Enable turning a method into an async method or iterator in VB

Enables an edit that updates a regular method to an async method or an iterator in VB. As in C#, there is the restriction in the presence of an active statement in the method body since the debugger doesn't support remapping active statements to a different method (from the original method to the new MoveNext added due to the change to state machine).

src/EditorFeatures/VisualBasicTest/EditAndContinue/ActiveStatementTests.vb

@@ -4386,32 +4386,179 @@ End Class
 #Region "State Machines"
         <Fact>
         Public Sub MethodToIteratorMethod_WithActiveStatement()
-            ' TODO
+            Dim src1 = "
+Imports System
+Imports System.Collections.Generic
+Class C
+    Function F() As IEnumerable(Of Integer)
+        <AS:0>Console.WriteLine(1)</AS:0>
+        Return {1, 1}
+    End Function
+End Class
+"
+            Dim src2 = "
+Imports System
+Imports System.Collections.Generic
+Class C
+    Iterator Function F() As IEnumerable(Of Integer)
+        <AS:0>Console.WriteLine(1)</AS:0>
+        Yield 1
+    End Function
+End Class
+"
+            Dim edits = GetTopEdits(src1, src2)
+            Dim active = GetActiveStatements(src1, src2)
+
+            edits.VerifyRudeDiagnostics(active,
+                Diagnostic(RudeEditKind.InsertAroundActiveStatement, "Yield 1", "Yield statement"))
         End Sub
 
         <Fact>
         Public Sub MethodToIteratorMethod_WithActiveStatementInLambda()
-            ' TODO
+            Dim src1 = "
+Imports System
+Imports System.Collections.Generic
+Class C
+    Function F() As IEnumerable(Of Integer)
+        Dim a = Sub() <AS:0>Console.WriteLine(1)</AS:0>
+        a()
+        Return {1, 1}
+    End Function
+End Class
+"
+            Dim src2 = "
+Imports System
+Imports System.Collections.Generic
+Class C
+    Iterator Function F() As IEnumerable(Of Integer)
+        Dim a = Sub() <AS:0>Console.WriteLine(1)</AS:0>
+        a()
+        Yield 1
+    End Function
+End Class
+"
+            Dim edits = GetTopEdits(src1, src2)
+            Dim active = GetActiveStatements(src1, src2)
+
+            ' should not contain RUDE_EDIT_INSERT_AROUND
+            edits.VerifyRudeDiagnostics(active,
+                Diagnostic(RudeEditKind.RUDE_EDIT_LAMBDA_EXPRESSION, "Sub()", "method"))
         End Sub
 
         <Fact>
         Public Sub MethodToIteratorMethod_WithoutActiveStatement()
-            ' TODO
+            Dim src1 = "
+Imports System
+Imports System.Collections.Generic
+Class C
+    Function F() As IEnumerable(Of Integer)
+        Console.WriteLine(1)
+        Return {1, 1}
+    End Function
+End Class
+"
+            Dim src2 = "
+Imports System
+Imports System.Collections.Generic
+Class C
+    Iterator Function F() As IEnumerable(Of Integer)
+        Console.WriteLine(1)
+        Yield 1
+    End Function
+End Class
+"
+            Dim edits = GetTopEdits(src1, src2)
+            Dim active = GetActiveStatements(src1, src2)
+
+            edits.VerifyRudeDiagnostics(active)
         End Sub
 
         <Fact>
         Public Sub MethodToAsyncMethod_WithActiveStatement()
-            ' TODO
+            Dim src1 = "
+Imports System
+Imports System.Threading.Tasks
+Class C
+    Function F() As Task(Of Integer)
+        <AS:0>Console.WriteLine(1)</AS:0>
+        Return Task.FromResult(1)
+    End Function
+End Class
+"
+            Dim src2 = "
+Imports System
+Imports System.Threading.Tasks
+Class C
+    Async Function F() As Task(Of Integer)
+        <AS:0>Console.WriteLine(1)</AS:0>
+        Return Await Task.FromResult(1)
+    End Function
+End Class
+"
+            Dim edits = GetTopEdits(src1, src2)
+            Dim active = GetActiveStatements(src1, src2)
+
+            edits.VerifyRudeDiagnostics(active,
+                Diagnostic(RudeEditKind.InsertAroundActiveStatement, "Await", "Await expression"))
         End Sub
 
         <Fact>
         Public Sub MethodToAsyncMethod_WithActiveStatementInLambda()
-            ' TODO
+            Dim src1 = "
+Imports System
+Imports System.Threading.Tasks
+Class C
+    Function F() As Task(Of Integer)
+        Dim a = Sub() <AS:0>Console.WriteLine(1)</AS:0>
+        a()
+        Return Task.FromResult(1)
+    End Function
+End Class
+"
+            Dim src2 = "
+Imports System
+Imports System.Threading.Tasks
+Class C
+    Async Function F() As Task(Of Integer)
+        Dim a = Sub() <AS:0>Console.WriteLine(1)</AS:0>
+        a()
+        Return Await Task.FromResult(1)
+    End Function
+End Class
+"
+            Dim edits = GetTopEdits(src1, src2)
+            Dim active = GetActiveStatements(src1, src2)
+
+            edits.VerifyRudeDiagnostics(active,
+                Diagnostic(RudeEditKind.RUDE_EDIT_LAMBDA_EXPRESSION, "Sub()", "method"))
         End Sub
 
         <Fact>
         Public Sub MethodToAsyncMethod_WithoutActiveStatement()
-            ' TODO
+            Dim src1 = "
+Imports System
+Imports System.Threading.Tasks
+Class C
+    Function F() As Task(Of Integer)
+        Console.WriteLine(1)
+        Return Task.FromResult(1)
+    End Function
+End Class
+"
+            Dim src2 = "
+Imports System
+Imports System.Threading.Tasks
+Class C
+    Async Function F() As Task(Of Integer)
+        Console.WriteLine(1)
+        Return Await Task.FromResult(1)
+    End Function
+End Class
+"
+            Dim edits = GetTopEdits(src1, src2)
+            Dim active = GetActiveStatements(src1, src2)
+
+            edits.VerifyRudeDiagnostics(active)
         End Sub
 #End Region
 

src/EditorFeatures/VisualBasicTest/EditAndContinue/RudeEditTopLevelTests.vb

@@ -1905,8 +1905,7 @@ End Class
             edits.VerifyEdits(
                 "Update [Async Function F() As Task(Of String)]@11 -> [Function F() As Task(Of String)]@11")
 
-            edits.VerifyRudeDiagnostics(
-                Diagnostic(RudeEditKind.ModifiersUpdate, "Function F()", "method"))
+            edits.VerifyRudeDiagnostics()
         End Sub
 
         <Fact>

src/Features/VisualBasic/EditAndContinue/VisualBasicEditAndContinueAnalyzer.vb

@@ -2378,7 +2378,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.EditAndContinue
                     Return
                 End If
 
-                If Not SyntaxFactory.AreEquivalent(oldNode.Modifiers, newNode.Modifiers) Then
+                If Not ClassifyMethodModifierUpdate(oldNode.Modifiers, newNode.Modifiers) Then
                     ReportError(RudeEditKind.ModifiersUpdate)
                     Return
                 End If
@@ -2395,6 +2395,32 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.EditAndContinue
                 End If
             End Sub
 
+            Private Function ClassifyMethodModifierUpdate(oldModifiers As SyntaxTokenList, newModifiers As SyntaxTokenList) As Boolean
+                Dim oldAsyncIndex = oldModifiers.IndexOf(SyntaxKind.AsyncKeyword)
+                Dim newAsyncIndex = newModifiers.IndexOf(SyntaxKind.AsyncKeyword)
+
+                If oldAsyncIndex >= 0 Then
+                    oldModifiers = oldModifiers.RemoveAt(oldAsyncIndex)
+                End If
+
+                If newAsyncIndex >= 0 Then
+                    newModifiers = newModifiers.RemoveAt(newAsyncIndex)
+                End If
+
+                Dim oldIteratorIndex = oldModifiers.IndexOf(SyntaxKind.IteratorKeyword)
+                Dim newIteratorIndex = newModifiers.IndexOf(SyntaxKind.IteratorKeyword)
+
+                If oldIteratorIndex >= 0 Then
+                    oldModifiers = oldModifiers.RemoveAt(oldIteratorIndex)
+                End If
+
+                If newIteratorIndex >= 0 Then
+                    newModifiers = newModifiers.RemoveAt(newIteratorIndex)
+                End If
+
+                Return SyntaxFactory.AreEquivalent(oldModifiers, newModifiers)
+            End Function
+
             Private Sub ClassifyUpdate(oldNode As DeclareStatementSyntax, newNode As DeclareStatementSyntax)
                 If Not SyntaxFactory.AreEquivalent(oldNode.Identifier, newNode.Identifier) Then
                     ReportError(RudeEditKind.Renamed)