Use pattern matching to check for null (dotnet#996)

.editorconfig

@@ -36,6 +36,7 @@ roslynator_infinite_loop_style = while
 roslynator_doc_comment_summary_style = multi_line
 roslynator_enum_flag_value_style = shift_operator
 roslynator_blank_line_after_file_scoped_namespace_declaration = true
+roslynator_null_check_style = pattern_matching
 
 csharp_style_namespace_declarations = file_scoped:suggestion
 
@@ -134,6 +135,7 @@ dotnet_diagnostic.RCS1189.severity = suggestion
 dotnet_diagnostic.RCS1207.severity = suggestion
 dotnet_diagnostic.RCS1237.severity = none
 dotnet_diagnostic.RCS1244.severity = suggestion
+dotnet_diagnostic.RCS1248.severity = suggestion
 dotnet_diagnostic.RCS1250.severity = suggestion
 dotnet_diagnostic.RCS1252.severity = suggestion
 dotnet_diagnostic.RCS1253.severity = suggestion

src/Analyzers.CodeFixes/CSharp/CodeFixes/AddOrRemoveParenthesesWhenCreatingNewObjectCodeFixProvider.cs

@@ -32,7 +32,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
         Document document = context.Document;
         Diagnostic diagnostic = context.Diagnostics[0];
 
-        if (objectCreationExpression.ArgumentList != null)
+        if (objectCreationExpression.ArgumentList is not null)
         {
             CodeAction codeAction = CodeAction.Create(
                 "Remove parentheses",

src/Analyzers.CodeFixes/CSharp/CodeFixes/AvoidNullReferenceExceptionCodeFixProvider.cs

@@ -66,7 +66,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
 
         bool IsPartOfLeftSideOfAssignment()
         {
-            for (SyntaxNode node = expression; node != null; node = node.Parent)
+            for (SyntaxNode node = expression; node is not null; node = node.Parent)
             {
                 var assignmentExpression = node.Parent as AssignmentExpressionSyntax;
 

src/Analyzers.CodeFixes/CSharp/CodeFixes/BinaryExpressionCodeFixProvider.cs

@@ -78,7 +78,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
                     {
                         ExpressionSyntax expression = binaryExpression.Left;
 
-                        if (expression == null
+                        if (expression is null
                             || !context.Span.Contains(expression.Span))
                         {
                             expression = binaryExpression.Right;
@@ -348,11 +348,11 @@ private static ConditionalAccessExpressionSyntax CreateConditionalAccess(Express
         }
 
         BinaryExpressionSyntax newBinaryExpression = BinaryExpression(
-            (binaryExpression != null)
+            (binaryExpression is not null)
                 ? right.Kind()
                 : SyntaxKind.EqualsExpression,
             nullCheck.Expression.WithLeadingTrivia(logicalAnd.GetLeadingTrivia()),
-            (binaryExpression != null)
+            (binaryExpression is not null)
                 ? ((BinaryExpressionSyntax)right).OperatorToken
                 : Token(SyntaxKind.EqualsEqualsToken).WithTriviaFrom(logicalAnd.OperatorToken),
             newRight)

src/Analyzers.CodeFixes/CSharp/CodeFixes/BlockCodeFixProvider.cs

@@ -154,7 +154,7 @@ static SyntaxTriviaList AddTriviaIfNecessary(SyntaxTriviaList trivia, SyntaxTriv
         {
             ExpressionSyntax right = SimpleAssignmentExpression(expression, assignment.Right.WithoutTrivia()).Parenthesize();
 
-            if (valueName != null)
+            if (valueName is not null)
                 right = SimpleMemberAccessExpression(right.Parenthesize(), valueName);
 
             coalesceExpression = CoalesceExpression(expression, right);

src/Analyzers.CodeFixes/CSharp/CodeFixes/ConditionalExpressionCodeFixProvider.cs

@@ -102,7 +102,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
                             semanticModel,
                             context.CancellationToken);
 
-                        if (recursiveCodeAction != null)
+                        if (recursiveCodeAction is not null)
                             context.RegisterCodeFix(recursiveCodeAction, diagnostic);
 
                         break;

src/Analyzers.CodeFixes/CSharp/CodeFixes/EnumDeclarationCodeFixProvider.cs

@@ -66,7 +66,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
 
                         ImmutableArray<ulong> values = enumInfo
                             .Fields
-                            .Where(f => f.HasValue && ((EnumMemberDeclarationSyntax)f.Symbol.GetSyntax(context.CancellationToken)).EqualsValue != null)
+                            .Where(f => f.HasValue && ((EnumMemberDeclarationSyntax)f.Symbol.GetSyntax(context.CancellationToken)).EqualsValue is not null)
                             .Select(f => f.Value)
                             .ToImmutableArray();
 
@@ -209,7 +209,7 @@ private static bool AreSeparatedWithEmptyLine(SeparatedSyntaxList<EnumMemberDecl
 
         for (int i = 0; i < members.Count; i++)
         {
-            if (members[i].EqualsValue == null)
+            if (members[i].EqualsValue is null)
             {
                 IFieldSymbol fieldSymbol = semanticModel.GetDeclaredSymbol(members[i], cancellationToken);
 
@@ -230,7 +230,7 @@ private static bool AreSeparatedWithEmptyLine(SeparatedSyntaxList<EnumMemberDecl
                     value = SymbolUtility.GetEnumValueAsUInt64(fieldSymbol.ConstantValue, enumSymbol);
                 }
 
-                if (value != null)
+                if (value is not null)
                 {
                     reservedValues.Add(value.Value);
 
@@ -292,7 +292,7 @@ IEnumerable<ExpressionSyntax> GetExpressionsToRewrite()
             {
                 ExpressionSyntax expression = member.EqualsValue?.Value.WalkDownParentheses();
 
-                if (expression != null
+                if (expression is not null
                     && semanticModel.GetDeclaredSymbol(member, cancellationToken) is IFieldSymbol fieldSymbol
                     && fieldSymbol.HasConstantValue)
                 {

src/Analyzers.CodeFixes/CSharp/CodeFixes/EnumMemberDeclarationCodeFixProvider.cs

@@ -170,7 +170,7 @@ private static IdentifierNameSyntax CreateIdentifierName(in EnumFieldSymbolInfo
 
         EnumMemberDeclarationSyntax newEnumMember;
 
-        if (equalsValue != null)
+        if (equalsValue is not null)
         {
             IdentifierNameSyntax newValue = IdentifierName(Identifier(equalsValue.Value.GetLeadingTrivia(), valueText, equalsValue.Value.GetTrailingTrivia()));
             newEnumMember = enumMember.WithEqualsValue(equalsValue.WithValue(newValue));

src/Analyzers.CodeFixes/CSharp/CodeFixes/IfStatementCodeFixProvider.cs

@@ -153,9 +153,9 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
         SyntaxList<StatementSyntax> newStatements;
 
         if (ifStatement.Statement.SingleNonBlockStatementOrDefault() is ThrowStatementSyntax throwStatement
-            && throwStatement.Expression == null)
+            && throwStatement.Expression is null)
         {
-            if (elseClause != null)
+            if (elseClause is not null)
             {
                 newStatements = ReplaceStatement(elseClause.Statement);
             }

src/Analyzers.CodeFixes/CSharp/CodeFixes/OptimizeStringBuilderAppendCallCodeFixProvider.cs

@@ -212,7 +212,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
                 arguments = ReplaceStringLiteralWithCharacterLiteral(arguments);
             }
 
-            if (newExpression == null)
+            if (newExpression is null)
             {
                 arguments = arguments.Replace(arguments[0], arguments[0].WithLeadingTrivia(interpolatedString.GetLeadingTrivia()));
 
@@ -336,11 +336,11 @@ private static ImmutableArray<ArgumentSyntax> ReplaceStringLiteralWithCharacterL
     {
         ArgumentSyntax argument = arguments.SingleOrDefault(shouldThrow: false);
 
-        if (argument != null)
+        if (argument is not null)
         {
             ExpressionSyntax expression = argument.Expression;
 
-            if (expression != null)
+            if (expression is not null)
             {
                 ExpressionSyntax newExpression = ReplaceStringLiteralWithCharacterLiteral(expression);
 

src/Analyzers.CodeFixes/CSharp/CodeFixes/OrderElementsInDocumentationCommentCodeFixProvider.cs

@@ -112,7 +112,7 @@ SyntaxList<XmlNodeSyntax> GetNewContent()
                         ? ((XmlElementSyntax)element).GetAttributeValue("name")
                         : ((XmlEmptyElementSyntax)element).GetAttributeValue("name");
 
-                    if (value != null)
+                    if (value is not null)
                     {
                         ranks[element] = indexOf(nodes, value);
                     }

src/Analyzers.CodeFixes/CSharp/CodeFixes/RemovePartialModifierFromTypeWithSinglePartCodeFixProvider.cs

@@ -37,7 +37,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
             ct =>
             {
                 TypeDeclarationSyntax newTypeDeclaration = typeDeclaration.ReplaceNodes(
-                    typeDeclaration.Members.OfType<MethodDeclarationSyntax>().Where(f => f.Modifiers.Contains(SyntaxKind.PartialKeyword) && f.BodyOrExpressionBody() != null),
+                    typeDeclaration.Members.OfType<MethodDeclarationSyntax>().Where(f => f.Modifiers.Contains(SyntaxKind.PartialKeyword) && f.BodyOrExpressionBody() is not null),
                     (f, _) => f.RemoveModifier(SyntaxKind.PartialKeyword));
 
                 int count = newTypeDeclaration.Members.Count;

src/Analyzers.CodeFixes/CSharp/CodeFixes/RemoveRedundantAssignmentCodeFixProvider.cs

@@ -94,7 +94,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
 
         ExpressionSyntax value = initializer?.Value;
 
-        VariableDeclaratorSyntax newDeclarator = (value != null)
+        VariableDeclaratorSyntax newDeclarator = (value is not null)
             ? declarator.ReplaceNode(value, right)
             : declarator.WithInitializer(EqualsValueClause(right));
 

src/Analyzers.CodeFixes/CSharp/CodeFixes/UnnecessaryAssignmentCodeFixProvider.cs

@@ -195,11 +195,11 @@ static SwitchSectionSyntax CreateNewSection(SwitchSectionSyntax section)
 
             VariableDeclaratorSyntax declarator = declarators.FirstOrDefault(f => SymbolEqualityComparer.Default.Equals(semanticModel.GetDeclaredSymbol(f, cancellationToken), symbol));
 
-            if (declarator != null)
+            if (declarator is not null)
             {
                 ExpressionSyntax value = declarator.Initializer?.Value;
 
-                if (removeReturnStatement || value != null)
+                if (removeReturnStatement || value is not null)
                 {
                     IEnumerable<ReferencedSymbol> referencedSymbols = await SymbolFinder.FindReferencesAsync(symbol, document.Solution(), cancellationToken).ConfigureAwait(false);
 
@@ -246,7 +246,7 @@ static SwitchSectionSyntax CreateNewSection(SwitchSectionSyntax section)
         {
             statementsInfo = statementsInfo.RemoveNode(returnStatement, SyntaxRefactorings.GetRemoveOptions(returnStatement));
         }
-        else if (newReturnExpression != null)
+        else if (newReturnExpression is not null)
         {
             ReturnStatementSyntax newReturnStatement = returnStatement.WithExpression(newReturnExpression.WithTriviaFrom(returnExpression));
 

src/Analyzers.CodeFixes/CSharp/CodeFixes/UseAutoPropertyCodeFixProvider.cs

@@ -136,7 +136,7 @@ public override async Task RegisterCodeFixesAsync(CodeFixContext context)
 
         SyntaxNode nodeToRemove = newRoot.GetAnnotatedNodes(_removeAnnotation).FirstOrDefault();
 
-        if (nodeToRemove != null)
+        if (nodeToRemove is not null)
             newRoot = newRoot.RemoveNode(nodeToRemove, SyntaxRemoveOptions.KeepUnbalancedDirectives);
 
         return document.WithSyntaxRoot(newRoot);
@@ -146,7 +146,7 @@ private static ISymbol GetFieldSymbol(PropertyDeclarationSyntax property, Semant
     {
         ArrowExpressionClauseSyntax expressionBody = property.ExpressionBody;
 
-        if (expressionBody != null)
+        if (expressionBody is not null)
         {
             return semanticModel.GetSymbol(expressionBody.Expression, cancellationToken);
         }
@@ -156,7 +156,7 @@ private static ISymbol GetFieldSymbol(PropertyDeclarationSyntax property, Semant
 
             BlockSyntax body = getter.Body;
 
-            if (body != null)
+            if (body is not null)
             {
                 var returnStatement = (ReturnStatementSyntax)body.Statements[0];
 
@@ -173,7 +173,7 @@ public static PropertyDeclarationSyntax CreateAutoProperty(PropertyDeclarationSy
     {
         AccessorListSyntax accessorList = property.AccessorList;
 
-        if (accessorList != null)
+        if (accessorList is not null)
         {
             SyntaxList<AccessorDeclarationSyntax> newAccessors = accessorList
                 .Accessors
@@ -214,7 +214,7 @@ public static PropertyDeclarationSyntax CreateAutoProperty(PropertyDeclarationSy
             accessorList: accessorList,
             expressionBody: default(ArrowExpressionClauseSyntax),
             initializer: initializer,
-            semicolonToken: (initializer != null) ? SemicolonToken() : default);
+            semicolonToken: (initializer is not null) ? SemicolonToken() : default);
 
         return newProperty
             .WithTriviaFrom(property)

src/Analyzers.CodeFixes/CSharp/Refactorings/AddSummaryToDocumentationCommentRefactoring.cs

@@ -57,7 +57,7 @@ private static string CreateSummaryElement(string indent, string text = null)
         sb.Append(indent);
         sb.AppendLine("/// </summary>");
 
-        if (text == null)
+        if (text is null)
             sb.Append(indent);
 
         return sb.ToString();

src/Analyzers.CodeFixes/CSharp/Refactorings/DeclareUsingDirectiveOnTopLevelRefactoring.cs

@@ -58,9 +58,9 @@ NameSyntax EnsureFullyQualifiedName()
         {
             ISymbol symbol = semanticModel.GetSymbol(name, cancellationToken);
 
-            if (symbol != null)
+            if (symbol is not null)
             {
-                if (semanticModel.GetAliasInfo(name, cancellationToken) != null
+                if (semanticModel.GetAliasInfo(name, cancellationToken) is not null
                     || !symbol.ContainingNamespace.IsGlobalNamespace)
                 {
                     SymbolKind kind = symbol.Kind;

src/Analyzers.CodeFixes/CSharp/Refactorings/Documentation/DocumentationCommentRefactoring`1.cs

@@ -137,7 +137,7 @@ internal abstract class DocumentationCommentRefactoring<TNode> where TNode : Syn
                         {
                             XmlElementSyntax previousElement = GetPreviousElement(comment, element);
 
-                            if (previousElement != null)
+                            if (previousElement is not null)
                             {
                                 insertIndex = previousElement.FullSpan.End;
                             }

src/Analyzers.CodeFixes/CSharp/Refactorings/FormatAccessorListRefactoring.cs

@@ -19,7 +19,7 @@ internal static class FormatAccessorListRefactoring
         AccessorListSyntax accessorList,
         CancellationToken cancellationToken)
     {
-        if (accessorList.Accessors.All(f => f.BodyOrExpressionBody() == null))
+        if (accessorList.Accessors.All(f => f.BodyOrExpressionBody() is null))
         {
             SyntaxNode parent = accessorList.Parent;
 
@@ -120,7 +120,7 @@ private static bool ShouldBeFormatted(AccessorDeclarationSyntax accessor)
     {
         BlockSyntax body = accessor.Body;
 
-        if (body != null)
+        if (body is not null)
         {
             SyntaxList<StatementSyntax> statements = body.Statements;
 
@@ -137,7 +137,7 @@ private static bool ShouldBeFormatted(AccessorDeclarationSyntax accessor)
         {
             ArrowExpressionClauseSyntax expressionBody = accessor.ExpressionBody;
 
-            if (expressionBody != null
+            if (expressionBody is not null
                 && accessor.SyntaxTree.IsMultiLineSpan(TextSpan.FromBounds(accessor.Keyword.SpanStart, accessor.Span.End))
                 && expressionBody.Expression?.IsSingleLine() == true)
             {

src/Analyzers.CodeFixes/CSharp/Refactorings/RemoveEmptyInitializerRefactoring.cs

@@ -22,7 +22,7 @@ internal static class RemoveEmptyInitializerRefactoring
         InitializerExpressionSyntax initializer = objectCreationExpression.Initializer;
 
         ObjectCreationExpressionSyntax newNode = objectCreationExpression.WithInitializer(null);
-        if (argumentList == null)
+        if (argumentList is null)
         {
             TypeSyntax type = objectCreationExpression.Type;
 

src/Analyzers.CodeFixes/CSharp/Refactorings/SimplifyNullCheckRefactoring.cs

@@ -31,7 +31,7 @@ internal static class SimplifyNullCheckRefactoring
 
         var castExpression = whenNotNull as CastExpressionSyntax;
 
-        ExpressionSyntax expression = (castExpression != null)
+        ExpressionSyntax expression = (castExpression is not null)
             ? UseConditionalAccessAnalyzer.FindExpressionThatCanBeConditionallyAccessed(nullCheck.Expression, castExpression.Expression, semanticModel, cancellationToken)
             : UseConditionalAccessAnalyzer.FindExpressionThatCanBeConditionallyAccessed(nullCheck.Expression, whenNotNull, semanticModel, cancellationToken);
 
@@ -66,7 +66,7 @@ internal static class SimplifyNullCheckRefactoring
                     {
                         newNode = ParseExpression($"{expression}?{whenNotNull.ToString().Substring(memberAccessExpression.Span.End - whenNotNull.SpanStart)}");
 
-                        if (castExpression != null)
+                        if (castExpression is not null)
                         {
                             newNode = castExpression
                                 .WithExpression(newNode.Parenthesize())
@@ -77,7 +77,7 @@ internal static class SimplifyNullCheckRefactoring
             }
         }
 
-        if (newNode == null)
+        if (newNode is null)
             newNode = ParseExpression(whenNotNull.ToString().Insert(expression.Span.End - whenNotNull.SpanStart, "?"));
 
         if (coalesce