Use segmented arrays for VirtualChar storage

See https://devdiv.visualstudio.com/DevDiv/_workitems/edit/1460018

src/Compilers/Core/Portable/Collections/ImmutableArrayExtensions.cs

@@ -13,6 +13,7 @@
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.PooledObjects;
+using Microsoft.CodeAnalysis.Collections;
 
 #if DEBUG
 using System.Linq;
@@ -862,5 +863,33 @@ internal static int BinarySearch<TElement, TValue>(this ReadOnlySpan<TElement> a
 
             return ~low;
         }
+
+        internal static int BinarySearch<TElement, TValue>(this ImmutableSegmentedList<TElement> array, TValue value, Func<TElement, TValue, int> comparer)
+        {
+            int low = 0;
+            int high = array.Count - 1;
+
+            while (low <= high)
+            {
+                int middle = low + ((high - low) >> 1);
+                int comparison = comparer(array[middle], value);
+
+                if (comparison == 0)
+                {
+                    return middle;
+                }
+
+                if (comparison > 0)
+                {
+                    high = middle - 1;
+                }
+                else
+                {
+                    low = middle + 1;
+                }
+            }
+
+            return ~low;
+        }
     }
 }

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/CSharp/EmbeddedLanguages/VirtualChars/CSharpVirtualCharService.cs

@@ -4,6 +4,7 @@
 
 using System.Diagnostics;
 using System.Text;
+using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.CSharp.LanguageServices;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
 using Microsoft.CodeAnalysis.EmbeddedLanguages.VirtualChars;
@@ -102,7 +103,7 @@ private static VirtualCharSequence TryConvertRawStringToVirtualChars(
             var tokenText = token.Text;
             var offset = token.SpanStart;
 
-            using var _ = ArrayBuilder<VirtualChar>.GetInstance(out var result);
+            var result = ImmutableSegmentedList.CreateBuilder<VirtualChar>();
 
             var startIndexInclusive = 0;
             var endIndexExclusive = tokenText.Length;
@@ -186,14 +187,14 @@ private static VirtualCharSequence CreateVirtualCharSequence(
             string tokenText, int offset, int startIndexInclusive, int endIndexExclusive, ArrayBuilder<(char ch, TextSpan span)> charResults)
         {
             // Second pass.  Convert those characters to Runes.
-            using var _ = ArrayBuilder<VirtualChar>.GetInstance(out var runeResults);
+            var runeResults = ImmutableSegmentedList.CreateBuilder<VirtualChar>();
 
             ConvertCharactersToRunes(charResults, runeResults);
 
             return CreateVirtualCharSequence(tokenText, offset, startIndexInclusive, endIndexExclusive, runeResults);
         }
 
-        private static void ConvertCharactersToRunes(ArrayBuilder<(char ch, TextSpan span)> charResults, ArrayBuilder<VirtualChar> runeResults)
+        private static void ConvertCharactersToRunes(ArrayBuilder<(char ch, TextSpan span)> charResults, ImmutableSegmentedList<VirtualChar>.Builder runeResults)
         {
             for (var i = 0; i < charResults.Count;)
             {

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/EmbeddedLanguages/VirtualChars/AbstractVirtualCharService.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Diagnostics;
 using System.Text;
+using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.LanguageServices;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Microsoft.CodeAnalysis.Text;
@@ -147,7 +148,7 @@ protected static VirtualCharSequence TryConvertSimpleDoubleQuoteString(
             var startIndexInclusive = startDelimiter.Length;
             var endIndexExclusive = tokenText.Length - endDelimiter.Length;
 
-            using var _ = ArrayBuilder<VirtualChar>.GetInstance(out var result);
+            var result = ImmutableSegmentedList.CreateBuilder<VirtualChar>();
             var offset = token.SpanStart;
 
             for (var index = startIndexInclusive; index < endIndexExclusive;)
@@ -164,7 +165,7 @@ protected static VirtualCharSequence TryConvertSimpleDoubleQuoteString(
                         return default;
 
                     result.Add(VirtualChar.Create(new Rune(tokenText[index]), span));
-                    index += result.Last().Span.Length;
+                    index += result[^1].Span.Length;
                     continue;
                 }
 
@@ -178,7 +179,7 @@ protected static VirtualCharSequence TryConvertSimpleDoubleQuoteString(
         /// <summary>
         /// Returns the number of characters to jump forward (either 1 or 2);
         /// </summary>
-        protected static int ConvertTextAtIndexToRune(string tokenText, int index, ArrayBuilder<VirtualChar> result, int offset)
+        protected static int ConvertTextAtIndexToRune(string tokenText, int index, ImmutableSegmentedList<VirtualChar>.Builder result, int offset)
         {
             if (Rune.TryCreate(tokenText[index], out var rune))
             {
@@ -208,7 +209,7 @@ protected static bool IsOpenOrCloseBrace(char ch)
         protected static VirtualCharSequence CreateVirtualCharSequence(
             string tokenText, int offset,
             int startIndexInclusive, int endIndexExclusive,
-            ArrayBuilder<VirtualChar> result)
+            ImmutableSegmentedList<VirtualChar>.Builder result)
         {
             // Check if we actually needed to create any special virtual chars.
             // if not, we can avoid the entire array allocation and just wrap

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/EmbeddedLanguages/VirtualChars/VirtualCharSequence.Chunks.cs

@@ -5,6 +5,7 @@
 using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Text;
+using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis.EmbeddedLanguages.VirtualChars
@@ -29,23 +30,23 @@ protected Chunk()
         }
 
         /// <summary>
-        /// Thin wrapper over an actual <see cref="ImmutableArray{VirtualChar}"/>.
+        /// Thin wrapper over an actual <see cref="ImmutableSegmentedList{T}"/>.
         /// This will be the common construct we generate when getting the
         /// <see cref="Chunk"/> for a string token that has escapes in it.
         /// </summary>
-        private class ImmutableArrayChunk : Chunk
+        private class ImmutableSegmentedListChunk : Chunk
         {
-            private readonly ImmutableArray<VirtualChar> _array;
+            private readonly ImmutableSegmentedList<VirtualChar> _array;
 
-            public ImmutableArrayChunk(ImmutableArray<VirtualChar> array)
+            public ImmutableSegmentedListChunk(ImmutableSegmentedList<VirtualChar> array)
                 => _array = array;
 
-            public override int Length => _array.Length;
+            public override int Length => _array.Count;
             public override VirtualChar this[int index] => _array[index];
 
             public override VirtualChar? Find(int position)
             {
-                if (_array.Length == 0)
+                if (_array.IsEmpty)
                     return null;
 
                 if (position < _array[0].Span.Start || position >= _array[^1].Span.End)

src/Workspaces/SharedUtilitiesAndExtensions/Compiler/Core/EmbeddedLanguages/VirtualChars/VirtualCharSequence.cs

@@ -5,6 +5,7 @@
 using System;
 using System.Collections.Immutable;
 using System.Diagnostics;
+using Microsoft.CodeAnalysis.Collections;
 using Microsoft.CodeAnalysis.PooledObjects;
 using Microsoft.CodeAnalysis.Text;
 
@@ -27,10 +28,10 @@ namespace Microsoft.CodeAnalysis.EmbeddedLanguages.VirtualChars
     /// </summary>
     internal partial struct VirtualCharSequence
     {
-        public static readonly VirtualCharSequence Empty = Create(ImmutableArray<VirtualChar>.Empty);
+        public static readonly VirtualCharSequence Empty = Create(ImmutableSegmentedList<VirtualChar>.Empty);
 
-        public static VirtualCharSequence Create(ImmutableArray<VirtualChar> virtualChars)
-            => new(new ImmutableArrayChunk(virtualChars));
+        public static VirtualCharSequence Create(ImmutableSegmentedList<VirtualChar> virtualChars)
+            => new(new ImmutableSegmentedListChunk(virtualChars));
 
         public static VirtualCharSequence Create(int firstVirtualCharPosition, string underlyingData)
             => new(new StringChunk(firstVirtualCharPosition, underlyingData));