Resynthesize ?? expressions from Kernel.

pkg/analyzer/lib/src/kernel/resynthesize.dart

 // Copyright (c) 2017, 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.
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/standard_ast_factory.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/element/element.dart';
@@ skipping 244 matching lines @@
       return AstTestFactory.prefixExpression(TokenType.BANG, operand);
     }
 
     if (expr is kernel.LogicalExpression) {
       var operator = _toBinaryOperatorTokenType(expr.operator);
       var left = build(expr.left);
       var right = build(expr.right);
       return AstTestFactory.binaryExpression(left, operator, right);
     }
 
+    if (expr is kernel.Let) {
+      var body = expr.body;
+      if (body is kernel.ConditionalExpression) {
+        var condition = body.condition;
+        var otherwiseExpr = body.otherwise;
+        if (condition is kernel.MethodInvocation) {
+          var equalsReceiver = condition.receiver;
+          if (equalsReceiver is kernel.VariableGet &&
+              condition.name.name == '==' &&
+              condition.arguments.positional.length == 1 &&
+              condition.arguments.positional[0] is kernel.NullLiteral &&
+              otherwiseExpr is kernel.VariableGet &&
+              otherwiseExpr.variable == equalsReceiver.variable) {
+            var left = build(expr.variable.initializer);
+            var right = build(body.then);
+            return AstTestFactory.binaryExpression(
+                left, TokenType.QUESTION_QUESTION, right);
+          }
+        }
+      }
+    }
+
     if (expr is kernel.MethodInvocation) {
       kernel.Member member = expr.interfaceTarget;
       if (member is kernel.Procedure) {
         if (member.kind == kernel.ProcedureKind.Operator) {
           var left = build(expr.receiver);
           String operatorName = expr.name.name;
           List<kernel.Expression> args = expr.arguments.positional;
           if (args.isEmpty) {
             if (operatorName == 'unary-') {
               return AstTestFactory.prefixExpression(TokenType.MINUS, left);
@@ skipping 572 matching lines @@
         for (var typeParameter in ctx.typeParameters) {
           if (typeParameter.name == name) {
             return typeParameter;
           }
         }
       }
     }
     throw new StateError('Not found $kernelTypeParameter in $context');
   }
 }