Plugin config format validation (and tests).

pkg/analyzer/lib/src/plugin/plugin_configuration.dart

 // Copyright (c) 2015, 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 analyzer.src.plugin.plugin_configuration;
 
 import 'package:analyzer/plugin/options.dart';
 import 'package:yaml/yaml.dart';
 
 const _analyzerOptionScope = 'analyzer';
@@ skipping 13 matching lines @@
           libraryUri: details['library_uri'],
           packageName: details['package_name'],
           path: details['path']);
     }
   }
 
   return null;
 }
 
 PluginInfo _processPluginNode(dynamic node) {
-  if (node is String) {
-    return new PluginInfo(name: node);
-  }
   if (node is YamlMap) {
     if (node.length == 1) {
       return new PluginInfo(name: node.keys.first, version: node.values.first);
     }
   }
   return null;
 }
 
 typedef ErrorHandler(Exception);
 
@@ skipping 11 matching lines @@
       if (analyzerOptions is YamlMap) {
         var pluginConfig = analyzerOptions[_pluginOptionScope];
         if (pluginConfig is YamlMap) {
           pluginConfig.forEach((name, details) {
             var plugin = _processPluginMapping(name, details);
             if (plugin != null) {
               plugins.add(plugin);
             }
           });
         } else {
-          var plugin = _processPluginNode(pluginConfig);
-          if (plugin != null) {
-            plugins.add(plugin);
+          // Anything but an empty list of plugins is treated as a format error.
+          if (pluginConfig != null) {
+            throw new PluginConfigFormatException(
+                'Unrecognized plugin config format (expected `YamlMap`, got `${pluginConfig.runtimeType}`)',
+                pluginConfig);
           }
         }
       }
     }
 
     return new PluginConfig(plugins);
   }
 }
 
+/// Thrown on bad plugin config format.
+class PluginConfigFormatException implements Exception {
+  /// Descriptive message.
+  final message;
+
+  /// The `plugin:` yaml node for generating detailed error feedback.
+  final yamlNode;
+  PluginConfigFormatException(this.message, this.yamlNode);
+}
+
 /// Extracts plugin config details from analysis options.
 class PluginConfigOptionsProcessor extends OptionsProcessor {
   final ErrorHandler _errorHandler;
 
   PluginConfig _config;
 
   PluginConfigOptionsProcessor([this._errorHandler]);
 
   /// The processed plugin config.
   PluginConfig get config => _config;
@@ skipping 20 matching lines @@
   final String packageName;
   final String path;
   PluginInfo(
       {this.name,
       this.version,
       this.className,
       this.libraryUri,
       this.packageName,
       this.path});
 }