perf: use ValueListBuilder<T> for constant buffers (#1529)

Follow on from #1502, using `ValueListBuilder` to replace known
`List<Doc>` sizes.

- Most of these changes aren't measurable in the benchmarks, many are
insignificant, although I suspect this is partly due to the limited code
found in the benchmark file.
- This PR will increase the performance benefits of #1524



@belav what do you think the best way of replacing a list that uses a
collection initializer is?

I can either add the items directly into the scratch buffer and manually
update `Length`
```C#
var docs = new ValueListBuilder<Doc>
([
    Modifiers.Print(node.Modifiers, context),
    Token.Print(node.DelegateKeyword, context),
    null,null
]);
docs.Length = 2;
```

Or create the buffer and then append the items via params.
```C#
var docs = new ValueListBuilder<Doc>([null, null, null, null]);
docs.Append(
    Modifiers.Print(node.Modifiers, context),
    Token.Print(node.DelegateKeyword, context)
);
```
Or Append each item
```C#
var docs = new ValueListBuilder<Doc>([null, null, null, null]);
docs.Append(Modifiers.Print(node.Modifiers, context));
docs.Append(Token.Print(node.DelegateKeyword, context));
```

---------

Co-authored-by: Bela VanderVoort <[email protected]>

Author: TimothyMakkison

Src/CSharpier/DocTypes/Doc.cs

@@ -56,6 +56,16 @@ public static Doc Concat(List<Doc> contents) =>
 
     public static Doc Concat(params Doc[] contents) => new Concat(contents);
 
+    public static Doc Concat(ref ValueListBuilder<Doc> contents)
+    {
+        return contents.Length switch
+        {
+            0 => Null,
+            1 => contents[0],
+            _ => new Concat(contents.AsSpan().ToArray()),
+        };
+    }
+
     public static Doc Join(Doc separator, IEnumerable<Doc> enumerable)
     {
         var docs = new List<Doc>();

Src/CSharpier/SyntaxPrinter/AttributeLists.cs

@@ -13,7 +13,7 @@ PrintingContext context
             return Doc.Null;
         }
 
-        var docs = new List<Doc>();
+        var docs = new ValueListBuilder<Doc>([null, null]);
         Doc separator = node
             is TypeParameterSyntax
                 or ParameterSyntax
@@ -22,13 +22,15 @@ or AccessorDeclarationSyntax
             ? Doc.Line
             : Doc.HardLine;
 
-        docs.Add(Doc.Join(separator, attributeLists.Select(o => AttributeList.Print(o, context))));
+        docs.Append(
+            Doc.Join(separator, attributeLists.Select(o => AttributeList.Print(o, context)))
+        );
 
         if (node is not (ParameterSyntax or TypeParameterSyntax))
         {
-            docs.Add(separator);
+            docs.Append(separator);
         }
 
-        return Doc.Concat(docs);
+        return Doc.Concat(ref docs);
     }
 }

Src/CSharpier/SyntaxPrinter/SeparatedSyntaxList.cs

@@ -144,12 +144,7 @@ private static Doc Print<T>(
             docs.Append(unFormattedCode.ToString().Trim());
         }
 
-        var output = docs.Length switch
-        {
-            0 => Doc.Null,
-            1 => docs[0],
-            _ => Doc.Concat(docs.AsSpan().ToArray()),
-        };
+        var output = Doc.Concat(ref docs);
         docs.Dispose();
 
         return output;

Src/CSharpier/SyntaxPrinter/SyntaxNodePrinters/AnonymousMethodExpression.cs

@@ -4,19 +4,17 @@ internal static class AnonymousMethodExpression
 {
     public static Doc Print(AnonymousMethodExpressionSyntax node, PrintingContext context)
     {
-        var docs = new List<Doc>
-        {
-            Modifiers.Print(node.Modifiers, context),
-            Token.Print(node.DelegateKeyword, context),
-        };
+        var docs = new ValueListBuilder<Doc>([null, null, null, null]);
+        docs.Append(Modifiers.Print(node.Modifiers, context));
+        docs.Append(Token.Print(node.DelegateKeyword, context));
 
         if (node.ParameterList != null)
         {
-            docs.Add(ParameterList.Print(node.ParameterList, context));
+            docs.Append(ParameterList.Print(node.ParameterList, context));
         }
 
-        docs.Add(Block.Print(node.Block, context));
+        docs.Append(Block.Print(node.Block, context));
 
-        return Doc.Concat(docs);
+        return Doc.Concat(ref docs);
     }
 }

Src/CSharpier/SyntaxPrinter/SyntaxNodePrinters/AnonymousObjectMemberDeclarator.cs

@@ -4,21 +4,21 @@ internal static class AnonymousObjectMemberDeclarator
 {
     public static Doc Print(AnonymousObjectMemberDeclaratorSyntax node, PrintingContext context)
     {
-        var docs = new List<Doc>();
+        var docs = new ValueListBuilder<Doc>([null, null, null, null]);
         if (
             node.Parent is AnonymousObjectCreationExpressionSyntax parent
             && node != parent.Initializers.First()
         )
         {
-            docs.Add(ExtraNewLines.Print(node));
+            docs.Append(ExtraNewLines.Print(node));
         }
 
         if (node.NameEquals != null)
         {
-            docs.Add(Token.PrintWithSuffix(node.NameEquals.Name.Identifier, " ", context));
-            docs.Add(Token.PrintWithSuffix(node.NameEquals.EqualsToken, " ", context));
+            docs.Append(Token.PrintWithSuffix(node.NameEquals.Name.Identifier, " ", context));
+            docs.Append(Token.PrintWithSuffix(node.NameEquals.EqualsToken, " ", context));
         }
-        docs.Add(Node.Print(node.Expression, context));
-        return Doc.Concat(docs);
+        docs.Append(Node.Print(node.Expression, context));
+        return Doc.Concat(ref docs);
     }
 }

Src/CSharpier/SyntaxPrinter/SyntaxNodePrinters/Argument.cs

@@ -9,17 +9,17 @@ public static Doc Print(ArgumentSyntax node, PrintingContext context)
 
     public static Doc PrintModifiers(ArgumentSyntax node, PrintingContext context)
     {
-        var docs = new List<Doc>(2);
+        var docs = new ValueListBuilder<Doc>([null, null]);
         if (node.NameColon != null)
         {
-            docs.Add(BaseExpressionColon.Print(node.NameColon, context));
+            docs.Append(BaseExpressionColon.Print(node.NameColon, context));
         }
 
         if (node.RefKindKeyword.RawSyntaxKind() != SyntaxKind.None)
         {
-            docs.Add(Token.PrintWithSuffix(node.RefKindKeyword, " ", context));
+            docs.Append(Token.PrintWithSuffix(node.RefKindKeyword, " ", context));
         }
 
-        return Doc.Concat(docs);
+        return Doc.Concat(ref docs);
     }
 }

Src/CSharpier/SyntaxPrinter/SyntaxNodePrinters/AttributeList.cs

@@ -9,19 +9,19 @@ public static Doc Print(AttributeListSyntax node, PrintingContext context)
             return CSharpierIgnore.PrintWithoutFormatting(node, context).Trim();
         }
 
-        var docs = new List<Doc>();
+        var docs = new ValueListBuilder<Doc>([null, null, null, null, null, null, null]);
         if (
             node.Parent is CompilationUnitSyntax compilationUnitSyntax
             && compilationUnitSyntax.AttributeLists.First() != node
         )
         {
-            docs.Add(ExtraNewLines.Print(node));
+            docs.Append(ExtraNewLines.Print(node));
         }
 
-        docs.Add(Token.Print(node.OpenBracketToken, context));
+        docs.Append(Token.Print(node.OpenBracketToken, context));
         if (node.Target != null)
         {
-            docs.Add(
+            docs.Append(
                 Token.Print(node.Target.Identifier, context),
                 Token.PrintWithSuffix(node.Target.ColonToken, " ", context)
             );
@@ -72,17 +72,19 @@ node.Parent is CompilationUnitSyntax compilationUnitSyntax
             context
         );
 
-        docs.Add(
+        docs.Append(
             node.Attributes.Count > 1
                 ? Doc.Indent(Doc.SoftLine, printSeparatedSyntaxList)
                 : printSeparatedSyntaxList
         );
 
-        docs.Add(
-            node.Attributes.Count > 1 ? Doc.SoftLine : Doc.Null,
-            Token.Print(node.CloseBracketToken, context)
-        );
+        if (node.Attributes.Count > 1)
+        {
+            docs.Append(Doc.SoftLine);
+        }
+
+        docs.Append(Token.Print(node.CloseBracketToken, context));
 
-        return Doc.Group(docs);
+        return Doc.Group(docs.AsSpan().ToArray());
     }
 }

Src/CSharpier/SyntaxPrinter/SyntaxNodePrinters/BaseFieldDeclaration.cs

@@ -4,20 +4,20 @@ internal static class BaseFieldDeclaration
 {
     public static Doc Print(BaseFieldDeclarationSyntax node, PrintingContext context)
     {
-        var docs = new List<Doc>
-        {
-            AttributeLists.Print(node, node.AttributeLists, context),
-            Modifiers.PrintSorted(node.Modifiers, context),
-        };
+        var docs = new ValueListBuilder<Doc>([null, null, null, null, null]);
+        docs.Append(AttributeLists.Print(node, node.AttributeLists, context));
+        docs.Append(Modifiers.PrintSorted(node.Modifiers, context));
         if (node is EventFieldDeclarationSyntax eventFieldDeclarationSyntax)
         {
-            docs.Add(Token.PrintWithSuffix(eventFieldDeclarationSyntax.EventKeyword, " ", context));
+            docs.Append(
+                Token.PrintWithSuffix(eventFieldDeclarationSyntax.EventKeyword, " ", context)
+            );
         }
 
-        docs.Add(
+        docs.Append(
             VariableDeclaration.Print(node.Declaration, context),
             Token.Print(node.SemicolonToken, context)
         );
-        return Doc.Concat(docs);
+        return Doc.Concat(ref docs);
     }
 }

Src/CSharpier/SyntaxPrinter/SyntaxNodePrinters/BasePropertyDeclaration.cs

@@ -38,11 +38,9 @@ public static Doc Print(BasePropertyDeclarationSyntax node, PrintingContext cont
             semicolonToken = eventDeclarationSyntax.SemicolonToken;
         }
 
-        var docs = new List<Doc> { AttributeLists.Print(node, node.AttributeLists, context) };
-
         return Doc.Group(
             Doc.Concat(
-                Doc.Concat(docs),
+                AttributeLists.Print(node, node.AttributeLists, context),
                 Modifiers.PrintSorted(node.Modifiers, context),
                 eventKeyword,
                 Node.Print(node.Type, context),
@@ -112,7 +110,7 @@ private static Doc PrintAccessorDeclarationSyntax(
         PrintingContext context
     )
     {
-        var docs = new List<Doc>();
+        var docs = new ValueListBuilder<Doc>([null, null, null, null, null, null]);
         if (
             node.AttributeLists.Count > 1
             || node.Body != null
@@ -123,28 +121,28 @@ PrintingContext context
             )
         )
         {
-            docs.Add(Doc.HardLine);
+            docs.Append(Doc.HardLine);
         }
         else
         {
-            docs.Add(separator);
+            docs.Append(separator);
         }
 
-        docs.Add(AttributeLists.Print(node, node.AttributeLists, context));
-        docs.Add(Modifiers.PrintSorted(node.Modifiers, context));
-        docs.Add(Token.Print(node.Keyword, context));
+        docs.Append(AttributeLists.Print(node, node.AttributeLists, context));
+        docs.Append(Modifiers.PrintSorted(node.Modifiers, context));
+        docs.Append(Token.Print(node.Keyword, context));
 
         if (node.Body != null)
         {
-            docs.Add(Block.Print(node.Body, context));
+            docs.Append(Block.Print(node.Body, context));
         }
         else if (node.ExpressionBody != null)
         {
-            docs.Add(ArrowExpressionClause.Print(node.ExpressionBody, context));
+            docs.Append(ArrowExpressionClause.Print(node.ExpressionBody, context));
         }
 
-        docs.Add(Token.Print(node.SemicolonToken, context));
+        docs.Append(Token.Print(node.SemicolonToken, context));
 
-        return Doc.Concat(docs);
+        return Doc.Concat(ref docs);
     }
 }

Src/CSharpier/SyntaxPrinter/SyntaxNodePrinters/DelegateDeclaration.cs

@@ -4,23 +4,25 @@ internal static class DelegateDeclaration
 {
     public static Doc Print(DelegateDeclarationSyntax node, PrintingContext context)
     {
-        var docs = new List<Doc>
-        {
-            AttributeLists.Print(node, node.AttributeLists, context),
-            Modifiers.PrintSorted(node.Modifiers, context),
-            Token.PrintWithSuffix(node.DelegateKeyword, " ", context),
-            Node.Print(node.ReturnType, context),
-            { " ", Token.Print(node.Identifier, context) },
-        };
+        var docs = new ValueListBuilder<Doc>(
+            [null, null, null, null, null, null, null, null, null, null]
+        );
+        docs.Append(AttributeLists.Print(node, node.AttributeLists, context));
+        docs.Append(Modifiers.PrintSorted(node.Modifiers, context));
+        docs.Append(Token.PrintWithSuffix(node.DelegateKeyword, " ", context));
+        docs.Append(Node.Print(node.ReturnType, context));
+        docs.Append(" ");
+        docs.Append(Token.Print(node.Identifier, context));
+
         if (node.TypeParameterList != null)
         {
-            docs.Add(Node.Print(node.TypeParameterList, context));
+            docs.Append(Node.Print(node.TypeParameterList, context));
         }
-        docs.Add(
+        docs.Append(
             Node.Print(node.ParameterList, context),
             ConstraintClauses.Print(node.ConstraintClauses, context),
             Token.Print(node.SemicolonToken, context)
         );
-        return Doc.Concat(docs);
+        return Doc.Concat(ref docs);
     }
 }