Removed generic constraint check. Changed C# null check from (v is null) to (v == null).

src/EditorFeatures/CSharpTest/UseIsNullCheck/UseIsNullCheckTests.cs

@@ -36,7 +36,7 @@ class C
 {
     void M(string s)
     {
-        if (s is null)
+        if (s == null)
             return;
     }
 }");
@@ -62,7 +62,7 @@ class C
 {
     void M(string s)
     {
-        if (s is null)
+        if (s == null)
             return;
     }
 }");
@@ -88,7 +88,7 @@ class C
 {
     void M(string s)
     {
-        if (s is null)
+        if (s == null)
             return;
     }
 }");
@@ -114,7 +114,7 @@ class C
 {
     void M(string s)
     {
-        if (s is null)
+        if (s == null)
             return;
     }
 }");
@@ -140,7 +140,7 @@ class C
 {
     void M(string s)
     {
-        if (!(s is null))
+        if (s != null)
             return;
     }
 }");
@@ -183,8 +183,8 @@ class C
 {
     void M(string s1, string s2)
     {
-        if (s1 is null ||
-            s2 is null)
+        if (s1 == null ||
+            s2 == null)
             return;
     }
 }");
@@ -211,8 +211,8 @@ class C
 {
     void M(string s1, string s2)
     {
-        if (s1 is null ||
-            s2 is null)
+        if (s1 == null ||
+            s2 == null)
             return;
     }
 }");
@@ -222,7 +222,7 @@ void M(string s1, string s2)
         [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsUseIsNullCheck)]
         public async Task TestMissingIfValueParameterTypeIsUnconstraintGeneric()
         {
-            await TestMissingAsync(
+            await TestInRegularAndScriptAsync(
 @"
 class C
 {
@@ -234,6 +234,17 @@ public static void NotNull<T>(T value, string parameterName)
         }
     }
 }
+", @"
+class C
+{
+    public static void NotNull<T>(T value, string parameterName)
+    {
+        if (value == null)
+        {
+            throw new System.ArgumentNullException(parameterName);
+        }
+    }
+}
 ");
         }
 
@@ -259,7 +270,7 @@ class C
 {
     public static void NotNull<T>(T value, string parameterName) where T:class
     {
-        if (value is null)
+        if (value == null)
         {
             throw new System.ArgumentNullException(parameterName);
         }

src/Features/CSharp/Portable/UseIsNullCheck/CSharpUseIsNullCheckCodeFixProvider.cs

@@ -17,12 +17,16 @@ protected override string GetIsNullTitle()
         protected override string GetIsNotNullTitle()
             => GetIsNullTitle();
 
-        protected override SyntaxNode CreateIsNullCheck(SyntaxNode argument)
-            => SyntaxFactory.IsPatternExpression(
+        private static SyntaxNode CreateNullCheck(SyntaxNode argument, SyntaxKind comparisonOperator)
+            => SyntaxFactory.BinaryExpression(
+                comparisonOperator,
                 (ExpressionSyntax)argument,
-                SyntaxFactory.ConstantPattern(SyntaxFactory.LiteralExpression(SyntaxKind.NullLiteralExpression))).Parenthesize();
+                SyntaxFactory.LiteralExpression(SyntaxKind.NullLiteralExpression)).Parenthesize();
+
+        protected override SyntaxNode CreateIsNullCheck(SyntaxNode argument)
+            => CreateNullCheck(argument, SyntaxKind.EqualsExpression);
 
         protected override SyntaxNode CreateIsNotNullCheck(SyntaxNode notExpression, SyntaxNode argument)
-            => ((PrefixUnaryExpressionSyntax)notExpression).WithOperand((ExpressionSyntax)CreateIsNullCheck(argument));
+            => CreateNullCheck(argument, SyntaxKind.NotEqualsExpression);
     }
 }

src/Features/Core/Portable/UseIsNullCheck/AbstractUseIsNullDiagnosticAnalyzer.cs

@@ -109,11 +109,6 @@ private void AnalyzeSyntax(SyntaxNodeAnalysisContext context, IMethodSymbol refe
                 return;
             }
 
-            if (HasUnconstraintGenericParameter(syntaxFacts, semanticModel, arguments[0], arguments[1], cancellationToken))
-            {
-                return;
-            }
-
             var additionalLocations = ImmutableArray.Create(invocation.GetLocation());
             var properties = ImmutableDictionary<string, string>.Empty;
 
@@ -130,22 +125,6 @@ private void AnalyzeSyntax(SyntaxNodeAnalysisContext context, IMethodSymbol refe
                     additionalLocations, properties));
         }
 
-        private static bool HasUnconstraintGenericParameter(ISyntaxFactsService syntaxFacts, SemanticModel semanticModel, SyntaxNode node1, SyntaxNode node2, CancellationToken cancellationToken)
-        {
-            var valueNode = syntaxFacts.IsNullLiteralExpression(node1) ? node2 : node1;
-            var argumentExpression = syntaxFacts.GetExpressionOfArgument(valueNode);
-            if (argumentExpression != null)
-            {
-                var parameterType = semanticModel.GetTypeInfo(argumentExpression, cancellationToken).Type;
-                if (parameterType is ITypeParameterSymbol typeParameter)
-                {
-                    return !typeParameter.HasReferenceTypeConstraint;
-                }
-            }
-
-            return false;
-        }
-
         private static bool MatchesPattern(ISyntaxFactsService syntaxFacts, SyntaxNode node1, SyntaxNode node2)
             => syntaxFacts.IsNullLiteralExpression(syntaxFacts.GetExpressionOfArgument(node1)) &&
                !syntaxFacts.IsNullLiteralExpression(syntaxFacts.GetExpressionOfArgument(node2));