Use pattern matching

src/Analyzers/CSharp/Analyzers/UseCollectionExpression/CSharpUseCollectionExpressionForBuilderDiagnosticAnalyzer.cs

@@ -126,8 +126,7 @@ void FadeOutCode(SyntaxNodeAnalysisContext context, AnalysisResult analysisResul
         if (createSymbol is not IMethodSymbol { IsStatic: true } createMethod)
             return null;
 
-        var factoryType = semanticModel.GetSymbolInfo(memberAccessExpression.Expression, cancellationToken).Symbol as INamedTypeSymbol;
-        if (factoryType is null)
+        if (semanticModel.GetSymbolInfo(memberAccessExpression.Expression, cancellationToken).Symbol is not INamedTypeSymbol factoryType)
             return null;
 
         // has to be the form:

src/Analyzers/CSharp/CodeFixes/Iterator/CSharpChangeToIEnumerableCodeFixProvider.cs

@@ -86,14 +86,12 @@ internal sealed class CSharpChangeToIEnumerableCodeFixProvider() : AbstractItera
             newDocument = document.WithSyntaxRoot(root.ReplaceNode(node, newOperator));
         }
 
-        var oldAccessor = node.Parent?.Parent as PropertyDeclarationSyntax;
-        if (oldAccessor != null)
+        if (node.Parent?.Parent is PropertyDeclarationSyntax oldAccessor)
         {
             newDocument = document.WithSyntaxRoot(root.ReplaceNode(oldAccessor, oldAccessor.WithType(newReturnType)));
         }
 
-        var oldIndexer = node.Parent?.Parent as IndexerDeclarationSyntax;
-        if (oldIndexer != null)
+        if (node.Parent?.Parent is IndexerDeclarationSyntax oldIndexer)
         {
             newDocument = document.WithSyntaxRoot(root.ReplaceNode(oldIndexer, oldIndexer.WithType(newReturnType)));
         }

src/Analyzers/CSharp/CodeFixes/RemoveUnnecessaryLambdaExpression/CSharpRemoveUnnecessaryLambdaExpressionCodeFixProvider.cs

@@ -43,8 +43,7 @@ protected override Task FixAllAsync(
     {
         foreach (var diagnostic in diagnostics)
         {
-            var anonymousFunction = diagnostic.AdditionalLocations[0].FindNode(getInnermostNodeForTie: true, cancellationToken) as AnonymousFunctionExpressionSyntax;
-            if (anonymousFunction is null)
+            if (diagnostic.AdditionalLocations[0].FindNode(getInnermostNodeForTie: true, cancellationToken) is not AnonymousFunctionExpressionSyntax anonymousFunction)
                 continue;
 
             editor.ReplaceNode(anonymousFunction,

src/Analyzers/Core/Analyzers/UseCollectionInitializer/UpdateExpressionState.cs

@@ -233,8 +233,7 @@ private bool TryAnalyzeMultiAddInvocation(
         // values)`  If the former, we only allow a single argument.  If the latter, we can allow multiple
         // expressions.  The former will be converted to a spread element.  The latter will be added
         // individually.
-        var method = this.SemanticModel.GetSymbolInfo(memberAccess, cancellationToken).GetAnySymbol() as IMethodSymbol;
-        if (method is null)
+        if (this.SemanticModel.GetSymbolInfo(memberAccess, cancellationToken).GetAnySymbol() is not IMethodSymbol method)
             return false;
 
         if (method.Parameters.Length != 1)

src/Analyzers/Core/CodeFixes/PopulateSwitch/AbstractPopulateSwitchCodeFixProvider.cs

@@ -141,8 +141,7 @@ private async Task FixOneDiagnosticAsync(
         var hasMissingDefaultCase = bool.Parse(diagnostic.Properties[PopulateSwitchStatementHelpers.MissingDefaultCase]!);
 
         var switchLocation = diagnostic.AdditionalLocations[0];
-        var switchNode = switchLocation.FindNode(getInnermostNodeForTie: true, cancellationToken) as TSwitchSyntax;
-        if (switchNode == null)
+        if (switchLocation.FindNode(getInnermostNodeForTie: true, cancellationToken) is not TSwitchSyntax switchNode)
             return;
 
         var model = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);

src/EditorFeatures/CSharp/EventHookup/EventHookupSessionManager_EventHookupSession.cs

@@ -247,12 +247,11 @@
             // If we didn't find an object name above, then the object name is the name of this class.
             // Note: For generic, it's ok(it's even a good idea) to exclude type variables,
             // because the name is only used as a prefix for the method name.
 
-            var typeDeclaration = syntaxFactsService.GetContainingTypeDeclaration(
-                semanticModel.SyntaxTree.GetRoot(),
-                plusEqualsToken.SpanStart) as BaseTypeDeclarationSyntax;
 
-            return typeDeclaration != null
+            return syntaxFactsService.GetContainingTypeDeclaration(
+                semanticModel.SyntaxTree.GetRoot(),
+                plusEqualsToken.SpanStart) is BaseTypeDeclarationSyntax typeDeclaration
                 ? typeDeclaration.Identifier.Text
                 : eventSymbol.ContainingType.Name;
         }

src/Features/CSharp/Portable/SignatureHelp/PrimaryConstructorBaseTypeSignatureHelpProvider.cs

@@ -74,8 +74,7 @@ private bool IsTriggerToken(SyntaxToken token)
             return null;
 
         var baseList = baseTypeSyntax.Parent as BaseListSyntax;
-        var namedTypeSyntax = baseList?.Parent as BaseTypeDeclarationSyntax;
-        if (namedTypeSyntax is null)
+        if (baseList?.Parent is not BaseTypeDeclarationSyntax namedTypeSyntax)
             return null;
 
         var semanticModel = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);

src/Features/Core/Portable/Completion/Providers/ImportCompletionProvider/ImportCompletionItem.cs

@@ -179,9 +179,7 @@ private static (ISymbol? symbol, int overloadCount) GetSymbolAndOverloadCount(Co
         // If we have SymbolKey data (i.e. this is an extension method item), use it to recover symbol
         if (item.TryGetProperty(MethodKey, out var methodSymbolKey))
         {
-            var methodSymbol = SymbolKey.ResolveString(methodSymbolKey, compilation).GetAnySymbol() as IMethodSymbol;
-
-            if (methodSymbol != null)
+            if (SymbolKey.ResolveString(methodSymbolKey, compilation).GetAnySymbol() is IMethodSymbol methodSymbol)
             {
                 var overloadCount = item.TryGetProperty(OverloadCountKey, out var overloadCountString) && int.TryParse(overloadCountString, out var count) ? count : 0;
 

src/Features/Core/Portable/Completion/Providers/Scripting/AbstractReferenceDirectiveCompletionProvider.cs

@@ -48,8 +48,7 @@ private static ImmutableArray<char> GetCommitCharacters()
 
     protected override async Task ProvideCompletionsAsync(CompletionContext context, string pathThroughLastSlash)
     {
-        var resolver = context.Document.Project.CompilationOptions.MetadataReferenceResolver as RuntimeMetadataReferenceResolver;
-        if (resolver != null && pathThroughLastSlash.IndexOfAny(s_pathIndicators) < 0)
+        if (context.Document.Project.CompilationOptions.MetadataReferenceResolver is RuntimeMetadataReferenceResolver resolver && pathThroughLastSlash.IndexOfAny(s_pathIndicators) < 0)
         {
             foreach (var (name, path) in resolver.TrustedPlatformAssemblies)
             {

src/Features/Core/Portable/GenerateComparisonOperators/GenerateComparisonOperatorsCodeRefactoringProvider.cs

@@ -62,8 +62,7 @@ public override async Task ComputeRefactoringsAsync(CodeRefactoringContext conte
         if (comparableType == null)
             return;
 
-        var containingType = semanticModel.GetDeclaredSymbol(typeDeclaration, cancellationToken) as INamedTypeSymbol;
-        if (containingType == null)
+        if (semanticModel.GetDeclaredSymbol(typeDeclaration, cancellationToken) is not INamedTypeSymbol containingType)
             return;
 
         using var _1 = ArrayBuilder<INamedTypeSymbol>.GetInstance(out var missingComparableTypes);

src/Features/Core/Portable/InlineMethod/AbstractInlineMethodRefactoringProvider.cs

@@ -91,8 +91,7 @@ public override async Task ComputeRefactoringsAsync(CodeRefactoringContext conte
         }
 
         var semanticModel = await document.GetRequiredSemanticModelAsync(cancellationToken).ConfigureAwait(false);
-        var calleeMethodSymbol = semanticModel.GetSymbolInfo(calleeInvocationNode, cancellationToken).GetAnySymbol() as IMethodSymbol;
-        if (calleeMethodSymbol == null)
+        if (semanticModel.GetSymbolInfo(calleeInvocationNode, cancellationToken).GetAnySymbol() is not IMethodSymbol calleeMethodSymbol)
         {
             return;
         }
@@ -125,8 +124,7 @@ public override async Task ComputeRefactoringsAsync(CodeRefactoringContext conte
         }
 
         var calleeMethodDeclarationSyntaxReference = calleeMethodDeclarationSyntaxReferences[0];
-        var calleeMethodNode = await calleeMethodDeclarationSyntaxReference.GetSyntaxAsync(cancellationToken).ConfigureAwait(false) as TMethodDeclarationSyntax;
-        if (calleeMethodNode == null)
+        if (await calleeMethodDeclarationSyntaxReference.GetSyntaxAsync(cancellationToken).ConfigureAwait(false) is not TMethodDeclarationSyntax calleeMethodNode)
         {
             return;
         }
@@ -222,8 +220,7 @@ public override async Task ComputeRefactoringsAsync(CodeRefactoringContext conte
         }
 
         var callerDeclarationNode = await callerReferences[0].GetSyntaxAsync(cancellationToken).ConfigureAwait(false);
-        var invocationOperation = semanticModel.GetOperation(calleeInvocationNode, cancellationToken) as IInvocationOperation;
-        if (invocationOperation == null)
+        if (semanticModel.GetOperation(calleeInvocationNode, cancellationToken) is not IInvocationOperation invocationOperation)
         {
             return;
         }

src/Features/Core/Portable/UseNamedArguments/AbstractUseNamedArgumentsCodeRefactoringProvider.cs

@@ -31,8 +31,7 @@ public async Task ComputeRefactoringsAsync(
 
             // We allow empty nodes here to find VB implicit arguments.
             var potentialArguments = await document.GetRelevantNodesAsync<TBaseArgumentSyntax>(textSpan, allowEmptyNodes: true, cancellationToken).ConfigureAwait(false);
-            var argument = potentialArguments.FirstOrDefault(n => n.Parent is TArgumentListSyntax) as TSimpleArgumentSyntax;
-            if (argument == null)
+            if (potentialArguments.FirstOrDefault(n => n.Parent is TArgumentListSyntax) is not TSimpleArgumentSyntax argument)
             {
                 return;
             }

src/VisualStudio/Core/Def/Workspace/VisualStudioSymbolNavigationService.cs

@@ -276,8 +276,7 @@ public async Task<bool> TrySymbolNavigationNotifyAsync(ISymbol symbol, Project p
         if (!TryGetVsHierarchyAndItemId(documentToUse, out var hierarchy, out var itemID))
             return null;
 
-        var navigationNotify = hierarchy as IVsSymbolicNavigationNotify;
-        if (navigationNotify == null)
+        if (hierarchy is not IVsSymbolicNavigationNotify navigationNotify)
             return null;
 
         return (hierarchy, itemID, navigationNotify);

src/VisualStudio/Core/Impl/SolutionExplorer/AnalyzersCommandHandler.cs

@@ -265,8 +265,7 @@ private void UpdateSeverityMenuItemsChecked()
         _setSeverityHiddenMenuItem.Checked = false;
         _setSeverityNoneMenuItem.Checked = false;
 
-        var workspace = TryGetWorkspace() as VisualStudioWorkspace;
-        if (workspace == null)
+        if (TryGetWorkspace() is not VisualStudioWorkspace workspace)
         {
             return;
         }
@@ -369,9 +368,8 @@ internal void OpenRuleSetHandler(object sender, EventArgs args)
         if (_tracker.SelectedFolder != null &&
             _serviceProvider != null)
         {
-            var workspace = _tracker.SelectedFolder.Workspace as VisualStudioWorkspace;
             var projectId = _tracker.SelectedFolder.ProjectId;
-            if (workspace != null)
+            if (_tracker.SelectedFolder.Workspace is VisualStudioWorkspace workspace)
             {
                 var ruleSetFile = workspace.TryGetRuleSetPathForProject(projectId);
 

src/VisualStudio/Core/Impl/SolutionExplorer/ContextMenuController.cs

@@ -35,10 +35,9 @@ public bool ShowContextMenu(IEnumerable<object> items, Point location)
 
         _updateMenu();
 
-        var shell = Shell.Package.GetGlobalService(typeof(SVsUIShell)) as IVsUIShell;
         var guidContextMenu = Guids.RoslynGroupId;
         var locationPoints = new[] { new POINTS() { x = (short)location.X, y = (short)location.Y } };
-        return shell != null && ErrorHandler.Succeeded(shell.ShowContextMenu(
+        return Shell.Package.GetGlobalService(typeof(SVsUIShell)) is IVsUIShell shell && ErrorHandler.Succeeded(shell.ShowContextMenu(
             0,
             ref guidContextMenu,
             _menuId,

src/VisualStudio/IntegrationTest/New.IntegrationTests/QuickInfoToStringConverter.cs

@@ -90,8 +90,7 @@ private static void BuildStringFromInlineCollection(InlineCollection inlines, St
         if (currentInline is LineBreak)
             return Environment.NewLine;
 
-        var run = currentInline as Run;
-        if (run == null)
+        if (currentInline is not Run run)
             return null;
 
         return run.Text;

src/VisualStudio/VisualStudioDiagnosticsToolWindow/OptionPages/InternalOptionsControl.cs

@@ -45,8 +45,7 @@ public InternalOptionsControl(IEnumerable<IOption2> options, OptionStore optionS
         {
             foreach (var item in optionsPanel.Children.OfType<CheckBox>())
             {
-                var title = item.Content as string;
-                if (title == null)
+                if (item.Content is not string title)
                 {
                     continue;
                 }

src/Workspaces/Core/Portable/Log/AggregateLogger.cs

@@ -51,8 +51,7 @@ public static ILogger AddOrReplace(ILogger newLogger, ILogger oldLogger, Func<IL
             return newLogger;
         }
 
-        var aggregateLogger = oldLogger as AggregateLogger;
-        if (aggregateLogger == null)
+        if (oldLogger is not AggregateLogger aggregateLogger)
         {
             // replace old logger with new logger
             if (predicate(oldLogger))
@@ -86,8 +85,7 @@ public static ILogger AddOrReplace(ILogger newLogger, ILogger oldLogger, Func<IL
 
     public static ILogger Remove(ILogger logger, Func<ILogger, bool> predicate)
     {
-        var aggregateLogger = logger as AggregateLogger;
-        if (aggregateLogger == null)
+        if (logger is not AggregateLogger aggregateLogger)
         {
             // remove the logger
             if (predicate(logger))

src/Workspaces/Core/Portable/Shared/Extensions/ISymbolExtensions.cs

@@ -309,8 +309,7 @@ private static XNode[] RewriteInheritdocElements(ISymbol symbol, HashSet<ISymbol
             }
         }
 
-        var container = node as XContainer;
-        if (container == null)
+        if (node is not XContainer container)
         {
             return [Copy(node, copyAttributeAnnotations: false)];
         }

src/Workspaces/Core/Portable/Utilities/Documentation/XmlDocumentationProvider.cs

@@ -112,8 +112,7 @@ protected override Stream GetSourceStream(CancellationToken cancellationToken)
 
         public override bool Equals(object obj)
         {
-            var other = obj as ContentBasedXmlDocumentationProvider;
-            return other != null && EqualsHelper(other);
+            return obj is ContentBasedXmlDocumentationProvider other && EqualsHelper(other);
         }
 
         private bool EqualsHelper(ContentBasedXmlDocumentationProvider other)
@@ -162,8 +161,7 @@ protected override Stream GetSourceStream(CancellationToken cancellationToken)
 
         public override bool Equals(object obj)
         {
-            var other = obj as FileBasedXmlDocumentationProvider;
-            return other != null && _filePath == other._filePath;
+            return obj is FileBasedXmlDocumentationProvider other && _filePath == other._filePath;
         }
 
         public override int GetHashCode()

src/Workspaces/CoreTest/SolutionTests/SolutionTests.cs

@@ -2866,8 +2866,7 @@ private static async Task ValidateSolutionAndCompilationsAsync(Solution solution
                     {
                         compilation.References.Single(r =>
                         {
-                            var cr = r as CompilationReference;
-                            return cr != null && cr.Compilation == compilationReference.Compilation;
+                            return r is CompilationReference cr && cr.Compilation == compilationReference.Compilation;
                         });
                     }
                 }

src/Workspaces/Remote/ServiceHub/Services/EncapsulateField/RemoteEncapsulateFieldService.cs

@@ -38,8 +38,7 @@ protected override IRemoteEncapsulateFieldService CreateService(in ServiceConstr
 
             foreach (var key in fieldSymbolKeys)
             {
-                var resolved = SymbolKey.ResolveString(key, compilation, cancellationToken: cancellationToken).GetAnySymbol() as IFieldSymbol;
-                if (resolved == null)
+                if (SymbolKey.ResolveString(key, compilation, cancellationToken: cancellationToken).GetAnySymbol() is not IFieldSymbol resolved)
                     return [];
 
                 fields.Add(resolved);

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Extensions/ISymbolExtensions_Accessibility.cs

@@ -409,8 +409,7 @@ private static bool IsPrivateSymbolAccessible(
     {
         Debug.Assert(within is INamedTypeSymbol or IAssemblySymbol);
 
-        var withinType = within as INamedTypeSymbol;
-        if (withinType == null)
+        if (within is not INamedTypeSymbol withinType)
         {
             // If we're not within a type, we can't access a private symbol
             return false;

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/Extensions/ITypeSymbolExtensions.cs

@@ -578,10 +578,9 @@ private static IEnumerable<T> SelectAccessibleMembers<T>(this IEnumerable<ITypeS
         // SPEC: argument is more specific and no type argument is less specific than the
         // SPEC: corresponding type argument in the other.
 
-        var n1 = t1 as INamedTypeSymbol;
         var n2 = t2 as INamedTypeSymbol;
 
-        if (n1 == null)
+        if (t1 is not INamedTypeSymbol n1)
         {
             return null;
         }