Option support for `enableSuperMixins` (and more).

pkg/analyzer/lib/src/generated/utilities_general.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 engine.utilities.general;
 
 import 'dart:collection';
 import 'dart:developer' show UserTag;
 
 /**
+ * Test if the given [value] is `true` or the string "true" (case-insensitive).
+ */
+bool isTrue(Object value) =>
+    value is bool ? value : toLowerCase(value) == 'true';
+
+/**
+ * Safely convert this [value] to lower case, returning `null` if [value] is
+ * null.
+ */
+String toLowerCase(Object value) => value?.toString()?.toLowerCase();
+
+/**
+ * Safely convert this [value] to upper case, returning `null` if [value] is
+ * null.
+ */
+String toUpperCase(Object value) => value?.toString()?.toUpperCase();
+
+/**
  * Jenkins hash function, optimized for small integers.
  * Borrowed from sdk/lib/math/jenkins_smi_hash.dart.
  */
 class JenkinsSmiHash {
   static int combine(int hash, int value) {
     hash = 0x1fffffff & (hash + value);
     hash = 0x1fffffff & (hash + ((0x0007ffff & hash) << 10));
     return hash ^ (hash >> 6);
   }
 
@@ skipping 145 matching lines @@
 
   makeCurrentWhile(f()) {
     PerformanceTag prevTag = makeCurrent();
     try {
       return f();
     } finally {
       prevTag.makeCurrent();
     }
   }
 }