Remove hashset for fallback projects

Realised that this was unnecessary with recent changes

Author: davidwengier

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/DefaultRazorDynamicFileInfoProvider.cs

@@ -270,7 +270,13 @@ public Task RemoveDynamicFileInfoAsync(ProjectId projectId, string? projectFileP
             throw new ArgumentNullException(nameof(filePath));
         }
 
-        _fallbackProjectManager.DynamicFileRemoved(projectId, projectFilePath, filePath);
+        var projectKey = TryFindProjectKeyForProjectId(projectId);
+        if (projectKey is not { } razorProjectKey)
+        {
+            return Task.CompletedTask;
+        }
+
+        _fallbackProjectManager.DynamicFileRemoved(projectId, razorProjectKey, projectFilePath, filePath);
 
         // ---------------------------------------------------------- NOTE & CAUTION --------------------------------------------------------------
         //

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/ProjectSystem/FallbackProjectManager.cs

@@ -2,7 +2,6 @@
 // Licensed under the MIT license. See License.txt in the project root for license information.
 
 using System;
-using System.Collections.Immutable;
 using System.Composition;
 using System.IO;
 using Microsoft.AspNetCore.Razor.Telemetry;
@@ -30,23 +29,16 @@ internal sealed class FallbackProjectManager(
     private readonly ProjectSnapshotManagerAccessor _projectSnapshotManagerAccessor = projectSnapshotManagerAccessor;
     private readonly ITelemetryReporter _telemetryReporter = telemetryReporter;
 
-    private ImmutableHashSet<ProjectId> _fallbackProjectIds = ImmutableHashSet<ProjectId>.Empty;
-
     internal void DynamicFileAdded(ProjectId projectId, ProjectKey razorProjectKey, string projectFilePath, string filePath)
     {
         try
         {
             var project = _projectSnapshotManagerAccessor.Instance.GetLoadedProject(razorProjectKey);
-            if (_fallbackProjectIds.Contains(projectId))
+            if (project is ProjectSnapshot { HostProject: FallbackHostProject })
             {
-                // The project might have started as a fallback project, but it might have been upgraded by our getting CPS info
-                // about it. In that case, leave the CPS bits to do the work
-                if (project is ProjectSnapshot { HostProject: FallbackHostProject })
-                {
-                    // If this is a fallback project, then Roslyn may not track documents in the project, so these dynamic file notifications
-                    // are the only way to know about files in the project.
-                    AddFallbackDocument(razorProjectKey, filePath, projectFilePath);
-                }
+                // If this is a fallback project, then Roslyn may not track documents in the project, so these dynamic file notifications
+                // are the only way to know about files in the project.
+                AddFallbackDocument(razorProjectKey, filePath, projectFilePath);
             }
             else if (project is null)
             {
@@ -62,11 +54,12 @@ internal void DynamicFileAdded(ProjectId projectId, ProjectKey razorProjectKey,
         }
     }
 
-    internal void DynamicFileRemoved(ProjectId projectId, string projectFilePath, string filePath)
+    internal void DynamicFileRemoved(ProjectId projectId, ProjectKey razorProjectKey, string projectFilePath, string filePath)
     {
         try
         {
-            if (_fallbackProjectIds.Contains(projectId))
+            var project = _projectSnapshotManagerAccessor.Instance.GetLoadedProject(razorProjectKey);
+            if (project is ProjectSnapshot { HostProject: FallbackHostProject })
             {
                 // If this is a fallback project, then Roslyn may not track documents in the project, so these dynamic file notifications
                 // are the only way to know about files in the project.
@@ -93,11 +86,6 @@ private void AddFallbackProject(ProjectId projectId, string filePath)
             return;
         }
 
-        if (!ImmutableInterlocked.Update(ref _fallbackProjectIds, (set, id) => set.Add(id), project.Id))
-        {
-            return;
-        }
-
         var rootNamespace = project.DefaultNamespace;
 
         // We create this as a fallback project so that other parts of the system can reason about them - eg we don't do code
@@ -182,21 +170,4 @@ private void RemoveFallbackDocument(ProjectId projectId, string filePath, string
 
         return project;
     }
-
-    internal TestAccessor GetTestAccessor()
-    {
-        return new TestAccessor(this);
-    }
-
-    internal readonly struct TestAccessor
-    {
-        private readonly FallbackProjectManager _instance;
-
-        internal TestAccessor(FallbackProjectManager instance)
-        {
-            _instance = instance;
-        }
-
-        internal ImmutableHashSet<ProjectId> ProjectIds => _instance._fallbackProjectIds;
-    }
 }

src/Razor/test/Microsoft.CodeAnalysis.Razor.Workspaces.Test/ProjectSystem/FallbackProjectManagerTest.cs

@@ -48,7 +48,8 @@ public void DynamicFileAdded_KnownProject_DoesNothing()
 
         _fallbackProjectManger.DynamicFileAdded(projectId, hostProject.Key, SomeProject.FilePath, SomeProjectFile1.FilePath);
 
-        Assert.Empty(_fallbackProjectManger.GetTestAccessor().ProjectIds);
+        var project = Assert.Single(_projectSnapshotManager.GetProjects());
+        Assert.IsNotType<FallbackHostProject>(((ProjectSnapshot)project).HostProject);
     }
 
     [Fact]
@@ -63,9 +64,6 @@ public void DynamicFileAdded_UnknownProject_Adds()
 
         _fallbackProjectManger.DynamicFileAdded(projectId, SomeProject.Key, SomeProject.FilePath, SomeProjectFile1.FilePath);
 
-        var actualId = Assert.Single(_fallbackProjectManger.GetTestAccessor().ProjectIds);
-        Assert.Equal(projectId, actualId);
-
         var project = Assert.Single(_projectSnapshotManager.GetProjects());
         Assert.Equal("DisplayName", project.DisplayName);
         Assert.Equal("RootNamespace", project.RootNamespace);