Remove tail recursion and enable cancellation

src/EditorFeatures/Core/Implementation/Formatting/FormatCommandHandler.FormatDocument.cs

@@ -49,7 +49,7 @@ private bool TryExecuteCommand(FormatDocumentCommandArgs args)
             _waitIndicator.Wait(
                 title: EditorFeaturesResources.FormatDocument,
                 message: EditorFeaturesResources.FormattingDocument,
-                allowCancel: false,
+                allowCancel: true,
                 action: waitContext =>
                 {
                     Format(args.TextView, document, null, waitContext.CancellationToken);

src/EditorFeatures/Core/Implementation/Formatting/FormatCommandHandler.FormatSelection.cs

@@ -52,7 +52,7 @@ private bool TryExecuteCommand(FormatSelectionCommandArgs args)
             _waitIndicator.Wait(
                 title: EditorFeaturesResources.FormatSelection,
                 message: EditorFeaturesResources.FormattingCurrentlySelected,
-                allowCancel: false,
+                allowCancel: true,
                 action: waitContext =>
             {
                 var buffer = args.SubjectBuffer;

src/EditorFeatures/Core/Implementation/Formatting/FormatCommandHandler.Paste.cs

@@ -29,7 +29,7 @@ public void ExecuteCommand(PasteCommandArgs args, Action nextHandler)
             _waitIndicator.Wait(
                 title: EditorFeaturesResources.FormatPaste,
                 message: EditorFeaturesResources.FormattingPastedText,
-                allowCancel: false,
+                allowCancel: true,
                 action: c => ExecuteCommandWorker(args, nextHandler, c.CancellationToken));
         }
 

src/Workspaces/Core/Portable/Formatting/Context/FormattingContext.cs

@@ -409,25 +409,28 @@ public IEnumerable<IndentBlockOperation> GetAllRelativeIndentBlockOperations()
             return _relativeIndentationTree.GetIntersectingInOrderIntervals(this.TreeData.StartPosition, this.TreeData.EndPosition, this).Select(i => i.Operation);
         }
 
-        public SyntaxToken GetEndTokenForRelativeIndentationSpan(SyntaxToken token)
+        public SyntaxToken GetEndTokenForRelativeIndentationSpan(SyntaxToken token, CancellationToken cancellationToken)
         {
-            var span = token.Span;
-            var indentationData = _relativeIndentationTree.GetSmallestContainingInterval(span.Start, 0);
-            if (indentationData == null)
+            while (true)
             {
-                // this means the given token is not inside of inseparable regions
-                return token;
-            }
+                var span = token.Span;
+                var indentationData = _relativeIndentationTree.GetSmallestContainingInterval(span.Start, 0);
+                if (indentationData == null)
+                {
+                    // this means the given token is not inside of inseparable regions
+                    return token;
+                }
 
-            // recursively find the end token outside of inseparable regions
-            var nextToken = indentationData.EndToken.GetNextToken(includeZeroWidth: true);
-            if (nextToken.RawKind == 0)
-            {
-                // reached end of tree
-                return default(SyntaxToken);
-            }
+                // recursively find the end token outside of inseparable regions
+                token = indentationData.EndToken.GetNextToken(includeZeroWidth: true);
+                if (token.RawKind == 0)
+                {
+                    // reached end of tree
+                    return default(SyntaxToken);
+                }
 
-            return GetEndTokenForRelativeIndentationSpan(nextToken);
+                cancellationToken.ThrowIfCancellationRequested();
+            }
         }
 
         private AnchorData GetAnchorData(SyntaxToken token)

src/Workspaces/Core/Portable/Formatting/Engine/AbstractFormatEngine.Partitioner.cs

@@ -2,6 +2,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Threading;
 using Microsoft.CodeAnalysis.Text;
 using Roslyn.Utilities;
 
@@ -28,7 +29,7 @@ public Partitioner(FormattingContext context, TokenStream tokenStream, TokenPair
                 _operationPairs = operationPairs;
             }
 
-            public List<IEnumerable<TokenPairWithOperations>> GetPartitions(int partitionCount)
+            public List<IEnumerable<TokenPairWithOperations>> GetPartitions(int partitionCount, CancellationToken cancellationToken)
             {
                 Contract.ThrowIfFalse(partitionCount > 0);
 
@@ -58,7 +59,7 @@ public List<IEnumerable<TokenPairWithOperations>> GetPartitions(int partitionCou
                         break;
                     }
 
-                    var nextToken = _context.GetEndTokenForRelativeIndentationSpan(_operationPairs[nextPartitionStartOperationIndex].Token1);
+                    var nextToken = _context.GetEndTokenForRelativeIndentationSpan(_operationPairs[nextPartitionStartOperationIndex].Token1, cancellationToken);
                     if (nextToken.RawKind == 0)
                     {
                         // reached the last token in the tree
@@ -79,6 +80,8 @@ public List<IEnumerable<TokenPairWithOperations>> GetPartitions(int partitionCou
 
                     list.Add(GetOperationPairsFromTo(currentOperationIndex, nextTokenWithIndex.IndexInStream));
                     currentOperationIndex = nextTokenWithIndex.IndexInStream;
+
+                    cancellationToken.ThrowIfCancellationRequested();
                 }
 
                 return list;

src/Workspaces/Core/Portable/Formatting/Engine/AbstractFormatEngine.cs

@@ -441,7 +441,9 @@ private void ApplySpaceAndWrappingOperations(
                 var partitioner = new Partitioner(context, tokenStream, tokenOperations);
 
                 // always create task 1 more than current processor count
-                var partitions = partitioner.GetPartitions(this.TaskExecutor == TaskExecutor.Synchronous ? 1 : Environment.ProcessorCount + 1);
+                var partitions = partitioner.GetPartitions(this.TaskExecutor == TaskExecutor.Synchronous ? 1 : Environment.ProcessorCount + 1, cancellationToken);
+
+                cancellationToken.ThrowIfCancellationRequested();
 
                 var tasks = new Task[partitions.Count];
                 for (int i = 0; i < partitions.Count; i++)