Generate pattern tree as comment

For example:

    // Required:
    //   Either:
    //     Required:
    //       Command(ship, False) -> CommandNode ship Bool
    //       Command(new, False) -> CommandNode new Bool
    //       OneOrMore:
    //         Argument(<name>, []) -> ArgumentNode <name> List
    //     Required:
    //       Command(ship, False) -> CommandNode ship Bool
    //       Argument(<name>, []) -> ArgumentNode <name> List
    //       Command(move, False) -> CommandNode move Bool
    //       Argument(<x>, ) -> ArgumentNode <x> String
    //       Argument(<y>, ) -> ArgumentNode <y> String
    //       Optional:
    //         Option(,--speed,1,10) -> OptionNode speed String
    //     Required:
    //       Command(ship, False) -> CommandNode ship Bool
    //       Command(shoot, False) -> CommandNode shoot Bool
    //       Argument(<x>, ) -> ArgumentNode <x> String
    //       Argument(<y>, ) -> ArgumentNode <y> String
    //     Required:
    //       Command(mine, False) -> CommandNode mine Bool
    //       Required:
    //         Either:
    //           Command(set, False) -> CommandNode set Bool
    //           Command(remove, False) -> CommandNode remove Bool
    //       Argument(<x>, ) -> ArgumentNode <x> String
    //       Argument(<y>, ) -> ArgumentNode <y> String
    //       Optional:
    //         Either:
    //           Option(,--moored,0,False) -> OptionNode moored Bool
    //           Option(,--drifting,0,False) -> OptionNode drifting Bool
    //     Required:
    //       Required:
    //         Option(-h,--help,0,False) -> OptionNode help Bool
    //     Required:
    //       Option(,--version,0,False) -> OptionNode version Bool

src/DocoptNet.CodeGeneration/IndentingStringBuilder.cs

@@ -43,6 +43,12 @@ public IndentingStringBuilder Append(char value)
             return this;
         }
 
+        public IndentingStringBuilder Append(char value, int repeatCount)
+        {
+            OnAppending().Append(value, repeatCount);
+            return this;
+        }
+
         public IndentingStringBuilder Append(string value)
         {
             OnAppending().Append(value);

src/DocoptNet.CodeGeneration/SourceGenerator.cs

@@ -118,8 +118,24 @@ public static SourceText Generate(string? ns, string name, SourceText text, Enco
               .Append(quote).Append(usage.Replace(quote, quote + quote)).Append(quote).Append(";")
               .AppendLine();
 
-            foreach (var node in new Docopt().GetNodes(usage))
-                sb.Append("// ").Append(node.ToString()).AppendLine();
+            void AppendTree(Pattern pattern, int level = 0)
+            {
+                sb.Append("// ").Append(' ', level * 2);
+                switch (pattern)
+                {
+                    case BranchPattern { Children: var children } branch:
+                        sb.Append(branch.GetType().Name).Append(":").AppendLine();
+                        foreach (var child in children)
+                            AppendTree(child, level + 1);
+                        break;
+                    case LeafPattern leaf:
+                        sb.Append(leaf.ToString()).Append(" -> ").Append(leaf.ToNode().ToString()).AppendLine();
+                        break;
+                }
+            }
+
+            AppendTree(new Docopt().ParsePattern(usage));
+            sb.AppendLine();
 
             using (var reader = new StringReader(new Docopt().GenerateCode(usage)))
             {

src/DocoptNet/Docopt.cs

@@ -78,6 +78,27 @@ protected IDictionary<string, ValueObject> Apply(string doc, Tokens tokens,
             }
         }
 
+        // TODO consider consolidating duplication with portions of Apply above
+        internal Pattern ParsePattern(string doc)
+        {
+            var usageSections = ParseSection("usage:", doc);
+            if (usageSections.Length == 0)
+                throw new DocoptLanguageErrorException("\"usage:\" (case-insensitive) not found.");
+            if (usageSections.Length > 1)
+                throw new DocoptLanguageErrorException("More that one \"usage:\" (case-insensitive).");
+            var exitUsage = usageSections[0];
+            var options = ParseDefaults(doc);
+            var pattern = ParsePattern(FormalUsage(exitUsage), options);
+            var patternOptions = pattern.Flat<Option>().Distinct().ToList();
+            // [default] syntax for argument is disabled
+            foreach (OptionsShortcut optionsShortcut in pattern.Flat(typeof (OptionsShortcut)))
+            {
+                var docOptions = ParseDefaults(doc);
+                optionsShortcut.Children = docOptions.Distinct().Except(patternOptions).ToList();
+            }
+            return pattern.Fix();
+        }
+
         private void SetDefaultPrintExitHandlerIfNecessary(bool exit)
         {
             if (exit && PrintExit == null)