There have been numerous complaints and feedback tickets around docum…

…ent munging in VB aspx scenarios during line commit for several years. The underlying issue is that the aspx editor resets all projection spans upon an impactful edit (eg, changing an <%= to an <%#), thus causing large diffs to be detected and seen as dirty ranges to incorporate into the commit. These large dirty ranges end up causing the line commit code behave poorly, throwing exceptions and modifying document contents in undesirable ways. (#71471)

I believe the simplest and most effective way to address this is to simply remove all dirty state information upon projection spans reset. At the very worst, the user won't get line commit information when these spans weren't reset in an impactful way. I've verified that normal editing within the VB spans doesn't cause projection resets and thus continues to perform line commits as expected.

Addresses https://developercommunity.visualstudio.com/t/aspx-code-corruption-with-ExternalSourc/10123117#T-ND10552491

src/EditorFeatures/VisualBasic/LineCommit/CommitBufferManager.vb

@@ -7,6 +7,7 @@ Imports System.Threading.Tasks
 Imports Microsoft.CodeAnalysis.Editor.Shared.Utilities
 Imports Microsoft.CodeAnalysis.Text
 Imports Microsoft.VisualStudio.Text
+Imports Microsoft.VisualStudio.Text.Projection
 
 Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.LineCommit
     ''' <summary>
@@ -63,6 +64,11 @@ Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.LineCommit
                 If _referencingViews = 1 Then
                     AddHandler _buffer.Changing, AddressOf OnTextBufferChanging
                     AddHandler _buffer.Changed, AddressOf OnTextBufferChanged
+
+                    Dim projectionBuffer = TryCast(_buffer, IProjectionBuffer)
+                    If projectionBuffer IsNot Nothing Then
+                        AddHandler projectionBuffer.SourceSpansChanged, AddressOf OnSourceSpansChanged
+                    End If
                 End If
             End SyncLock
         End Sub
@@ -79,6 +85,11 @@ Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.LineCommit
                     If _referencingViews = 0 Then
                         RemoveHandler _buffer.Changed, AddressOf OnTextBufferChanged
                         RemoveHandler _buffer.Changing, AddressOf OnTextBufferChanging
+
+                        Dim projectionBuffer = TryCast(_buffer, IProjectionBuffer)
+                        If projectionBuffer IsNot Nothing Then
+                            RemoveHandler projectionBuffer.SourceSpansChanged, AddressOf OnSourceSpansChanged
+                        End If
                     End If
                 End If
             End SyncLock
@@ -292,6 +303,14 @@ Namespace Microsoft.CodeAnalysis.Editor.VisualBasic.LineCommit
             End If
         End Sub
 
+        Private Sub OnSourceSpansChanged(sender As Object, e As ProjectionSourceSpansChangedEventArgs)
+            ' DirtyState information should be purged when source spans change, as the new buffer content
+            ' may be unrelated to prior content. Aspx and legacy razor may generate significant differences
+            ' during generations (eg, converting a <%= to a <%# in aspx), causing unnecessary (and troublesome) large
+            ' dirty state ranges.
+            _dirtyState = Nothing
+        End Sub
+
         Private Shared Async Function ForceComputeInternalsVisibleToAsync(document As Document, cancellationToken As CancellationToken) As Task
             Dim project = document.Project
             Dim compilation = Await project.GetCompilationAsync(cancellationToken).ConfigureAwait(False)