Extract syntax parsing helpers into SyntaxHelper and refactor ClassVisitor to use them

Author: machibuse

Source/Porticle.Grpc.TypeMapper/ClassVisitor.cs

@@ -2,6 +2,7 @@
 using Microsoft.CodeAnalysis;
 using Microsoft.CodeAnalysis.CSharp;
 using Microsoft.CodeAnalysis.CSharp.Syntax;
+using static Porticle.Grpc.TypeMapper.SyntaxHelper;
 
 namespace Porticle.Grpc.TypeMapper;
 
@@ -43,28 +44,4 @@ public class ClassVisitor(TaskLoggingHelper log, bool wrapAllNonNullableStrings,
 
         return node;
     }
-
-    private static ClassDeclarationSyntax ClassFromSource(string classCode)
-    {
-        var syntaxTree = CSharpSyntaxTree.ParseText(classCode);
-        var root = syntaxTree.GetRoot();
-        var nestedClass = root.DescendantNodes().OfType<ClassDeclarationSyntax>().Single();
-        return nestedClass.WithLeadingTrivia(SyntaxFactory.CarriageReturnLineFeed).WithTrailingTrivia(SyntaxFactory.CarriageReturnLineFeed);
-    }
-
-    private static InterfaceDeclarationSyntax InterfaceFromSource(string classCode)
-    {
-        var syntaxTree = CSharpSyntaxTree.ParseText(classCode);
-        var root = syntaxTree.GetRoot();
-        var nestedClass = root.DescendantNodes().OfType<InterfaceDeclarationSyntax>().Single();
-        return nestedClass.WithLeadingTrivia(SyntaxFactory.CarriageReturnLineFeed).WithTrailingTrivia(SyntaxFactory.CarriageReturnLineFeed);
-    }
-
-    private static MethodDeclarationSyntax MethodFromSource(string methodCode)
-    {
-        var syntaxTree = CSharpSyntaxTree.ParseText("class _ { " + methodCode + " }");
-        var root = syntaxTree.GetRoot();
-        var method = root.DescendantNodes().OfType<MethodDeclarationSyntax>().Single();
-        return method.WithLeadingTrivia(SyntaxFactory.CarriageReturnLineFeed).WithTrailingTrivia(SyntaxFactory.CarriageReturnLineFeed);
-    }
 }

Source/Porticle.Grpc.TypeMapper/SyntaxHelper.cs

@@ -0,0 +1,44 @@
+using Microsoft.CodeAnalysis;
+using Microsoft.CodeAnalysis.CSharp;
+using Microsoft.CodeAnalysis.CSharp.Syntax;
+
+namespace Porticle.Grpc.TypeMapper;
+
+public static class SyntaxHelper
+{
+    /// <summary>
+    ///     Parses C# source code and extracts the contained class declaration.
+    /// </summary>
+    /// <param name="classCode">The complete C# source code containing exactly one class declaration.</param>
+    public static ClassDeclarationSyntax ClassFromSource(string classCode)
+    {
+        var syntaxTree = CSharpSyntaxTree.ParseText(classCode);
+        var root = syntaxTree.GetRoot();
+        var nestedClass = root.DescendantNodes().OfType<ClassDeclarationSyntax>().Single();
+        return nestedClass.WithLeadingTrivia(SyntaxFactory.CarriageReturnLineFeed).WithTrailingTrivia(SyntaxFactory.CarriageReturnLineFeed);
+    }
+
+    /// <summary>
+    ///     Parses C# source code and extracts the contained interface declaration.
+    /// </summary>
+    /// <param name="classCode">The complete C# source code containing exactly one interface declaration.</param>
+    public static InterfaceDeclarationSyntax InterfaceFromSource(string classCode)
+    {
+        var syntaxTree = CSharpSyntaxTree.ParseText(classCode);
+        var root = syntaxTree.GetRoot();
+        var nestedClass = root.DescendantNodes().OfType<InterfaceDeclarationSyntax>().Single();
+        return nestedClass.WithLeadingTrivia(SyntaxFactory.CarriageReturnLineFeed).WithTrailingTrivia(SyntaxFactory.CarriageReturnLineFeed);
+    }
+
+    /// <summary>
+    ///     Parses the source code of a single method and extracts the contained method declaration.
+    /// </summary>
+    /// <param name="methodCode">The method source code (without enclosing class).</param>
+    public static MethodDeclarationSyntax MethodFromSource(string methodCode)
+    {
+        var syntaxTree = CSharpSyntaxTree.ParseText("class _ { " + methodCode + " }");
+        var root = syntaxTree.GetRoot();
+        var method = root.DescendantNodes().OfType<MethodDeclarationSyntax>().Single();
+        return method.WithLeadingTrivia(SyntaxFactory.CarriageReturnLineFeed).WithTrailingTrivia(SyntaxFactory.CarriageReturnLineFeed);
+    }
+}