Better error message for mismatched parameter names between message and translation

pkg/intl/lib/src/intl_message.dart

 // Copyright (c) 2013, 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.
 
 /**
  * This provides classes to represent the internal structure of the
  * arguments to `Intl.message`. It is used when parsing sources to extract
  * messages or to generate code for message substitution. Normal programs
  * using Intl would not import this library.
  *
@@ skipping 51 matching lines @@
    */
   get arguments => parent == null ? const [] : parent.arguments;
 
   /**
    * We find the examples from the top-level [MainMessage] and use those
    * when writing out variables. [MainMessage] overrides this to return
    * the actual examples.
    */
   get examples => parent == null ? const [] : parent.examples;
 
+  /**
+   * The name of the top-level [MainMessage].
+   */
+  String get name => parent == null ? '<unnamed>' : parent.name;
+
   String checkValidity(MethodInvocation node, List arguments,
                        String outerName, FormalParameterList outerArgs) {
     var hasArgs = arguments.any(
         (each) => each is NamedExpression && each.name.label.name == 'args');
     var hasParameters = !outerArgs.parameters.isEmpty;
     if (!hasArgs && hasParameters) {
       return "The 'args' argument for Intl.message must be specified";
     }
 
     var messageName = arguments.firstWhere(
@@ skipping 185 matching lines @@
 
   /** The index in the list of parameters of the containing function. */
   int _index;
   int get index {
     if (_index != null) return _index;
     if (arguments.isEmpty) return null;
     // We may have been given an all-uppercase version of the name, so compare
     // case-insensitive.
     _index = arguments.map((x) => x.toUpperCase()).toList()
         .indexOf(_variableNameUpper);
+    if (_index == -1) {
+      throw new ArgumentError(
+          "Cannot find parameter named '$_variableNameUpper' in "
+          "message named '$name'. Available "
+          "parameters are $arguments");
+    }
     return _index;
   }
 
   /**
    * The variable name we get from parsing. This may be an all uppercase version
    * of the Dart argument name.
    */
   String _variableNameUpper;
 
   /**
@@ skipping 397 matching lines @@
     out.write('(');
     out.write(mainArgument);
     var args = codeAttributeNames;
     out.write(", {");
     args.fold(out, (buffer, arg) => buffer..write(
         "'$arg': '${this[arg].toCode()}', "));
     out.write("})}");
     return out.toString();
   }
 }