enhance ContextBuilder getAnalysisOptions to handle lints

pkg/analyzer/lib/src/context/builder.dart

Index: pkg/analyzer/lib/src/context/builder.dart
diff --git a/pkg/analyzer/lib/src/context/builder.dart b/pkg/analyzer/lib/src/context/builder.dart
index eef1373e1cc693f0f254f73485e4ffd71fe54d45..05421729840a748034c0dfa91208f933c66ed52c 100644
--- a/pkg/analyzer/lib/src/context/builder.dart
+++ b/pkg/analyzer/lib/src/context/builder.dart
@@ -25,6 +25,7 @@ import 'package:analyzer/src/generated/gn.dart';
 import 'package:analyzer/src/generated/sdk.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/src/generated/workspace.dart';
+import 'package:analyzer/src/lint/registry.dart';
 import 'package:analyzer/src/summary/summary_sdk.dart';
 import 'package:analyzer/src/task/options.dart';
 import 'package:args/args.dart';
@@ -410,6 +411,10 @@ class ContextBuilder {
       applyToAnalysisOptions(options, optionMap);
       if (builderOptions.argResults != null) {
         applyAnalysisOptionFlags(options, builderOptions.argResults);
+        // If lints turned on but none specified, then enable default lints
+        if (options.lint && options.lintRules.isEmpty) {
+          options.lintRules = Registry.ruleRegistry.defaultRules;
+        }
       }
     }
     return options;