UpToDate;
 /// </summary>
 internal sealed class SolutionBuildContext
 {
-
     /// <summary>
     /// A cache of timestamps for the absolute paths of both source and target of copy items
     /// across all projects.