Merge pull request #19730 from CyrusNajmabadi/patternMatchingNullable

Don't offer to convert to pattern matching when type is nullable.

src/EditorFeatures/CSharpTest/UsePatternMatching/CSharpIsAndCastCheckTests.cs

@@ -516,6 +516,26 @@ static void N(ParameterSyntax parameter)
             parent = parent.Parent;
         }
     }
+}");
+        }
+
+        [WorkItem(429612, "https://devdiv.visualstudio.com/DevDiv/_workitems/edit/429612")]
+        [Fact, Trait(Traits.Feature, Traits.Features.CodeActionsInlineTypeCheck)]
+        public async Task TestMissingWithNullableType()
+        {
+            await TestMissingInRegularAndScriptAsync(
+@"
+class C
+{
+    public object Convert(object value)
+    {
+        if (value is bool?)
+        {
+            [|bool?|] tmp = (bool?)value;
+        }
+
+        return null;
+    }
 }");
         }
     }

src/Features/CSharp/Portable/UsePatternMatching/CSharpIsAndCastCheckDiagnosticAnalyzer.cs

@@ -8,6 +8,7 @@
 using Microsoft.CodeAnalysis.CSharp.Extensions;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.Diagnostics;
+using Microsoft.CodeAnalysis.Shared.Extensions;
 
 namespace Microsoft.CodeAnalysis.CSharp.UsePatternMatching
 {
@@ -144,6 +145,13 @@ private void SyntaxNodeAction(SyntaxNodeAnalysisContext syntaxContext)
             var semanticModel = syntaxContext.SemanticModel;
             var localSymbol = (ILocalSymbol)semanticModel.GetDeclaredSymbol(declarator);
             var isType = semanticModel.GetTypeInfo(castExpression.Type).Type;
+
+            if (isType.IsNullable())
+            {
+                // not legal to write "if (x is int? y)"
+                return;
+            }
+
             if (!localSymbol.Type.Equals(isType))
             {
                 // we have something like: