Switch to "is null"

Author: GrahamTheCoder

CodeConverter/CSharp/BuiltInVisualBasicOperatorSubstitutions.cs

@@ -59,10 +59,10 @@ public async Task<ExpressionSyntax> ConvertNothingComparisonOrNullAsync(VBSyntax
                     return null;
                 }
                 var csOtherArg = (ExpressionSyntax)await ConvertIsOrIsNotExpressionArgAsync(vbOtherArg);
-                var couldHaveOverloadedOperators = !_semanticModel.GetTypeInfo(vbOtherArg).Type.IsSpecialType();
-                var isReferenceComparison = node.IsKind(VBasic.SyntaxKind.IsExpression, VBasic.SyntaxKind.IsNotExpression);
+                var typeSymbol = _semanticModel.GetTypeInfo(vbOtherArg).Type;
+                var isReferenceComparison = typeSymbol?.IsValueType != true || node.IsKind(VBasic.SyntaxKind.IsExpression, VBasic.SyntaxKind.IsNotExpression);
                 var notted = node.IsKind(VBasic.SyntaxKind.IsNotExpression, VBasic.SyntaxKind.NotEqualsExpression) || negateExpression;
-                return notted ? CommonConversions.NotNothingComparison(csOtherArg, isReferenceComparison) : CommonConversions.NothingComparison(csOtherArg, isReferenceComparison, couldHaveOverloadedOperators);
+                return notted ? CommonConversions.NotNothingComparison(csOtherArg, isReferenceComparison) : CommonConversions.NothingComparison(csOtherArg, isReferenceComparison);
             }
 
             private async Task<CSharpSyntaxNode> ConvertIsOrIsNotExpressionArgAsync(VBSyntax.ExpressionSyntax binaryExpressionArg)

CodeConverter/CSharp/CommonConversions.cs

@@ -658,17 +658,20 @@ public static CSSyntax.ParameterListSyntax CreateParameterList(IEnumerable<Synta
         public static CSSyntax.BinaryExpressionSyntax NotNothingComparison(ExpressionSyntax otherArgument, bool isReferenceType)
         {
             if (isReferenceType) {
+                // When we upgrade the CodeAnalysis version, we'll be able to use a RecursivePattern of "{}" instead
                 return SyntaxFactory.BinaryExpression(CSSyntaxKind.IsExpression, otherArgument, ValidSyntaxFactory.ObjectType);
             }
             return SyntaxFactory.BinaryExpression(CSSyntaxKind.NotEqualsExpression, otherArgument, ValidSyntaxFactory.DefaultExpression);
         }
 
-        public static ExpressionSyntax NothingComparison(ExpressionSyntax otherArgument, bool isReferenceType, bool couldHaveOverloadedOperators)
+        public static ExpressionSyntax NothingComparison(ExpressionSyntax otherArgument, bool isReferenceType)
         {
-            // Old project style doesn't support is pattern expressions (or indeed anything beyond c#7.3), so can't use "x is null"
-            var literal = isReferenceType ? ValidSyntaxFactory.NullExpression : (ExpressionSyntax)ValidSyntaxFactory.DefaultExpression;
-            if (isReferenceType && couldHaveOverloadedOperators) otherArgument = SyntaxFactory.ParenthesizedExpression(SyntaxFactory.CastExpression(ValidSyntaxFactory.ObjectType, otherArgument));
-            return SyntaxFactory.BinaryExpression(CSSyntaxKind.EqualsExpression, otherArgument, literal);
+            if (isReferenceType) {
+                return SyntaxFactory.IsPatternExpression(otherArgument,
+                    SyntaxFactory.ConstantPattern(ValidSyntaxFactory.NullExpression));
+            }
+
+            return SyntaxFactory.BinaryExpression(CSSyntaxKind.EqualsExpression, otherArgument, ValidSyntaxFactory.DefaultExpression);
         }
     }
 }

Tests/CSharp/ExpressionTests/ExpressionTests.cs

@@ -399,7 +399,7 @@ public partial class GenericComparison
 {
     public void m<T>(T p)
     {
-        if (p == null)
+        if (p is null)
             return;
     }
 }");
@@ -1347,7 +1347,7 @@ public partial class Foo
 
     protected void OnBar(EventArgs e)
     {
-        if ((object)Bar == null)
+        if (Bar is null)
         {
             Debug.WriteLine(""No subscriber"");
         }

Tests/CSharp/StatementTests/StatementTests.cs

@@ -1376,7 +1376,7 @@ internal partial class TestClass
 {
     private void TestMethod(object nullObject)
     {
-        if (nullObject == null)
+        if (nullObject is null)
             throw new ArgumentNullException(nameof(nullObject));
         lock (nullObject)
             Console.WriteLine(nullObject);
@@ -1397,7 +1397,7 @@ internal partial class TestClass
 {
     private void TestMethod(object nullObject)
     {
-        if (nullObject == null)
+        if (nullObject is null)
             throw new ArgumentNullException(nameof(nullObject));
     }
 }");

Tests/CSharp/TypeCastTests.cs

@@ -402,7 +402,7 @@ public partial class MultipleCasts
 {
     public static T ToGenericParameter<T>(object Value)
     {
-        if (Value == null)
+        if (Value is null)
         {
             return default;
         }