Default trailing comma support to `true` (#26647).

pkg/analyzer/lib/src/task/options.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.task.options;
 
 import 'dart:collection';
 
 import 'package:analyzer/analyzer.dart';
 import 'package:analyzer/plugin/options.dart';
@@ skipping 31 matching lines @@
         AnalysisContext context, Map<String, Object> options) =>
     _processor.configure(context, options);
 
 /// `analyzer` analysis options constants.
 class AnalyzerOptions {
   static const String analyzer = 'analyzer';
   static const String enableAsync = 'enableAsync';
   static const String enableGenericMethods = 'enableGenericMethods';
   static const String enableStrictCallChecks = 'enableStrictCallChecks';
   static const String enableSuperMixins = 'enableSuperMixins';
-  static const String enableTrailingCommas = 'enableTrailingCommas';
 
   static const String errors = 'errors';
   static const String exclude = 'exclude';
   static const String language = 'language';
   static const String plugins = 'plugins';
   static const String strong_mode = 'strong-mode';
 
   // Strong mode options, see AnalysisOptionsImpl for documentation.
   static const String implicitCasts = 'implicit-casts';
   static const String implicitDynamic = 'implicit-dynamic';
@@ skipping 18 matching lines @@
     language,
     plugins,
     strong_mode
   ];
 
   /// Supported `analyzer` language configuration options.
   static const List<String> languageOptions = const [
     enableAsync,
     enableGenericMethods,
     enableStrictCallChecks,
-    enableSuperMixins,
-    enableTrailingCommas
+    enableSuperMixins
   ];
 }
 
 /// Validates `analyzer` options.
 class AnalyzerOptionsValidator extends CompositeValidator {
   AnalyzerOptionsValidator()
       : super([
           new TopLevelAnalyzerOptionsValidator(),
           new StrongModeOptionValueValidator(),
           new ErrorFilterOptionValidator(),
@@ skipping 394 matching lines @@
       }
     }
     if (feature == AnalyzerOptions.enableSuperMixins) {
       if (isTrue(value)) {
         AnalysisOptionsImpl options =
             new AnalysisOptionsImpl.from(context.analysisOptions);
         options.enableSuperMixins = true;
         context.analysisOptions = options;
       }
     }
-    if (feature == AnalyzerOptions.enableTrailingCommas) {
-      if (isTrue(value)) {
-        AnalysisOptionsImpl options =
-            new AnalysisOptionsImpl.from(context.analysisOptions);
-        options.enableTrailingCommas = true;
-        context.analysisOptions = options;
-      }
-    }
     if (feature == AnalyzerOptions.enableGenericMethods) {
       if (isTrue(value)) {
         AnalysisOptionsImpl options =
             new AnalysisOptionsImpl.from(context.analysisOptions);
         options.enableGenericMethods = true;
         context.analysisOptions = options;
       }
     }
   }
 
@@ skipping 85 matching lines @@
         }
       });
     } else if (config is Map) {
       options.strongMode = true;
       config.forEach((k, v) => _applyStrongModeOption(options, k, v));
     } else {
       options.strongMode = config is bool ? config : false;
     }
   }
 }