perf: use ValueListBuilder for PrivatePrintLeadingTrivia

Author: TimothyMakkison

Src/CSharpier.Core/CSharp/SyntaxPrinter/SyntaxNodePrinters/CompilationUnit.cs

@@ -29,9 +29,14 @@ public static Doc Print(CompilationUnitSyntax node, PrintingContext context)
                 && previousList.Contents[^2] is HardLine
             )
             {
-                while (list.Contents[0] is HardLine { SkipBreakIfFirstInGroup: true })
+                for (
+                    var i = 0;
+                    i < list.Contents.Count
+                        && list.Contents[i] is HardLine { SkipBreakIfFirstInGroup: true };
+                    i++
+                )
                 {
-                    list.Contents.RemoveAt(0);
+                    docs[i] = Doc.Null;
                 }
 
                 docs.Add(finalTrivia);

Src/CSharpier.Core/CSharp/SyntaxPrinter/Token.cs

@@ -237,7 +237,7 @@ private static Doc PrivatePrintLeadingTrivia(
             return Doc.Null;
         }
 
-        var docs = new List<Doc>();
+        var docs = new ValueListBuilder<Doc>([null, null, null, null, null, null, null, null]);
 
         // we don't print any new lines until we run into a comment or directive
         // the PrintExtraNewLines method takes care of printing the initial new lines for a given node
@@ -250,28 +250,28 @@ private static Doc PrivatePrintLeadingTrivia(
 
             if (printNewLines && kind == SyntaxKind.EndOfLineTrivia)
             {
-                if (docs.Count > 0 && docs[^1] == Doc.HardLineSkipBreakIfFirstInGroup)
+                if (docs.Length > 0 && docs[^1] == Doc.HardLineSkipBreakIfFirstInGroup)
                 {
                     printNewLines = false;
                 }
 
                 if (
                     !(
-                        docs.Count > 1
+                        docs.Length > 1
                         && docs[^1] == Doc.HardLineSkipBreakIfFirstInGroup
                         && docs[^2] is LeadingComment { Type: CommentType.SingleLine }
                     )
                 )
                 {
-                    docs.Add(Doc.HardLineSkipBreakIfFirstInGroup);
+                    docs.Append(Doc.HardLineSkipBreakIfFirstInGroup);
                 }
             }
             if (kind is not (SyntaxKind.EndOfLineTrivia or SyntaxKind.WhitespaceTrivia))
             {
                 printNewLines = true;
             }
 
-            void AddLeadingComment(CommentType commentType)
+            void AddLeadingComment(CommentType commentType, ref ValueListBuilder<Doc> docs)
             {
                 var comment = trivia.ToFullString().TrimEnd('\n', '\r');
                 if (
@@ -283,43 +283,43 @@ void AddLeadingComment(CommentType commentType)
                     comment = leadingTrivia[x - 1] + comment;
                 }
 
-                docs.Add(Doc.LeadingComment(comment, commentType));
+                docs.Append(Doc.LeadingComment(comment, commentType));
             }
 
             if (IsSingleLineComment(kind))
             {
-                AddLeadingComment(CommentType.SingleLine);
-                docs.Add(
+                AddLeadingComment(CommentType.SingleLine, ref docs);
+                docs.Append(
                     kind == SyntaxKind.SingleLineDocumentationCommentTrivia
                         ? Doc.HardLineSkipBreakIfFirstInGroup
                         : Doc.Null
                 );
             }
             else if (IsMultiLineComment(kind))
             {
-                AddLeadingComment(CommentType.MultiLine);
+                AddLeadingComment(CommentType.MultiLine, ref docs);
             }
             else if (kind == SyntaxKind.DisabledTextTrivia)
             {
-                docs.Add(Doc.Trim, trivia.ToString());
+                docs.Append(Doc.Trim, trivia.ToString());
             }
             else if (IsRegion(kind))
             {
                 var triviaText = trivia.ToString();
-                docs.Add(Doc.HardLineIfNoPreviousLine);
-                docs.Add(Doc.Trim);
-                docs.Add(
+                docs.Append(Doc.HardLineIfNoPreviousLine);
+                docs.Append(Doc.Trim);
+                docs.Append(
                     kind == SyntaxKind.RegionDirectiveTrivia
                         ? Doc.BeginRegion(triviaText)
                         : Doc.EndRegion(triviaText)
                 );
-                docs.Add(Doc.HardLine);
+                docs.Append(Doc.HardLine);
             }
             else if (trivia.IsDirective)
             {
                 var triviaText = trivia.ToString();
 
-                docs.Add(
+                docs.Append(
                     // adding two of these to ensure we get a new line when a directive follows a trailing comment
                     Doc.HardLineIfNoPreviousLineSkipBreakIfFirstInGroup,
                     Doc.HardLineIfNoPreviousLineSkipBreakIfFirstInGroup,
@@ -337,16 +337,16 @@ void AddLeadingComment(CommentType commentType)
                     )
                     {
                         x++;
-                        docs.Add(Doc.HardLineSkipBreakIfFirstInGroup);
+                        docs.Append(Doc.HardLineSkipBreakIfFirstInGroup);
                     }
                     printNewLines = false;
                 }
             }
         }
 
-        while (skipLastHardline && docs.Count != 0 && docs.Last() is HardLine or NullDoc)
+        while (skipLastHardline && docs.Length != 0 && docs[^1] is HardLine or NullDoc)
         {
-            docs.RemoveAt(docs.Count - 1);
+            docs.Pop();
         }
 
         if (context.State.NextTriviaNeedsLine)
@@ -362,7 +362,7 @@ void AddLeadingComment(CommentType commentType)
             }
             else
             {
-                var index = docs.Count - 1;
+                var index = docs.Length - 1;
                 while (
                     index >= 0
                     && (docs[index] is HardLine or LeadingComment || docs[index] == Doc.Null)
@@ -373,7 +373,7 @@ void AddLeadingComment(CommentType commentType)
                 // this handles an edge case where we get here but already added the line
                 // it relates to the fact that single line comments include new line directives
                 if (
-                    index + 2 >= docs.Count
+                    index + 2 >= docs.Length
                     || !(docs[index + 1] is HardLine && docs[index + 2] is HardLine)
                 )
                 {
@@ -383,7 +383,7 @@ void AddLeadingComment(CommentType commentType)
             context.State.NextTriviaNeedsLine = false;
         }
 
-        return docs.Count > 0 ? Doc.Concat(docs) : Doc.Null;
+        return Doc.Concat(ref docs);
     }
 
     private static bool IsSingleLineComment(SyntaxKind kind) =>

Src/CSharpier.Core/Utilities/ValueListBuilder.cs

@@ -87,18 +87,16 @@ private void AppendMultiChar(scoped ReadOnlySpan<T> source)
         this.pos += source.Length;
     }
 
-    public void Insert(int index, scoped ReadOnlySpan<T> source)
+    public void Insert(int index, T item)
     {
-        Debug.Assert(index == 0, "Implementation currently only supports index == 0");
-
-        if ((uint)(this.pos + source.Length) > (uint)this.span.Length)
+        if ((uint)(this.pos + 1) > (uint)this.span.Length)
         {
-            this.Grow(source.Length);
+            this.Grow(1);
         }
 
-        this.span[..this.pos].CopyTo(this.span[source.Length..]);
-        source.CopyTo(this.span);
-        this.pos += source.Length;
+        span.Slice(index, this.pos - index).CopyTo(this.span.Slice(index + 1));
+        this.span[index] = item;
+        this.pos += 1;
     }
 
     [MethodImpl(MethodImplOptions.AggressiveInlining)]
@@ -139,6 +137,13 @@ private void AddWithResize(T item)
         this.pos = pos + 1;
     }
 
+    [MethodImpl(MethodImplOptions.AggressiveInlining)]
+    public T Pop()
+    {
+        this.pos--;
+        return this.span[this.pos];
+    }
+
     public readonly ReadOnlySpan<T> AsSpan()
     {
         return this.span[..this.pos];