Make InConversion and OutConversion optional

src/Compilers/CSharp/Portable/Operations/CSharpArgument.cs

@@ -12,9 +12,9 @@ internal abstract class BaseCSharpArgument : BaseArgument, IArgument
         {
         }
 
-        public override CommonConversion InConversion => default(CommonConversion);
+        public override Optional<CommonConversion> InConversion => default;
 
-        public override CommonConversion OutConversion => default(CommonConversion);
+        public override Optional<CommonConversion> OutConversion => default;
     }
 
     internal sealed partial class CSharpArgument : BaseCSharpArgument

src/Compilers/Core/Portable/Generated/Operations.xml.Generated.cs

@@ -206,8 +206,8 @@ internal abstract partial class BaseArgument : Operation, IArgument
         /// </summary>
         public IParameterSymbol Parameter { get; }
         protected abstract IOperation ValueImpl { get; }
-        public abstract CommonConversion InConversion { get; }
-        public abstract CommonConversion OutConversion { get; }
+        public abstract Optional<CommonConversion> InConversion { get; }
+        public abstract Optional<CommonConversion> OutConversion { get; }
         public override IEnumerable<IOperation> Children
         {
             get

src/Compilers/Core/Portable/Operations/IArgument.cs

@@ -26,11 +26,11 @@ public interface IArgument : IOperation
         /// <summary>
         /// Conversion applied to the argument value passing it into the target method. Applicable only to VB Reference arguments.
         /// </summary>
-        CommonConversion InConversion { get; }
+        Optional<CommonConversion> InConversion { get; }
         /// <summary>
         /// Conversion applied to the argument value after the invocation. Applicable only to VB Reference arguments.
         /// </summary>
-        CommonConversion OutConversion { get; }
+        Optional<CommonConversion> OutConversion { get; }
     }
 }
 

src/Compilers/Core/Portable/PublicAPI.Unshipped.txt

@@ -345,8 +345,8 @@ Microsoft.CodeAnalysis.Semantics.IAnonymousObjectCreationExpression
 Microsoft.CodeAnalysis.Semantics.IAnonymousObjectCreationExpression.Initializers.get -> System.Collections.Immutable.ImmutableArray<Microsoft.CodeAnalysis.IOperation>
 Microsoft.CodeAnalysis.Semantics.IArgument
 Microsoft.CodeAnalysis.Semantics.IArgument.ArgumentKind.get -> Microsoft.CodeAnalysis.Semantics.ArgumentKind
-Microsoft.CodeAnalysis.Semantics.IArgument.InConversion.get -> Microsoft.CodeAnalysis.Semantics.CommonConversion
-Microsoft.CodeAnalysis.Semantics.IArgument.OutConversion.get -> Microsoft.CodeAnalysis.Semantics.CommonConversion
+Microsoft.CodeAnalysis.Semantics.IArgument.InConversion.get -> Microsoft.CodeAnalysis.Optional<Microsoft.CodeAnalysis.Semantics.CommonConversion>
+Microsoft.CodeAnalysis.Semantics.IArgument.OutConversion.get -> Microsoft.CodeAnalysis.Optional<Microsoft.CodeAnalysis.Semantics.CommonConversion>
 Microsoft.CodeAnalysis.Semantics.IArgument.Parameter.get -> Microsoft.CodeAnalysis.IParameterSymbol
 Microsoft.CodeAnalysis.Semantics.IArgument.Value.get -> Microsoft.CodeAnalysis.IOperation
 Microsoft.CodeAnalysis.Semantics.IArrayCreationExpression

src/Compilers/VisualBasic/Portable/Operations/VisualBasicArgument.vb

@@ -17,15 +17,15 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
 
         Friend ReadOnly Property OutConversionInternal As Conversion
 
-        Public Overrides ReadOnly Property InConversion As CommonConversion
+        Public Overrides ReadOnly Property InConversion As [Optional](Of CommonConversion)
             Get
-                Return InConversionInternal.ToCommonConversion()
+                Return If(InConversionInternal = Nothing, New [Optional](Of CommonConversion)(), InConversionInternal.ToCommonConversion())
             End Get
         End Property
 
-        Public Overrides ReadOnly Property OutConversion As CommonConversion
+        Public Overrides ReadOnly Property OutConversion As [Optional](Of CommonConversion)
             Get
-                Return OutConversionInternal.ToCommonConversion()
+                Return If(OutConversionInternal = Nothing, New [Optional](Of CommonConversion)(), OutConversionInternal.ToCommonConversion())
             End Get
         End Property
     End Class

src/Test/Utilities/Portable/Compilation/OperationTreeVerifier.cs

@@ -623,15 +623,21 @@ public override void VisitArgument(IArgument operation)
             LogString(")");
             LogCommonPropertiesAndNewLine(operation);
 
-            Indent();
-            LogConversion(operation.InConversion, "InConversion");
-            Unindent();
-            LogNewLine();
+            if (operation.InConversion.HasValue)
+            {
+                Indent();
+                LogConversion(operation.InConversion.Value, "InConversion");
+                Unindent();
+                LogNewLine();
+            }
 
-            Indent();
-            LogConversion(operation.OutConversion, "OutConversion");
-            Unindent();
-            LogNewLine();
+            if (operation.OutConversion.HasValue)
+            {
+                Indent();
+                LogConversion(operation.OutConversion.Value, "OutConversion");
+                Unindent();
+                LogNewLine();
+            }
 
             Visit(operation.Value);
         }