Uses pooled array builder for formatting spans

Improves performance by utilizing a pooled array builder
to avoid allocations when collecting formatting spans.

This change reduces memory pressure and improves the
efficiency of the formatting process.

Author: DustinCampbell

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Formatting/FormattingContext.cs

@@ -11,6 +11,7 @@
 using System.Threading.Tasks;
 using Microsoft.AspNetCore.Razor.Language;
 using Microsoft.AspNetCore.Razor.Language.Syntax;
+using Microsoft.AspNetCore.Razor.PooledObjects;
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.Razor.ProjectSystem;
 using Microsoft.CodeAnalysis.Text;
@@ -19,7 +20,7 @@ namespace Microsoft.CodeAnalysis.Razor.Formatting;
 
 internal sealed class FormattingContext
 {
-    private IReadOnlyList<FormattingSpan>? _formattingSpans;
+    private ImmutableArray<FormattingSpan>? _formattingSpans;
     private IReadOnlyDictionary<int, IndentationContext>? _indentations;
     private readonly bool _useNewFormattingEngine;
 
@@ -143,25 +144,27 @@ public IReadOnlyDictionary<int, IndentationContext> GetIndentations()
         return _indentations;
     }
 
-    private IReadOnlyList<FormattingSpan> GetFormattingSpans()
+    private ImmutableArray<FormattingSpan> GetFormattingSpans()
     {
-        if (_formattingSpans is null)
+        return _formattingSpans ??= ComputeFormattingSpans(CodeDocument);
+
+        static ImmutableArray<FormattingSpan> ComputeFormattingSpans(RazorCodeDocument codeDocument)
         {
-            var syntaxTree = CodeDocument.GetRequiredSyntaxTree();
-            var inGlobalNamespace = CodeDocument.TryGetNamespace(fallbackToRootNamespace: true, out var @namespace) &&
+            var syntaxTree = codeDocument.GetRequiredSyntaxTree();
+            var inGlobalNamespace = codeDocument.TryGetNamespace(fallbackToRootNamespace: true, out var @namespace) &&
                 string.IsNullOrEmpty(@namespace);
-            _formattingSpans = GetFormattingSpans(syntaxTree, inGlobalNamespace: inGlobalNamespace);
-        }
 
-        return _formattingSpans;
+            return GetFormattingSpans(syntaxTree, inGlobalNamespace: inGlobalNamespace);
+        }
     }
 
-    private static IReadOnlyList<FormattingSpan> GetFormattingSpans(RazorSyntaxTree syntaxTree, bool inGlobalNamespace)
+    private static ImmutableArray<FormattingSpan> GetFormattingSpans(RazorSyntaxTree syntaxTree, bool inGlobalNamespace)
     {
-        var visitor = new FormattingVisitor(inGlobalNamespace: inGlobalNamespace);
-        visitor.Visit(syntaxTree.Root);
+        using var _ = ArrayBuilderPool<FormattingSpan>.GetPooledObject(out var formattingSpans);
+
+        FormattingVisitor.VisitRoot(syntaxTree, formattingSpans, inGlobalNamespace);
 
-        return visitor.FormattingSpans;
+        return formattingSpans.ToImmutableAndClear();
     }
 
     /// <summary>

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Formatting/FormattingVisitor.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Collections.Immutable;
 using System.Diagnostics;
 using System.Linq;
 using Microsoft.AspNetCore.Razor.Language;
@@ -13,27 +14,32 @@ namespace Microsoft.CodeAnalysis.Razor.Formatting;
 
 using Microsoft.AspNetCore.Razor.Language.Syntax;
 
-internal class FormattingVisitor : SyntaxWalker
+internal sealed class FormattingVisitor : SyntaxWalker
 {
     private const string HtmlTag = "html";
 
+    private readonly ImmutableArray<FormattingSpan>.Builder _spans;
     private readonly bool _inGlobalNamespace;
-    private readonly List<FormattingSpan> _spans;
     private FormattingBlockKind _currentBlockKind;
     private SyntaxNode? _currentBlock;
     private int _currentHtmlIndentationLevel = 0;
     private int _currentRazorIndentationLevel = 0;
     private int _currentComponentIndentationLevel = 0;
     private bool _isInClassBody = false;
 
-    public FormattingVisitor(bool inGlobalNamespace)
+    private FormattingVisitor(ImmutableArray<FormattingSpan>.Builder spans, bool inGlobalNamespace)
     {
         _inGlobalNamespace = inGlobalNamespace;
-        _spans = new List<FormattingSpan>();
+        _spans = spans;
         _currentBlockKind = FormattingBlockKind.Markup;
     }
 
-    public IReadOnlyList<FormattingSpan> FormattingSpans => _spans;
+    public static void VisitRoot(
+        RazorSyntaxTree syntaxTree, ImmutableArray<FormattingSpan>.Builder spans, bool inGlobalNamespace)
+    {
+        var visitor = new FormattingVisitor(spans, inGlobalNamespace);
+        visitor.Visit(syntaxTree.Root);
+    }
 
     public override void VisitRazorCommentBlock(RazorCommentBlockSyntax node)
     {