Implement AnalysisDriver.getErrors() using performWork().

One possible issue with not doing this is that we would not apply
changes reported as changeFile(path).

Change-Id: Ic88ec05f997c9f90c6bd877d4612f01a6086364d
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/168221
Reviewed-by: Samuel Rawlins <srawlins@google.com>
Reviewed-by: Brian Wilkerson <brianwilkerson@google.com>
Commit-Queue: Konstantin Shcheglov <scheglov@google.com>

Author: scheglov

pkg/analyzer/lib/src/dart/analysis/driver.dart

@@ -174,6 +174,14 @@ class AnalysisDriver implements AnalysisDriverGeneric {
   /// The list of tasks to compute files referencing a name.
   final _referencingNameTasks = <_FilesReferencingNameTask>[];
 
+  /// The mapping from the files for which errors were requested using
+  /// [getErrors] to the [Completer]s to report the result.
+  final _errorsRequestedFiles = <String, List<Completer<ErrorsResult>>>{};
+
+  /// The requests from [_errorsRequestedFiles] for files which were found to
+  /// be parts without known libraries, so delayed.
+  final _errorsRequestedParts = <String, List<Completer<ErrorsResult>>>{};
+
   /// The mapping from the files for which the index was requested using
   /// [getIndex] to the [Completer]s to report the result.
   final _indexRequestedFiles =
@@ -385,6 +393,9 @@ class AnalysisDriver implements AnalysisDriverGeneric {
         _referencingNameTasks.isNotEmpty) {
       return AnalysisDriverPriority.interactive;
     }
+    if (_errorsRequestedFiles.isNotEmpty) {
+      return AnalysisDriverPriority.interactive;
+    }
     if (_indexRequestedFiles.isNotEmpty) {
       return AnalysisDriverPriority.interactive;
     }
@@ -416,7 +427,8 @@ class AnalysisDriver implements AnalysisDriverGeneric {
     if (_fileTracker.hasPendingFiles) {
       return AnalysisDriverPriority.general;
     }
-    if (_requestedParts.isNotEmpty ||
+    if (_errorsRequestedParts.isNotEmpty ||
+        _requestedParts.isNotEmpty ||
         _partsToAnalyze.isNotEmpty ||
         _unitElementSignatureParts.isNotEmpty ||
         _unitElementRequestedParts.isNotEmpty) {
@@ -547,19 +559,12 @@ class AnalysisDriver implements AnalysisDriverGeneric {
       return null;
     }
 
-    // Ask the analysis result without unit, so return cached errors.
-    // If no cached analysis result, it will be computed.
-    ResolvedUnitResult analysisResult = _computeAnalysisResult(path);
-
-    // If not computed yet, because a part file without a known library,
-    // we have to compute the full analysis result, with the unit.
-    analysisResult ??= await getResult(path);
-    if (analysisResult == null) {
-      return null;
-    }
-
-    return ErrorsResultImpl(currentSession, path, analysisResult.uri,
-        analysisResult.lineInfo, analysisResult.isPart, analysisResult.errors);
+    var completer = Completer<ErrorsResult>();
+    _errorsRequestedFiles
+        .putIfAbsent(path, () => <Completer<ErrorsResult>>[])
+        .add(completer);
+    _scheduler.notify(this);
+    return completer.future;
   }
 
   /// Return a [Future] that completes with the list of added files that
@@ -967,6 +972,21 @@ class AnalysisDriver implements AnalysisDriverGeneric {
       return;
     }
 
+    // Process an error request.
+    if (_errorsRequestedFiles.isNotEmpty) {
+      var path = _errorsRequestedFiles.keys.first;
+      var completers = _errorsRequestedFiles.remove(path);
+      var result = _computeErrors(path: path, asIsIfPartWithoutLibrary: false);
+      if (result != null) {
+        completers.forEach((completer) {
+          completer.complete(result);
+        });
+      } else {
+        _errorsRequestedParts.putIfAbsent(path, () => []).addAll(completers);
+      }
+      return;
+    }
+
     // Process an index request.
     if (_indexRequestedFiles.isNotEmpty) {
       String path = _indexRequestedFiles.keys.first;
@@ -1147,6 +1167,17 @@ class AnalysisDriver implements AnalysisDriverGeneric {
       });
       return;
     }
+
+    // Compute errors in a part.
+    if (_errorsRequestedParts.isNotEmpty) {
+      var path = _errorsRequestedParts.keys.first;
+      var completers = _errorsRequestedParts.remove(path);
+      var result = _computeErrors(path: path, asIsIfPartWithoutLibrary: true);
+      completers.forEach((completer) {
+        completer.complete(result);
+      });
+      return;
+    }
   }
 
   /// Remove the file with the given [path] from the list of files to analyze.
@@ -1334,6 +1365,21 @@ class AnalysisDriver implements AnalysisDriverGeneric {
     return Uint8List.fromList(bytes).buffer.asUint32List();
   }
 
+  ErrorsResult _computeErrors({
+    @required String path,
+    @required bool asIsIfPartWithoutLibrary,
+  }) {
+    ResolvedUnitResult analysisResult = _computeAnalysisResult(path,
+        withUnit: false, asIsIfPartWithoutLibrary: asIsIfPartWithoutLibrary);
+
+    if (analysisResult == null) {
+      return null;
+    }
+
+    return ErrorsResultImpl(currentSession, path, analysisResult.uri,
+        analysisResult.lineInfo, analysisResult.isPart, analysisResult.errors);
+  }
+
   AnalysisDriverUnitIndex _computeIndex(String path) {
     AnalysisResult analysisResult = _computeAnalysisResult(path,
         withUnit: false, asIsIfPartWithoutLibrary: true);