refactor library prefix suggestion generation

pkg/analysis_server/lib/src/services/completion/imported_computer.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.computer.dart.toplevel;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol.dart' as protocol show Element,
     ElementKind;
@@ skipping 82 matching lines @@
       // as they will be included by the LocalComputer
       excludedLibs.add(request.unit.element.library);
 
       // Build the set of visible and excluded libraries
       // and the list of names that should be shown or hidden
       request.unit.directives.forEach((Directive directive) {
         if (directive is ImportDirective) {
           ImportElement element = directive.element;
           if (element != null) {
             LibraryElement lib = element.importedLibrary;
-            if (directive.prefix == null) {
+            SimpleIdentifier prefix = directive.prefix;
+            if (prefix == null) {
               visibleLibs.add(lib);
               directive.combinators.forEach((Combinator combinator) {
                 if (combinator is ShowCombinator) {
                   showNames[lib] =
                       combinator.shownNames.map((SimpleIdentifier id) => id.name).toSet();
                 } else if (combinator is HideCombinator) {
                   hideNames[lib] =
                       combinator.hiddenNames.map((SimpleIdentifier id) => id.name).toSet();
                 }
               });
             } else {
+              String completion = prefix.name;
+              if (completion != null && completion.length > 0) {
+                CompletionSuggestion suggestion = new CompletionSuggestion(
+                    CompletionSuggestionKind.LIBRARY_PREFIX,
+                    CompletionRelevance.DEFAULT,
+                    completion,
+                    completion.length,
+                    0,
+                    element.isDeprecated,
+                    false);
+                suggestion.element = new protocol.Element.fromEngine(lib);
+                request.suggestions.add(suggestion);
+              }
               excludedLibs.add(lib);
             }
           }
         }
       });
 
       // Compute the set of possible classes, functions, and top level variables
       matches.forEach((SearchMatch match) {
         if (match.kind == MatchKind.DECLARATION) {
           Element element = match.element;
@@ skipping 41 matching lines @@
 
               request.suggestions.add(suggestion);
             }
           }
         }
       });
       return true;
     });
   }
 }