Reduce LOH allocs when applying code fixes.

src/Workspaces/Core/Portable/LinkedFileDiffMerging/AbstractLinkedFileMergeConflictCommentAdditionService.cs

@@ -16,7 +16,7 @@ internal abstract class AbstractLinkedFileMergeConflictCommentAdditionService :
 {
     internal abstract string GetConflictCommentText(string header, string beforeString, string afterString);
 
-    public IEnumerable<TextChange> CreateEdits(SourceText originalSourceText, IEnumerable<UnmergedDocumentChanges> unmergedChanges)
+    public List<TextChange> CreateEdits(SourceText originalSourceText, List<UnmergedDocumentChanges> unmergedChanges)
     {
         var commentChanges = new List<TextChange>();
 
@@ -31,9 +31,9 @@ public IEnumerable<TextChange> CreateEdits(SourceText originalSourceText, IEnume
         return commentChanges;
     }
 
-    private static IEnumerable<IEnumerable<TextChange>> PartitionChangesForDocument(IEnumerable<TextChange> changes, SourceText originalSourceText)
+    private static List<List<TextChange>> PartitionChangesForDocument(IEnumerable<TextChange> changes, SourceText originalSourceText)
     {
-        var partitionedChanges = new List<IEnumerable<TextChange>>();
+        var partitionedChanges = new List<List<TextChange>>();
         var currentPartition = new List<TextChange>
         {
             changes.First()

src/Workspaces/Core/Portable/LinkedFileDiffMerging/IMergeConflictHandler.cs

@@ -2,14 +2,12 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System.Collections.Generic;
 using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis;
 
 internal interface IMergeConflictHandler
 {
-    IEnumerable<TextChange> CreateEdits(SourceText originalSourceText, IEnumerable<UnmergedDocumentChanges> unmergedChanges);
+    List<TextChange> CreateEdits(SourceText originalSourceText, List<UnmergedDocumentChanges> unmergedChanges);
 }

src/Workspaces/Core/Portable/LinkedFileDiffMerging/LinkedFileDiffMergingSession.cs

@@ -62,8 +62,8 @@ internal async Task<LinkedFileMergeSessionResult> MergeDiffsAsync(IMergeConflict
     }
 
     private async Task<LinkedFileMergeResult> MergeLinkedDocumentGroupAsync(
-        IEnumerable<DocumentId> allLinkedDocuments,
-        IEnumerable<DocumentId> linkedDocumentGroup,
+        ImmutableArray<DocumentId> allLinkedDocuments,
+        IGrouping<string, DocumentId> linkedDocumentGroup,
         LinkedFileDiffMergingSessionInfo sessionInfo,
         IMergeConflictHandler mergeConflictHandler,
         CancellationToken cancellationToken)
@@ -73,7 +73,8 @@ private async Task<LinkedFileMergeResult> MergeLinkedDocumentGroupAsync(
         // Automatically merge non-conflicting diffs while collecting the conflicting diffs
 
         var textDifferencingService = oldSolution.Services.GetRequiredService<IDocumentTextDifferencingService>();
-        var appliedChanges = await textDifferencingService.GetTextChangesAsync(oldSolution.GetDocument(linkedDocumentGroup.First()), newSolution.GetDocument(linkedDocumentGroup.First()), cancellationToken).ConfigureAwait(false);
+        var appliedChanges = await textDifferencingService.GetTextChangesAsync(
+            oldSolution.GetDocument(linkedDocumentGroup.First()), newSolution.GetDocument(linkedDocumentGroup.First()), TextDifferenceTypes.Line, cancellationToken).ConfigureAwait(false);
         var unmergedChanges = new List<UnmergedDocumentChanges>();
 
         foreach (var documentId in linkedDocumentGroup.Skip(1))
@@ -93,10 +94,10 @@ private async Task<LinkedFileMergeResult> MergeLinkedDocumentGroupAsync(
 
         // Add comments in source explaining diffs that could not be merged
 
-        IEnumerable<TextChange> allChanges;
-        IList<TextSpan> mergeConflictResolutionSpan = [];
+        ImmutableArray<TextChange> allChanges;
+        var mergeConflictResolutionSpan = new List<TextSpan>();
 
-        if (unmergedChanges.Any())
+        if (unmergedChanges.Count != 0)
         {
             mergeConflictHandler ??= oldSolution.GetDocument(linkedDocumentGroup.First()).GetLanguageService<ILinkedFileMergeConflictCommentAdditionService>();
             var mergeConflictTextEdits = mergeConflictHandler.CreateEdits(originalSourceText, unmergedChanges);
@@ -125,12 +126,13 @@ private static async Task<ImmutableArray<TextChange>> AddDocumentMergeChangesAsy
         CancellationToken cancellationToken)
     {
         var unmergedDocumentChanges = new List<TextChange>();
-        var successfullyMergedChanges = ArrayBuilder<TextChange>.GetInstance();
+        using var _ = ArrayBuilder<TextChange>.GetInstance(out var successfullyMergedChanges);
 
         var cumulativeChangeIndex = 0;
 
-        var textchanges = await textDiffService.GetTextChangesAsync(oldDocument, newDocument, cancellationToken).ConfigureAwait(false);
-        foreach (var change in textchanges)
+        var textChanges = await textDiffService.GetTextChangesAsync(
+            oldDocument, newDocument, TextDifferenceTypes.Line, cancellationToken).ConfigureAwait(false);
+        foreach (var change in textChanges)
         {
             while (cumulativeChangeIndex < cumulativeChanges.Count && cumulativeChanges[cumulativeChangeIndex].Span.End < change.Span.Start)
             {
@@ -196,25 +198,25 @@ private static async Task<ImmutableArray<TextChange>> AddDocumentMergeChangesAsy
             groupSessionInfo.IsolatedDiffs++;
         }
 
-        if (unmergedDocumentChanges.Any())
+        if (unmergedDocumentChanges.Count != 0)
         {
             unmergedChanges.Add(new UnmergedDocumentChanges(
-                unmergedDocumentChanges.AsEnumerable(),
+                unmergedDocumentChanges,
                 oldDocument.Project.Name,
                 oldDocument.Id));
         }
 
-        return successfullyMergedChanges.ToImmutableAndFree();
+        return successfullyMergedChanges.ToImmutableAndClear();
     }
 
-    private static IEnumerable<TextChange> MergeChangesWithMergeFailComments(
-        IEnumerable<TextChange> mergedChanges,
-        IEnumerable<TextChange> commentChanges,
-        IList<TextSpan> mergeConflictResolutionSpans,
+    private static ImmutableArray<TextChange> MergeChangesWithMergeFailComments(
+        ImmutableArray<TextChange> mergedChanges,
+        List<TextChange> commentChanges,
+        List<TextSpan> mergeConflictResolutionSpans,
         LinkedFileGroupSessionInfo groupSessionInfo)
     {
-        var mergedChangesList = NormalizeChanges(mergedChanges).ToList();
-        var commentChangesList = NormalizeChanges(commentChanges).ToList();
+        var mergedChangesList = NormalizeChanges(mergedChanges);
+        var commentChangesList = NormalizeChanges(commentChanges);
 
         var combinedChanges = new List<TextChange>();
         var insertedMergeConflictCommentsAtAdjustedLocation = 0;
@@ -270,17 +272,15 @@ private static IEnumerable<TextChange> MergeChangesWithMergeFailComments(
         groupSessionInfo.InsertedMergeConflictComments = commentChanges.Count();
         groupSessionInfo.InsertedMergeConflictCommentsAtAdjustedLocation = insertedMergeConflictCommentsAtAdjustedLocation;
 
-        return NormalizeChanges(combinedChanges);
+        return NormalizeChanges(combinedChanges).ToImmutableArray();
     }
 
-    private static IEnumerable<TextChange> NormalizeChanges(IEnumerable<TextChange> changes)
+    private static IList<TextChange> NormalizeChanges(IList<TextChange> changes)
     {
-        if (changes.Count() <= 1)
-        {
+        if (changes.Count <= 1)
             return changes;
-        }
 
-        changes = changes.OrderBy(c => c.Span.Start);
+        var orderedChanges = changes.OrderBy(c => c.Span.Start).ToList();
         var normalizedChanges = new List<TextChange>();
 
         var currentChange = changes.First();
@@ -309,7 +309,7 @@ public void LogLinkedFileResult(LinkedFileGroupSessionInfo info)
             => LinkedFileGroups.Add(info);
     }
 
-    internal class LinkedFileGroupSessionInfo
+    internal sealed class LinkedFileGroupSessionInfo
     {
         public int LinkedDocuments;
         public int DocumentsWithChanges;

src/Workspaces/Core/Portable/LinkedFileDiffMerging/LinkedFileMergeResult.cs

@@ -2,18 +2,17 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Linq;
 using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis;
 
-internal sealed class LinkedFileMergeResult(IEnumerable<DocumentId> documentIds, SourceText mergedSourceText, IEnumerable<TextSpan> mergeConflictResolutionSpans)
+internal sealed class LinkedFileMergeResult(ImmutableArray<DocumentId> documentIds, SourceText mergedSourceText, List<TextSpan> mergeConflictResolutionSpans)
 {
-    public IEnumerable<DocumentId> DocumentIds { get; internal set; } = documentIds;
-    public SourceText MergedSourceText { get; internal set; } = mergedSourceText;
-    public IEnumerable<TextSpan> MergeConflictResolutionSpans { get; } = mergeConflictResolutionSpans;
-    public bool HasMergeConflicts { get { return MergeConflictResolutionSpans.Any(); } }
+    public ImmutableArray<DocumentId> DocumentIds => documentIds;
+    public SourceText MergedSourceText => mergedSourceText;
+    public List<TextSpan> MergeConflictResolutionSpans => mergeConflictResolutionSpans;
+    public bool HasMergeConflicts => MergeConflictResolutionSpans.Count != 0;
 }

src/Workspaces/Core/Portable/LinkedFileDiffMerging/LinkedFileMergeSessionResult.cs

@@ -2,8 +2,6 @@
 // The .NET Foundation licenses this file to you under the MIT license.
 // See the LICENSE file in the project root for more information.
 
-#nullable disable
-
 using System.Collections.Generic;
 using Microsoft.CodeAnalysis.Text;
 
@@ -13,19 +11,16 @@ internal sealed class LinkedFileMergeSessionResult
 {
     public Solution MergedSolution { get; }
 
-    private readonly Dictionary<DocumentId, IEnumerable<TextSpan>> _mergeConflictCommentSpans = [];
-    public Dictionary<DocumentId, IEnumerable<TextSpan>> MergeConflictCommentSpans => _mergeConflictCommentSpans;
+    public readonly Dictionary<DocumentId, List<TextSpan>> MergeConflictCommentSpans = [];
 
-    public LinkedFileMergeSessionResult(Solution mergedSolution, IEnumerable<LinkedFileMergeResult> fileMergeResults)
+    public LinkedFileMergeSessionResult(Solution mergedSolution, List<LinkedFileMergeResult> fileMergeResults)
     {
         this.MergedSolution = mergedSolution;
 
         foreach (var fileMergeResult in fileMergeResults)
         {
             foreach (var documentId in fileMergeResult.DocumentIds)
-            {
-                _mergeConflictCommentSpans.Add(documentId, fileMergeResult.MergeConflictResolutionSpans);
-            }
+                MergeConflictCommentSpans.Add(documentId, fileMergeResult.MergeConflictResolutionSpans);
         }
     }
 }

src/Workspaces/Core/Portable/LinkedFileDiffMerging/UnmergedDocumentChanges.cs

@@ -9,9 +9,9 @@
 
 namespace Microsoft.CodeAnalysis;
 
-internal sealed class UnmergedDocumentChanges(IEnumerable<TextChange> unmergedChanges, string projectName, DocumentId documentId)
+internal sealed class UnmergedDocumentChanges(List<TextChange> unmergedChanges, string projectName, DocumentId documentId)
 {
-    public IEnumerable<TextChange> UnmergedChanges { get; } = unmergedChanges;
+    public List<TextChange> UnmergedChanges { get; } = unmergedChanges;
     public string ProjectName { get; } = projectName;
     public DocumentId DocumentId { get; } = documentId;
 }