Null annotate all the undo units we create for workspace change application

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.AbstractAddDocumentUndoUnit.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Text;
 using Microsoft.VisualStudio.OLE.Interop;

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.AbstractAddRemoveUndoUnit.cs

@@ -2,9 +2,10 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System;
 using Microsoft.CodeAnalysis;
-using Microsoft.CodeAnalysis.AddImport;
 using Microsoft.VisualStudio.OLE.Interop;
 
 namespace Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.AbstractRemoveDocumentUndoUnit.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System.Collections.Generic;
 using System.Linq;
 using Microsoft.CodeAnalysis;
@@ -25,7 +27,7 @@ private abstract class AbstractRemoveDocumentUndoUnit : AbstractAddRemoveUndoUni
 
             protected abstract IReadOnlyList<DocumentId> GetDocumentIds(Project fromProject);
 
-            protected abstract TextDocument GetDocument(Solution currentSolution);
+            protected abstract TextDocument? GetDocument(Solution currentSolution);
 
             public override void Do(IOleUndoManager pUndoManager)
             {

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.AddAdditionalDocumentUndoUnit.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Text;
 

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.AddAnalyzerConfigDocumentUndoUnit.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Text;
 

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.AddDocumentUndoUnit.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Text;
 

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.AddMetadataReferenceUndoUnit.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System;
 using System.IO;
 using System.Linq;
@@ -29,22 +31,25 @@ public override void Do(IOleUndoManager pUndoManager)
             {
                 var currentSolution = Workspace.CurrentSolution;
                 var fromProject = currentSolution.GetProject(FromProjectId);
-                var reference = fromProject?.MetadataReferences.OfType<PortableExecutableReference>()
-                                            .FirstOrDefault(p => StringComparer.OrdinalIgnoreCase.Equals(p.FilePath, _filePath));
-
-                if (reference == null)
+                if (fromProject != null)
                 {
-                    try
-                    {
-                        reference = MetadataReference.CreateFromFile(_filePath);
-                    }
-                    catch (IOException)
+                    var reference = fromProject.MetadataReferences.OfType<PortableExecutableReference>()
+                                               .FirstOrDefault(p => StringComparer.OrdinalIgnoreCase.Equals(p.FilePath, _filePath));
+
+                    if (reference == null)
                     {
-                        return;
-                    }
+                        try
+                        {
+                            reference = MetadataReference.CreateFromFile(_filePath);
+                        }
+                        catch (IOException)
+                        {
+                            return;
+                        }
 
-                    var updatedProject = fromProject.AddMetadataReference(reference);
-                    Workspace.TryApplyChanges(updatedProject.Solution);
+                        var updatedProject = fromProject.AddMetadataReference(reference);
+                        Workspace.TryApplyChanges(updatedProject.Solution);
+                    }
                 }
             }
 

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.AddProjectReferenceUndoUnit.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System.Linq;
 using System.Threading;
 using Microsoft.CodeAnalysis;

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.RemoveAdditionalDocumentUndoUnit.cs

@@ -2,6 +2,9 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
+using System;
 using System.Collections.Generic;
 using Microsoft.CodeAnalysis;
 
@@ -21,7 +24,7 @@ private class RemoveAdditionalDocumentUndoUnit : AbstractRemoveDocumentUndoUnit
             protected override IReadOnlyList<DocumentId> GetDocumentIds(Project fromProject)
                 => fromProject.AdditionalDocumentIds;
 
-            protected override TextDocument GetDocument(Solution currentSolution)
+            protected override TextDocument? GetDocument(Solution currentSolution)
                 => currentSolution.GetAdditionalDocument(this.DocumentId);
         }
     }

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.RemoveAnalyzerConfigDocumentUndoUnit.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System.Collections.Generic;
 using Microsoft.CodeAnalysis;
 
@@ -21,7 +23,7 @@ private class RemoveAnalyzerConfigDocumentUndoUnit : AbstractRemoveDocumentUndoU
             protected override IReadOnlyList<DocumentId> GetDocumentIds(Project fromProject)
                 => fromProject.State.AnalyzerConfigDocumentIds.AsImmutable();
 
-            protected override TextDocument GetDocument(Solution currentSolution)
+            protected override TextDocument? GetDocument(Solution currentSolution)
                 => currentSolution.GetAnalyzerConfigDocument(this.DocumentId);
         }
     }

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.RemoveDocumentUndoUnit.cs

@@ -2,8 +2,11 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System.Collections.Generic;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Shared.Extensions;
 
 namespace Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem
 {
@@ -21,7 +24,7 @@ private class RemoveDocumentUndoUnit : AbstractRemoveDocumentUndoUnit
             protected override IReadOnlyList<DocumentId> GetDocumentIds(Project fromProject)
                 => fromProject.DocumentIds;
 
-            protected override TextDocument GetDocument(Solution currentSolution)
+            protected override TextDocument? GetDocument(Solution currentSolution)
                 => currentSolution.GetDocument(this.DocumentId);
         }
     }

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.RemoveMetadataReferenceUndoUnit.cs

@@ -2,10 +2,13 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System;
 using System.IO;
 using System.Linq;
 using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.VisualStudio.OLE.Interop;
 
 namespace Microsoft.VisualStudio.LanguageServices.Implementation.ProjectSystem
@@ -29,13 +32,16 @@ public override void Do(IOleUndoManager pUndoManager)
             {
                 var currentSolution = Workspace.CurrentSolution;
                 var fromProject = currentSolution.GetProject(FromProjectId);
-                var reference = fromProject?.MetadataReferences.OfType<PortableExecutableReference>()
-                                            .FirstOrDefault(p => StringComparer.OrdinalIgnoreCase.Equals(p.FilePath, _filePath));
-
-                if (reference != null)
+                if (fromProject != null)
                 {
-                    var updatedProject = fromProject.RemoveMetadataReference(reference);
-                    Workspace.TryApplyChanges(updatedProject.Solution);
+                    var reference = fromProject.MetadataReferences.OfType<PortableExecutableReference>()
+                                               .FirstOrDefault(p => StringComparer.OrdinalIgnoreCase.Equals(p.FilePath!, _filePath));
+
+                    if (reference != null)
+                    {
+                        var updatedProject = fromProject.RemoveMetadataReference(reference);
+                        Workspace.TryApplyChanges(updatedProject.Solution);
+                    }
                 }
             }
 

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.RemoveProjectReferenceUndoUnit.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System.Linq;
 using Microsoft.CodeAnalysis;
 using Microsoft.VisualStudio.OLE.Interop;

src/VisualStudio/Core/Def/Implementation/ProjectSystem/VisualStudioWorkspaceImpl.RenameDocumentUndoUnit.cs

@@ -2,6 +2,8 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
+#nullable enable
+
 using System;
 using System.Linq;
 using Microsoft.VisualStudio.OLE.Interop;