In summaries, don't drop unsafe prefixes.

pkg/analyzer/test/src/summary/resynthesize_test.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 test.src.serialization.elements_test;
 
 import 'dart:convert';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dart/ast/ast.dart';
 import 'package:analyzer/src/dart/element/element.dart';
 import 'package:analyzer/src/dart/element/member.dart';
 import 'package:analyzer/src/dart/element/type.dart';
 import 'package:analyzer/src/generated/constant.dart' show DartObject;
 import 'package:analyzer/src/generated/element_handle.dart';
 import 'package:analyzer/src/generated/engine.dart';
 import 'package:analyzer/src/generated/resolver.dart'
     show Namespace, TypeProvider;
 import 'package:analyzer/src/generated/source.dart';
+import 'package:analyzer/src/generated/testing/ast_factory.dart';
 import 'package:analyzer/src/summary/idl.dart';
 import 'package:analyzer/src/summary/resynthesize.dart';
 import 'package:analyzer/src/summary/summarize_elements.dart';
 import 'package:unittest/unittest.dart';
 
 import '../../generated/resolver_test.dart';
 import '../../reflective_tests.dart';
 import 'summary_common.dart' show canonicalize;
 
 main() {
@@ skipping 309 matching lines @@
       // ConstantAstCloner does not copy static types, and constant values
       // computer does not use static types. So, we don't set them during
       // resynthesis and should not check them here.
       if (o is ParenthesizedExpression) {
         // We don't resynthesize parenthesis, so just ignore it.
         compareConstAsts(r, o.expression, desc);
       } else if (o is SimpleIdentifier && r is SimpleIdentifier) {
         expect(r.name, o.name, reason: desc);
         compareElements(r.staticElement, o.staticElement, desc);
       } else if (o is PrefixedIdentifier && r is SimpleIdentifier) {
-        // We often don't resynthesize prefixed identifiers.
-        // We use simple identifiers with correct elements.
-        compareConstAsts(r, o.identifier, desc);
+        // We don't resynthesize prefixed identifiers when the prefix refers to
+        // a PrefixElement or a ClassElement.  We use simple identifiers with
+        // correct elements.
+        if (o.prefix.staticElement is PrefixElement ||
+            o.prefix.staticElement is ClassElement) {
+          compareConstAsts(r, o.identifier, desc);
+        } else {
+          fail('Prefix of type ${o.prefix.staticElement.runtimeType} should not'
+              ' have been elided');
+        }
+      } else if (o is PropertyAccess &&
+          o.target is PrefixedIdentifier &&
+          r is PrefixedIdentifier) {
+        // We don't resynthesize prefixed identifiers when the prefix refers to
+        // a PrefixElement or a ClassElement.  Which means that if the original
+        // expression was e.g. `prefix.topLevelVariableName.length`, it will get
+        // resynthesized as `topLevelVariableName.length`
+        PrefixedIdentifier oTarget = o.target;
+        if (oTarget.prefix.staticElement is PrefixElement ||
+            oTarget.prefix.staticElement is ClassElement) {
+          compareConstAsts(r,
+              AstFactory.identifier(oTarget.identifier, o.propertyName), desc);
+        } else {
+          fail('Prefix of type ${oTarget.prefix.staticElement.runtimeType}'
+              ' should not have been elided');
+        }
       } else if (o is PrefixedIdentifier && r is PrefixedIdentifier) {
         compareConstAsts(r.prefix, o.prefix, desc);
         compareConstAsts(r.identifier, o.identifier, desc);
       } else if (o is PropertyAccess && r is PropertyAccess) {
         compareConstAsts(r.target, o.target, desc);
         expect(r.propertyName.name, o.propertyName.name, reason: desc);
         compareElements(
             r.propertyName.staticElement, o.propertyName.staticElement, desc);
       } else if (o is PropertyAccess && r is SimpleIdentifier) {
         // We don't resynthesize property access.
@@ skipping 3591 matching lines @@
       fail('Unexpectedly tried to get unlinked summary for $uri');
     }
     return serializedUnit;
   }
 
   @override
   bool hasLibrarySummary(String uri) {
     return true;
   }
 }