Guard against files that are not being analyzed (issue 29493)

pkg/analysis_server/lib/src/domain_completion.dart

Index: pkg/analysis_server/lib/src/domain_completion.dart
diff --git a/pkg/analysis_server/lib/src/domain_completion.dart b/pkg/analysis_server/lib/src/domain_completion.dart
index efaa1d9b50d327fe474b8f0b034066d84826af3c..682615be5b9c258179d8a1aac7798d6ccecb14a3 100644
--- a/pkg/analysis_server/lib/src/domain_completion.dart
+++ b/pkg/analysis_server/lib/src/domain_completion.dart
@@ -83,9 +83,11 @@ class CompletionDomainHandler extends AbstractRequestHandler {
       String file = params.file;
       int offset = params.offset;
       AnalysisDriver driver = server.getAnalysisDriver(file);
-      requestParams = new plugin.CompletionGetSuggestionsParams(file, offset);
-      pluginFutures = server.pluginManager
-          .broadcastRequest(requestParams, contextRoot: driver.contextRoot);
+      if (driver != null) {
+        requestParams = new plugin.CompletionGetSuggestionsParams(file, offset);
+        pluginFutures = server.pluginManager
+            .broadcastRequest(requestParams, contextRoot: driver.contextRoot);
+      }
     }
     //
     // Compute completions generated by server.
@@ -154,6 +156,12 @@ class CompletionDomainHandler extends AbstractRequestHandler {
     });
   }
 
+  void ifMatchesRequestClear(CompletionRequest completionRequest) {
+    if (_currentRequest == completionRequest) {
+      _currentRequest = null;
+    }
+  }
+
   /**
    * Process a `completion.getSuggestions` request.
    */
@@ -253,17 +261,6 @@ class CompletionDomainHandler extends AbstractRequestHandler {
     });
   }
 
-  void setNewRequest(CompletionRequest completionRequest) {
-    _abortCurrentRequest();
-    _currentRequest = completionRequest;
-  }
-
-  void ifMatchesRequestClear(CompletionRequest completionRequest) {
-    if (_currentRequest == completionRequest) {
-      _currentRequest = null;
-    }
-  }
-
   /**
    * If tracking code completion performance over time, then
    * record addition information about the request in the performance record.
@@ -295,6 +292,11 @@ class CompletionDomainHandler extends AbstractRequestHandler {
         .toNotification());
   }
 
+  void setNewRequest(CompletionRequest completionRequest) {
+    _abortCurrentRequest();
+    _currentRequest = completionRequest;
+  }
+
   /**
    * Abort the current completion request, if any.
    */