Improvements to task model

pkg/analyzer/lib/task/dart.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 analyzer.task.dart;
 
 import 'package:analyzer/src/generated/ast.dart';
+import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/error.dart';
 import 'package:analyzer/src/generated/scanner.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:analyzer/task/general.dart';
 import 'package:analyzer/task/model.dart';
 
 /**
+ * The compilation unit associated with a [Source] after it has had all
+ * declarations bound to the element defined by the declaration.
+ *
+ * The result is only available for targets representing a Dart compilation unit.
+ */
+final ResultDescriptor<CompilationUnit> BUILT_UNIT =
+    new ResultDescriptor<CompilationUnit>('BUILT_UNIT', null);
+
+/**
+ * The element model associated with a single compilation unit.
+ *
+ * The result is only available for targets representing a Dart compilation unit.
+ */
+final ResultDescriptor<CompilationUnitElement> COMPILATION_UNIT_ELEMENT =
+    new ResultDescriptor<CompilationUnitElement>('COMPILATION_UNIT_ELEMENT', null);
+
+/**
  * The sources of the libraries that are exported from a library.
  *
  * The list will be empty if there are no exported libraries, but will not be
  * `null`.
  *
  * The result is only available for targets representing a Dart library.
  */
 final ResultDescriptor<List<Source>> EXPORTED_LIBRARIES =
-    new ResultDescriptor<List<Source>>('EXPORTED_LIBRARIES');
+    new ResultDescriptor<List<Source>>('EXPORTED_LIBRARIES', Source.EMPTY_ARRAY);
 
 /**
  * The sources of the libraries that are imported into a library.
  *
  * The list will be empty if there are no imported libraries, but will not be
  * `null`.
  *
  * The result is only available for targets representing a Dart library.
  */
 final ResultDescriptor<List<Source>> IMPORTED_LIBRARIES =
-    new ResultDescriptor<List<Source>>('IMPORTED_LIBRARIES');
+    new ResultDescriptor<List<Source>>('IMPORTED_LIBRARIES', Source.EMPTY_ARRAY);
 
 /**
  * The sources of the parts that are included in a library.
  *
  * The list will be empty if there are no parts, but will not be `null`. The
  * list does *not* include the source for the defining compilation unit.
  *
  * The result is only available for targets representing a Dart library.
  */
 final ResultDescriptor<List<Source>> INCLUDED_PARTS =
-    new ResultDescriptor<List<Source>>('INCLUDED_PARTS');
+    new ResultDescriptor<List<Source>>('INCLUDED_PARTS', Source.EMPTY_ARRAY);
 
 /**
  * The errors produced while parsing a compilation unit.
  *
  * The list will be empty if there were no errors, but will not be `null`.
  *
  * The result is only available for targets representing a Dart compilation unit.
  */
 final ResultDescriptor<List<AnalysisError>> PARSE_ERRORS =
     new ResultDescriptor<List<AnalysisError>>(
         'PARSE_ERRORS',
+        AnalysisError.NO_ERRORS,
         contributesTo: ANALYSIS_ERRORS);
 
 /**
  * The compilation unit AST produced while parsing a compilation unit.
  *
  * The AST structure will not have resolution information associated with it.
  *
  * The result is only available for targets representing a Dart compilation unit.
  */
 final ResultDescriptor<CompilationUnit> PARSED_UNIT =
-    new ResultDescriptor<CompilationUnit>('PARSED_UNIT');
+    new ResultDescriptor<CompilationUnit>('PARSED_UNIT', null);
 
 /**
  * The errors produced while scanning a compilation unit.
  *
  * The list will be empty if there were no errors, but will not be `null`.
  *
  * The result is only available for targets representing a Dart compilation unit.
  */
 final ResultDescriptor<List<AnalysisError>> SCAN_ERRORS =
     new ResultDescriptor<List<AnalysisError>>(
         'SCAN_ERRORS',
+        AnalysisError.NO_ERRORS,
         contributesTo: ANALYSIS_ERRORS);
 
 /**
  * The token stream produced while scanning a compilation unit.
  *
  * The value is the first token in the file, or the special end-of-file marker
  * at the end of the stream if the file does not contain any tokens.
  *
  * The result is only available for targets representing a Dart compilation unit.
  */
 final ResultDescriptor<Token> TOKEN_STREAM =
-    new ResultDescriptor<Token>('TOKEN_STREAM');
+    new ResultDescriptor<Token>('TOKEN_STREAM', null);