Allow nameof to access instance members.

src/Compilers/CSharp/Portable/Binder/Binder_Expressions.cs

@@ -1891,18 +1891,19 @@ private BoundExpression SynthesizeReceiver(SyntaxNode node, Symbol member, Diagn
                 (currentType.IsInterface && (declaringType.IsObjectType() || currentType.AllInterfacesNoUseSiteDiagnostics.Contains(declaringType))))
             {
                 bool hasErrors = false;
-                if (EnclosingNameofArgument != node)
+                if (!IsInsideNameof || EnclosingNameofArgument != node && !((CSharpParseOptions)node.SyntaxTree.Options).IsFeatureEnabled(MessageID.IDS_FeatureNameofAccessInstanceMembersInAllContexts))
                 {
+                    var diagnosticsTemp = IsInsideNameof ? new DiagnosticBag() : diagnostics;
                     if (InFieldInitializer && !currentType.IsScriptClass)
                     {
                         //can't access "this" in field initializers
-                        Error(diagnostics, ErrorCode.ERR_FieldInitRefNonstatic, node, member);
+                        Error(diagnosticsTemp, ErrorCode.ERR_FieldInitRefNonstatic, node, member);
                         hasErrors = true;
                     }
                     else if (InConstructorInitializer || InAttributeArgument)
                     {
                         //can't access "this" in constructor initializers or attribute arguments
-                        Error(diagnostics, ErrorCode.ERR_ObjectRequired, node, member);
+                        Error(diagnosticsTemp, ErrorCode.ERR_ObjectRequired, node, member);
                         hasErrors = true;
                     }
                     else
@@ -1915,12 +1916,17 @@ private BoundExpression SynthesizeReceiver(SyntaxNode node, Symbol member, Diagn
                         if (!locationIsInstanceMember)
                         {
                             // error CS0120: An object reference is required for the non-static field, method, or property '{0}'
-                            Error(diagnostics, ErrorCode.ERR_ObjectRequired, node, member);
+                            Error(diagnosticsTemp, ErrorCode.ERR_ObjectRequired, node, member);
                             hasErrors = true;
                         }
                     }
 
-                    hasErrors = hasErrors || IsRefOrOutThisParameterCaptured(node, diagnostics);
+                    hasErrors = hasErrors || IsRefOrOutThisParameterCaptured(node, diagnosticsTemp);
+
+                    if (hasErrors && IsInsideNameof)
+                    {
+                        CheckFeatureAvailability(node, MessageID.IDS_FeatureNameofAccessInstanceMembersInAllContexts, diagnostics);
+                    }
                 }
 
                 return ThisReference(node, currentType, hasErrors, wasCompilerGenerated: true);

src/Compilers/CSharp/Portable/CSharpResources.resx

@@ -1,17 +1,17 @@
 <?xml version="1.0" encoding="utf-8"?>
 <root>
-  <!--
-    Microsoft ResX Schema
-
+  <!-- 
+    Microsoft ResX Schema 
+    
     Version 2.0
-
-    The primary goals of this format is to allow a simple XML format
-    that is mostly human readable. The generation and parsing of the
-    various data types are done through the TypeConverter classes
+    
+    The primary goals of this format is to allow a simple XML format 
+    that is mostly human readable. The generation and parsing of the 
+    various data types are done through the TypeConverter classes 
     associated with the data types.
-
+    
     Example:
-
+    
     ... ado.net/XML headers & schema ...
     <resheader name="resmimetype">text/microsoft-resx</resheader>
     <resheader name="version">2.0</resheader>
@@ -26,36 +26,36 @@
         <value>[base64 mime encoded string representing a byte array form of the .NET Framework object]</value>
         <comment>This is a comment</comment>
     </data>
-
-    There are any number of "resheader" rows that contain simple
+                
+    There are any number of "resheader" rows that contain simple 
     name/value pairs.
-
-    Each data row contains a name, and value. The row also contains a
-    type or mimetype. Type corresponds to a .NET class that support
-    text/value conversion through the TypeConverter architecture.
-    Classes that don't support this are serialized and stored with the
+    
+    Each data row contains a name, and value. The row also contains a 
+    type or mimetype. Type corresponds to a .NET class that support 
+    text/value conversion through the TypeConverter architecture. 
+    Classes that don't support this are serialized and stored with the 
     mimetype set.
-
-    The mimetype is used for serialized objects, and tells the
-    ResXResourceReader how to depersist the object. This is currently not
+    
+    The mimetype is used for serialized objects, and tells the 
+    ResXResourceReader how to depersist the object. This is currently not 
     extensible. For a given mimetype the value must be set accordingly:
-
-    Note - application/x-microsoft.net.object.binary.base64 is the format
-    that the ResXResourceWriter will generate, however the reader can
+    
+    Note - application/x-microsoft.net.object.binary.base64 is the format 
+    that the ResXResourceWriter will generate, however the reader can 
     read any of the formats listed below.
-
+    
     mimetype: application/x-microsoft.net.object.binary.base64
-    value   : The object must be serialized with
+    value   : The object must be serialized with 
             : System.Runtime.Serialization.Formatters.Binary.BinaryFormatter
             : and then encoded with base64 encoding.
-
+    
     mimetype: application/x-microsoft.net.object.soap.base64
-    value   : The object must be serialized with
+    value   : The object must be serialized with 
             : System.Runtime.Serialization.Formatters.Soap.SoapFormatter
             : and then encoded with base64 encoding.
 
     mimetype: application/x-microsoft.net.object.bytearray.base64
-    value   : The object must be serialized into a byte array
+    value   : The object must be serialized into a byte array 
             : using a System.ComponentModel.TypeConverter
             : and then encoded with base64 encoding.
     -->
@@ -6588,4 +6588,7 @@ To remove the warning, you can use /reference instead (set the Embed Interop Typ
   <data name="WRN_UnreadRecordParameter_Title" xml:space="preserve">
     <value>Parameter is unread. Did you forget to use it to initialize the property with that name?</value>
   </data>
-</root>
+  <data name="IDS_FeatureNameofAccessInstanceMembersInAllContexts" xml:space="preserve">
+    <value>nameof can access instance members in all contexts</value>
+  </data>
+</root>

src/Compilers/CSharp/Portable/Errors/MessageID.cs

@@ -214,6 +214,8 @@ internal enum MessageID
         IDS_Parameter = MessageBase + 12789,
         IDS_Return = MessageBase + 12790,
         IDS_FeatureVarianceSafetyForStaticInterfaceMembers = MessageBase + 12791,
+
+        IDS_FeatureNameofAccessInstanceMembersInAllContexts = MessageBase + 12792,
     }
 
     // Message IDs may refer to strings that need to be localized.
@@ -320,6 +322,10 @@ internal static LanguageVersion RequiredVersion(this MessageID feature)
             // Checks are in the LanguageParser unless otherwise noted.
             switch (feature)
             {
+                // preview features.
+                case MessageID.IDS_FeatureNameofAccessInstanceMembersInAllContexts:
+                    return LanguageVersion.Preview;
+
                 // C# 9.0 features.
                 case MessageID.IDS_FeatureLambdaDiscardParameters: // semantic check
                 case MessageID.IDS_FeatureFunctionPointers: