Add a fallback mode for building summaries.

pkg/analyzer/lib/src/summary/idl.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.
 
 /**
  * This file is an "idl" style description of the summary format.  It
  * contains abstract classes which declare the interface for reading data from
  * summaries.  It is parsed and transformed into code that implements the
  * summary format.
  *
@@ skipping 419 matching lines @@
    * Information about entities in the export namespace of the library that are
    * not in the public namespace of the library (that is, entities that are
    * brought into the namespace via `export` directives).
    *
    * Sorted by name.
    */
   @Id(4)
   List<LinkedExportName> get exportNames;
 
   /**
+   * Indicates whether this library was summarized in "fallback mode".  If
+   * true, all other fields in the data structure have their default values.
+   */
+  @Id(5)
+  bool get fallbackMode;
+
+  /**
    * For each import in [UnlinkedUnit.imports], an index into [dependencies]
    * of the library being imported.
    */
   @Id(1)
   List<int> get importDependencies;
 
   /**
    * The number of elements in [dependencies] which are not "linked"
    * dependencies (that is, the number of libraries in the direct imports plus
    * the transitive closure of exports, plus the library itself).
@@ skipping 1771 matching lines @@
 
 /**
  * Unlinked summary information about a compilation unit ("part file").
  */
 @TopLevel('UUnt')
 abstract class UnlinkedUnit extends base.SummaryClass {
   factory UnlinkedUnit.fromBuffer(List<int> buffer) =>
       generated.readUnlinkedUnit(buffer);
 
   /**
+   * If this compilation unit was summarized in fallback mode, the path where
+   * the compilation unit may be found on disk.  Otherwise empty.
+   *
+   * When this field is non-empty, all other fields in the data structure have
+   * their default values.
+   */
+  @Id(16)
+  String get fallbackModePath;
+
+  /**
    * Classes declared in the compilation unit.
    */
   @Id(2)
   List<UnlinkedClass> get classes;
 
   /**
    * Code range of the unit.
    */
   @informative
   @Id(15)
@@ skipping 203 matching lines @@
    */
   @Id(11)
   int get visibleLength;
 
   /**
    * If a local variable, the beginning of the visible range; zero otherwise.
    */
   @Id(12)
   int get visibleOffset;
 }