fix completion replacement offset/length for invalid token in switch statement

pkg/analysis_server/lib/src/services/completion/dart_completion_manager.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.dart;
 
 import 'dart:async';
 
 import 'package:analysis_server/completion/completion_core.dart'
     show CompletionRequest;
@@ skipping 109 matching lines @@
     });
   }
 
   /**
    * Compute suggestions based upon cached information only
    * then send an initial response to the client.
    * Return a list of contributors for which [computeFull] should be called
    */
   List<DartCompletionContributor> computeFast(
       DartCompletionRequest request, CompletionPerformance performance) {
+    bool isKeywordOrIdentifier(Token token) =>
+        token.type == TokenType.KEYWORD || token.type == TokenType.IDENTIFIER;
+
     return performance.logElapseTime('computeFast', () {
       CompilationUnit unit = context.parseCompilationUnit(source);
       request.unit = unit;
       request.target = new CompletionTarget.forOffset(unit, request.offset);
       request.replacementOffset = request.offset;
       request.replacementLength = 0;
       if (request.offset < 0 || request.offset > unit.end) {
         sendResults(request, true);
         return [];
       }
 
       var entity = request.target.entity;
       Token token = entity is AstNode ? entity.beginToken : entity;
-      if (token != null &&
-          token.offset <= request.offset &&
-          (token.type == TokenType.KEYWORD ||
-              token.type == TokenType.IDENTIFIER)) {
-        request.replacementOffset = token.offset;
-        request.replacementLength = token.length;
+      if (token != null && request.offset < token.offset) {

[Brian Wilkerson, 2015/08/03 13:53:07]

Does this need to be a loop, or is the previous token guaranteed to contain the
request offset?

[danrubel, 2015/08/03 21:00:12]

I considered that but did not have a test case that required a loop. Suggestion
welcome... which I will address in a subsequent CL.

+        token = token.previous;
+      }
+      if (token != null) {
+        if (request.offset == token.offset && !isKeywordOrIdentifier(token)) {

[Brian Wilkerson, 2015/08/03 13:53:07]

A comment about why this is necessary would be good. It isn't clear to me why we
want to back up to a token that doesn't contain the request offset.

[danrubel, 2015/08/03 21:00:12]

Good point. Added.

+          token = token.previous;
+        }
+        if (token != null && isKeywordOrIdentifier(token)) {
+          if (token.offset <= request.offset && request.offset <= token.end) {
+            request.replacementOffset = token.offset;
+            request.replacementLength = token.length;
+          }
+        }
       }
 
       List<DartCompletionContributor> todo = new List.from(contributors);
       todo.removeWhere((DartCompletionContributor c) {
         return performance.logElapseTime('computeFast ${c.runtimeType}', () {
           return c.computeFast(request);
         });
       });
       commonUsageComputer.computeFast(request);
       sendResults(request, todo.isEmpty);
@@ skipping 214 matching lines @@
             parameterNames: suggestion.parameterNames,
             parameterTypes: suggestion.parameterTypes,
             requiredParameterCount: suggestion.requiredParameterCount,
             hasNamedParameters: suggestion.hasNamedParameters,
             returnType: suggestion.returnType,
             element: suggestion.element);
       }
     }
   }
 }