This is a partial fix for #3819 - #r in VB

I've done some manual testing, but there are no unit tests.

Existing unit tests are pass, except for ParseXml.Bug674567.  The fix is
either to change the baseline or to merge
https://github.com/dotnet/roslyn/pull/3957.

Conflicts:
	src/Compilers/VisualBasic/Portable/Scanner/Scanner.vb
	src/Compilers/VisualBasic/Portable/Syntax/CompilationUnitSyntax.vb
	src/Compilers/VisualBasic/Test/Semantic/Compilation/CompilationAPITests.vb

src/Compilers/CSharp/Portable/Declarations/DeclarationTreeBuilder.cs

@@ -149,13 +149,12 @@ private static ImmutableArray<ReferenceDirective> GetReferenceDirectives(Compila
                 return ImmutableArray<ReferenceDirective>.Empty;
             }
 
-            var directives = new ReferenceDirective[directiveNodes.Count];
-            for (int i = 0; i < directives.Length; i++)
+            var directives = ArrayBuilder<ReferenceDirective>.GetInstance(directiveNodes.Count);
+            foreach (var directiveNode in directiveNodes)
             {
-                directives[i] = new ReferenceDirective(directiveNodes[i].File.ValueText, new SourceLocation(directiveNodes[i]));
+                directives.Add(new ReferenceDirective(directiveNode.File.ValueText, new SourceLocation(directiveNode)));
             }
-
-            return directives.AsImmutableOrNull();
+            return directives.ToImmutableAndFree();
         }
 
         private SingleNamespaceOrTypeDeclaration CreateScriptClass(

src/Compilers/VisualBasic/Portable/Declarations/DeclarationTreeBuilder.vb

@@ -91,20 +91,18 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
             Return children
         End Function
 
-        Private Function GetReferenceDirectives(compilationUnit As CompilationUnitSyntax) As ImmutableArray(Of ReferenceDirective)
-            Dim directiveNodes = compilationUnit.GetReferenceDirectives(Function(d) Not d.File.ContainsDiagnostics AndAlso Not String.IsNullOrEmpty(d.File.ValueText))
-
+        Private Shared Function GetReferenceDirectives(compilationUnit As CompilationUnitSyntax) As ImmutableArray(Of ReferenceDirective)
+            Dim directiveNodes = compilationUnit.GetReferenceDirectives(
+                Function(d) Not d.File.ContainsDiagnostics AndAlso Not String.IsNullOrEmpty(d.File.ValueText))
             If directiveNodes.Count = 0 Then
                 Return ImmutableArray(Of ReferenceDirective).Empty
             End If
 
-            Dim directives = New ReferenceDirective(directiveNodes.Count - 1) {}
-
-            For i = 0 To directives.Length - 1
-                directives(i) = New ReferenceDirective(directiveNodes(i).File.ValueText, directiveNodes(i).GetLocation())
+            Dim directives = ArrayBuilder(Of ReferenceDirective).GetInstance(directiveNodes.Count)
+            For Each directiveNode In directiveNodes
+                directives.Add(New ReferenceDirective(directiveNode.File.ValueText, New SourceLocation(directiveNode)))
             Next
-
-            Return directives.AsImmutableOrNull()
+            Return directives.ToImmutableAndFree()
         End Function
 
         Private Function CreateImplicitClass(parent As VisualBasicSyntaxNode, memberNames As String(), children As ImmutableArray(Of SingleTypeDeclaration), declFlags As SingleTypeDeclaration.TypeDeclarationFlags) As SingleNamespaceOrTypeDeclaration
@@ -162,6 +160,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
             Dim syntaxRef = _syntaxTree.GetReference(node)
             Dim implicitClass As SingleNamespaceOrTypeDeclaration = Nothing
 
+            Dim referenceDirectives As ImmutableArray(Of ReferenceDirective)
             If _syntaxTree.Options.Kind <> SourceCodeKind.Regular Then
                 Dim childrenBuilder = ArrayBuilder(Of SingleNamespaceOrTypeDeclaration).GetInstance()
                 Dim scriptChildren = ArrayBuilder(Of SingleTypeDeclaration).GetInstance()
@@ -185,8 +184,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
 
                 implicitClass = CreateScriptClass(node, scriptChildren.ToImmutableAndFree(), memberNames, declFlags)
                 children = childrenBuilder.ToImmutableAndFree()
+                referenceDirectives = GetReferenceDirectives(node)
             Else
                 children = VisitNamespaceChildren(node, node.Members, implicitClass).ToImmutableAndFree()
+                referenceDirectives = ImmutableArray(Of ReferenceDirective).Empty
             End If
 
             ' Find children within NamespaceGlobal separately
@@ -198,7 +199,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
                     hasImports:=True,
                     treeNode:=_syntaxTree.GetReference(node),
                     children:=globalChildren.Concat(nonGlobal),
-                    referenceDirectives:=ImmutableArray(Of ReferenceDirective).Empty,
+                    referenceDirectives:=referenceDirectives,
                     hasAssemblyAttributes:=node.Attributes.Any)
             Else
                 ' Project-level root namespace. All children without explicit global are children
@@ -213,7 +214,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Symbols
                     hasImports:=True,
                     treeNode:=_syntaxTree.GetReference(node),
                     children:=newChildren,
-                    referenceDirectives:=ImmutableArray(Of ReferenceDirective).Empty,
+                    referenceDirectives:=referenceDirectives,
                     hasAssemblyAttributes:=node.Attributes.Any)
             End If
         End Function

src/Compilers/VisualBasic/Portable/Parser/ParseConditional.vb

@@ -76,6 +76,9 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                         Case SyntaxKind.EnableKeyword, SyntaxKind.DisableKeyword
                             statement = ParseWarningDirective(hashToken)
 
+                        Case SyntaxKind.ReferenceKeyword
+                            statement = ParseReferenceDirective(hashToken)
+
                         Case Else
                             statement = ParseBadDirective(hashToken)
                     End Select
@@ -248,7 +251,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
 
         Private Function ParseRegionDirective(hashToken As PunctuationSyntax) As RegionDirectiveTriviaSyntax
             Debug.Assert(CurrentToken.Kind = SyntaxKind.IdentifierToken AndAlso DirectCast(CurrentToken, IdentifierTokenSyntax).PossibleKeywordKind = SyntaxKind.RegionKeyword,
-                         "ParseRegionDirective called with wrong token.")
+                         $"{NameOf(ParseRegionDirective)} called with wrong token.")
 
             Dim identifier = DirectCast(CurrentToken, IdentifierTokenSyntax)
             GetNextToken()
@@ -262,7 +265,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
 
         Private Function ParseExternalSourceDirective(hashToken As PunctuationSyntax) As ExternalSourceDirectiveTriviaSyntax
             Debug.Assert(CurrentToken.Kind = SyntaxKind.IdentifierToken AndAlso DirectCast(CurrentToken, IdentifierTokenSyntax).PossibleKeywordKind = SyntaxKind.ExternalSourceKeyword,
-                         "ParseExternalSourceDirective called with wrong token")
+                         $"{NameOf(ParseExternalSourceDirective)} called with wrong token")
 
             Dim identifier = DirectCast(CurrentToken, IdentifierTokenSyntax)
             Dim externalSourceKeyword = _scanner.MakeKeyword(identifier)
@@ -309,7 +312,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
 
         Private Function ParseExternalChecksumDirective(hashToken As PunctuationSyntax) As ExternalChecksumDirectiveTriviaSyntax
             Debug.Assert(CurrentToken.Kind = SyntaxKind.IdentifierToken AndAlso DirectCast(CurrentToken, IdentifierTokenSyntax).PossibleKeywordKind = SyntaxKind.ExternalChecksumKeyword,
-                          "ParseExternalChecksumDirective called with wrong token")
+                          $"{NameOf(ParseExternalChecksumDirective)} called with wrong token")
 
             Dim identifier = DirectCast(CurrentToken, IdentifierTokenSyntax)
             Dim externalChecksumKeyword = _scanner.MakeKeyword(identifier)
@@ -377,12 +380,12 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
 
         Private Function ParseWarningDirective(hashToken As PunctuationSyntax) As DirectiveTriviaSyntax
             Debug.Assert(CurrentToken.Kind = SyntaxKind.IdentifierToken,
-                         "ParseWarningDirective called with token that is not an IdentifierToken")
+                         $"{NameOf(ParseWarningDirective)} called with token that is not an {NameOf(SyntaxKind.IdentifierToken)}")
             Dim identifier = DirectCast(CurrentToken, IdentifierTokenSyntax)
 
             Debug.Assert((identifier.PossibleKeywordKind = SyntaxKind.EnableKeyword) OrElse
                          (identifier.PossibleKeywordKind = SyntaxKind.DisableKeyword),
-                         "ParseWarningDirective called with token that is neither EnableKeyword nor DisableKeyword")
+                         $"{NameOf(ParseWarningDirective)} called with token that is neither {NameOf(SyntaxKind.EnableKeyword)} nor {NameOf(SyntaxKind.DisableKeyword)}")
             Dim enableOrDisableKeyword = _scanner.MakeKeyword(identifier)
 
             GetNextToken()
@@ -439,6 +442,24 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
             Return statement
         End Function
 
+        Private Function ParseReferenceDirective(hashToken As PunctuationSyntax) As DirectiveTriviaSyntax
+            Debug.Assert(CurrentToken.Kind = SyntaxKind.IdentifierToken AndAlso DirectCast(CurrentToken, IdentifierTokenSyntax).PossibleKeywordKind = SyntaxKind.ReferenceKeyword,
+                         $"{NameOf(ParseReferenceDirective)} called with wrong token.")
+
+            Dim identifier = DirectCast(CurrentToken, IdentifierTokenSyntax)
+            GetNextToken()
+            Dim referenceKeyword = _scanner.MakeKeyword(identifier)
+
+            If Not IsScript Then
+                referenceKeyword = AddError(referenceKeyword, ERRID.ERR_ReferenceDirectiveOnlyAllowedInScripts)
+            End If
+
+            Dim title As StringLiteralTokenSyntax = Nothing
+            VerifyExpectedToken(SyntaxKind.StringLiteralToken, title)
+
+            Return SyntaxFactory.ReferenceDirectiveTrivia(hashToken, referenceKeyword, title)
+        End Function
+
         Private Shared Function ParseBadDirective(hashToken As PunctuationSyntax) As BadDirectiveTriviaSyntax
             Dim badDirective = InternalSyntaxFactory.BadDirectiveTrivia(hashToken)
 

src/Compilers/VisualBasic/Portable/Scanner/Directives.vb

@@ -208,7 +208,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                 Case SyntaxKind.ExternalChecksumDirectiveTrivia,
                     SyntaxKind.BadDirectiveTrivia,
                     SyntaxKind.EnableWarningDirectiveTrivia, 'TODO: Add support for processing #Enable and #Disable
-                    SyntaxKind.DisableWarningDirectiveTrivia
+                    SyntaxKind.DisableWarningDirectiveTrivia,
+                    SyntaxKind.ReferenceDirectiveTrivia
 
                     ' These directives require no processing
 

src/Compilers/VisualBasic/Portable/Scanner/KeywordTable.vb

@@ -131,6 +131,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax
                 SyntaxKind.PublicKeyword, None,
                 SyntaxKind.RaiseEventKeyword, None,
                 SyntaxKind.ReadOnlyKeyword, None,
+                SyntaxKind.ReferenceKeyword, None,
                 SyntaxKind.ReDimKeyword, None,
                 SyntaxKind.REMKeyword, CanFollowExpr,
                 SyntaxKind.RemoveHandlerKeyword, None,
@@ -297,7 +298,11 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax
 
             Dim kind As SyntaxKind
             If Not s_keywords.TryGetValue(tokenName, kind) Then
-                kind = SyntaxKind.IdentifierToken
+                ' s_keywords includes preprocessor keywords, but only one of
+                ' "r" and "reference".  GetProcessorKeywordKind supports both.
+                Dim preprocessorKind = SyntaxFacts.GetPreprocessorKeywordKind(tokenName)
+                Debug.Assert(preprocessorKind = SyntaxKind.None OrElse preprocessorKind = SyntaxKind.ReferenceKeyword)
+                kind = If(preprocessorKind <> SyntaxKind.None, preprocessorKind, SyntaxKind.IdentifierToken)
             End If
             Return kind
         End Function

src/Compilers/VisualBasic/Portable/Scanner/Scanner.vb

@@ -1469,7 +1469,7 @@ FullWidthRepeat:
         End Function
 
         Private Function TokenOfStringCached(spelling As String) As SyntaxKind
-            If spelling.Length = 1 OrElse spelling.Length > 16 Then
+            If spelling.Length > 16 Then
                 Return SyntaxKind.IdentifierToken
             End If
 

src/Compilers/VisualBasic/Portable/Syntax/CompilationUnitSyntax.vb

 ' Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
-Imports System
-Imports System.Collections.Generic
-Imports Microsoft.CodeAnalysis.Text
-Imports Microsoft.CodeAnalysis.VisualBasic.Symbols
-Imports Microsoft.CodeAnalysis.VisualBasic.Syntax
-
 Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax
 
     Partial Public NotInheritable Class CompilationUnitSyntax

src/Compilers/VisualBasic/Portable/Syntax/InternalSyntax/SyntaxNodeFactories.vb

@@ -342,6 +342,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                 SyntaxKind.OrderKeyword,
                 SyntaxKind.PreserveKeyword,
                 SyntaxKind.RegionKeyword,
+                SyntaxKind.ReferenceKeyword,
                 SyntaxKind.SkipKeyword,
                 SyntaxKind.StrictKeyword,
                 SyntaxKind.TextKeyword,

src/Compilers/VisualBasic/Portable/Syntax/SyntaxKindFacts.vb

@@ -18,9 +18,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
         ''' Determine if the kind represents a contextual keyword
         ''' </summary>
         Public Shared Function IsContextualKeyword(kind As SyntaxKind) As Boolean
-            Return kind - SyntaxKind.AggregateKeyword <=
-                    SyntaxKind.YieldKeyword - SyntaxKind.AggregateKeyword
-
+            Return kind = SyntaxKind.ReferenceKeyword OrElse
+                (SyntaxKind.AggregateKeyword <= kind AndAlso kind <= SyntaxKind.YieldKeyword)
         End Function
 
         ''' <summary>
@@ -66,6 +65,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                     SyntaxKind.RegionKeyword,
                     SyntaxKind.EndKeyword,
                     SyntaxKind.ConstKeyword,
+                    SyntaxKind.ReferenceKeyword,
                     SyntaxKind.EnableKeyword,
                     SyntaxKind.DisableKeyword,
                     SyntaxKind.ExternalSourceKeyword,
@@ -272,6 +272,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
             SyntaxKind.OutKeyword,
             SyntaxKind.PreserveKeyword,
             SyntaxKind.RegionKeyword,
+            SyntaxKind.ReferenceKeyword,
             SyntaxKind.SkipKeyword,
             SyntaxKind.StrictKeyword,
             SyntaxKind.TakeKeyword,
@@ -354,6 +355,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                                                             SyntaxKind.EndKeyword,
                                                             SyntaxKind.RegionKeyword,
                                                             SyntaxKind.ConstKeyword,
+                                                            SyntaxKind.ReferenceKeyword,
                                                             SyntaxKind.EnableKeyword,
                                                             SyntaxKind.DisableKeyword,
                                                             SyntaxKind.WarningKeyword,
@@ -797,6 +799,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                    {"out", SyntaxKind.OutKeyword},
                    {"preserve", SyntaxKind.PreserveKeyword},
                    {"region", SyntaxKind.RegionKeyword},
+                   {"reference", SyntaxKind.ReferenceKeyword},
+                   {"r", SyntaxKind.ReferenceKeyword},
                    {"skip", SyntaxKind.SkipKeyword},
                    {"strict", SyntaxKind.StrictKeyword},
                    {"take", SyntaxKind.TakeKeyword},
@@ -831,6 +835,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
                    {"const", SyntaxKind.ConstKeyword},
                    {"externalsource", SyntaxKind.ExternalSourceKeyword},
                    {"externalchecksum", SyntaxKind.ExternalChecksumKeyword},
+                   {"reference", SyntaxKind.ReferenceKeyword},
+                   {"r", SyntaxKind.ReferenceKeyword},
                    {"enable", SyntaxKind.EnableKeyword},
                    {"disable", SyntaxKind.DisableKeyword}
             }

src/Compilers/VisualBasic/Portable/VBResources.Designer.vb

@@ -3783,7 +3783,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
         End Property
         
         '''<summary>
-        '''  Looks up a localized string similar to &apos;If&apos;, &apos;ElseIf&apos;, &apos;Else&apos;, &apos;Const&apos;, &apos;Region&apos;, &apos;ExternalSource&apos;, &apos;ExternalChecksum&apos;, &apos;Enable&apos;, &apos;Disable&apos;, or &apos;End&apos; expected..
+        '''  Looks up a localized string similar to &apos;If&apos;, &apos;ElseIf&apos;, &apos;Else&apos;, &apos;Const&apos;, &apos;Region&apos;, &apos;ExternalSource&apos;, &apos;ExternalChecksum&apos;, &apos;Enable&apos;, &apos;Disable&apos;, &apos;End&apos;, &apos;R&apos;, or &apos;Reference&apos; expected..
         '''</summary>
         Friend ReadOnly Property ERR_ExpectedConditionalDirective() As String
             Get

src/Compilers/VisualBasic/Portable/VBResources.resx

@@ -742,7 +742,7 @@
     <value>'{0}' is not valid on a local variable declaration.</value>
   </data>
   <data name="ERR_ExpectedConditionalDirective" xml:space="preserve">
-    <value>'If', 'ElseIf', 'Else', 'Const', 'Region', 'ExternalSource', 'ExternalChecksum', 'Enable', 'Disable', or 'End' expected.</value>
+    <value>'If', 'ElseIf', 'Else', 'Const', 'Region', 'ExternalSource', 'ExternalChecksum', 'Enable', 'Disable', 'End', 'R', or 'Reference' expected.</value>
   </data>
   <data name="ERR_ExpectedEQ" xml:space="preserve">
     <value>'=' expected.</value>

src/Compilers/VisualBasic/Test/Semantic/Compilation/CompilationAPITests.vb

@@ -1496,6 +1496,7 @@ End Class
             Dim a = VisualBasicCompilation.Create("c", syntaxTrees:={ta})
 
             ' add:
+
             Dim ab = a.AddSyntaxTrees(tb)
             Assert.True(a.ReferenceManagerEquals(ab))
 
@@ -1503,39 +1504,41 @@ End Class
             Assert.True(a.ReferenceManagerEquals(ac))
 
             Dim ar = a.AddSyntaxTrees(tr)
-            Assert.True(a.ReferenceManagerEquals(ar))
+            Assert.False(a.ReferenceManagerEquals(ar))
 
             Dim arc = ar.AddSyntaxTrees(tc)
             Assert.True(ar.ReferenceManagerEquals(arc))
 
             ' remove:
+
             Dim ar2 = arc.RemoveSyntaxTrees(tc)
             Assert.True(arc.ReferenceManagerEquals(ar2))
 
             Dim c = arc.RemoveSyntaxTrees(ta, tr)
-            Assert.True(arc.ReferenceManagerEquals(c))
+            Assert.False(arc.ReferenceManagerEquals(c))
 
             Dim none1 = c.RemoveSyntaxTrees(tc)
             Assert.True(c.ReferenceManagerEquals(none1))
 
             Dim none2 = arc.RemoveAllSyntaxTrees()
-            Assert.True(arc.ReferenceManagerEquals(none2))
+            Assert.False(arc.ReferenceManagerEquals(none2))
 
             Dim none3 = ac.RemoveAllSyntaxTrees()
             Assert.True(ac.ReferenceManagerEquals(none3))
 
             ' replace:
+
             Dim asc = arc.ReplaceSyntaxTree(tr, ts)
-            Assert.True(arc.ReferenceManagerEquals(asc))
+            Assert.False(arc.ReferenceManagerEquals(asc))
 
             Dim brc = arc.ReplaceSyntaxTree(ta, tb)
             Assert.True(arc.ReferenceManagerEquals(brc))
 
             Dim abc = arc.ReplaceSyntaxTree(tr, tb)
-            Assert.True(arc.ReferenceManagerEquals(abc))
+            Assert.False(arc.ReferenceManagerEquals(abc))
 
             Dim ars = arc.ReplaceSyntaxTree(tc, ts)
-            Assert.True(arc.ReferenceManagerEquals(ars))
+            Assert.False(arc.ReferenceManagerEquals(ars))
         End Sub
 
         Private Class EvolvingTestReference

src/Compilers/VisualBasic/Test/Syntax/Syntax/SyntaxFactsTest.vb

@@ -102,7 +102,7 @@ Public Class SyntaxFactsTests
         Assert.Equal(SyntaxKind.None, SyntaxFacts.GetContextualKeywordKind(String.Empty))
         Assert.Equal(SyntaxKind.None, SyntaxFacts.GetBaseTypeStatementKind(SyntaxKind.ForKeyword))
 
-        Dim expected = New String() {"aggregate", "all", "ansi", "ascending", "assembly", "async", "auto", "await", "binary", "by", "compare", "custom", "descending", "distinct", "equals", "explicit", "externalsource", "externalchecksum", "from", "group", "infer", "into", "isfalse", "istrue", "iterator", "join", "key", "mid", "off", "order", "out", "preserve", "region", "skip", "strict", "take", "text", "unicode", "until", "where", "type", "xml", "yield", "enable", "disable", "warning"}
+        Dim expected = New String() {"aggregate", "all", "ansi", "ascending", "assembly", "async", "auto", "await", "binary", "by", "compare", "custom", "descending", "distinct", "equals", "explicit", "externalsource", "externalchecksum", "from", "group", "infer", "into", "isfalse", "istrue", "iterator", "join", "key", "mid", "off", "order", "out", "preserve", "region", "skip", "strict", "take", "text", "unicode", "until", "where", "type", "xml", "yield", "enable", "disable", "warning", "reference"}
         For Each item In expected
             Assert.NotEqual(SyntaxKind.None, SyntaxFacts.GetContextualKeywordKind(item))
         Next

src/Workspaces/VisualBasic/Portable/Classification/Worker.vb

@@ -167,6 +167,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Classification
                              SyntaxKind.ExternalSourceKeyword,
                              SyntaxKind.ExternalChecksumKeyword,
                              SyntaxKind.EnableKeyword,
+                             SyntaxKind.ReferenceKeyword,
                              SyntaxKind.WarningKeyword,
                              SyntaxKind.DisableKeyword
 
@@ -180,4 +181,4 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Classification
             Next
         End Sub
     End Class
-End Namespace
\ No newline at end of file
+End Namespace