[Mono-bugs] [Bug 77959][Wis] New - Optional ParameterAttribute and nullref in Cecil

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Changed by armand at dotnet.org.za.

http://bugzilla.ximian.com/show_bug.cgi?id=77959

--- shadow/77959	2006-03-30 05:22:27.000000000 -0500
+++ shadow/77959.tmp.18787	2006-03-30 05:22:27.000000000 -0500
@@ -0,0 +1,100 @@
+Bug#: 77959
+Product: Mono: Class Libraries
+Version: 1.1
+OS: 
+OS Details: 
+Status: NEW   
+Resolution: 
+Severity: 
+Priority: Wishlist
+Component: Mono.Cecil
+AssignedTo: mono at evain.net                            
+ReportedBy: armand at dotnet.org.za               
+QAContact: mono-bugs at ximian.com
+TargetMilestone: ---
+URL: 
+Cc: 
+Summary: Optional ParameterAttribute and nullref in Cecil
+
+Description of Problem:
+Background:The Microsoft.VisualBasic assembly contains a special marker
+attribute used to mark parameters as optional as there's no support for
+optional parameters in C#. 
+The assembly is then disassembled after compilatation and a perl script
+used to add the opt flag to the parameter etc and reassembled. 
+
+I tried running this process through Mono.Cecil and the following issues
+came up:
+1) The ParamAttributes value for Opt is 0x0004 in Mono.Cecil and in the old
+CLI specifications. However running an assembly through Microsoft's ildasm
+it seems to pick up paramattributes optional if the value is 0x0010 which
+is consistent with the 0x0013 mask supplied in Serge Lidin's ".NET IL
+Assembler" book. I just checked the updated draft of Partition II of the
+CLI specs and the updated value is 0x0010 :-) Maybe a bug in the old CLI
+spec :P
+
+23.1.13	Flags for params [ParamAttributes]
+Flag	Value	Description
+In	0x0001	Param is [In]
+Out	0x0002	Param is [out]
+Optional	0x0010	Param is optional
+
+2) The second issue is the handling of nullref (p121) where parameter
+default values is set to null. According to the spec a nullref should be
+encoded as a  "ELEMENT_TYPE_CLASS with a Value of zero" so I've modified
+WriteConstant in ReflectionWriter to check for a null Constant value and
+update the ElementType accordingly. I haven't spent enough time on it to
+determine whether this is actuallly the appropriate or only place to add
+such a modification but have included my diff below.
+
+
+Index: ParamAttributes.cs
+===================================================================
+--- ParamAttributes.cs	(revision 58723)
++++ ParamAttributes.cs	(working copy)
+@@ -34,7 +34,7 @@
+ 	public enum ParamAttributes : ushort {
+ 		In					= 0x0001,	// Param is [In]
+ 		Out					= 0x0002,	// Param is [Out]
+-		Optional			= 0x0004,	// Param is optional
++		Optional			= 0x0010,	// Param is optional
+ 		HasDefault			= 0x1000,	// Param has default value
+ 		HasFieldMarshal		= 0x2000,	// Param has field marshal
+ 		Unused				= 0xcfe0	 // Reserved: shall be zero in a conforming
+implementation
+
+
+Index: ReflectionWriter.cs
+===================================================================
+--- ReflectionWriter.cs	(revision 58723)
++++ ReflectionWriter.cs	(working copy)
+@@ -617,15 +617,20 @@
+ 		{
+ 			ConstantTable cTable = m_tableWriter.GetConstantTable ();
+ 			ElementType et;
+-			if (type is TypeDefinition && (type as TypeDefinition).IsEnum) {
+-				Type t = hc.Constant.GetType ();
+-				if (t.IsEnum)
+-					t = Enum.GetUnderlyingType (t);
++            if (type is TypeDefinition && (type as TypeDefinition).IsEnum) {
++                Type t = hc.Constant.GetType();
++                if (t.IsEnum)
++                    t = Enum.GetUnderlyingType(t);
+ 
+-				et = GetCorrespondingType (string.Concat (t.Namespace, '.', t.Name));
+-			} else
+-				et = GetCorrespondingType (type.FullName);
+-
++                et = GetCorrespondingType(string.Concat(t.Namespace, '.',
+t.Name));
++            }
++            else {
++                if (hc.Constant == null)
++                    et = ElementType.Class;
++                else
++                    et = GetCorrespondingType(type.FullName);
++            }
++                
+ 			ConstantRow cRow = m_rowWriter.CreateConstantRow (
+ 				et,
+ 				hc.MetadataToken,