perf: fast comparison using FullSpan and source code

Author: TimothyMakkison

Src/CSharpier.Cli/CommandLineFormatter.cs

@@ -479,7 +479,10 @@ CancellationToken cancellationToken
         {
             IFormattingValidator? formattingValidator = null;
 
-            if (printerOptions.Formatter is Formatter.CSharp or Formatter.CSharpScript)
+            if (
+                printerOptions.Formatter is Formatter.CSharp or Formatter.CSharpScript
+                && fileToFormatInfo.FileContents != codeFormattingResult.Code
+            )
             {
                 var sourceCodeKind =
                     printerOptions.Formatter is Formatter.CSharpScript

Src/CSharpier.Core/CSharp/SyntaxNodeComparer.cs

@@ -322,6 +322,17 @@ private CompareResult Compare(SyntaxTrivia originalTrivia, SyntaxTrivia formatte
             : NotEqual(originalTrivia.Span, formattedTrivia.Span);
     }
 
+    private bool CompareFullSpan(SyntaxNode originalStart, SyntaxNode formattedStart)
+    {
+        var originalSpan = OriginalSourceCode
+            .AsSpan()
+            .Slice(originalStart.FullSpan.Start, originalStart.FullSpan.Length);
+        var formattedSpan = NewSourceCode
+            .AsSpan()
+            .Slice(formattedStart.FullSpan.Start, formattedStart.FullSpan.Length);
+        return originalSpan == formattedSpan;
+    }
+
     private static CompareResult CompareComment(
         string originalComment,
         string formattedComment,

Src/CSharpier.Generators/SyntaxNodeComparerGenerator.cs

@@ -141,6 +141,18 @@ private static void GenerateMethod(StringBuilder sourceBuilder, INamedTypeSymbol
             """
         );
 
+        if (
+            type.BaseType?.ToDisplayString()
+                == "Microsoft.CodeAnalysis.CSharp.Syntax.TypeDeclarationSyntax"
+            || type.ToDisplayString()
+                == "Microsoft.CodeAnalysis.CSharp.Syntax.MethodDeclarationSyntax"
+        )
+        {
+            sourceBuilder.AppendLine(
+                $"            if (CompareFullSpan(originalNode, formattedNode)) return Equal;"
+            );
+        }
+
         foreach (var propertySymbol in type.GetAllProperties().OrderBy(o => o.Name))
         {
             var propertyName = propertySymbol.Name;