Extended Keyword Parsing to cover member lookup expressions.

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

@@ -46,7 +46,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
         '    bool BailIfFirstTokenRejected                 // bail (return NULL) if the first token isn't a valid expression-starter, rather than reporting an error or setting ErrorInConstruct
         Private Function ParseExpressionCore(
             Optional pendingPrecedence As OperatorPrecedence = OperatorPrecedence.PrecedenceNone,
-            Optional bailIfFirstTokenRejected As Boolean = False
+            Optional bailIfFirstTokenRejected As Boolean = False,
+            Optional prevTerm As ExpressionSyntax = Nothing
         ) As ExpressionSyntax
 
             Try
@@ -107,7 +108,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                         expression = SyntaxFactory.AddressOfExpression(startToken, Operand)
 
                     Case Else
-                        expression = ParseTerm(bailIfFirstTokenRejected)
+                        expression = ParseTerm(bailIfFirstTokenRejected, prevTerm:=prevTerm)
 
                         If expression Is Nothing Then
                             Return Nothing
@@ -157,7 +158,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                         'Binary.Opcode = Opcode
 
                         'Binary.Left = Expr
-                        Dim rightOperand As ExpressionSyntax = ParseExpressionCore(precedence)
+                        Dim rightOperand As ExpressionSyntax = ParseExpressionCore(precedence, prevTerm:=prevTerm)
 
                         expression = SyntaxFactory.BinaryExpression(GetBinaryOperatorHelper([operator]), expression, [operator], rightOperand)
 
@@ -174,8 +175,9 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
         End Function
 
         Private Function ParseTerm(
-            Optional BailIfFirstTokenRejected As Boolean = False,
-            Optional RedimOrNewParent As Boolean = False
+            Optional bailIfFirstTokenRejected As Boolean = False,
+            Optional redimOrNewParent As Boolean = False,
+            Optional prevTerm As ExpressionSyntax = Nothing
         ) As ExpressionSyntax
 
             '// Note: this function will only ever return NULL if the flag "BailIfFirstTokenIsRejected" is set,
@@ -232,10 +234,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                     term = ParseSimpleNameExpressionAllowingKeywordAndTypeArguments()
 
                 Case SyntaxKind.ExclamationToken
-                    term = ParseQualifiedExpr(Nothing)
+                    term = ParseQualifiedExpr(prevTerm)
 
                 Case SyntaxKind.DotToken
-                    term = ParseQualifiedExpr(Nothing)
+                    term = ParseQualifiedExpr(prevTerm)
 
                 Case SyntaxKind.GlobalKeyword
                     ' NB. GetNextToken has the side-effect of advancing CurrentToken.
@@ -296,7 +298,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                     Dim tokenHasFullWidthChars As Boolean = TokenContainsFullWidthChars(start)
 
                     If tokenHasFullWidthChars Then
-                        If BailIfFirstTokenRejected Then
+                        If bailIfFirstTokenRejected Then
                             Return Nothing
                         End If
 
@@ -410,19 +412,33 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                 Case SyntaxKind.DollarSignDoubleQuoteToken
 
                     term = ParseInterpolatedStringExpression()
-
                 Case Else
-
                     If start.Kind = SyntaxKind.QuestionToken AndAlso CanStartConsequenceExpression(Me.PeekToken(1).Kind, qualified:=False) Then
                         ' This looks like ?. or ?! 
 
                         Dim qToken = DirectCast(start, PunctuationSyntax)
                         qToken = CheckFeatureAvailability(Feature.NullPropagatingOperator, qToken)
 
                         GetNextToken()
-                        term = SyntaxFactory.ConditionalAccessExpression(term, qToken, ParsePostFixExpression(RedimOrNewParent, term:=Nothing))
+                        term = SyntaxFactory.ConditionalAccessExpression(term, qToken, ParsePostFixExpression(redimOrNewParent, term:=Nothing))
                     Else
-                        If BailIfFirstTokenRejected Then
+                        If start.IsKeyword Then
+
+                            ' Is it in the form : [keyword] [qualifier] [identifier]
+                            ' If so treat the keyword as an identifier and continue to parse.
+                            Dim nextToken = PeekNextToken()
+                            If nextToken.Kind = SyntaxKind.DotToken OrElse nextToken.Kind = SyntaxKind.QuestionToken Then
+                                Dim keywordAsIdentifier = ParseSimpleNameExpressionAllowingKeywordAndTypeArguments()
+                                keywordAsIdentifier = ReportSyntaxError(keywordAsIdentifier, ERRID.ERR_InvalidUseOfKeyword)
+                                Dim _InvocationExpression_ = ParseExpressionCore(prevTerm:=keywordAsIdentifier)
+                                If _InvocationExpression_.Kind = SyntaxKind.InvocationExpression Then
+                                    Return _InvocationExpression_
+                                End If
+                            End If
+
+                        End If
+
+                        If bailIfFirstTokenRejected Then
                             Return Nothing
                         End If
 
@@ -439,7 +455,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                 ' Valid suffixes are ".", "!", and "(". Everything else is considered
                 ' to end the term.
 
-                term = ParsePostFixExpression(RedimOrNewParent, term)
+                term = ParsePostFixExpression(redimOrNewParent, term)
             End If
 
             If CurrentToken IsNot Nothing AndAlso CurrentToken.Kind = SyntaxKind.QuestionToken Then

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

@@ -332,4 +332,4 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
 
     End Class
 
-End Namespace
+End Namespace

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

@@ -417,7 +417,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
 
             ' peeking current token is strange, but ok. Note that it ignores the state.
             If tokenOffset = 0 Then
-                Debug.Assert(_currentToken.State = state)
+                Debug.Assert(_currentToken.State = state, $"_CurrentToken.State:={_currentToken.State} state:={state}")
 
                 Return GetCurrentToken()
             End If

src/Compilers/VisualBasic/Test/Syntax/Parser/InterpolatedStringParsingTests.vb

@@ -922,4 +922,22 @@ BC30648: String constants must end with a double quote.
 
     End Sub
 
+    <Fact>
+    Public Sub Test_KeywordExpression()
+        Dim code =
+"Class Example
+  Public ReadOnly Property [End] As Integer
+  Public Overrides Function ToString() As String
+    Return $""{End.ToString()})""
+  End Function
+End Class"
+        Dim result = Parse(code)
+        Dim diagnostics = result.GetDiagnostics.ToImmutableListOrEmpty
+        result.AssertTheseDiagnostics(
+        <expected>
+BC30183: Keyword is not valid as an identifier.
+    Return $"{End.ToString()})"
+              ~~~
+</expected>)
+    End Sub
 End Class