Cache documentation comments to improve completion performance

I'm not convinced that this is the right way to cache comments, so
feedback is welcome.

Change-Id: I2bd393b80e05c26199020e19daf0eadeb99d8c2b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/199303
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>

pkg/analysis_server/lib/src/analysis_server.dart

@@ -685,6 +685,7 @@ class ServerContextManagerCallbacks extends ContextManagerCallbacks {
         _notificationManager.recordAnalysisErrors(NotificationManager.serverId,
             path, server.doAnalysisError_listFromEngine(result));
       }
+      analysisServer.getDocumentationCacheFor(result)?.cacheFromResult(result);
       var unit = result.unit;
       if (unit != null) {
         if (analysisServer._hasAnalysisServiceSubscription(

pkg/analysis_server/lib/src/analysis_server_abstract.dart

@@ -15,6 +15,7 @@ import 'package:analysis_server/src/plugin/plugin_manager.dart';
 import 'package:analysis_server/src/plugin/plugin_watcher.dart';
 import 'package:analysis_server/src/server/crash_reporting_attachments.dart';
 import 'package:analysis_server/src/server/diagnostic_server.dart';
+import 'package:analysis_server/src/services/completion/dart/documentation_cache.dart';
 import 'package:analysis_server/src/services/correction/namespace.dart';
 import 'package:analysis_server/src/services/pub/pub_api.dart';
 import 'package:analysis_server/src/services/pub/pub_package_service.dart';
@@ -25,6 +26,7 @@ import 'package:analysis_server/src/utilities/file_string_sink.dart';
 import 'package:analysis_server/src/utilities/null_string_sink.dart';
 import 'package:analysis_server/src/utilities/request_statistics.dart';
 import 'package:analysis_server/src/utilities/tee_string_sink.dart';
+import 'package:analyzer/dart/analysis/analysis_context.dart';
 import 'package:analyzer/dart/analysis/results.dart';
 import 'package:analyzer/dart/analysis/session.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ -83,6 +85,10 @@ abstract class AbstractAnalysisServer {
   DeclarationsTracker? declarationsTracker;
   DeclarationsTrackerData? declarationsTrackerData;
 
+  /// A map from analysis contexts to the documentation cache associated with
+  /// each context.
+  Map<AnalysisContext, DocumentationCache> documentationForContext = {};
+
   /// The DiagnosticServer for this AnalysisServer. If available, it can be used
   /// to start an http diagnostics server or return the port for an existing
   /// server.
@@ -217,6 +223,7 @@ abstract class AbstractAnalysisServer {
 
   void addContextsToDeclarationsTracker() {
     declarationsTracker?.discardContexts();
+    documentationForContext.clear();
     for (var driver in driverMap.values) {
       declarationsTracker?.addContext(driver.analysisContext!);
       driver.resetUriResolution();
@@ -275,6 +282,19 @@ abstract class AbstractAnalysisServer {
         DartdocDirectiveInfo();
   }
 
+  /// Return the object used to cache the documentation for elements in the
+  /// context that produced the [result], or `null` if there is no cache for the
+  /// context.
+  DocumentationCache? getDocumentationCacheFor(ResolvedUnitResult result) {
+    var context = result.session.analysisContext;
+    var tracker = declarationsTracker?.getContext(context);
+    if (tracker == null) {
+      return null;
+    }
+    return documentationForContext.putIfAbsent(
+        context, () => DocumentationCache(tracker.dartdocDirectiveInfo));
+  }
+
   /// Return a [Future] that completes with the [Element] at the given
   /// [offset] of the given [file], or with `null` if there is no node at the
   /// [offset] or the node does not have an element.

pkg/analysis_server/lib/src/domain_completion.dart

@@ -108,7 +108,9 @@ class CompletionDomainHandler extends AbstractRequestHandler {
       await perf.runAsync(contributorTag, (performance) async {
         try {
           suggestions.addAll(
-            await manager.computeSuggestions(performance, request),
+            await manager.computeSuggestions(performance, request,
+                documentationCache:
+                    server.getDocumentationCacheFor(request.result)),
           );
         } on AbortCompletion {
           suggestions.clear();

pkg/analysis_server/lib/src/services/completion/dart/completion_manager.dart

@@ -9,6 +9,7 @@ import 'package:analysis_server/src/services/completion/completion_core.dart';
 import 'package:analysis_server/src/services/completion/completion_performance.dart';
 import 'package:analysis_server/src/services/completion/dart/arglist_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/combinator_contributor.dart';
+import 'package:analysis_server/src/services/completion/dart/documentation_cache.dart';
 import 'package:analysis_server/src/services/completion/dart/extension_member_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/feature_computer.dart';
 import 'package:analysis_server/src/services/completion/dart/field_formal_contributor.dart';
@@ -93,6 +94,7 @@ class DartCompletionManager {
     bool enableOverrideContributor = true,
     bool enableUriContributor = true,
     CompletionPreference? completionPreference,
+    DocumentationCache? documentationCache,
   }) async {
     request.checkAborted();
     var pathContext = request.resourceProvider.pathContext;
@@ -105,6 +107,7 @@ class DartCompletionManager {
       request,
       dartdocDirectiveInfo,
       completionPreference: completionPreference,
+      documentationCache: documentationCache,
     );
 
     // Don't suggest in comments.
@@ -297,6 +300,8 @@ class DartCompletionRequestImpl implements DartCompletionRequest {
   @override
   final CompletionPreference completionPreference;
 
+  final DocumentationCache? documentationCache;
+
   DartCompletionRequestImpl._(
       this.result,
       this.resourceProvider,
@@ -308,7 +313,8 @@ class DartCompletionRequestImpl implements DartCompletionRequest {
       this.dartdocDirectiveInfo,
       this._originalRequest,
       this.performance,
-      {CompletionPreference? completionPreference})
+      {CompletionPreference? completionPreference,
+      this.documentationCache})
       : featureComputer =
             FeatureComputer(result.typeSystem, result.typeProvider),
         completionPreference =
@@ -431,7 +437,8 @@ class DartCompletionRequestImpl implements DartCompletionRequest {
       OperationPerformanceImpl performance,
       CompletionRequest request,
       DartdocDirectiveInfo? dartdocDirectiveInfo,
-      {CompletionPreference? completionPreference}) async {
+      {CompletionPreference? completionPreference,
+      DocumentationCache? documentationCache}) async {
     request.checkAborted();
 
     return performance.run(
@@ -453,6 +460,7 @@ class DartCompletionRequestImpl implements DartCompletionRequest {
           request,
           (request as CompletionRequestImpl).performance,
           completionPreference: completionPreference,
+          documentationCache: documentationCache,
         );
       },
     );

pkg/analysis_server/lib/src/services/completion/dart/documentation_cache.dart

@@ -0,0 +1,196 @@
+// Copyright (c) 2021, 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.
+
+import 'package:analysis_server/src/computer/computer_hover.dart';
+import 'package:analyzer/dart/analysis/results.dart';
+import 'package:analyzer/dart/element/element.dart';
+import 'package:analyzer/src/dartdoc/dartdoc_directive_info.dart';
+
+/// Cached data about the documentation associated with the elements declared in
+/// a single analysis context.
+class DocumentationCache {
+  /// A shared instance for elements that have no documentation.
+  static final DocumentationWithSummary _emptyDocs =
+      DocumentationWithSummary(full: '', summary: '');
+
+  /// The object used to compute the documentation associated with a single
+  /// element.
+  final DartdocDirectiveInfo dartdocDirectiveInfo;
+
+  /// The documentation associated with the elements that have been cached. The
+  /// cache is keyed by the path of the file containing the declaration of the
+  /// element and the qualified name of the element.
+  final Map<String, Map<String, DocumentationWithSummary>> documentationCache =
+      {};
+
+  /// Initialize a newly created cache.
+  DocumentationCache(this.dartdocDirectiveInfo);
+
+  /// Fill the cache with data from the [result].
+  void cacheFromResult(ResolvedUnitResult result) {
+    var element = result.unit?.declaredElement;
+    if (element != null) {
+      _cacheFromElement(element);
+      for (var library in result.libraryElement.importedLibraries) {
+        _cacheLibrary(library);
+      }
+    }
+  }
+
+  /// Return the data cached for the given [element], or `null` if there is no
+  /// cached data.
+  DocumentationWithSummary? dataFor(Element element) {
+    var parent = element.enclosingElement;
+    if (parent == null) {
+      return null;
+    }
+    var key = element.name;
+    if (key == null) {
+      return null;
+    }
+    if (parent is! CompilationUnitElement) {
+      var parentName = parent.name;
+      if (parentName == null) {
+        return null;
+      }
+      key = '$parentName.$key';
+      parent = parent.enclosingElement;
+    }
+    if (parent is CompilationUnitElement) {
+      var elementMap = documentationCache[_keyForUnit(parent)];
+      return elementMap?[key];
+    }
+    return null;
+  }
+
+  /// Fill the cache with data from the [compilationUnit].
+  void _cacheFromElement(CompilationUnitElement compilationUnit) {
+    var elementMap =
+        documentationCache.putIfAbsent(_keyForUnit(compilationUnit), () => {});
+    for (var element in compilationUnit.accessors) {
+      if (!element.isSynthetic) {
+        elementMap.cacheTopLevelElement(dartdocDirectiveInfo, element);
+      }
+    }
+    for (var element in compilationUnit.enums) {
+      var parentKey =
+          elementMap.cacheTopLevelElement(dartdocDirectiveInfo, element);
+      if (parentKey != null) {
+        for (var member in element.fields) {
+          elementMap.cacheMember(dartdocDirectiveInfo, parentKey, member);
+        }
+      }
+    }
+    for (var element in compilationUnit.extensions) {
+      var parentKey =
+          elementMap.cacheTopLevelElement(dartdocDirectiveInfo, element);
+      if (parentKey != null) {
+        for (var member in element.accessors) {
+          if (!element.isSynthetic) {
+            elementMap.cacheMember(dartdocDirectiveInfo, parentKey, member);
+          }
+        }
+        for (var member in element.fields) {
+          if (!element.isSynthetic) {
+            elementMap.cacheMember(dartdocDirectiveInfo, parentKey, member);
+          }
+        }
+        for (var member in element.methods) {
+          elementMap.cacheMember(dartdocDirectiveInfo, parentKey, member);
+        }
+      }
+    }
+    for (var element in compilationUnit.functions) {
+      elementMap.cacheTopLevelElement(dartdocDirectiveInfo, element);
+    }
+    for (var element in [...compilationUnit.mixins, ...compilationUnit.types]) {
+      var parentKey =
+          elementMap.cacheTopLevelElement(dartdocDirectiveInfo, element);
+      if (parentKey != null) {
+        for (var member in element.accessors) {
+          if (!element.isSynthetic) {
+            elementMap.cacheMember(dartdocDirectiveInfo, parentKey, member);
+          }
+        }
+        for (var member in element.fields) {
+          if (!element.isSynthetic) {
+            elementMap.cacheMember(dartdocDirectiveInfo, parentKey, member);
+          }
+        }
+        for (var member in element.methods) {
+          elementMap.cacheMember(dartdocDirectiveInfo, parentKey, member);
+        }
+      }
+    }
+    for (var element in compilationUnit.topLevelVariables) {
+      if (!element.isSynthetic) {
+        elementMap.cacheTopLevelElement(dartdocDirectiveInfo, element);
+      }
+    }
+    for (var element in compilationUnit.typeAliases) {
+      elementMap.cacheTopLevelElement(dartdocDirectiveInfo, element);
+    }
+  }
+
+  /// Cache the data for the given [library] and every library exported from it
+  /// if it hasn't already been cached.
+  void _cacheLibrary(LibraryElement library) {
+    if (_hasDataFor(library.definingCompilationUnit)) {
+      return;
+    }
+    for (var unit in library.units) {
+      _cacheFromElement(unit);
+    }
+    for (var exported in library.exportedLibraries) {
+      _cacheLibrary(exported);
+    }
+  }
+
+  /// Return `true` if the cache contains data for the [compilationUnit].
+  bool _hasDataFor(CompilationUnitElement compilationUnit) {
+    return documentationCache.containsKey(_keyForUnit(compilationUnit));
+  }
+
+  /// Return the key used in the [documentationCache] for the [compilationUnit].
+  String _keyForUnit(CompilationUnitElement compilationUnit) =>
+      compilationUnit.source.fullName;
+}
+
+extension on Map<String, DocumentationWithSummary> {
+  /// Cache the data associated with the top-level [element], and return the
+  /// [key] used for the element. This does not cache any data associated with
+  /// any other elements, including children of the [element].
+  String? cacheTopLevelElement(
+      DartdocDirectiveInfo dartdocDirectiveInfo, Element element) {
+    var key = element.name;
+    if (key == null) {
+      return null;
+    }
+    cacheElement(dartdocDirectiveInfo, key, element);
+    return key;
+  }
+
+  /// Cache the data associated with the [member] element given that the key
+  /// associated with the member's parent is [parentKey].
+  void cacheMember(DartdocDirectiveInfo dartdocDirectiveInfo, String parentKey,
+      Element member) {
+    var name = member.name;
+    if (name == null) {
+      return null;
+    }
+    cacheElement(dartdocDirectiveInfo, '$parentKey.$name', member);
+  }
+
+  /// Cache the data associated with the [element], using the given [key].
+  DocumentationWithSummary? cacheElement(
+      DartdocDirectiveInfo dartdocDirectiveInfo, String key, Element element) {
+    var documentation = DartUnitHoverComputer.computeDocumentation(
+        dartdocDirectiveInfo, element,
+        includeSummary: true);
+    if (documentation is DocumentationWithSummary) {
+      return this[key] = documentation;
+    }
+    return this[key] = DocumentationCache._emptyDocs;
+  }
+}

pkg/analysis_server/lib/src/services/completion/dart/suggestion_builder.dart

@@ -10,6 +10,7 @@ import 'package:analysis_server/src/protocol_server.dart' as protocol;
 import 'package:analysis_server/src/protocol_server.dart'
     hide Element, ElementKind;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
+import 'package:analysis_server/src/services/completion/dart/completion_manager.dart';
 import 'package:analysis_server/src/services/completion/dart/feature_computer.dart';
 import 'package:analysis_server/src/services/completion/dart/utilities.dart';
 import 'package:analysis_server/src/utilities/extensions/ast.dart';
@@ -1110,6 +1111,16 @@ class SuggestionBuilder {
   /// If the [element] has a documentation comment, fill the [suggestion]'s
   /// documentation fields.
   void _setDocumentation(CompletionSuggestion suggestion, Element element) {
+    final request = this.request;
+    if (request is DartCompletionRequestImpl) {
+      var documentationCache = request.documentationCache;
+      var data = documentationCache?.dataFor(element);
+      if (data != null) {
+        suggestion.docComplete = data.full;
+        suggestion.docSummary = data.summary;
+        return;
+      }
+    }
     var doc = DartUnitHoverComputer.computeDocumentation(
         request.dartdocDirectiveInfo, element,
         includeSummary: true);

pkg/analysis_server/tool/code_completion/completion_metrics.dart

@@ -13,6 +13,7 @@ import 'package:analysis_server/src/protocol_server.dart' as protocol;
 import 'package:analysis_server/src/services/completion/completion_core.dart';
 import 'package:analysis_server/src/services/completion/completion_performance.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart';
+import 'package:analysis_server/src/services/completion/dart/documentation_cache.dart';
 import 'package:analysis_server/src/services/completion/dart/feature_computer.dart';
 import 'package:analysis_server/src/services/completion/dart/probability_range.dart';
 import 'package:analysis_server/src/services/completion/dart/relevance_tables.g.dart';
@@ -1034,6 +1035,8 @@ class CompletionMetricsComputer {
       MetricsSuggestionListener listener,
       OperationPerformanceImpl performance,
       CompletionRequestImpl request,
+      DartdocDirectiveInfo dartdocDirectiveInfo,
+      DocumentationCache? documentationCache,
       [DeclarationsTracker? declarationsTracker,
       protocol.CompletionAvailableSuggestionsParams?
           availableSuggestionsParams]) async {
@@ -1042,9 +1045,10 @@ class CompletionMetricsComputer {
     if (declarationsTracker == null) {
       // available suggestions == false
       suggestions = await DartCompletionManager(
-        dartdocDirectiveInfo: DartdocDirectiveInfo(),
+        dartdocDirectiveInfo: dartdocDirectiveInfo,
         listener: listener,
-      ).computeSuggestions(performance, request);
+      ).computeSuggestions(performance, request,
+          documentationCache: documentationCache);
     } else {
       // available suggestions == true
       var includedElementKinds = <protocol.ElementKind>{};
@@ -1053,12 +1057,13 @@ class CompletionMetricsComputer {
           <protocol.IncludedSuggestionRelevanceTag>[];
       var includedSuggestionSetList = <protocol.IncludedSuggestionSet>[];
       suggestions = await DartCompletionManager(
-        dartdocDirectiveInfo: DartdocDirectiveInfo(),
+        dartdocDirectiveInfo: dartdocDirectiveInfo,
         includedElementKinds: includedElementKinds,
         includedElementNames: includedElementNames,
         includedSuggestionRelevanceTags: includedSuggestionRelevanceTagList,
         listener: listener,
-      ).computeSuggestions(performance, request);
+      ).computeSuggestions(performance, request,
+          documentationCache: documentationCache);
 
       computeIncludedSetList(declarationsTracker, request.result,
           includedSuggestionSetList, includedElementNames);
@@ -1141,118 +1146,26 @@ class CompletionMetricsComputer {
 
     // Loop through each file, resolve the file and call
     // forEachExpectedCompletion
+
+    var dartdocDirectiveInfo = DartdocDirectiveInfo();
+    var documentationCache = DocumentationCache(dartdocDirectiveInfo);
+    var results = <ResolvedUnitResult>[];
     var pathContext = context.contextRoot.resourceProvider.pathContext;
     for (var filePath in context.contextRoot.analyzedFiles()) {
       if (file_paths.isDart(pathContext, filePath)) {
         try {
-          _resolvedUnitResult = await context.currentSession
-              .getResolvedUnit2(filePath) as ResolvedUnitResult;
+          var result = await context.currentSession.getResolvedUnit2(filePath)
+              as ResolvedUnitResult;
 
-          var analysisError = getFirstErrorOrNull(_resolvedUnitResult);
+          var analysisError = getFirstErrorOrNull(result);
           if (analysisError != null) {
             print('File $filePath skipped due to errors such as:');
             print('  ${analysisError.toString()}');
             print('');
             continue;
-          }
-
-          // Use the ExpectedCompletionsVisitor to compute the set of expected
-          // completions for this CompilationUnit.
-          final visitor = ExpectedCompletionsVisitor(filePath);
-          _resolvedUnitResult.unit!.accept(visitor);
-
-          for (var expectedCompletion in visitor.expectedCompletions) {
-            var resolvedUnitResult = _resolvedUnitResult;
-
-            // If an overlay option is being used, compute the overlay file, and
-            // have the context reanalyze the file
-            if (options.overlay != CompletionMetricsOptions.OVERLAY_NONE) {
-              var overlayContents = _getOverlayContents(
-                  _resolvedUnitResult.content!, expectedCompletion);
-
-              _provider.setOverlay(filePath,
-                  content: overlayContents,
-                  modificationStamp: overlayModificationStamp++);
-              context.driver.changeFile(filePath);
-              resolvedUnitResult = await context.currentSession
-                  .getResolvedUnit2(filePath) as ResolvedUnitResult;
-            }
-
-            // As this point the completion suggestions are computed,
-            // and results are collected with varying settings for
-            // comparison:
-
-            Future<int> handleExpectedCompletion(
-                {required MetricsSuggestionListener listener,
-                required CompletionMetrics metrics}) async {
-              var stopwatch = Stopwatch()..start();
-              var request = CompletionRequestImpl(
-                resolvedUnitResult,
-                expectedCompletion.offset,
-                CompletionPerformance(),
-              );
-              var directiveInfo = DartdocDirectiveInfo();
-
-              late OpType opType;
-              late List<protocol.CompletionSuggestion> suggestions;
-              await request.performance.runRequestOperation(
-                (performance) async {
-                  var dartRequest = await DartCompletionRequestImpl.from(
-                      performance, request, directiveInfo);
-                  opType =
-                      OpType.forCompletion(dartRequest.target, request.offset);
-                  suggestions = await _computeCompletionSuggestions(
-                    listener,
-                    performance,
-                    request,
-                    metrics.availableSuggestions ? declarationsTracker : null,
-                    metrics.availableSuggestions
-                        ? availableSuggestionsParams
-                        : null,
-                  );
-                },
-              );
-              stopwatch.stop();
-
-              return forEachExpectedCompletion(
-                  request,
-                  listener,
-                  expectedCompletion,
-                  opType.completionLocation,
-                  suggestions,
-                  metrics,
-                  stopwatch.elapsedMilliseconds);
-            }
-
-            var bestRank = -1;
-            var bestName = '';
-            var defaultTag = getCurrentTag();
-            for (var metrics in targetMetrics) {
-              // Compute the completions.
-              metrics.enable();
-              metrics.userTag.makeCurrent();
-              // if (FeatureComputer.noDisabledFeatures) {
-              //   var line = expectedCompletion.lineNumber;
-              //   var column = expectedCompletion.columnNumber;
-              //   print('$filePath:$line:$column');
-              // }
-              var listener = MetricsSuggestionListener();
-              var rank = await handleExpectedCompletion(
-                  listener: listener, metrics: metrics);
-              if (bestRank < 0 || rank < bestRank) {
-                bestRank = rank;
-                bestName = metrics.name;
-              }
-              defaultTag.makeCurrent();
-              metrics.disable();
-            }
-            rankComparison.count(bestName);
-
-            // If an overlay option is being used, remove the overlay applied
-            // earlier
-            if (options.overlay != CompletionMetricsOptions.OVERLAY_NONE) {
-              _provider.removeOverlay(filePath);
-            }
+          } else {
+            results.add(result);
+            documentationCache.cacheFromResult(result);
           }
         } catch (exception, stackTrace) {
           print('Exception caught analyzing: $filePath');
@@ -1261,6 +1174,104 @@ class CompletionMetricsComputer {
         }
       }
     }
+    for (var result in results) {
+      _resolvedUnitResult = result;
+      var filePath = result.path!;
+      // Use the ExpectedCompletionsVisitor to compute the set of expected
+      // completions for this CompilationUnit.
+      final visitor = ExpectedCompletionsVisitor(filePath);
+      _resolvedUnitResult.unit!.accept(visitor);
+
+      for (var expectedCompletion in visitor.expectedCompletions) {
+        var resolvedUnitResult = _resolvedUnitResult;
+
+        // If an overlay option is being used, compute the overlay file, and
+        // have the context reanalyze the file
+        if (options.overlay != CompletionMetricsOptions.OVERLAY_NONE) {
+          var overlayContents = _getOverlayContents(
+              _resolvedUnitResult.content!, expectedCompletion);
+
+          _provider.setOverlay(filePath,
+              content: overlayContents,
+              modificationStamp: overlayModificationStamp++);
+          context.driver.changeFile(filePath);
+          resolvedUnitResult = await context.currentSession
+              .getResolvedUnit2(filePath) as ResolvedUnitResult;
+        }
+
+        // As this point the completion suggestions are computed,
+        // and results are collected with varying settings for
+        // comparison:
+
+        Future<int> handleExpectedCompletion(
+            {required MetricsSuggestionListener listener,
+            required CompletionMetrics metrics}) async {
+          var stopwatch = Stopwatch()..start();
+          var request = CompletionRequestImpl(
+            resolvedUnitResult,
+            expectedCompletion.offset,
+            CompletionPerformance(),
+          );
+          var directiveInfo = DartdocDirectiveInfo();
+
+          late OpType opType;
+          late List<protocol.CompletionSuggestion> suggestions;
+          await request.performance.runRequestOperation(
+            (performance) async {
+              var dartRequest = await DartCompletionRequestImpl.from(
+                  performance, request, directiveInfo);
+              opType = OpType.forCompletion(dartRequest.target, request.offset);
+              suggestions = await _computeCompletionSuggestions(
+                listener,
+                performance,
+                request,
+                dartdocDirectiveInfo,
+                documentationCache,
+                metrics.availableSuggestions ? declarationsTracker : null,
+                metrics.availableSuggestions
+                    ? availableSuggestionsParams
+                    : null,
+              );
+            },
+          );
+          stopwatch.stop();
+
+          return forEachExpectedCompletion(
+              request,
+              listener,
+              expectedCompletion,
+              opType.completionLocation,
+              suggestions,
+              metrics,
+              stopwatch.elapsedMilliseconds);
+        }
+
+        var bestRank = -1;
+        var bestName = '';
+        var defaultTag = getCurrentTag();
+        for (var metrics in targetMetrics) {
+          // Compute the completions.
+          metrics.enable();
+          metrics.userTag.makeCurrent();
+          var listener = MetricsSuggestionListener();
+          var rank = await handleExpectedCompletion(
+              listener: listener, metrics: metrics);
+          if (bestRank < 0 || rank < bestRank) {
+            bestRank = rank;
+            bestName = metrics.name;
+          }
+          defaultTag.makeCurrent();
+          metrics.disable();
+        }
+        rankComparison.count(bestName);
+
+        // If an overlay option is being used, remove the overlay applied
+        // earlier.
+        if (options.overlay != CompletionMetricsOptions.OVERLAY_NONE) {
+          _provider.removeOverlay(filePath);
+        }
+      }
+    }
   }
 
   List<protocol.CompletionSuggestion> _filterSuggestions(

pkg/analyzer/lib/src/dartdoc/dartdoc_directive_info.dart

@@ -177,7 +177,7 @@ class DartdocDirectiveInfo {
       }
       start = eolIndex + 1;
     }
-    if (lastNonEmpty < firstNonEmpty) {
+    if (firstNonEmpty < 0 || lastNonEmpty < firstNonEmpty) {
       // All of the lines are empty.
       return const <String>[];
     }