add logging code to track unexpected situation - fixes #24630

pkg/analysis_server/lib/src/services/completion/suggestion_builder.dart

Index: pkg/analysis_server/lib/src/services/completion/suggestion_builder.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/suggestion_builder.dart b/pkg/analysis_server/lib/src/services/completion/suggestion_builder.dart
index 4496adb9d702971a057e23b8d6520179f052cdbe..e6aa2679c30bfab2cb03028f8f8b3453e8febe7c 100644
--- a/pkg/analysis_server/lib/src/services/completion/suggestion_builder.dart
+++ b/pkg/analysis_server/lib/src/services/completion/suggestion_builder.dart
@@ -16,6 +16,7 @@ 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';
 
@@ -438,6 +439,8 @@ class InterfaceTypeSuggestionBuilder {
         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;