Merge pull request #14822 from AlekseyTs/Issue14761_1

Adjust the way parser handles line-If termination.

src/Compilers/VisualBasic/Portable/Parser/BlockContexts/BlockContext.vb

@@ -301,17 +301,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
 
         Friend MustOverride Function ProcessStatementTerminator(lambdaContext As BlockContext) As BlockContext
 
-        Friend Overridable Function ProcessElseAsStatementTerminator() As BlockContext
-            ' Nothing to do. The Else should be processed as a
-            ' statement associated with this context.
-            Return Me
-        End Function
-
-        Friend Overridable Function ProcessOtherAsStatementTerminator() As BlockContext
-            ' Nothing to do.
-            Return Me
-        End Function
-
         Friend MustOverride ReadOnly Property IsSingleLine As Boolean
 
         Friend Overridable ReadOnly Property IsLambda As Boolean

src/Compilers/VisualBasic/Portable/Parser/BlockContexts/SingleLineElseContext.vb

@@ -14,6 +14,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
             MyBase.New(kind, statement, prevContext)
 
             Debug.Assert(kind = SyntaxKind.SingleLineElseClause)
+            Debug.Assert(prevContext.BlockKind = SyntaxKind.SingleLineIfStatement)
         End Sub
 
         Friend Overrides Function ProcessSyntax(node As VisualBasicSyntaxNode) As BlockContext
@@ -92,34 +93,90 @@ EndBlock:
                     End If
                     GoTo EndBlock
 
+                Case Else
+                    Throw ExceptionUtilities.UnexpectedValue(token.Kind)
+            End Select
+        End Function
+
+        Friend Overrides Function ResyncAndProcessStatementTerminator(statement As StatementSyntax, lambdaContext As BlockContext) As BlockContext
+            Dim token = Parser.CurrentToken
+            Select Case token.Kind
+                Case SyntaxKind.StatementTerminatorToken, SyntaxKind.EndOfFileToken, SyntaxKind.ColonToken
+                    Return ProcessStatementTerminator(lambdaContext)
+
                 Case SyntaxKind.ElseKeyword
-                    ' Terminated by Else from containing block.
-                    Parser.ConsumedStatementTerminator(allowLeadingMultilineTrivia:=False)
-                    Return ProcessElseAsStatementTerminator()
+                    If TreatElseAsStatementTerminator Then
+                        ' Terminated by Else from containing block.
+                        Parser.ConsumedStatementTerminator(allowLeadingMultilineTrivia:=False)
+                        Return ProcessElseAsStatementTerminator()
+                    End If
+
+                    Return MyBase.ResyncAndProcessStatementTerminator(statement, lambdaContext)
 
                 Case Else
                     ' Terminated if we've already seen at least one statement.
                     If _statements.Count > 0 Then
-                        Return ProcessOtherAsStatementTerminator()
-                    End If
-                    ' Terminated if the next token can follow a statement.
-                    If Parser.CanFollowStatementButIsNotSelectFollowingExpression(token) Then
-                        Return ProcessOtherAsStatementTerminator()
+                        If TreatOtherAsStatementTerminator Then
+                            Return ProcessOtherAsStatementTerminator()
+                        End If
+
+                        Return MyBase.ResyncAndProcessStatementTerminator(statement, lambdaContext)
                     End If
+
                     Parser.ConsumedStatementTerminator(allowLeadingMultilineTrivia:=False)
                     Return Me
-
             End Select
         End Function
 
-        Friend Overrides Function ProcessElseAsStatementTerminator() As BlockContext
-            Dim context = EndBlock(Nothing)
-            Return context.ProcessElseAsStatementTerminator()
-        End Function
-
-        Friend Overrides Function ProcessOtherAsStatementTerminator() As BlockContext
-            Dim context = EndBlock(Nothing)
-            Return context.ProcessOtherAsStatementTerminator()
+        Private ReadOnly Property TreatElseAsStatementTerminator As Boolean
+            Get
+                ' We can treat 'Else' as a valid statement terminator only
+                ' if there is a line-If without Else up the block context chain, or
+                ' if we are inside a single-line statement lambda and the 'Else' terminates the lambda.
+                Debug.Assert(BlockKind = SyntaxKind.SingleLineElseClause)
+                Debug.Assert(PrevBlock.BlockKind = SyntaxKind.SingleLineIfStatement)
+
+                Dim possiblyLineIfWithoutElse = PrevBlock.PrevBlock
+
+                While possiblyLineIfWithoutElse.BlockKind <> SyntaxKind.SingleLineIfStatement
+                    Select Case possiblyLineIfWithoutElse.BlockKind
+                        Case SyntaxKind.SingleLineElseClause
+                            ' This is a line-If with Else, jump out of it
+                            Debug.Assert(possiblyLineIfWithoutElse.PrevBlock.BlockKind = SyntaxKind.SingleLineIfStatement)
+                            possiblyLineIfWithoutElse = possiblyLineIfWithoutElse.PrevBlock.PrevBlock
+
+                        Case SyntaxKind.SingleLineSubLambdaExpression
+                            Return True
+
+                        Case Else
+                            Return False
+                    End Select
+                End While
+
+                Debug.Assert(possiblyLineIfWithoutElse.BlockKind = SyntaxKind.SingleLineIfStatement)
+                Return True
+            End Get
+        End Property
+
+        Private Function ProcessElseAsStatementTerminator() As BlockContext
+            Dim context = EndBlock(Nothing) ' This gets us out of entire line-if context
+
+            While context.BlockKind <> SyntaxKind.SingleLineIfStatement
+                Select Case context.BlockKind
+                    Case SyntaxKind.SingleLineElseClause
+                        ' This is a line-If with Else, jump out of it
+                        context = context.EndBlock(Nothing) ' This gets us out of entire line-if context
+
+                    Case SyntaxKind.SingleLineSubLambdaExpression
+                        ' This will force termination of the single line lambda
+                        Return context.PrevBlock
+
+                    Case Else
+                        Throw ExceptionUtilities.UnexpectedValue(context.BlockKind)
+                End Select
+            End While
+
+            Return context
         End Function
 
     End Class

src/Compilers/VisualBasic/Portable/Parser/BlockContexts/SingleLineIfBlockContext.vb

@@ -11,6 +11,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
         Inherits SingleLineIfOrElseBlockContext
 
         Private _optionalElseClause As SingleLineElseClauseSyntax
+        Private _haveElseClause As Boolean
 
         Friend Sub New(statement As StatementSyntax, prevContext As BlockContext)
             MyBase.New(SyntaxKind.SingleLineIfStatement, statement, prevContext)
@@ -36,6 +37,11 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                     Return Me.EndBlock(Nothing)
 
                 Case SyntaxKind.ElseStatement
+                    If _haveElseClause Then
+                        Throw ExceptionUtilities.Unreachable
+                    End If
+
+                    _haveElseClause = True
                     Return New SingleLineElseContext(SyntaxKind.SingleLineElseClause, DirectCast(node, StatementSyntax), Me)
 
                 Case SyntaxKind.SingleLineElseClause
@@ -90,6 +96,17 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                     Parser.ConsumeColonInSingleLineExpression()
                     Return Me
 
+                Case Else
+                    Throw ExceptionUtilities.UnexpectedValue(token.Kind)
+            End Select
+        End Function
+
+        Friend Overrides Function ResyncAndProcessStatementTerminator(statement As StatementSyntax, lambdaContext As BlockContext) As BlockContext
+            Dim token = Parser.CurrentToken
+            Select Case token.Kind
+                Case SyntaxKind.StatementTerminatorToken, SyntaxKind.EndOfFileToken, SyntaxKind.ColonToken
+                    Return ProcessStatementTerminator(lambdaContext)
+
                 Case SyntaxKind.ElseKeyword
                     Parser.ConsumedStatementTerminator(allowLeadingMultilineTrivia:=False)
                     Return Me
@@ -97,19 +114,18 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
                 Case Else
                     ' Terminated if we've already seen at least one statement.
                     If _statements.Count > 0 Then
-                        Return ProcessOtherAsStatementTerminator()
+                        If TreatOtherAsStatementTerminator Then
+                            Return ProcessOtherAsStatementTerminator()
+                        End If
+
+                        Return MyBase.ResyncAndProcessStatementTerminator(statement, lambdaContext)
                     End If
+
                     Parser.ConsumedStatementTerminator(allowLeadingMultilineTrivia:=False)
                     Return Me
-
             End Select
         End Function
 
-        Friend Overrides Function ProcessOtherAsStatementTerminator() As BlockContext
-            Dim context = EndBlock(Nothing)
-            Return context.ProcessOtherAsStatementTerminator()
-        End Function
-
     End Class
 
 End Namespace

src/Compilers/VisualBasic/Portable/Parser/BlockContexts/SingleLineIfOrElseBlockContext.vb

@@ -9,15 +9,54 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
             MyBase.New(kind, statement, prevContext)
         End Sub
 
-        Friend Overrides Function ResyncAndProcessStatementTerminator(statement As StatementSyntax, lambdaContext As BlockContext) As BlockContext
-            Return ProcessStatementTerminator(lambdaContext)
-        End Function
-
         Friend Overrides ReadOnly Property IsSingleLine As Boolean
             Get
                 Return True
             End Get
         End Property
+
+        Protected ReadOnly Property TreatOtherAsStatementTerminator As Boolean
+            Get
+                ' Is this line-If, or immediately enclosing line-If(s), 
+                ' a body of a single-line statement lambda. Then the token 
+                ' terminates the lambda
+                Dim parentContext As BlockContext = PrevBlock
+
+                Do
+                    Select Case parentContext.BlockKind
+                        Case SyntaxKind.SingleLineElseClause,
+                             SyntaxKind.SingleLineIfStatement
+                            parentContext = parentContext.PrevBlock
+
+                        Case SyntaxKind.SingleLineSubLambdaExpression
+                            Return True
+
+                        Case Else
+                            Return False
+                    End Select
+                Loop
+            End Get
+        End Property
+
+        Protected Function ProcessOtherAsStatementTerminator() As BlockContext
+            Dim context = EndBlock(Nothing)
+
+            Do
+                Select Case context.BlockKind
+                    Case SyntaxKind.SingleLineElseClause,
+                         SyntaxKind.SingleLineIfStatement
+                        context = context.EndBlock(Nothing)
+
+                    Case SyntaxKind.SingleLineSubLambdaExpression
+                        ' This will force termination of the single line lambda
+                        Return context.PrevBlock
+
+                    Case Else
+                        Throw ExceptionUtilities.UnexpectedValue(context.BlockKind)
+                End Select
+            Loop
+        End Function
+
     End Class
 
 End Namespace

src/Compilers/VisualBasic/Portable/Parser/BlockContexts/SingleLineLambdaContext.vb

@@ -85,16 +85,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
             Return PrevBlock
         End Function
 
-        Friend Overrides Function ProcessElseAsStatementTerminator() As BlockContext
-            ' Else from outer If terminates the lambda.
-            Return PrevBlock
-        End Function
-
-        Friend Overrides Function ProcessOtherAsStatementTerminator() As BlockContext
-            ' Other non-terminator terminates the lambda.
-            Return PrevBlock
-        End Function
-
         Friend Overrides ReadOnly Property IsSingleLine As Boolean
             Get
                 Return True

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

@@ -62,11 +62,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Syntax.InternalSyntax
             ' // enabled), and it isn't possible to look back past the first token of a
             ' // line, so test if this is the first token of the last read line.
 
-            ' // (bug 32704) "else" is a special case in the construct "if foo then resume else statement"
-
             ' REM and XmlDocComment are now trivia so they have been removed from the test
-            Return SyntaxFacts.IsTerminator(t.Kind) OrElse
-                (Context.IsLineIf AndAlso t.Kind = SyntaxKind.ElseKeyword)
+            Return SyntaxFacts.IsTerminator(t.Kind)
         End Function
 
         ' // Parser::CanFollowStatement -- Can this token follow a complete statement?