add logging code to track unexpected situation - fixes #24630

pkg/analysis_server/lib/src/services/completion/suggestion_builder.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.completion.suggestion.builder;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analysis_server/src/protocol_server.dart' as protocol;
 import 'package:analysis_server/src/protocol_server.dart'
     hide Element, ElementKind;
 import 'package:analysis_server/src/services/completion/dart_completion_manager.dart';
 import 'package:analyzer/src/generated/ast.dart';
 import 'package:analyzer/src/generated/element.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 import 'package:analyzer/src/generated/source.dart';
 import 'package:path/path.dart' as path;
+import 'package:analyzer/src/generated/engine.dart' as engine;

[scheglov, 2015/10/22 16:26:33]

sort?

[danrubel, 2015/10/22 16:50:51]

Good point. Done.

 
 const String DYNAMIC = 'dynamic';
 
 /**
  * Return a suggestion based upon the given element
  * or `null` if a suggestion is not appropriate for the given element.
  * If the suggestion is not currently in scope, then specify
  * importForSource as the source to which an import should be added.
  */
 CompletionSuggestion createSuggestion(Element element,
@@ skipping 402 matching lines @@
 
   /**
    * Add suggestions for the visible members in the given interface
    */
   static void suggestionsFor(DartCompletionRequest request, DartType type,
       {bool isSuper: false, String containingMethodName: null}) {
     CompilationUnit compilationUnit =
         request.target.containingNode.getAncestor((n) => n is CompilationUnit);
     CompilationUnitElement unitElem = compilationUnit.element;
     if (unitElem == null) {
+      engine.AnalysisEngine.instance.logger
+          .logInformation('Completion expected resolved AST');

[scheglov, 2015/10/22 16:26:33]

Maybe we should include name of the source, if it's accessible.

[danrubel, 2015/10/22 16:50:51]

There is a lot of additional information that would be useful here including the
source, but all of it, including file name, offset, actual source code on which
the completion request was made, etc. is available as part of the log.

       return;
     }
     LibraryElement library = unitElem.library;
     if (type is DynamicTypeImpl) {
       type = request.cache.objectClassElement.type;
     }
     if (type is InterfaceType) {
       new InterfaceTypeSuggestionBuilder(request)
           ._buildSuggestions(type, library, isSuper, containingMethodName);
     }
@@ skipping 221 matching lines @@
    * or `false` if [computeFull] should be called.
    */
   bool computeFast(AstNode node);
 
   /**
    * Return a future that computes the suggestions given a fully resolved AST.
    * The future returns `true` if suggestions were added, else `false`.
    */
   Future<bool> computeFull(AstNode node);
 }