Fix hang in Solution Explorer search through transitive package items…

… of dependencies tree (#5917)

* Revert "Reduce number of Dataflow updates through dependency tree code (#5508)"

This reverts commit d85c6ea.

Turns out that the search provider uses `GetLatestVersionAsync` on this
data source, meaning it must propagate a value for every input version.
I will fix the original issue in a different way, by updating the
consumer to ignore version-only changes instead.

* Avoid tree updates when the value is unchanged

This replaces the approach taken in #5508 in a way that doesn't interfere with Solution Explorer search.

src/NuGet.Clients/NuGet.VisualStudio.Implementation/SolutionExplorer/AssetsFileDependenciesDataSource.cs

@@ -4,7 +4,6 @@
 #nullable enable
 
 using System;
-using System.Collections.Generic;
 using System.ComponentModel.Composition;
 using System.IO;
 using System.Threading.Tasks.Dataflow;
@@ -39,7 +38,7 @@ protected override IDisposable LinkExternalInput(ITargetBlock<IProjectVersionedV
 
             string? lastAssetsFilePath = null;
             DateTime lastTimestampUtc = DateTime.MinValue;
-            AssetsFileDependenciesSnapshot? lastSnapshot = null;
+            AssetsFileDependenciesSnapshot lastSnapshot = AssetsFileDependenciesSnapshot.Empty;
 
             var intermediateBlock =
                 new BufferBlock<IProjectVersionedValue<IProjectSubscriptionUpdate>>(
@@ -49,7 +48,7 @@ IReceivableSourceBlock<IProjectVersionedValue<IProjectSubscriptionUpdate>> proje
                 = _activeConfiguredProjectSubscriptionService.ProjectRuleSource.SourceBlock;
 
             IPropagatorBlock<IProjectVersionedValue<ValueTuple<IProjectSnapshot, IProjectSubscriptionUpdate>>, IProjectVersionedValue<AssetsFileDependenciesSnapshot>> transformBlock
-                = DataflowBlockSlim.CreateTransformManyBlock<IProjectVersionedValue<ValueTuple<IProjectSnapshot, IProjectSubscriptionUpdate>>, IProjectVersionedValue<AssetsFileDependenciesSnapshot>>(Transform, skipIntermediateInputData: true, skipIntermediateOutputData: true);
+                = DataflowBlockSlim.CreateTransformBlock<IProjectVersionedValue<ValueTuple<IProjectSnapshot, IProjectSubscriptionUpdate>>, IProjectVersionedValue<AssetsFileDependenciesSnapshot>>(Transform, skipIntermediateInputData: true, skipIntermediateOutputData: true);
 
             return new DisposableBag
             {
@@ -76,15 +75,15 @@ IPropagatorBlock<IProjectVersionedValue<ValueTuple<IProjectSnapshot, IProjectSub
                 PropagateCompletion = true  // Make sure source block completion and faults flow onto the target block to avoid hangs.
             };
 
-            IEnumerable<IProjectVersionedValue<AssetsFileDependenciesSnapshot>> Transform(IProjectVersionedValue<ValueTuple<IProjectSnapshot, IProjectSubscriptionUpdate>> update)
+            IProjectVersionedValue<AssetsFileDependenciesSnapshot> Transform(IProjectVersionedValue<ValueTuple<IProjectSnapshot, IProjectSubscriptionUpdate>> update)
             {
                 var projectSnapshot = (IProjectSnapshot2)update.Value.Item1;
                 IProjectSubscriptionUpdate subscriptionUpdate = update.Value.Item2;
 
                 string? path = null;
                 DateTime timestampUtc = DateTime.MinValue;
 
-                AssetsFileDependenciesSnapshot? snapshot = lastSnapshot;
+                AssetsFileDependenciesSnapshot snapshot = lastSnapshot;
 
                 if (subscriptionUpdate.CurrentState.TryGetValue(ConfigurationGeneralRule.SchemaName, out IProjectRuleSnapshot ruleSnapshot))
                 {
@@ -116,21 +115,13 @@ IEnumerable<IProjectVersionedValue<AssetsFileDependenciesSnapshot>> Transform(IP
                                 lastAssetsFilePath = path;
                                 lastTimestampUtc = timestampUtc;
 
-                                snapshot ??= AssetsFileDependenciesSnapshot.Empty;
-
-                                lastSnapshot = snapshot = snapshot.UpdateFromAssetsFile(path);
-
-                                yield return new ProjectVersionedValue<AssetsFileDependenciesSnapshot>(snapshot, update.DataSourceVersions);
+                                lastSnapshot = snapshot = lastSnapshot.UpdateFromAssetsFile(path);
                             }
                         }
                     }
                 }
 
-                if (lastSnapshot is null)
-                {
-                    lastSnapshot = AssetsFileDependenciesSnapshot.Empty;
-                    yield return new ProjectVersionedValue<AssetsFileDependenciesSnapshot>(lastSnapshot, update.DataSourceVersions);
-                }
+                return new ProjectVersionedValue<AssetsFileDependenciesSnapshot>(snapshot, update.DataSourceVersions);
             }
         }
     }

src/NuGet.Clients/NuGet.VisualStudio.Implementation/SolutionExplorer/AssetsFileTopLevelDependenciesCollectionSourceProvider.cs

@@ -92,11 +92,21 @@ protected override bool TryCreateCollectionSource(
 
             var collectionSource = new AggregateRelationCollectionSource(hierarchyItem);
             AggregateContainsRelationCollection? collection = null;
+            AssetsFileDependenciesSnapshot? lastSnapshot = null;
 
             var actionBlock = new ActionBlock<IProjectVersionedValue<AssetsFileDependenciesSnapshot>>(
                 async versionedValue =>
                 {
                     AssetsFileDependenciesSnapshot snapshot = versionedValue.Value;
+
+                    if (ReferenceEquals(snapshot, lastSnapshot))
+                    {
+                        // Skip version-only updates.
+                        return;
+                    }
+
+                    lastSnapshot = snapshot;
+
                     if (snapshot.TryGetTarget(target, out AssetsFileTarget? targetData))
                     {
                         if (TryGetLibrary(targetData, libraryName, out AssetsFileTargetLibrary? library))