Reduce allocations from newline information allocated by ChangedText.GetLinesCore

src/Compilers/Core/CodeAnalysisTest/Text/CompositeTextTests.cs

@@ -0,0 +1,88 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using Microsoft.CodeAnalysis.PooledObjects;
+using Microsoft.CodeAnalysis.Text;
+using Xunit;
+
+namespace Microsoft.CodeAnalysis.UnitTests.Text;
+
+public sealed class CompositeTextTests
+{
+    [Theory]
+    [InlineData("abcdefghijkl")]
+    [InlineData(["\r\r\r\r\r\r\r\r\r\r\r\r"])]
+    [InlineData(["\n\n\n\n\n\n\n\n\n\n\n\n"])]
+    [InlineData(["\r\n\r\n\r\n\r\n\r\n\r\n"])]
+    [InlineData(["\n\r\n\r\n\r\n\r\n\r\n\r"])]
+    [InlineData(["a\r\nb\r\nc\r\nd\r\n"])]
+    [InlineData(["\ra\n\rb\n\rc\n\rd\n"])]
+    [InlineData(["\na\r\nb\r\nc\r\nd\r"])]
+    [InlineData(["ab\r\ncd\r\nef\r\n"])]
+    [InlineData(["ab\r\r\ncd\r\r\nef"])]
+    [InlineData(["ab\n\n\rcd\n\n\ref"])]
+    public void CompositeTextLinesEqualSourceTextLinesPermutations(string contents)
+    {
+        // Please try to limit the inputs to this method to around 12 chars or less, as much longer than that
+        // will blow up the number of potential permutations.
+        foreach (var (sourceText, compositeText) in CreateSourceAndCompositeTexts(contents))
+        {
+            var sourceLinesText = GetLinesTexts(sourceText.Lines);
+            var compositeLinesText = GetLinesTexts(compositeText.Lines);
+
+            Assert.True(sourceLinesText.SequenceEqual(compositeLinesText));
+
+            for (var i = 0; i < sourceText.Length; i++)
+            {
+                Assert.Equal(sourceText.Lines.IndexOf(i), compositeText.Lines.IndexOf(i));
+            }
+        }
+    }
+
+    private static IEnumerable<string> GetLinesTexts(TextLineCollection textLines)
+    {
+        return textLines.Select(l => l.Text!.ToString(l.SpanIncludingLineBreak));
+    }
+
+    // Returns all possible permutations of contents into SourceText arrays of length between minSourceTextCount and maxSourceTextCount
+    private static IEnumerable<(SourceText, CompositeText)> CreateSourceAndCompositeTexts(string contents, int minSourceTextCount = 2, int maxSourceTextCount = 4)
+    {
+        var sourceText = SourceText.From(contents);
+
+        for (var sourceTextCount = minSourceTextCount; sourceTextCount <= Math.Min(maxSourceTextCount, contents.Length); sourceTextCount++)
+        {
+            foreach (var sourceTexts in CreateSourceTextPermutations(contents, sourceTextCount))
+            {
+                var sourceTextsBuilder = ArrayBuilder<SourceText>.GetInstance();
+                sourceTextsBuilder.AddRange(sourceTexts);
+
+                var compositeText = (CompositeText)CompositeText.ToSourceText(sourceTextsBuilder, sourceText, adjustSegments: false);
+                yield return (sourceText, compositeText);
+            }
+        }
+    }
+
+    private static IEnumerable<SourceText[]> CreateSourceTextPermutations(string contents, int requestedSourceTextCount)
+    {
+        if (requestedSourceTextCount == 1)
+        {
+            yield return [SourceText.From(contents)];
+        }
+        else
+        {
+            var maximalSourceTextLength = (contents.Length - requestedSourceTextCount) + 1;
+            for (int i = 1; i <= maximalSourceTextLength; i++)
+            {
+                var sourceText = SourceText.From(contents[..i]);
+                foreach (var otherSourceTexts in CreateSourceTextPermutations(contents.Substring(i), requestedSourceTextCount - 1))
+                {
+                    yield return [sourceText, .. otherSourceTexts];
+                }
+            }
+        }
+    }
+}

src/Compilers/Core/CodeAnalysisTest/Text/TextChangeTests.cs

@@ -320,14 +320,14 @@ public void TestOptimizedSourceTextLinesRemoveCrLf()
         }
 
         [Fact]
-        public void TestOptimizedSourceTextLinesBrakeCrLf()
+        public void TestOptimizedSourceTextLinesBreakCrLf()
         {
             AssertChangedTextLinesHelper("Test\r\nMessage",
                 new TextChange(new TextSpan(5, 0), "aaaaaa"));
         }
 
         [Fact]
-        public void TestOptimizedSourceTextLinesBrakeCrLfWithLfPrefixedAndCrSuffixed()
+        public void TestOptimizedSourceTextLinesBreakCrLfWithLfPrefixedAndCrSuffixed()
         {
             AssertChangedTextLinesHelper("Test\r\nMessage",
                 new TextChange(new TextSpan(5, 0), "\naaaaaa\r"));

src/Compilers/Core/Portable/Text/ChangedText.cs

@@ -7,8 +7,6 @@
 using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Text;
-using Microsoft.CodeAnalysis.Collections;
-using Microsoft.CodeAnalysis.PooledObjects;
 using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Text
@@ -264,108 +262,8 @@ private static ImmutableArray<TextChangeRange> Merge(IReadOnlyList<ImmutableArra
             return merged;
         }
 
-        /// <summary>
-        /// Computes line starts faster given already computed line starts from text before the change.
-        /// </summary>
         protected override TextLineCollection GetLinesCore()
-        {
-            SourceText? oldText;
-            TextLineCollection? oldLineInfo;
-
-            if (!_info.WeakOldText.TryGetTarget(out oldText) || !oldText.TryGetLines(out oldLineInfo))
-            {
-                // no old line starts? do it the hard way.
-                return base.GetLinesCore();
-            }
-
-            // compute line starts given changes and line starts already computed from previous text
-            var lineStarts = new SegmentedList<int>(capacity: oldLineInfo.Count)
-            {
-                0
-            };
-
-            // position in the original document
-            var position = 0;
-
-            // delta generated by already processed changes (position in the new document = position + delta)
-            var delta = 0;
-
-            // true if last segment ends with CR and we need to check for CR+LF code below assumes that both CR and LF are also line breaks alone
-            var endsWithCR = false;
-
-            foreach (var change in _info.ChangeRanges)
-            {
-                // include existing line starts that occur before this change
-                if (change.Span.Start > position)
-                {
-                    if (endsWithCR && _newText[position + delta] == '\n')
-                    {
-                        // remove last added line start (it was due to previous CR)
-                        // a new line start including the LF will be added next
-                        lineStarts.RemoveAt(lineStarts.Count - 1);
-                    }
-
-                    var lps = oldLineInfo.GetLinePositionSpan(TextSpan.FromBounds(position, change.Span.Start));
-                    for (int i = lps.Start.Line + 1; i <= lps.End.Line; i++)
-                    {
-                        lineStarts.Add(oldLineInfo[i].Start + delta);
-                    }
-
-                    endsWithCR = oldText[change.Span.Start - 1] == '\r';
-
-                    // in case change is inserted between CR+LF we treat CR as line break alone, 
-                    // but this line break might be retracted and replaced with new one in case LF is inserted  
-                    if (endsWithCR && change.Span.Start < oldText.Length && oldText[change.Span.Start] == '\n')
-                    {
-                        lineStarts.Add(change.Span.Start + delta);
-                    }
-                }
-
-                // include line starts that occur within newly inserted text
-                if (change.NewLength > 0)
-                {
-                    var changeStart = change.Span.Start + delta;
-                    var text = GetSubText(new TextSpan(changeStart, change.NewLength));
-
-                    if (endsWithCR && text[0] == '\n')
-                    {
-                        // remove last added line start (it was due to previous CR)
-                        // a new line start including the LF will be added next
-                        lineStarts.RemoveAt(lineStarts.Count - 1);
-                    }
-
-                    // Skip first line (it is always at offset 0 and corresponds to the previous line)
-                    for (int i = 1; i < text.Lines.Count; i++)
-                    {
-                        lineStarts.Add(changeStart + text.Lines[i].Start);
-                    }
-
-                    endsWithCR = text[change.NewLength - 1] == '\r';
-                }
-
-                position = change.Span.End;
-                delta += (change.NewLength - change.Span.Length);
-            }
-
-            // include existing line starts that occur after all changes
-            if (position < oldText.Length)
-            {
-                if (endsWithCR && _newText[position + delta] == '\n')
-                {
-                    // remove last added line start (it was due to previous CR)
-                    // a new line start including the LF will be added next
-                    lineStarts.RemoveAt(lineStarts.Count - 1);
-                }
-
-                var lps = oldLineInfo.GetLinePositionSpan(TextSpan.FromBounds(position, oldText.Length));
-                for (int i = lps.Start.Line + 1; i <= lps.End.Line; i++)
-                {
-                    lineStarts.Add(oldLineInfo[i].Start + delta);
-                }
-            }
-
-            return new LineInfo(this, lineStarts);
-        }
+            => _newText.Lines;
 
         internal static class TestAccessor
         {