Issue 23027. Try to make priority files analyzable.

pkg/analysis_server/lib/src/analysis_server.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 analysis.server;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:math' show max;
 
@@ skipping 445 matching lines @@
     // try to find a context that analysed the file
     for (AnalysisContext context in folderMap.values) {
       Source source = file != null
           ? ContextManager.createSourceInContext(context, file)
           : null;
       SourceKind kind = context.getKindOf(source);
       if (kind != SourceKind.UNKNOWN) {
         return new ContextSourcePair(context, source);
       }
     }
+    // try to find a context for which the file is a priority source
+    for (InternalAnalysisContext context in folderMap.values) {
+      List<Source> sources = context.getSourcesWithFullName(path);
+      if (sources.isNotEmpty) {
+        Source source = sources.first;
+        return new ContextSourcePair(context, source);
+      }
+    }
     // file-based source
     Source fileSource = file != null ? file.createSource() : null;
     return new ContextSourcePair(null, fileSource);
   }
 
   /**
    * Returns [Element]s at the given [offset] of the given [file].
    *
    * May be empty if cannot be resolved, but not `null`.
    */
@@ skipping 433 matching lines @@
    */
   void setPriorityFiles(String requestId, List<String> files) {
     // Note: when a file is a priority file, that information needs to be
     // propagated to all contexts that analyze the file, so that all contexts
     // will be able to do incremental resolution of the file.  See
     // dartbug.com/22209.
     Map<AnalysisContext, List<Source>> sourceMap =
         new HashMap<AnalysisContext, List<Source>>();
     List<String> unanalyzed = new List<String>();
     Source firstSource = null;
-    files.forEach((file) {
+    files.forEach((String file) {
       ContextSourcePair contextSource = getContextSourcePair(file);
       AnalysisContext preferredContext = contextSource.context;
       Source source = contextSource.source;
+      // Try to make the file analyzable.
+      // If it is not in any context yet, add it to the first one which
+      // could use it, e.g. imports its package, even if not the library.
+      if (preferredContext == null) {
+        Resource resource = resourceProvider.getResource(file);
+        if (resource is File && resource.exists) {
+          for (AnalysisContext context in folderMap.values) {
+            Uri uri = context.sourceFactory.restoreUri(source);
+            if (uri.scheme != 'file') {
+              preferredContext = context;
+              source = ContextManager.createSourceInContext(context, resource);
+              break;
+            }
+          }
+        }
+      }
+      // Fill the source map.
       bool contextFound = false;
       for (AnalysisContext context in folderMap.values) {
         if (context == preferredContext ||
             context.getKindOf(source) != SourceKind.UNKNOWN) {
           sourceMap.putIfAbsent(context, () => <Source>[]).add(source);
           contextFound = true;
         }
       }
       if (firstSource == null) {
         firstSource = source;
@@ skipping 514 matching lines @@
   /**
    * The [PerformanceTag] for time spent in server request handlers.
    */
   static PerformanceTag serverRequests = new PerformanceTag('serverRequests');
 
   /**
    * The [PerformanceTag] for time spent in split store microtasks.
    */
   static PerformanceTag splitStore = new PerformanceTag('splitStore');
 }