Issue 21496. Fix for inlining negate/decrement into negate.

pkg/analysis_server/lib/src/services/refactoring/inline_local.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 services.src.refactoring.inline_local;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol_server.dart' hide Element;
 import 'package:analysis_server/src/services/correction/source_range.dart';
@@ skipping 119 matching lines @@
           _variableNode.getAncestor((node) => node is VariableDeclarationStatement);
       SourceRange range = utils.getLinesRangeStatements([declarationStatement]);
       doSourceChange_addElementEdit(
           change,
           unitElement,
           newSourceEdit_range(range, ''));
     }
     // prepare initializer
     Expression initializer = _variableNode.initializer;
     String initializerCode = utils.getNodeText(initializer);
-    int initializerPrecedence = getExpressionPrecedence(initializer);
     // replace references
     for (SearchMatch reference in _references) {
       SourceRange range = reference.sourceRange;
       // prepare context
       int offset = range.offset;
       AstNode node = utils.findNode(offset);
       AstNode parent = node.parent;
       // prepare code
       String codeForReference;
       if (parent is InterpolationExpression) {
@@ skipping 13 matching lines @@
               codeForReference = codeForReference.substring(1);
             } else if (codeForReference.startsWith('\r\n')) {
               codeForReference = codeForReference.substring(2);
             }
           }
         } else if (_shouldBeExpressionInterpolation(parent, initializer)) {
           codeForReference = '{$initializerCode}';
         } else {
           codeForReference = initializerCode;
         }
-      } else if (initializerPrecedence < getExpressionParentPrecedence(node)) {
+      } else if (_shouldUseParenthesis(initializer, node)) {
         codeForReference = '($initializerCode)';
       } else {
         codeForReference = initializerCode;
       }
       // do replace
       doSourceChange_addElementEdit(
           change,
           unitElement,
           newSourceEdit_range(range, codeForReference));
     }
     // done
     return new Future.value(change);
   }
 
   @override
   bool requiresPreview() => false;
 
   static bool _shouldBeExpressionInterpolation(InterpolationExpression target,
       Expression expression) {
     TokenType targetType = target.beginToken.type;
     return targetType == TokenType.STRING_INTERPOLATION_IDENTIFIER &&
         expression is! SimpleIdentifier;
   }
+
+  static bool _shouldUseParenthesis(Expression init, AstNode node) {
+    // check precedence
+    int initPrecedence = getExpressionPrecedence(init);
+    if (initPrecedence < getExpressionParentPrecedence(node)) {
+      return true;
+    }
+    // special case for '-'
+    AstNode parent = node.parent;
+    if (init is PrefixExpression && parent is PrefixExpression) {
+      if (parent.operator.type == TokenType.MINUS) {
+        TokenType initializerOperator = init.operator.type;
+        if (initializerOperator == TokenType.MINUS ||
+            initializerOperator == TokenType.MINUS_MINUS) {
+          return true;
+        }
+      }
+    }
+    // no () is needed
+    return false;
+  }
 }