Fix #2808: Insert cast to object when statically casting from dynamic to a reference type.

ICSharpCode.Decompiler.Tests/TestCases/Pretty/DynamicTests.cs

@@ -42,6 +42,10 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			}
 		}
 
+		public interface I
+		{
+		}
+
 		private static dynamic field;
 		private static object objectField;
 		public dynamic Property { get; set; }
@@ -492,6 +496,26 @@ namespace ICSharpCode.Decompiler.Tests.TestCases.Pretty
 			return (int)(dynamic)o;
 		}
 
+		private static dynamic GetI()
+		{
+			return null;
+		}
+
+		public I Test()
+		{
+			return GetI();
+		}
+
+		public I Test1()
+		{
+			return (I)GetI();
+		}
+
+		public I Test2()
+		{
+			return (I)(object)GetI();
+		}
+
 #if CS72
 		public void RefParams(ref object a, ref dynamic b, ref dynamic c)
 		{

ICSharpCode.Decompiler/CSharp/TranslatedExpression.cs

@@ -535,6 +535,17 @@ namespace ICSharpCode.Decompiler.CSharp
 						.ConvertTo(targetType, expressionBuilder, checkForOverflow, allowImplicitConversion);
 				}
 			}
+			else if (type.Kind == TypeKind.Dynamic && targetType.IsReferenceType == true && !targetType.IsKnownType(KnownTypeCode.Object))
+			{
+				// "static" conversion between dynamic and a reference type requires us to add a cast to object,
+				// otherwise recompilation would produce a dynamic cast.
+				// (T)dynamicExpression is a "dynamic" cast
+				// (T)(object)dynamicExpression is a "static" cast
+				// as "dynamic" casts are handled differently by ExpressionBuilder.VisitDynamicConvertInstruction
+				// we can always insert the cast to object, if we encounter a conversion from any reference type to dynamic.
+				return this.ConvertTo(compilation.FindType(KnownTypeCode.Object), expressionBuilder)
+					.ConvertTo(targetType, expressionBuilder, checkForOverflow, allowImplicitConversion);
+			}
 			if (targetType.Kind.IsAnyPointer() && (0.Equals(ResolveResult.ConstantValue) || 0u.Equals(ResolveResult.ConstantValue)))
 			{
 				if (allowImplicitConversion)