[Mono-bugs] [Bug 81380][Nor] New - Warning CS0183 incorrectly given for reference types

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Changed by chuck.esterbrook at gmail.com.

http://bugzilla.ximian.com/show_bug.cgi?id=81380

--- shadow/81380	2007-04-15 10:59:34.000000000 -0400
+++ shadow/81380.tmp.25356	2007-04-15 10:59:34.000000000 -0400
@@ -0,0 +1,71 @@
+Bug#: 81380
+Product: Mono: Compilers
+Version: 1.2
+OS: All
+OS Details: 
+Status: NEW   
+Resolution: 
+Severity: 
+Priority: Normal
+Component: C#
+AssignedTo: rharinath at novell.com                            
+ReportedBy: Chuck.Esterbrook at gmail.com               
+QAContact: mono-bugs at ximian.com
+TargetMilestone: ---
+URL: 
+Cc: 
+Summary: Warning CS0183 incorrectly given for reference types
+
+Description of Problem:
+
+Re: Warning CS0183: The given expression is always of the provided (`IFoo') type
+
+This warning is not valid for reference types since the boolean expression may evaluate to true or 
+false at runtime (null would give false). CS0183 should only be generated for value types because 
+that's the only situation where the evaluation of the "is" test will not vary.
+
+Steps to reproduce the problem:
+
+// test.cs
+using System;
+interface IFoo {
+}
+class Bar {
+}
+class Program {
+	public static void Main() {
+		IFoo foo = null;
+		if (foo is IFoo)
+			Console.WriteLine("got an IFoo"); // never prints
+		Bar bar = null;
+		if (bar is Bar)
+			Console.WriteLine("got a bar"); // never prints
+	}
+}
+// end of test.cs
+
+Actual Results:
+
+$ gmcs test.cs
+test.cs(15,11): warning CS0183: The given expression is always of the provided (`IFoo') type
+test.cs(18,11): warning CS0183: The given expression is always of the provided (`Bar') type
+Compilation succeeded - 2 warning(s)
+$ mono test.exe
+(no output)
+
+Expected Results:
+
+$ gmcs test.cs
+$ mono test.exe
+(no output)
+
+How often does this happen? 
+
+Always.
+
+Additional Information:
+
+"if (x is Foo)" can evaluate to false if "x" is null. Or it might evaluate to true.
+This is true even when the compile-time type of "x" is "Foo".
+
+See also: http://msdn2.microsoft.com/en-us/library/sb7782xb(vs.80).aspx