Make the impl of SyntaxNode.GetText more efficient

src/Compilers/Core/Portable/Syntax/SyntaxNode.cs

@@ -325,9 +325,10 @@ public virtual void WriteTo(TextWriter writer)
         /// <exception cref="ArgumentException"><paramref name="checksumAlgorithm"/> is not supported.</exception>
         public SourceText GetText(Encoding? encoding = null, SourceHashAlgorithm checksumAlgorithm = SourceHashAlgorithm.Sha1)
         {
-            var builder = new StringBuilder(this.Green.FullWidth);
-            this.WriteTo(new StringWriter(builder));
-            return new StringBuilderText(builder, encoding, checksumAlgorithm);
+            var fullWidth = this.Green.FullWidth;
+            var writer = SourceTextWriter.Create(encoding, checksumAlgorithm, fullWidth);
+            this.WriteTo(writer);
+            return writer.ToSourceText();
         }
 
         /// <summary>

src/Workspaces/CSharp/Portable/Workspace/LanguageServices/CSharpSyntaxTreeFactoryService.ParsedSyntaxTree.cs

@@ -48,8 +48,7 @@ public override SourceText GetText(CancellationToken cancellationToken)
         {
             if (_lazyText == null)
             {
-                var sourceText = SourceTextExtensions.CreateSourceText(GetRoot(cancellationToken), Encoding, _checksumAlgorithm, cancellationToken);
-                Interlocked.CompareExchange(ref _lazyText, sourceText, null);
+                Interlocked.CompareExchange(ref _lazyText, GetRoot(cancellationToken).GetText(Encoding, _checksumAlgorithm), null);
             }
 
             return _lazyText;

src/Workspaces/Core/Portable/Shared/Extensions/SourceTextExtensions.cs

@@ -4,9 +4,7 @@
 
 using System;
 using System.Collections.Immutable;
-using System.Diagnostics;
 using System.IO;
-using System.Linq;
 using System.Text;
 using System.Threading;
 using Microsoft.CodeAnalysis.Host;
@@ -238,87 +236,6 @@ public static SourceText ReadFrom(ITextFactoryService textService, ObjectReader
         return textService.CreateText(textReader, encoding, checksumAlgorithm, cancellationToken);
     }
 
-    public static SourceText CreateSourceText(
-        SyntaxNode node, Encoding? encoding, SourceHashAlgorithm checksumAlgorithm, CancellationToken cancellationToken)
-    {
-        // If this node is small enough to not go into the LOH, we can just fast path directly to creating a SourceText from it.
-        var totalLength = node.FullWidth();
-        if (totalLength <= SourceTextLengthThreshold)
-            return SourceText.From(node.ToFullString(), encoding, checksumAlgorithm);
-
-        // Allocate the space to write the node into.  Explicitly chunked so that nothing goes into the LOH.
-        var chunks = CreateChunks(totalLength);
-
-        // Write the node into that temp space.
-        using var chunkWriter = new CharArrayChunkTextWriter(totalLength, chunks, encoding!, cancellationToken);
-        node.WriteTo(chunkWriter);
-        Contract.ThrowIfTrue(totalLength != chunkWriter.Position);
-
-        // Call into the text service to make us a SourceText from the chunks.  Disposal of this reader will free all
-        // the intermediary chunks we allocated.
-
-        Contract.ThrowIfTrue(chunks.Any(static (c, s) => c.Length != s, CharArrayLength));
-
-        using var chunkReader = new CharArrayChunkTextReader(chunks, totalLength);
-        var result = SourceText.From(chunkReader, totalLength, encoding, checksumAlgorithm);
-        Contract.ThrowIfTrue(totalLength != chunkReader.Position);
-
-        return result;
-
-        static ImmutableArray<char[]> CreateChunks(int totalLength)
-        {
-            var numberOfChunks = 1 + (totalLength / CharArrayLength);
-            var buffer = new FixedSizeArrayBuilder<char[]>(numberOfChunks);
-            for (var i = 0; i < numberOfChunks; i++)
-                buffer.Add(s_charArrayPool.Allocate());
-
-            return buffer.MoveToImmutable();
-        }
-    }
-
-    private static int GetIndexFromPosition(int position) => position / CharArrayLength;
-    private static int GetColumnFromPosition(int position) => position % CharArrayLength;
-
-    private sealed class CharArrayChunkTextWriter(
-        int totalLength, ImmutableArray<char[]> chunks, Encoding encoding, CancellationToken cancellationToken) : TextWriter
-    {
-        private readonly int _totalLength = totalLength;
-        private readonly ImmutableArray<char[]> _chunks = chunks;
-        private readonly CancellationToken _cancellationToken = cancellationToken;
-
-        /// <summary>
-        /// Public so that caller can assert that writing out the text actually wrote out the full text of the node.
-        /// </summary>
-        public int Position { get; private set; }
-
-        public override Encoding Encoding { get; } = encoding;
-
-        public override void Write(string? value)
-        {
-            Contract.ThrowIfNull(value);
-
-            var valueSpan = value.AsSpan();
-            while (valueSpan.Length > 0)
-            {
-                _cancellationToken.ThrowIfCancellationRequested();
-
-                var chunk = _chunks[GetIndexFromPosition(Position)];
-                Contract.ThrowIfTrue(chunk.Length != CharArrayLength);
-
-                var chunkIndex = GetColumnFromPosition(Position);
-                Contract.ThrowIfTrue(chunkIndex >= CharArrayLength);
-
-                var count = Math.Min(valueSpan.Length, CharArrayLength - chunkIndex);
-                valueSpan[..count].CopyTo(chunk.AsSpan().Slice(chunkIndex, count));
-
-                Position += count;
-                valueSpan = valueSpan[count..];
-            }
-
-            Contract.ThrowIfTrue(Position > _totalLength);
-        }
-    }
-
     private sealed class CharArrayChunkTextReader(ImmutableArray<char[]> chunks, int length) : TextReaderWithLength(length)
     {
         private readonly ImmutableArray<char[]> _chunks = chunks;
@@ -329,6 +246,9 @@ private sealed class CharArrayChunkTextReader(ImmutableArray<char[]> chunks, int
         /// </summary>
         public int Position { get; private set; }
 
+        private static int GetIndexFromPosition(int position) => position / CharArrayLength;
+        private static int GetColumnFromPosition(int position) => position % CharArrayLength;
+
         public static TextReader CreateFromObjectReader(ObjectReader reader)
         {
             var length = reader.ReadInt32();

src/Workspaces/VisualBasic/Portable/Workspace/LanguageServices/VisualBasicSyntaxTreeFactoryService.ParsedSyntaxTree.vb

@@ -41,8 +41,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic
 
             Public Overrides Function GetText(Optional cancellationToken As CancellationToken = Nothing) As SourceText
                 If _lazyText Is Nothing Then
-                    Dim text = SourceTextExtensions.CreateSourceText(GetRoot(cancellationToken), Encoding, _checksumAlgorithm, cancellationToken)
-                    Interlocked.CompareExchange(_lazyText, text, Nothing)
+                    Interlocked.CompareExchange(_lazyText, GetRoot(cancellationToken).GetText(Encoding, _checksumAlgorithm), Nothing)
                 End If
 
                 Return _lazyText