Targeted Completion Prototype

src/EditorFeatures/Core/Shared/Extensions/GlyphExtensions.cs

@@ -207,6 +207,9 @@ public static ImageId GetImageId(this Glyph glyph)
                 case Glyph.NuGet:
                     return new ImageId(ImageCatalogGuid, KnownImageIds.NuGet);
 
+                case Glyph.MatchingType:
+                    return new ImageId(ImageCatalogGuid, KnownImageIds.Sync);
+
                 default:
                     throw new ArgumentException(nameof(glyph));
             }

src/Features/Core/Portable/Common/Glyph.cs

@@ -109,6 +109,7 @@ internal enum Glyph
         CompletionWarning,
 
         AddReference,
-        NuGet
+        NuGet,
+        MatchingType
     }
 }

src/Features/Core/Portable/Common/GlyphExtensions.cs

@@ -174,6 +174,9 @@ private static Glyph GetGlyph(string tag, ImmutableArray<string> allTags)
                             return Glyph.InterfacePublic;
                     }
 
+                case WellKnownTags.MatchingType:
+                    return Glyph.MatchingType;
+
                 case WellKnownTags.Intrinsic:
                     return Glyph.Intrinsic;
 

src/Features/Core/Portable/Completion/CompletionItemFilter.cs

@@ -78,6 +78,7 @@ public bool Matches(CompletionItem item)
         public static readonly CompletionItemFilter LocalAndParameterFilter = new CompletionItemFilter(FeaturesResources.Locals_and_parameters, ImmutableArray.Create(WellKnownTags.Local, WellKnownTags.Parameter), 'l');
         public static readonly CompletionItemFilter KeywordFilter = new CompletionItemFilter(FeaturesResources.Keywords, ImmutableArray.Create(WellKnownTags.Keyword), 'k');
         public static readonly CompletionItemFilter SnippetFilter = new CompletionItemFilter(FeaturesResources.Snippets, ImmutableArray.Create(WellKnownTags.Snippet), 't');
+        public static readonly CompletionItemFilter MatchingTypeFilter = new CompletionItemFilter(FeaturesResources.Matching_type, ImmutableArray.Create(WellKnownTags.MatchingType), 'j');
 
         public static readonly ImmutableArray<CompletionItemFilter> NamespaceFilters = ImmutableArray.Create(NamespaceFilter);
         public static readonly ImmutableArray<CompletionItemFilter> ClassFilters = ImmutableArray.Create(ClassFilter);
@@ -95,6 +96,7 @@ public bool Matches(CompletionItem item)
         public static readonly ImmutableArray<CompletionItemFilter> LocalAndParameterFilters = ImmutableArray.Create(LocalAndParameterFilter);
         public static readonly ImmutableArray<CompletionItemFilter> KeywordFilters = ImmutableArray.Create(KeywordFilter);
         public static readonly ImmutableArray<CompletionItemFilter> SnippetFilters = ImmutableArray.Create(SnippetFilter);
+        public static readonly ImmutableArray<CompletionItemFilter> MatchingTypeFilters = ImmutableArray.Create(MatchingTypeFilter);
 
         public static ImmutableArray<CompletionItemFilter> AllFilters { get; } =
             ImmutableArray.Create(
@@ -113,6 +115,7 @@ public bool Matches(CompletionItem item)
                 DelegateFilter,
                 NamespaceFilter,
                 KeywordFilter,
-                SnippetFilter);
+                SnippetFilter,
+                MatchingTypeFilter);
     }
 }

src/Features/Core/Portable/Completion/Providers/AbstractSymbolCompletionProvider.cs

@@ -46,18 +46,65 @@ protected virtual CompletionItemRules GetCompletionItemRules(IReadOnlyList<ISymb
         private ImmutableArray<CompletionItem> CreateItems(
             ImmutableArray<ISymbol> symbols,
             SyntaxContext context,
-            bool preselect)
+            bool preselect,
+            ImmutableArray<ITypeSymbol> inferredTypes = default)
         {
-            var tree = context.SyntaxTree;
+            var symbolGroups = from symbol in symbols
+                               let texts = GetDisplayAndSuffixAndInsertionText(symbol, context)
+                               group symbol by texts into g
+                               select g;
 
-            var q = from symbol in symbols
-                    let texts = GetDisplayAndSuffixAndInsertionText(symbol, context)
-                    group symbol by texts into g
-                    select this.CreateItem(
-                        g.Key.displayText, g.Key.suffix, g.Key.insertionText, g.ToList(), context,
+            var itemListBuilder = ImmutableArray.CreateBuilder<CompletionItem>();
+
+            foreach (var symbolGroup in symbolGroups)
+            {
+                var item = this.CreateItem(
+                        symbolGroup.Key.displayText, symbolGroup.Key.suffix, symbolGroup.Key.insertionText, symbolGroup.ToList(), context,
                         invalidProjectMap: null, totalProjects: null, preselect: preselect);
 
-            return q.ToImmutableArray();
+                if (symbolGroup.Any(s => ShouldIncludeInTargetTypedCompletionList(s, inferredTypes, context.SemanticModel, context.Position)))
+                {
+                    item = item.AddTag("MatchingType");
+                }
+
+                itemListBuilder.Add(item);
+            }
+
+            return itemListBuilder.ToImmutable();
+        }
+
+        private bool ShouldIncludeInTargetTypedCompletionList(ISymbol symbol, ImmutableArray<ITypeSymbol> inferredTypes, SemanticModel semanticModel, int position)
+        {
+            // When searching for identifiers of type C, exclude the symbol for the `C` type itself.
+            if (symbol.Kind == SymbolKind.NamedType)
+            {
+                return false;
+            }
+
+            // Avoid offering object.ToString() when a string is expected, for example.
+            if (symbol.ContainingType?.SpecialType == SpecialType.System_Object)
+            {
+                return false;
+            }
+
+            // Don't offer locals on the right-hand-side of their declaration: `int x = x`
+            if (symbol.Kind == SymbolKind.Local)
+            {
+                var local = (ILocalSymbol)symbol;
+                var declarationSyntax = symbol.DeclaringSyntaxReferences.Select(r => r.GetSyntax()).SingleOrDefault();
+                if (declarationSyntax != null && position < declarationSyntax.FullSpan.End)
+                {
+                    return false;
+                }
+            }
+
+            var type = symbol.GetMemberType() ?? symbol.GetSymbolType();
+            if (type == null)
+            {
+                return false;
+            }
+
+            return inferredTypes.Any(inferredType => semanticModel.Compilation.ClassifyCommonConversion(type, inferredType).IsImplicit);
         }
 
         /// <summary>
@@ -203,7 +250,11 @@ public override async Task ProvideCompletionsAsync(CompletionContext context)
             if (relatedDocumentIds.IsEmpty)
             {
                 var itemsForCurrentDocument = await GetSymbolsWorker(position, preselect, context, options, cancellationToken).ConfigureAwait(false);
-                return CreateItems(itemsForCurrentDocument, context, preselect);
+
+                var inferenceService = document.GetLanguageService<ITypeInferenceService>();
+                var inferredTypes = inferenceService.InferTypes(context.SemanticModel, position, cancellationToken);
+
+                return CreateItems(itemsForCurrentDocument, context, preselect, inferredTypes);
             }
 
             var contextAndSymbolLists = await GetPerContextSymbols(document, position, options, new[] { document.Id }.Concat(relatedDocumentIds), preselect, cancellationToken).ConfigureAwait(false);

src/Features/Core/Portable/FeaturesResources.Designer.cs

@@ -2304,6 +2304,15 @@ internal class FeaturesResources {
             }
         }
         
+        /// <summary>
+        ///   Looks up a localized string similar to Matching type.
+        /// </summary>
+        internal static string Matching_type {
+            get {
+                return ResourceManager.GetString("Matching_type", resourceCulture);
+            }
+        }
+        
         /// <summary>
         ///   Looks up a localized string similar to Member name can be simplified.
         /// </summary>

src/Features/Core/Portable/FeaturesResources.resx

@@ -1614,4 +1614,7 @@ This version used in: {2}</value>
   <data name="Add_parameter_to_constructor" xml:space="preserve">
     <value>Add parameter to constructor</value>
   </data>
+  <data name="Matching_type" xml:space="preserve">
+    <value>Matching type</value>
+  </data>
 </root>
\ No newline at end of file

src/Features/Core/Portable/xlf/FeaturesResources.cs.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.de.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.es.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.fr.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.it.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.ja.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.ko.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.pl.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.pt-BR.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.ru.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.tr.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.zh-Hans.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Features/Core/Portable/xlf/FeaturesResources.zh-Hant.xlf

@@ -192,6 +192,11 @@
         <target state="new">Make local function 'static'</target>
         <note />
       </trans-unit>
+      <trans-unit id="Matching_type">
+        <source>Matching type</source>
+        <target state="new">Matching type</target>
+        <note />
+      </trans-unit>
       <trans-unit id="Merge_with_nested_0_statement">
         <source>Merge with nested '{0}' statement</source>
         <target state="new">Merge with nested '{0}' statement</target>

src/Workspaces/Core/Portable/Tags/WellKnownTags.cs

@@ -52,6 +52,7 @@ public static class WellKnownTags
 
         internal const string AddReference = nameof(AddReference);
         internal const string NuGet = nameof(NuGet);
+        internal const string MatchingType = nameof(MatchingType);
     }
 
     internal static class WellKnownTagArrays
@@ -128,6 +129,7 @@ internal static class WellKnownTagArrays
 
         internal static readonly ImmutableArray<string> AddReference = ImmutableArray.Create(WellKnownTags.AddReference);
         internal static readonly ImmutableArray<string> NuGet = ImmutableArray.Create(WellKnownTags.NuGet);
+        internal static readonly ImmutableArray<string> MatchingType = ImmutableArray.Create(WellKnownTags.MatchingType);
 
         internal static readonly ImmutableArray<string> CSharpFile = ImmutableArray.Create(WellKnownTags.File, LanguageNames.CSharp);
         internal static readonly ImmutableArray<string> VisualBasicFile = ImmutableArray.Create(WellKnownTags.File, LanguageNames.VisualBasic);