Add EE support for My.InternalXmlHelper

Two things were preventing the EE from finding the type, which is needed
for XML literal operations in VB:

1. It is marked internal and the accessibility check happened in
AssemblySymbol, rather than the binder, so it was not hijacked.

2. It is marked with EmbeddedAttribute and is not from the SourceModule of
the compilation (it's from the module of the current frame).

We can resolve both of these problems by doing the lookups as though we
were in the module containing the current frame.  This required two
changes:

1. Remove InternalXmlHelper from WellKnownTypes and give it its own code
path.  Explicitly pass the appropriate module symbol to the new helper.

2. In Binder.CheckViability, look for a containing module before falling
back on the SourceModule of the compilation.

By preserving the accessibility checks during type lookup (but doing them
from the perspective of a different assembly), we retain the compiler's
protection against pulling in a copy from each VB reference (i.e.
ambiguity).

The main caveat is that My.InternalXmlHelper will not be found if it was
not embedded in the module containing the current frame - even if it is
unambiguously available in a referenced assembly.

Breaking change: unlike dev12, roslyn will only find My.InternalXmlHelper
in the source module.

Fixes #964

src/Compilers/CSharp/Test/Symbol/Symbols/MissingSpecialMember.cs

@@ -551,7 +551,6 @@ public void AllWellKnownTypes()
             {
                 switch (wkt)
                 {
-                    case WellKnownType.My_InternalXmlHelper:
                     case WellKnownType.Microsoft_VisualBasic_Embedded:
                     case WellKnownType.Microsoft_VisualBasic_CompilerServices_EmbeddedOperators:
                         // Not applicable in C#.
@@ -592,7 +591,6 @@ public void AllWellKnownTypeMembers()
                     case WellKnownMember.Count:
                         // Not a real value;
                         continue;
-                    case WellKnownMember.My_InternalXmlHelper__Value:
                     case WellKnownMember.Microsoft_VisualBasic_Embedded__ctor:
                     case WellKnownMember.Microsoft_VisualBasic_CompilerServices_EmbeddedOperators__CompareStringStringStringBoolean:
                         // C# can't embed VB core.

src/Compilers/Core/Portable/WellKnownMember.cs

@@ -306,8 +306,6 @@ internal enum WellKnownMember
         Microsoft_VisualBasic_Information__VbTypeName,
         Microsoft_VisualBasic_Interaction__CallByName,
 
-        My_InternalXmlHelper__Value,
-
         System_Runtime_CompilerServices_IAsyncStateMachine_MoveNext,
         System_Runtime_CompilerServices_IAsyncStateMachine_SetStateMachine,
 

src/Compilers/Core/Portable/WellKnownMembers.cs

@@ -2220,17 +2220,6 @@ static WellKnownMembers()
                     (byte)SignatureTypeCode.TypeHandle, (byte)WellKnownType.Microsoft_VisualBasic_CallType,
                     (byte)SignatureTypeCode.SZArray, (byte)SignatureTypeCode.TypeHandle, (byte)SpecialType.System_Object,
 
-                // My_InternalXmlHelper__Value
-                (byte)(MemberFlags.Property | MemberFlags.Static),                                                          // Flags
-                (byte)WellKnownType.My_InternalXmlHelper,                                                                   // DeclaringTypeId
-                0,                                                                                                          // Arity
-                    1,                                                                                                      // Method Signature
-                    (byte)SignatureTypeCode.TypeHandle, (byte)SpecialType.System_String,
-                    (byte)SignatureTypeCode.GenericTypeInstance,
-                    (byte)SignatureTypeCode.TypeHandle, (byte)SpecialType.System_Collections_Generic_IEnumerable_T,
-                    1,
-                    (byte)SignatureTypeCode.TypeHandle, (byte)WellKnownType.System_Xml_Linq_XElement,
-
                 // System_Runtime_CompilerServices_IAsyncStateMachine_MoveNext
                 (byte)(MemberFlags.Method | MemberFlags.Virtual),                                                           // Flags
                 (byte)WellKnownType.System_Runtime_CompilerServices_IAsyncStateMachine,                                     // DeclaringTypeId
@@ -2799,7 +2788,6 @@ static WellKnownMembers()
                 "TypeName",                                 // Microsoft_VisualBasic_Information__TypeName
                 "VbTypeName",                               // Microsoft_VisualBasic_Information__VbTypeName
                 "CallByName",                               // Microsoft_VisualBasic_Interaction__CallByName
-                "Value",                                    // My_InternalXmlHelper__Value
                 "MoveNext",                                 // System_Runtime_CompilerServices_IAsyncStateMachine_MoveNext
                 "SetStateMachine",                          // System_Runtime_CompilerServices_IAsyncStateMachine_SetStateMachine
                 "SetException",                             // System_Runtime_CompilerServices_AsyncVoidMethodBuilder__SetException

src/Compilers/Core/Portable/WellKnownTypes.cs

@@ -101,8 +101,6 @@ internal enum WellKnownType
         Microsoft_VisualBasic_Information,
         Microsoft_VisualBasic_Interaction,
 
-        My_InternalXmlHelper,
-
         // standard Func delegates - must be ordered by arity
         System_Func_T,
         System_Func_T2,
@@ -349,8 +347,6 @@ internal static class WellKnownTypes
             "Microsoft.VisualBasic.Information",
             "Microsoft.VisualBasic.Interaction",
 
-            "My.InternalXmlHelper",
-
             "System.Func`1",
             "System.Func`2",
             "System.Func`3",

src/Compilers/VisualBasic/Portable/Binding/Binder.vb

@@ -3,6 +3,7 @@
 Imports System.Collections.Concurrent
 Imports System.Collections.Generic
 Imports System.Collections.Immutable
+Imports System.Reflection.Metadata
 Imports System.Runtime.InteropServices
 Imports System.Threading
 Imports Microsoft.CodeAnalysis.RuntimeMembers
@@ -326,6 +327,15 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
             End Get
         End Property
 
+        Friend ReadOnly Property ContainingModule As ModuleSymbol
+            Get
+                ' If there's a containing member, it either is or has a containing module.
+                ' Otherwise, we'll just use the compilation's source module.
+                Dim containingMember = Me.ContainingMember
+                Return If(TryCast(containingMember, ModuleSymbol), If(containingMember?.ContainingModule, Me.Compilation.SourceModule))
+            End Get
+        End Property
+
         ''' <summary>
         ''' Tells whether binding is happening in a query context.
         ''' </summary>
@@ -452,6 +462,79 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
             Return type.GetUseSiteErrorInfo()
         End Function
 
+        Private Function GetInternalXmlHelperType(syntax As VisualBasicSyntaxNode, diagBag As DiagnosticBag) As NamedTypeSymbol
+            Dim typeSymbol = GetInternalXmlHelperType()
+
+            Dim useSiteError = GetUseSiteErrorForWellKnownType(typeSymbol)
+            If useSiteError IsNot Nothing Then
+                ReportDiagnostic(diagBag, syntax, useSiteError)
+            End If
+
+            Return typeSymbol
+        End Function
+
+        Private Function GetInternalXmlHelperType() As NamedTypeSymbol
+            Const globalMetadataName = "My.InternalXmlHelper"
+            Dim metadataName = globalMetadataName
+
+            Dim rootNamespace = Me.Compilation.Options.RootNamespace
+            Dim haveRootNamespace As Boolean = Not String.IsNullOrEmpty(rootNamespace)
+            If haveRootNamespace Then
+                metadataName = $"{rootNamespace}.{metadataName}"
+            End If
+
+            Dim emittedName = MetadataTypeName.FromFullName(metadataName, useCLSCompliantNameArityEncoding:=True)
+
+            Dim containingModule = Me.ContainingModule
+            Dim typeSymbol = containingModule.LookupTopLevelMetadataType(emittedName)
+
+            ' Roslyn emits the type into the global namespace so we should look there too.
+            If haveRootNamespace AndAlso TypeOf typeSymbol Is MissingMetadataTypeSymbol Then
+                Dim globalEmittedName = MetadataTypeName.FromFullName(globalMetadataName, useCLSCompliantNameArityEncoding:=True)
+                Dim globalTypeSymbol = containingModule.LookupTopLevelMetadataType(globalEmittedName)
+                If TypeOf globalTypeSymbol IsNot MissingMetadataTypeSymbol Then
+                    typeSymbol = globalTypeSymbol
+                End If
+            End If
+
+            Return typeSymbol
+        End Function
+
+        ''' <summary>
+        ''' WARN: Retrieves the symbol but does not check its viability (accessibility, etc).
+        ''' </summary>
+        Private Function GetInternalXmlHelperValueExtensionProperty() As PropertySymbol
+            For Each candidate As Symbol In GetInternalXmlHelperType().GetMembers("Value")
+                If Not candidate.IsShared OrElse candidate.Kind <> SymbolKind.Property Then
+                    Continue For
+                End If
+
+                Dim candidateProperty = DirectCast(candidate, PropertySymbol)
+                If candidateProperty.Type.SpecialType <> SpecialType.System_String OrElse
+                    candidateProperty.TypeCustomModifiers.Length > 0 OrElse
+                    candidateProperty.ParameterCount <> 1 Then
+
+                    Continue For
+                End If
+
+                Dim parameter = candidateProperty.Parameters(0)
+                If parameter.CustomModifiers.Length > 0 Then
+                    Continue For
+                End If
+
+                Dim parameterType = parameter.Type
+                If parameterType.OriginalDefinition.SpecialType <> SpecialType.System_Collections_Generic_IEnumerable_T OrElse
+                        DirectCast(parameterType, NamedTypeSymbol).TypeArgumentsNoUseSiteDiagnostics(0) <> Me.Compilation.GetWellKnownType(WellKnownType.System_Xml_Linq_XElement) Then
+                    Continue For
+                End If
+
+                ' Only one symbol can match the criteria above, so we don't have to worry about ambiguity.
+                Return candidateProperty
+            Next
+
+            Return Nothing
+        End Function
+
         ''' <summary>
         ''' This is a layer on top of the assembly version that generates a diagnostic if the well-known
         ''' member isn't found.

src/Compilers/VisualBasic/Portable/Binding/Binder_Lookup.vb

@@ -153,7 +153,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
             End If
 
             ' Check for external symbols marked with 'Microsoft.VisualBasic.Embedded' attribute
-            If Me.Compilation.SourceModule IsNot unwrappedSym.ContainingModule AndAlso unwrappedSym.IsHiddenByEmbeddedAttribute() Then
+            If unwrappedSym.ContainingModule IsNot Me.ContainingModule AndAlso unwrappedSym.IsHiddenByEmbeddedAttribute() Then
                 Return SingleLookupResult.Empty
             End If
 
@@ -1197,7 +1197,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                     Return
                 End If
 
-                Dim symbol = compilation.GetWellKnownTypeMember(WellKnownMember.My_InternalXmlHelper__Value)
+                Dim symbol = binder.GetInternalXmlHelperValueExtensionProperty()
                 Dim singleResult As SingleLookupResult
                 If symbol Is Nothing Then
                     ' Match the native compiler which reports ERR_XmlFeaturesNotAvailable in this case.

src/Compilers/VisualBasic/Portable/Binding/Binder_XmlLiterals.vb

@@ -354,7 +354,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
 
                 ' Generate method group and arguments for RemoveNamespaceAttributes.
                 removeNamespacesGroup = GetXmlMethodOrPropertyGroup(syntax,
-                                                                    GetWellKnownType(WellKnownType.My_InternalXmlHelper, syntax, diagnostics),
+                                                                    GetInternalXmlHelperType(syntax, diagnostics),
                                                                     StringConstants.XmlRemoveNamespaceAttributesMethodName,
                                                                     Nothing,
                                                                     diagnostics)
@@ -423,7 +423,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                                                               ImmutableArray.Create(Of BoundExpression)(prefix, [namespace]),
                                                               diagnostics)
             Else
-                Dim type = GetWellKnownType(WellKnownType.My_InternalXmlHelper, syntax, diagnostics)
+                Dim type = GetInternalXmlHelperType(syntax, diagnostics)
                 Dim group = GetXmlMethodOrPropertyGroup(syntax, type, StringConstants.XmlCreateNamespaceAttributeMethodName, Nothing, diagnostics)
                 objectCreation = BindInvocationExpressionIfGroupNotNothing(syntax, group, ImmutableArray.Create(Of BoundExpression)(prefix, [namespace]), diagnostics)
             End If
@@ -478,7 +478,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                 ' with embedded expression values since CreateAttribute handles Nothing values.
                 value = BindXmlEmbeddedExpression(DirectCast(valueSyntax, XmlEmbeddedExpressionSyntax), diagnostics)
                 Dim group = GetXmlMethodOrPropertyGroup(valueSyntax,
-                                                        GetWellKnownType(WellKnownType.My_InternalXmlHelper, syntax, diagnostics),
+                                                        GetInternalXmlHelperType(syntax, diagnostics),
                                                         StringConstants.XmlCreateAttributeMethodName,
                                                         Nothing,
                                                         diagnostics)
@@ -653,7 +653,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                 Dim useSiteDiagnostics As HashSet(Of DiagnosticInfo) = Nothing
                 If receiverType.IsOrDerivedFrom(xmlType, useSiteDiagnostics) OrElse receiverType.IsCompatibleWithGenericIEnumerableOfType(xmlType, useSiteDiagnostics) Then
                     group = GetXmlMethodOrPropertyGroup(syntax,
-                                                            GetWellKnownType(WellKnownType.My_InternalXmlHelper, syntax, diagnostics),
+                                                            GetInternalXmlHelperType(syntax, diagnostics),
                                                             StringConstants.XmlAttributeValueMethodName,
                                                             Nothing,
                                                             diagnostics)

src/Compilers/VisualBasic/Portable/Binding/ImportAliasesBinder.vb

@@ -66,6 +66,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                 End If
             Next
         End Sub
+
+        Public Overrides ReadOnly Property ContainingMember As Symbol
+            Get
+                Return Me.Compilation.SourceModule
+            End Get
+        End Property
     End Class
 
 End Namespace

src/Compilers/VisualBasic/Test/Symbol/SymbolsTests/XmlLiteralsTests_UseSiteErrors.vb

@@ -208,12 +208,9 @@ Namespace System.Xml.Linq
     Public Class XNamespace
     End Class
 End Namespace
-Namespace My
-    Public Module InternalXmlHelper
-        Public Function RemoveNamespaceAttributes(prefixes As String(), namespaces As XNamespace(), attributes As Object, o As Object) As Object
-            Return Nothing
-        End Function
-    End Module
+Namespace Microsoft.VisualBasic.CompilerServices
+    Public Class StandardModuleAttribute : Inherits System.Attribute
+    End Class
 End Namespace
     ]]></file>
 </compilation>)
@@ -222,11 +219,20 @@ End Namespace
 <compilation name="XAttributeTypeMissing">
     <file name="c.vb"><![CDATA[
 Option Strict On
+Imports System.Collections.Generic
+Imports System.Xml.Linq
 Class C
     Private F1 As Object = <x <%= Nothing %>/>
     Private F2 As Object = <x <%= "a" %>="b"/>
     Private F3 As Object = <x a=<%= "b" %>/>
 End Class
+Namespace My
+    Public Module InternalXmlHelper
+        Public Function RemoveNamespaceAttributes(prefixes As String(), namespaces As XNamespace(), attributes As Object, o As Object) As Object
+            Return Nothing
+        End Function
+    End Module
+End Namespace
     ]]></file>
 </compilation>, references:={New VisualBasicCompilationReference(compilation1)})
             compilation2.AssertTheseDiagnostics(<errors><![CDATA[
@@ -271,12 +277,9 @@ Namespace System.Xml.Linq
     Public Class XNamespace
     End Class
 End Namespace
-Namespace My
-    Public Module InternalXmlHelper
-        Public Function RemoveNamespaceAttributes(prefixes As String(), namespaces As XNamespace(), attributes As List(Of XAttribute), o As Object) As Object
-            Return Nothing
-        End Function
-    End Module
+Namespace Microsoft.VisualBasic.CompilerServices
+    Public Class StandardModuleAttribute : Inherits System.Attribute
+    End Class
 End Namespace
     ]]></file>
 </compilation>)
@@ -285,11 +288,20 @@ End Namespace
 <compilation name="XAttributeTypeMissing">
     <file name="c.vb"><![CDATA[
 Option Strict On
+Imports System.Collections.Generic
+Imports System.Xml.Linq
 Class C
     Private F1 As Object = <x <%= Nothing %>/>
     Private F2 As Object = <x <%= "a" %>="b"/>
     Private F3 As Object = <x a=<%= "b" %>/>
 End Class
+Namespace My
+    Public Module InternalXmlHelper
+        Public Function RemoveNamespaceAttributes(prefixes As String(), namespaces As XNamespace(), attributes As List(Of XAttribute), o As Object) As Object
+            Return Nothing
+        End Function
+    End Module
+End Namespace
     ]]></file>
 </compilation>, references:={New VisualBasicCompilationReference(compilation1)})
             compilation2.AssertTheseDiagnostics(<errors><![CDATA[
@@ -599,15 +611,9 @@ Namespace System.Xml.Linq
     Public Class XNamespace
     End Class
 End Namespace
-Namespace My
-    Public Module InternalXmlHelper
-        Public Function CreateNamespaceAttribute(name As XName, ns As XNamespace) As XAttribute
-            Return Nothing
-        End Function
-        Public Function RemoveNamespaceAttributes(prefixes As String(), namespaces As XNamespace(), attributes As Object, o As Object) As Object
-            Return Nothing
-        End Function
-    End Module
+Namespace Microsoft.VisualBasic.CompilerServices
+    Public Class StandardModuleAttribute : Inherits System.Attribute
+    End Class
 End Namespace
     ]]></file>
 </compilation>)
@@ -616,9 +622,21 @@ End Namespace
 <compilation name="XNamespaceGetMissing">
     <file name="c.vb"><![CDATA[
 Imports <xmlns:p="http://roslyn/">
+Imports System.Collections.Generic
+Imports System.Xml.Linq
 Class C
     Shared F As Object = <p:x><%= Nothing %></>
 End Class
+Namespace My
+    Public Module InternalXmlHelper
+        Public Function CreateNamespaceAttribute(name As XName, ns As XNamespace) As XAttribute
+            Return Nothing
+        End Function
+        Public Function RemoveNamespaceAttributes(prefixes As String(), namespaces As XNamespace(), attributes As Object, o As Object) As Object
+            Return Nothing
+        End Function
+    End Module
+End Namespace
     ]]></file>
 </compilation>, references:={New VisualBasicCompilationReference(compilation1)})
             compilation2.AssertTheseDiagnostics(<errors><![CDATA[
@@ -711,9 +729,9 @@ Namespace System.Xml.Linq
     Public Module Extensions
     End Module
 End Namespace
-Namespace My
-    Public Module InternalXmlHelper
-    End Module
+Namespace Microsoft.VisualBasic.CompilerServices
+    Public Class StandardModuleAttribute : Inherits System.Attribute
+    End Class
 End Namespace
     ]]></file>
 </compilation>)
@@ -728,6 +746,10 @@ Class C
     Private F2 As Object = F1.<x>
     Private F3 As Object = F1.@x
 End Class
+Namespace My
+    Public Module InternalXmlHelper
+    End Module
+End Namespace
     ]]></file>
 </compilation>, references:={New VisualBasicCompilationReference(compilation1)})
             compilation2.AssertTheseDiagnostics(<errors><![CDATA[
@@ -758,8 +780,8 @@ Namespace System.Xml.Linq
     End Class
 End Namespace
 Namespace Microsoft.VisualBasic.CompilerServices
-    Public Module InternalXmlHelper
-    End Module
+    Public Class StandardModuleAttribute : Inherits System.Attribute
+    End Class
 End Namespace
     ]]></file>
 </compilation>)
@@ -775,6 +797,10 @@ Class C
         Return x.Value
     End Function
 End Class
+Namespace My
+    Public Module InternalXmlHelper
+    End Module
+End Namespace
     ]]></file>
 </compilation>, references:={New VisualBasicCompilationReference(compilation1)})
             compilation2.AssertTheseDiagnostics(<errors><![CDATA[
@@ -798,13 +824,8 @@ Namespace System.Xml.Linq
     End Class
 End Namespace
 Namespace Microsoft.VisualBasic.CompilerServices
-    Public Module InternalXmlHelper
-        Public ReadOnly Property Value(x As IEnumerable(Of XElement), y As Object, z As Object) As Object
-            Get
-                Return Nothing
-            End Get
-        End Property
-    End Module
+    Public Class StandardModuleAttribute : Inherits System.Attribute
+    End Class
 End Namespace
     ]]></file>
 </compilation>)
@@ -820,6 +841,15 @@ Class C
         Return x.VALUE
     End Function
 End Class
+Namespace My
+    Public Module InternalXmlHelper
+        Public ReadOnly Property Value(x As IEnumerable(Of XElement), y As Object, z As Object) As Object
+            Get
+                Return Nothing
+            End Get
+        End Property
+    End Module
+End Namespace
     ]]></file>
 </compilation>, references:={New VisualBasicCompilationReference(compilation1)})
             compilation2.AssertTheseDiagnostics(<errors><![CDATA[

src/ExpressionEvaluator/VisualBasic/Test/ExpressionCompiler/ExpressionCompilerTests.vb

@@ -1720,8 +1720,8 @@ End Class
             Assert.Equal(DkmEvaluationResultStorageType.None, resultProperties.StorageType)
         End Sub
 
-        <WorkItem(964, "GitHub")>
-        <Fact(Skip:="964")>
+        <WorkItem(964, "https://github.com/dotnet/roslyn/issues/964")>
+        <Fact>
         Public Sub EvaluateXmlMemberAccess()
             Dim source =
 "Class C
@@ -1762,6 +1762,96 @@ End Class"
 }")
         End Sub
 
+        <WorkItem(964, "https://github.com/dotnet/roslyn/issues/964")>
+        <Fact>
+        Public Sub InternalXmlHelper_RootNamespace()
+            Dim source =
+"Class C
+    Shared Sub M(x As System.Xml.Linq.XElement)
+        Dim y = x.@<y>
+    End Sub
+End Class"
+            Dim allReferences = GetAllXmlReferences()
+            Dim comp = CreateCompilationWithReferences(
+                MakeSources(source),
+                options:=TestOptions.DebugDll.WithRootNamespace("Root"),
+                references:=allReferences)
+            Dim exeBytes As Byte() = Nothing
+            Dim pdbBytes As Byte() = Nothing
+            Dim references As ImmutableArray(Of MetadataReference) = Nothing
+            comp.EmitAndGetReferences(exeBytes, pdbBytes, references)
+            Dim runtime = CreateRuntimeInstance(
+                ExpressionCompilerUtilities.GenerateUniqueName(),
+                allReferences,
+                exeBytes,
+                Nothing)
+            Dim context = CreateMethodContext(runtime, "Root.C.M")
+            Dim errorMessage As String = Nothing
+            Dim testData = New CompilationTestData()
+            Dim result = context.CompileExpression("x.@a", errorMessage, testData, VisualBasicDiagnosticFormatter.Instance)
+            Assert.Null(errorMessage)
+            testData.GetMethodData("<>x.<>m0").VerifyIL(
+"{
+  // Code size       22 (0x16)
+  .maxstack  3
+  .locals init (String V_0)
+  IL_0000:  ldarg.0
+  IL_0001:  ldstr      ""a""
+  IL_0006:  ldstr      """"
+  IL_000b:  call       ""Function System.Xml.Linq.XName.Get(String, String) As System.Xml.Linq.XName""
+  IL_0010:  call       ""Function My.InternalXmlHelper.get_AttributeValue(System.Xml.Linq.XElement, System.Xml.Linq.XName) As String""
+  IL_0015:  ret
+}")
+        End Sub
+
+        <WorkItem(964, "https://github.com/dotnet/roslyn/issues/964")>
+        <Fact>
+        Public Sub InternalXmlHelper_AddedModules()
+            Dim sourceTemplate =
+"Class C{0}
+    Shared Sub M(x As System.Xml.Linq.XElement)
+        Dim y = x.@<y>
+    End Sub
+End Class"
+            Dim xmlReferences = GetAllXmlReferences()
+            Dim moduleOptions = New VisualBasicCompilationOptions(OutputKind.NetModule, optimizationLevel:=OptimizationLevel.Debug).WithExtendedCustomDebugInformation(True)
+
+            Dim tree1 = VisualBasicSyntaxTree.ParseText(String.Format(sourceTemplate, 1))
+            Dim tree2 = VisualBasicSyntaxTree.ParseText(String.Format(sourceTemplate, 2))
+            Dim ref1 = CreateCompilationWithReferences(tree1, xmlReferences, moduleOptions, assemblyName:="Module1").EmitToImageReference()
+            Dim ref2 = CreateCompilationWithReferences(tree2, xmlReferences, moduleOptions, assemblyName:="Module2").EmitToImageReference()
+
+            Dim tree = VisualBasicSyntaxTree.ParseText(String.Format(sourceTemplate, ""))
+            Dim compReferences = xmlReferences.Concat(ImmutableArray.Create(ref1, ref2))
+            Dim comp = CreateCompilationWithReferences(tree, compReferences, TestOptions.DebugDll, assemblyName:="Test")
+
+            Dim exeBytes As Byte() = Nothing
+            Dim pdbBytes As Byte() = Nothing
+            Dim references As ImmutableArray(Of MetadataReference) = Nothing
+            comp.EmitAndGetReferences(exeBytes, pdbBytes, references)
+            Dim runtime = CreateRuntimeInstance(
+                ExpressionCompilerUtilities.GenerateUniqueName(),
+                compReferences,
+                exeBytes,
+                Nothing)
+            Dim context = CreateMethodContext(runtime, "C1.M") ' In Module1
+            Dim errorMessage As String = Nothing
+            Dim testData = New CompilationTestData()
+            Dim result = context.CompileExpression("x.@a", errorMessage, testData, VisualBasicDiagnosticFormatter.Instance)
+            Assert.Null(errorMessage)
+            testData.GetMethodData("<>x.<>m0").VerifyIL(
+"{
+  // Code size       22 (0x16)
+  .maxstack  3
+  IL_0000:  ldarg.0
+  IL_0001:  ldstr      ""a""
+  IL_0006:  ldstr      """"
+  IL_000b:  call       ""Function System.Xml.Linq.XName.Get(String, String) As System.Xml.Linq.XName""
+  IL_0010:  call       ""Function My.InternalXmlHelper.get_AttributeValue(System.Xml.Linq.XElement, System.Xml.Linq.XName) As String""
+  IL_0015:  ret
+}")
+        End Sub
+
         <Fact>
         Public Sub AssignByRefParameter()
             Const source =
@@ -3177,8 +3267,8 @@ End Module
         End Sub
 
         <WorkItem(1042918)>
-        <WorkItem(964, "GitHub")>
-        <Fact(Skip:="964")>
+        <WorkItem(964, "https://github.com/dotnet/roslyn/issues/964")>
+        <Fact>
         Public Sub ConditionalAccessExpressionType()
             Dim source =
 "Class C
@@ -3190,6 +3280,7 @@ End Module
     End Function
     Private X As System.Xml.Linq.XElement
     Sub M()
+        Dim dummy = Me?.X.@a ' Ensure InternalXmlHelper is emitted.
     End Sub
 End Class"
             Dim allReferences = GetAllXmlReferences()
@@ -3217,12 +3308,13 @@ End Class"
 "{
   // Code size       25 (0x19)
   .maxstack  1
-  .locals init (Integer? V_0)
+  .locals init (String V_0,
+                Integer? V_1)
   IL_0000:  ldarg.0
   IL_0001:  brtrue.s   IL_000d
-  IL_0003:  ldloca.s   V_0
+  IL_0003:  ldloca.s   V_1
   IL_0005:  initobj    ""Integer?""
-  IL_000b:  ldloc.0
+  IL_000b:  ldloc.1
   IL_000c:  ret
   IL_000d:  ldarg.0
   IL_000e:  call       ""Function C.F() As Integer""
@@ -3244,6 +3336,7 @@ End Class"
 "{
   // Code size       32 (0x20)
   .maxstack  3
+  .locals init (String V_0)
   IL_0000:  ldarg.0
   IL_0001:  brtrue.s   IL_0005
   IL_0003:  ldnull
@@ -3275,6 +3368,7 @@ End Class"
 "{
   // Code size       17 (0x11)
   .maxstack  2
+  .locals init (String V_0)
   IL_0000:  ldarg.0
   IL_0001:  callvirt   ""Function C.G() As C""
   IL_0006:  dup