Allow completions to wait for analysis without requiring a busy wait loop.

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/src/protocol.dart';
 import 'package:analysis_server/src/services/completion/arglist_computer.dart';
@@ skipping 164 matching lines @@
             request.replacementOffset,
             request.replacementLength,
             request.suggestions,
             last));
     if (last) {
       controller.close();
     }
   }
 
   /**
-   * Return a future that completes when analysis is complete.
+   * Return a future that either (a) completes with the resolved compilation
+   * unit when analysis is complete, or (b) completes with null if the
+   * compilation unit is never going to be resolved.
    */
-  Future<CompilationUnit> waitForAnalysis([int waitCount = 10000]) {
-    //TODO (danrubel) replace this when new API is ready.
-    // I expect the new API to be either a stream of resolution events
-    // or a future that completes when the resolved library element is available
-    LibraryElement library = context.getLibraryElement(source);
-    if (library != null) {
-      CompilationUnit unit =
-          context.getResolvedCompilationUnit(source, library);
-      if (unit != null) {
-        return new Future.value(unit);
-      }
-    }
-    //TODO (danrubel) Remove this HACK
-    if (waitCount > 0) {
-      return new Future(() {
-        return waitForAnalysis(waitCount - 1);
-      });
-    }
-    return new Future.value(null);
+  Future<CompilationUnit> waitForAnalysis() {
+    return context.getLibraryElementFuture(
+        source).then((LibraryElement library) {
+      return context.getResolvedCompilationUnitFuture(source, library);
+    }).catchError((_) {
+      // This source file is not scheduled for analysis, so a resolved
+      // compilation unit is never going to get computed.
+      return null;
+    }, test: (e) => e is AnalysisNotScheduledError);
   }
 }
 
 /**
  * The context in which the completion is requested.
  */
 class DartCompletionRequest extends CompletionRequest {
   /**
    * The analysis context in which the completion is requested.
    */
@@ skipping 42 matching lines @@
    * containing the cursor is to be replaced when the suggestion is applied
    * (that is, the number of characters in the existing identifier).
    */
   int replacementLength;
 
   /**
    * The list of suggestions to be sent to the client.
    */
   final List<CompletionSuggestion> suggestions = <CompletionSuggestion>[];
 
+  DartCompletionRequest(this.context, this.searchEngine, this.source,
+      int offset, this.cache, CompletionPerformance performance)
+      : super(offset, performance);
+
   /**
    * Return the original text from the [replacementOffset] to the [offset]
    * that can be used to filter the suggestions on the server side.
    */
   String get filterText {
-    return context.getContents(source).data.substring(replacementOffset, offset);
+    return context.getContents(
+        source).data.substring(replacementOffset, offset);
   }
-
-  DartCompletionRequest(this.context, this.searchEngine, this.source,
-      int offset, this.cache, CompletionPerformance performance)
-      : super(offset, performance);
 }
 
 /**
  * Visitor used to determine the replacement offset and length
  * based upon the cursor location.
  */
 class _ReplacementOffsetBuilder extends SimpleAstVisitor {
   final DartCompletionRequest request;
 
   _ReplacementOffsetBuilder(this.request) {
     request.replacementOffset = request.offset;
     request.replacementLength = 0;
   }
 
   visitSimpleIdentifier(SimpleIdentifier node) {
     request.replacementOffset = node.offset;
     request.replacementLength = node.length;
   }
 }