Fixed false positive that caused a 'is operator always returns true' warning even though it returns false. (e.g. 'intVar is double')

ICSharpCode.NRefactory.CSharp/Refactoring/CodeIssues/ExpressionIsAlwaysOfProvidedTypeIssue.cs

@@ -27,6 +27,7 @@
 using System.Collections.Generic;
 using ICSharpCode.NRefactory.CSharp.Resolver;
 using ICSharpCode.NRefactory.Semantics;
+using ICSharpCode.NRefactory.TypeSystem;
 
 namespace ICSharpCode.NRefactory.CSharp.Refactoring
 {
@@ -59,7 +60,7 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 				var providedType = ctx.ResolveType (isExpression.Type);
 
 				var foundConversion = conversions.ImplicitConversion(type, providedType);
-				if (!foundConversion.IsValid)
+				if (!IsValidReferenceOrBoxingConversion(type, providedType))
 					return;
 
 				var action = new CodeAction (ctx.TranslateString ("Compare with 'null'"), 
@@ -68,6 +69,12 @@ namespace ICSharpCode.NRefactory.CSharp.Refactoring
 				AddIssue (isExpression, ctx.TranslateString ("Given expression is always of the provided type. " +
 					"Consider comparing with 'null' instead"), new [] { action });
 			}
+			
+			bool IsValidReferenceOrBoxingConversion(IType fromType, IType toType)
+			{
+				Conversion c = conversions.ImplicitConversion(fromType, toType);
+				return c.IsValid && (c.IsIdentityConversion || c.IsReferenceConversion || c.IsBoxingConversion);
+			}
 		}
 	}
 }

ICSharpCode.NRefactory.Tests/CSharp/CodeIssues/ExpressionIsAlwaysOfProvidedTypeIssueTests.cs

@@ -90,5 +90,19 @@ class TestClass
 }";
 			Test<ExpressionIsAlwaysOfProvidedTypeIssue> (input, 1, output);
 		}
+		
+		[Test]
+		public void IntIsNotDouble ()
+		{
+			var input = @"
+sealed class TestClass
+{
+	void TestMethod (int x)
+	{
+		if (x is double) ;
+	}
+}";
+			Test<ExpressionIsAlwaysOfProvidedTypeIssue> (input, 0);
+		}
 	}
 }