Handle metadata annotations in parameter lists with trailing commas.

lib/src/source_visitor.dart

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library dart_style.src.source_visitor;
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/src/generated/source.dart';
 
@@ skipping 2019 matching lines @@
   /// Parameter lists with trailing commas are formatted differently from
   /// regular parameter lists. They are treated more like collection literals.
   ///
   /// We don't reuse [_visitCollectionLiteral] here because there are enough
   /// weird differences around optional parameters that it's easiest just to
   /// give them their own method.
   void _visitTrailingCommaParameterList(FormalParameterList parameters) {
     // Can't have a trailing comma if there are no parameters.
     assert(parameters.parameters.isNotEmpty);
 
+    _metadataRules.add(new MetadataRule());
+
     // Always split the parameters.
     builder.startRule(new Rule.hard());
 
     token(parameters.leftParenthesis);
 
     // Find the parameter immediately preceding the optional parameters (if
     // there are any).
     FormalParameter lastRequired;
     for (var i = 0; i < parameters.parameters.length; i++) {
       if (parameters.parameters[i] is DefaultFormalParameter) {
         if (i > 0) lastRequired = parameters.parameters[i - 1];
         break;
       }
     }
 
     // If all parameters are optional, put the "[" or "{" right after "(".
     if (parameters.parameters.first is DefaultFormalParameter) {
       token(parameters.leftDelimiter);
     }
 
     // Process the parameters as a separate set of chunks.
     builder = builder.startBlock(null);
 
     for (var parameter in parameters.parameters) {
-      builder.nestExpression();
       visit(parameter);
 
       // The comma after the parameter.
       if (parameter.endToken.next.type == TokenType.COMMA) {
         token(parameter.endToken.next);
       }
 
       // If the optional parameters start after this one, put the delimiter
       // at the end of its line.
       if (parameter == lastRequired) {
         space();
         token(parameters.leftDelimiter);
         lastRequired = null;
       }
 
-      builder.unnest();
       newline();
     }
 
     // Put comments before the closing ")", "]", or "}" inside the block.
     var firstDelimiter =
         parameters.rightDelimiter ?? parameters.rightParenthesis;
     writePrecedingCommentsAndNewlines(firstDelimiter);
     builder = builder.endBlock(null, forceSplit: true);
     builder.endRule();
 
+    _metadataRules.removeLast();
+
     // Now write the delimiter itself.
     _writeText(firstDelimiter.lexeme, firstDelimiter.offset);
     if (firstDelimiter != parameters.rightParenthesis) {
       token(parameters.rightParenthesis);
     }
   }
 
   /// Gets the cost to split at an assignment (or `:` in the case of a named
   /// default value) with the given [rightHandSide].
   ///
@@ skipping 465 matching lines @@
   /// Gets the 1-based line number that the beginning of [token] lies on.
   int _startLine(Token token) => _lineInfo.getLocation(token.offset).lineNumber;
 
   /// Gets the 1-based line number that the end of [token] lies on.
   int _endLine(Token token) => _lineInfo.getLocation(token.end).lineNumber;
 
   /// Gets the 1-based column number that the beginning of [token] lies on.
   int _startColumn(Token token) =>
       _lineInfo.getLocation(token.offset).columnNumber;
 }