Clean up the return type of the contributors compute method

All of the contributors now contribute through the builder so the return
value was always an empty list.

Change-Id: I9e5746a7c7e2dc256a00c6091f6bf9d46331b617
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/150803
Reviewed-by: Konstantin Shcheglov <scheglov@google.com>
Commit-Queue: Brian Wilkerson <brianwilkerson@google.com>

pkg/analysis_server/lib/src/provisional/completion/dart/completion_dart.dart

@@ -13,7 +13,6 @@ import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/dartdoc/dartdoc_directive_info.dart';
 import 'package:analyzer/src/generated/source.dart';
-import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/src/utilities/completion/completion_target.dart';
 import 'package:analyzer_plugin/src/utilities/completion/optype.dart';
 
@@ -22,11 +21,9 @@ export 'package:analyzer_plugin/utilities/completion/relevance.dart';
 /// An object that contributes results for the `completion.getSuggestions`
 /// request results.
 abstract class DartCompletionContributor {
-  /// Return a [Future] that completes with a list of suggestions
-  /// for the given completion [request].
-  // TODO(brianwilkerson) When all of the suggestions are being built using the
-  //  builder, change the return type to `Future<void>`.
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  /// Return a [Future] that completes when the suggestions appropriate for the
+  /// given completion [request] have been added to the [builder].
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder);
 }
 

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

@@ -4,8 +4,6 @@
 
 import 'dart:async';
 
-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/suggestion_builder.dart';
 import 'package:analysis_server/src/utilities/flutter.dart';
@@ -29,11 +27,11 @@ class ArgListContributor extends DartCompletionContributor {
   ArgumentList argumentList;
 
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var executable = request.target.executableElement;
     if (executable == null) {
-      return const <CompletionSuggestion>[];
+      return;
     }
     var node = request.target.containingNode;
     if (node is ArgumentList) {
@@ -43,7 +41,6 @@ class ArgListContributor extends DartCompletionContributor {
     this.request = request;
     this.builder = builder;
     _addSuggestions(executable.parameters);
-    return const <CompletionSuggestion>[];
   }
 
   void _addDefaultParamSuggestions(Iterable<ParameterElement> parameters,

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

@@ -15,11 +15,11 @@ import 'package:analyzer/dart/element/element.dart';
 /// when the completion is in a show or hide combinator of an import or export.
 class CombinatorContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var node = request.target.containingNode;
     if (node is! Combinator) {
-      return const <CompletionSuggestion>[];
+      return;
     }
     // Build the list of suggestions.
     var directive = node.thisOrAncestorOfType<NamespaceDirective>();
@@ -35,7 +35,6 @@ class CombinatorContributor extends DartCompletionContributor {
         }
       }
     }
-    return const <CompletionSuggestion>[];
   }
 
   List<String> _getCombinatorNames(NamespaceDirective directive) {

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

@@ -184,14 +184,9 @@ class DartCompletionManager implements CompletionContributor {
         var contributorTag =
             'DartCompletionManager - ${contributor.runtimeType}';
         performance.logStartTime(contributorTag);
-        var contributorSuggestions =
-            await contributor.computeSuggestions(dartRequest, builder);
+        await contributor.computeSuggestions(dartRequest, builder);
         performance.logElapseTime(contributorTag);
         request.checkAborted();
-
-        for (var newSuggestion in contributorSuggestions) {
-          addSuggestionToMap(newSuggestion);
-        }
       }
       for (var newSuggestion in builder.suggestions) {
         addSuggestionToMap(newSuggestion);

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

@@ -4,8 +4,6 @@
 
 import 'dart:async';
 
-import 'package:analysis_server/src/protocol_server.dart'
-    show CompletionSuggestion;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ -23,13 +21,13 @@ class ExtensionMemberContributor extends DartCompletionContributor {
   MemberSuggestionBuilder memberBuilder;
 
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var containingLibrary = request.libraryElement;
     // Gracefully degrade if the library could not be determined, such as with a
     // detached part file or source change.
     if (containingLibrary == null) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     memberBuilder = MemberSuggestionBuilder(request, builder);
@@ -63,24 +61,23 @@ class ExtensionMemberContributor extends DartCompletionContributor {
           }
         }
       }
-
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     if (expression.isSynthetic) {
-      return const <CompletionSuggestion>[];
+      return;
     }
     if (expression is Identifier) {
       var elem = expression.staticElement;
       if (elem is ClassElement) {
         // Suggestions provided by StaticMemberContributor.
-        return const <CompletionSuggestion>[];
+        return;
       } else if (elem is ExtensionElement) {
         // Suggestions provided by StaticMemberContributor.
-        return const <CompletionSuggestion>[];
+        return;
       } else if (elem is PrefixElement) {
         // Suggestions provided by LibraryMemberContributor.
-        return const <CompletionSuggestion>[];
+        return;
       }
     }
     if (expression is ExtensionOverride) {
@@ -92,12 +89,11 @@ class ExtensionMemberContributor extends DartCompletionContributor {
         // get to this point, but there's an NPE if we invoke
         // `_resolveExtendedType` when `type` is `null`, so we guard against it
         // to ensure that we can return the suggestions from other providers.
-        return const <CompletionSuggestion>[];
+        return;
       }
       _addExtensionMembers(containingLibrary, type);
       expression.staticType;
     }
-    return const <CompletionSuggestion>[];
   }
 
   void _addExtensionMembers(LibraryElement containingLibrary, DartType type) {

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

@@ -4,8 +4,6 @@
 
 import 'dart:async';
 
-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/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ -16,19 +14,19 @@ import 'package:analyzer/dart/ast/ast.dart';
 /// expressions of the form `this.^` in a constructor's parameter list.
 class FieldFormalContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var node = request.target.containingNode;
     // TODO(brianwilkerson) We should suggest field formal parameters even if
     //  the user hasn't already typed the `this.` prefix, by including the
     //  prefix in the completion.
     if (node is! FieldFormalParameter) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     var constructor = node.thisOrAncestorOfType<ConstructorDeclaration>();
     if (constructor == null) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     // Compute the list of fields already referenced in the constructor.
@@ -52,7 +50,7 @@ class FieldFormalContributor extends DartCompletionContributor {
 
     var enclosingClass = constructor.thisOrAncestorOfType<ClassDeclaration>();
     if (enclosingClass == null) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     // Add suggestions for fields that are not already referenced.
@@ -71,6 +69,5 @@ class FieldFormalContributor extends DartCompletionContributor {
         }
       }
     }
-    return const <CompletionSuggestion>[];
   }
 }

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

@@ -4,8 +4,6 @@
 
 import 'dart:async';
 
-import 'package:analysis_server/src/protocol_server.dart'
-    show CompletionSuggestion;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/local_library_contributor.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart'
@@ -15,15 +13,15 @@ import 'package:analyzer/src/generated/resolver.dart';
 /// A contributor for calculating suggestions for imported top level members.
 class ImportedReferenceContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     if (!request.includeIdentifiers) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     var imports = request.libraryElement.imports;
     if (imports == null) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     // Traverse imports including dart:core
@@ -34,7 +32,6 @@ class ImportedReferenceContributor extends DartCompletionContributor {
             prefix: importElement.prefix?.name);
       }
     }
-    return const <CompletionSuggestion>[];
   }
 
   void _buildSuggestions(DartCompletionRequest request,

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

@@ -13,7 +13,6 @@ import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
 import 'package:analyzer/dart/ast/visitor.dart';
 import 'package:analyzer/src/dart/ast/token.dart';
-import 'package:analyzer_plugin/protocol/protocol_common.dart';
 import 'package:analyzer_plugin/src/utilities/completion/optype.dart';
 
 const ASYNC_STAR = 'async*';
@@ -29,14 +28,13 @@ const YIELD_STAR = 'yield*';
 /// are valid at the completion point.
 class KeywordContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     // Don't suggest anything right after double or integer literals.
     if (request.target.isDoubleOrIntLiteral()) {
-      return const <CompletionSuggestion>[];
+      return;
     }
     request.target.containingNode.accept(_KeywordVisitor(request, builder));
-    return const <CompletionSuggestion>[];
   }
 }
 

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

@@ -4,8 +4,6 @@
 
 import 'dart:async';
 
-import 'package:analysis_server/src/protocol_server.dart'
-    show CompletionSuggestion;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/completion_manager.dart'
     show DartCompletionRequestImpl;
@@ -19,7 +17,7 @@ import 'package:analyzer_plugin/src/utilities/visitors/local_declaration_visitor
 /// `continue` statements.
 class LabelContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var optype = (request as DartCompletionRequestImpl).opType;
 
@@ -33,7 +31,6 @@ class LabelContributor extends DartCompletionContributor {
             .visit(request.target.containingNode);
       }
     }
-    return const <CompletionSuggestion>[];
   }
 }
 

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

@@ -4,21 +4,20 @@
 
 import 'dart:async';
 
+import 'package:analysis_server/src/protocol_server.dart'
+    show CompletionSuggestionKind;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 
-import '../../../protocol_server.dart'
-    show CompletionSuggestion, CompletionSuggestionKind;
-
 /// A contributor that produces suggestions based on the members of a library
 /// when the library was imported using a prefix. More concretely, this class
 /// produces suggestions for expressions of the form `p.^`, where `p` is a
 /// prefix.
 class LibraryMemberContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     // Determine if the target looks like a library prefix.
     var targetId = request.dotTarget;
@@ -31,15 +30,15 @@ class LibraryMemberContributor extends DartCompletionContributor {
         if (containingLibrary != null) {
           var imports = containingLibrary.imports;
           if (imports != null) {
-            return _buildSuggestions(request, builder, elem, imports);
+            _buildSuggestions(request, builder, elem, imports);
+            return;
           }
         }
       }
     }
-    return const <CompletionSuggestion>[];
   }
 
-  List<CompletionSuggestion> _buildSuggestions(
+  void _buildSuggestions(
       DartCompletionRequest request,
       SuggestionBuilder builder,
       PrefixElement elem,
@@ -83,6 +82,5 @@ class LibraryMemberContributor extends DartCompletionContributor {
         }
       }
     }
-    return const <CompletionSuggestion>[];
   }
 }

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

@@ -4,8 +4,6 @@
 
 import 'dart:async';
 
-import 'package:analysis_server/src/protocol_server.dart'
-    show CompletionSuggestion;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 
@@ -13,15 +11,15 @@ import 'package:analysis_server/src/services/completion/dart/suggestion_builder.
 /// import directives.
 class LibraryPrefixContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     if (!request.includeIdentifiers) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     var imports = request.libraryElement.imports;
     if (imports == null) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     for (var element in imports) {
@@ -33,6 +31,5 @@ class LibraryPrefixContributor extends DartCompletionContributor {
         }
       }
     }
-    return const <CompletionSuggestion>[];
   }
 }

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

@@ -5,7 +5,7 @@
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol_server.dart'
-    show CompletionSuggestion, CompletionSuggestionKind;
+    show CompletionSuggestionKind;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart'
     show SuggestionBuilder;
@@ -148,15 +148,15 @@ class LibraryElementSuggestionBuilder extends GeneralizingElementVisitor {
 /// which the completion is requested.
 class LocalLibraryContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     if (!request.includeIdentifiers) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     var libraryUnits = request.result.unit.declaredElement.library.units;
     if (libraryUnits == null) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     var visitor = LibraryElementSuggestionBuilder(request, builder);
@@ -165,6 +165,5 @@ class LocalLibraryContributor extends DartCompletionContributor {
         unit.accept(visitor);
       }
     }
-    return const <CompletionSuggestion>[];
   }
 }

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

@@ -5,7 +5,7 @@
 import 'dart:async';
 
 import 'package:analysis_server/src/protocol_server.dart'
-    show CompletionSuggestion, CompletionSuggestionKind;
+    show CompletionSuggestionKind;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analysis_server/src/utilities/strings.dart';
@@ -37,7 +37,7 @@ class LocalReferenceContributor extends DartCompletionContributor {
   _VisibilityTracker visibilityTracker = _VisibilityTracker();
 
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var opType = request.opType;
     var node = request.target.containingNode;
@@ -92,7 +92,6 @@ class LocalReferenceContributor extends DartCompletionContributor {
         }
       }
     }
-    return const <CompletionSuggestion>[];
   }
 
   void _addSuggestionsForType(InterfaceType type, DartCompletionRequest request,

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

@@ -8,7 +8,6 @@ import 'package:analysis_server/src/provisional/completion/dart/completion_dart.
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
-import 'package:analyzer_plugin/protocol/protocol_common.dart' hide Element;
 
 /// A contributor that produces suggestions based on the named constructors
 /// defined on a given class. More concretely, this class produces suggestions
@@ -16,13 +15,13 @@ import 'package:analyzer_plugin/protocol/protocol_common.dart' hide Element;
 /// class.
 class NamedConstructorContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var node = request.target.containingNode;
     if (node is ConstructorName) {
       var libraryElement = request.libraryElement;
       if (libraryElement == null) {
-        return const <CompletionSuggestion>[];
+        return;
       }
       var typeName = node.type;
       if (typeName != null) {
@@ -35,7 +34,6 @@ class NamedConstructorContributor extends DartCompletionContributor {
         }
       }
     }
-    return const <CompletionSuggestion>[];
   }
 
   void _buildSuggestions(

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

@@ -4,7 +4,6 @@
 
 import 'dart:async';
 
-import 'package:analysis_server/src/protocol_server.dart';
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ -15,15 +14,15 @@ import 'package:analyzer_plugin/src/utilities/completion/completion_target.dart'
 /// inside a class declaration with templates for inherited members.
 class OverrideContributor implements DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var targetId = _getTargetId(request.target);
     if (targetId == null) {
-      return const <CompletionSuggestion>[];
+      return;
     }
     var classDecl = targetId.thisOrAncestorOfType<ClassOrMixinDeclaration>();
     if (classDecl == null) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     var inheritance = InheritanceManager3();
@@ -36,7 +35,6 @@ class OverrideContributor implements DartCompletionContributor {
         _namesToOverride(classElem.librarySource.uri, interface);
 
     // Build suggestions
-    var suggestions = <CompletionSuggestion>[];
     for (var name in namesToOverride) {
       var element = interfaceMap[name];
       // Gracefully degrade if the overridden element has not been resolved.
@@ -45,7 +43,6 @@ class OverrideContributor implements DartCompletionContributor {
         await builder.suggestOverride(targetId, element, invokeSuper);
       }
     }
-    return suggestions;
   }
 
   /// If the target looks like a partial identifier inside a class declaration

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

@@ -4,8 +4,6 @@
 
 import 'dart:async';
 
-import 'package:analysis_server/src/protocol_server.dart'
-    show CompletionSuggestion;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ -17,7 +15,7 @@ import 'package:analyzer/dart/element/element.dart';
 /// class, enum, or extension.
 class StaticMemberContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var library = request.libraryElement;
     if (library == null) {
@@ -25,7 +23,7 @@ class StaticMemberContributor extends DartCompletionContributor {
       // detached part file or source change.
       // TODO(brianwilkerson) Consider testing for this before invoking _any_ of
       //  the contributors.
-      return const <CompletionSuggestion>[];
+      return;
     }
     bool isVisible(Element element) => element.isAccessibleIn(library);
     var targetId = request.dotTarget;
@@ -76,6 +74,5 @@ class StaticMemberContributor extends DartCompletionContributor {
         }
       }
     }
-    return const <CompletionSuggestion>[];
   }
 }

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

@@ -5,8 +5,6 @@
 import 'dart:async';
 import 'dart:collection';
 
-import 'package:analysis_server/src/protocol_server.dart'
-    show CompletionSuggestion;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ -21,13 +19,13 @@ import 'package:analyzer_plugin/src/utilities/visitors/local_declaration_visitor
 /// instance of a type.
 class TypeMemberContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var containingLibrary = request.libraryElement;
     // Gracefully degrade if the library could not be determined, such as with a
     // detached part file or source change.
     if (containingLibrary == null) {
-      return const <CompletionSuggestion>[];
+      return;
     }
 
     // Recompute the target because resolution might have changed it.
@@ -35,17 +33,17 @@ class TypeMemberContributor extends DartCompletionContributor {
     if (expression == null ||
         expression.isSynthetic ||
         expression is ExtensionOverride) {
-      return const <CompletionSuggestion>[];
+      return;
     }
     if (expression is Identifier) {
       var elem = expression.staticElement;
       if (elem is ClassElement) {
         // Suggestions provided by StaticMemberContributor.
-        return const <CompletionSuggestion>[];
+        return;
       }
       if (elem is PrefixElement) {
         // Suggestions provided by LibraryMemberContributor.
-        return const <CompletionSuggestion>[];
+        return;
       }
     }
 
@@ -96,8 +94,6 @@ class TypeMemberContributor extends DartCompletionContributor {
       memberBuilder.buildSuggestions(type,
           mixins: mixins, superclassConstraints: superclassConstraints);
     }
-
-    return const <CompletionSuggestion>[];
   }
 }
 

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

@@ -5,8 +5,6 @@
 import 'dart:async';
 import 'dart:core';
 
-import 'package:analysis_server/src/protocol_server.dart'
-    show CompletionSuggestion;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analyzer/dart/ast/ast.dart';
@@ -25,11 +23,10 @@ class UriContributor extends DartCompletionContributor {
   static bool suggestFilePaths = true;
 
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var visitor = _UriSuggestionBuilder(request, builder);
     request.target.containingNode.accept(visitor);
-    return const <CompletionSuggestion>[];
   }
 }
 

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

@@ -4,8 +4,6 @@
 
 import 'dart:async';
 
-import 'package:analysis_server/src/protocol_server.dart'
-    show CompletionSuggestion;
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/dart/suggestion_builder.dart';
 import 'package:analysis_server/src/services/correction/name_suggestion.dart';
@@ -16,7 +14,7 @@ import 'package:analyzer_plugin/src/utilities/completion/completion_target.dart'
 /// static type of the variable.
 class VariableNameContributor extends DartCompletionContributor {
   @override
-  Future<List<CompletionSuggestion>> computeSuggestions(
+  Future<void> computeSuggestions(
       DartCompletionRequest request, SuggestionBuilder builder) async {
     var opType = request.opType;
 
@@ -65,7 +63,7 @@ class VariableNameContributor extends DartCompletionContributor {
         }
       }
       if (strName == null) {
-        return const <CompletionSuggestion>[];
+        return;
       }
 
       var doIncludePrivateVersion =
@@ -80,7 +78,6 @@ class VariableNameContributor extends DartCompletionContributor {
         }
       }
     }
-    return const <CompletionSuggestion>[];
   }
 
   /// Given some [name], add a suggestion with the name (unless the name is

pkg/analysis_server/test/services/completion/dart/completion_contributor_util.dart

@@ -55,8 +55,8 @@ abstract class DartCompletionContributorTest
   Future<List<CompletionSuggestion>> computeContributedSuggestions(
       DartCompletionRequest request) async {
     var builder = SuggestionBuilder(request);
-    var suggestions = await contributor.computeSuggestions(request, builder);
-    return [...suggestions, ...builder.suggestions];
+    await contributor.computeSuggestions(request, builder);
+    return builder.suggestions.toList();
   }
 
   DartCompletionContributor createContributor();