Named arg completion fixes (flutter-intellij#551)

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

Index: pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
diff --git a/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart b/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
index 579b7b8662c16a1b621dddba7de8b6008a459b3e..59ae61a2630ac5970382432c1c6c8b388a388521 100644
--- a/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
+++ b/pkg/analysis_server/lib/src/services/completion/dart/arglist_contributor.dart
@@ -14,6 +14,7 @@ import 'package:analysis_server/src/services/completion/dart/utilities.dart';
 import 'package:analysis_server/src/services/correction/flutter_util.dart';
 import 'package:analysis_server/src/utilities/documentation.dart';
 import 'package:analyzer/dart/ast/ast.dart';
+import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/src/generated/utilities_dart.dart';
 
@@ -251,6 +252,7 @@ class ArgListContributor extends DartCompletionContributor {
       if (appendColon) {
         completion += ': ';
       }
+      int selectionOffset = completion.length;
       if (appendComma) {
         completion += ',';
       }
@@ -258,7 +260,7 @@ class ArgListContributor extends DartCompletionContributor {
           CompletionSuggestionKind.NAMED_ARGUMENT,
           DART_RELEVANCE_NAMED_PARAMETER,
           completion,
-          completion.length,
+          selectionOffset,
           0,
           false,
           false,
@@ -305,7 +307,10 @@ class ArgListContributor extends DartCompletionContributor {
     } else if (_isInsertingToArgListWithNoSynthetic(request)) {
       _addDefaultParamSuggestions(parameters, true);
     } else if (_isInsertingToArgListWithSynthetic(request)) {
-      _addDefaultParamSuggestions(parameters);
+      var entity = request.target.entity;
+      bool followedByComma =
+          entity is AstNode && entity.endToken.next.type == TokenType.COMMA;

[Brian Wilkerson, 2017/04/26 20:53:40]

Should this / does this need to handle the case where entity is a Token?

[Brian Wilkerson, 2017/04/27 16:13:50]

I don't know whether there *are* any use cases, but if the entity *could* ever
be a token then we could test `entity.next.type == TokenType.COMMA`. Dan might
know when / whether entity could ever be a token at this point.

[danrubel, 2017/04/27 16:27:26]

I don't know and if it is not today then it might be tomorrow because the
scanner/parser is being replaced. I recommend coding this defensively to assume
either possibility.

[pquitslund, 2017/04/27 17:09:54]

Done.

+      _addDefaultParamSuggestions(parameters, !followedByComma);
     }
   }