Don't resolve symbols at insertion time for Partial-Type-Completion.

src/Features/CSharp/Portable/Completion/CompletionProviders/PartialTypeCompletionProvider.cs

 // Copyright (c) Microsoft.  All Rights Reserved.  Licensed under the Apache License, Version 2.0.  See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 using System.Linq;
 using System.Threading;
@@ -18,6 +19,8 @@ namespace Microsoft.CodeAnalysis.CSharp.Completion.Providers
 {
     internal partial class PartialTypeCompletionProvider : AbstractPartialTypeCompletionProvider
     {
+        private const string InsertionTextOnLessThan = nameof(InsertionTextOnLessThan);
+
         private static readonly SymbolDisplayFormat _symbolFormatWithGenerics =
             new SymbolDisplayFormat(
                 globalNamespaceStyle: SymbolDisplayGlobalNamespaceStyle.Omitted,
@@ -51,7 +54,8 @@ protected override Task<AbstractSyntaxContext> CreateSyntaxContextAsync(Document
             return Task.FromResult<AbstractSyntaxContext>(CSharpSyntaxContext.CreateContext(document.Project.Solution.Workspace, semanticModel, position, cancellationToken));
         }
 
-        protected override ValueTuple<string, string> GetDisplayAndInsertionText(INamedTypeSymbol symbol, AbstractSyntaxContext context)
+        protected override ValueTuple<string, string> GetDisplayAndInsertionText(
+            INamedTypeSymbol symbol, AbstractSyntaxContext context)
         {
             var displayAndInsertionText = symbol.ToMinimalDisplayString(context.SemanticModel, context.Position, _symbolFormatWithGenerics);
             return ValueTuple.Create(displayAndInsertionText, displayAndInsertionText);
@@ -68,19 +72,23 @@ protected override IEnumerable<INamedTypeSymbol> LookupCandidateSymbols(Abstract
 
         private static bool IsPartialTypeDeclaration(SyntaxNode syntax)
         {
-            var declarationSyntax  = syntax as BaseTypeDeclarationSyntax;
+            var declarationSyntax = syntax as BaseTypeDeclarationSyntax;
             return declarationSyntax != null && declarationSyntax.Modifiers.Any(modifier => modifier.IsKind(SyntaxKind.PartialKeyword));
         }
 
-        public async override Task<TextChange?> GetTextChangeAsync(Document document, CompletionItem selectedItem, char? ch, CancellationToken cancellationToken)
+        protected override CompletionItem AddAdditionalProperties(CompletionItem item, INamedTypeSymbol symbol, AbstractSyntaxContext context)
+        {
+            return item.AddProperty(InsertionTextOnLessThan, symbol.Name.EscapeIdentifier());
+        }
+
+        public async override Task<TextChange?> GetTextChangeAsync(
+            Document document, CompletionItem selectedItem, char? ch, CancellationToken cancellationToken)
         {
             if (ch == '<')
             {
-                var symbols = await SymbolCompletionItem.GetSymbolsAsync(selectedItem, document, cancellationToken).ConfigureAwait(false);
-
-                if (symbols.Length > 0)
+                string insertionText;
+                if (selectedItem.Properties.TryGetValue(InsertionTextOnLessThan, out insertionText))
                 {
-                    var insertionText = symbols[0].Name.EscapeIdentifier();
                     return new TextChange(selectedItem.Span, insertionText);
                 }
             }
@@ -88,4 +96,4 @@ private static bool IsPartialTypeDeclaration(SyntaxNode syntax)
             return await base.GetTextChangeAsync(document, selectedItem, ch, cancellationToken).ConfigureAwait(false);
         }
     }
-}
+}
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src/Features/Core/Portable/Completion/Providers/AbstractPartialTypeCompletionProvider.cs

@@ -37,7 +37,7 @@ public async sealed override Task ProvideCompletionsAsync(CompletionContext comp
                 if (declaredSymbol != null)
                 {
                     var symbols = LookupCandidateSymbols(syntaxContext, declaredSymbol, cancellationToken);
-                    var items = symbols?.Select(symbol => CreateCompletionItem(symbol, completionContext.CompletionListSpan, position, syntaxContext));
+                    var items = symbols?.Select(s => CreateCompletionItem(s, syntaxContext));
 
                     if (items != null)
                     {
@@ -47,19 +47,25 @@ public async sealed override Task ProvideCompletionsAsync(CompletionContext comp
             }
         }
 
-        private CompletionItem CreateCompletionItem(INamedTypeSymbol symbol, TextSpan textSpan, int position, AbstractSyntaxContext context)
+        private CompletionItem CreateCompletionItem(
+            INamedTypeSymbol symbol, AbstractSyntaxContext context)
         {
             var displayAndInsertionText = GetDisplayAndInsertionText(symbol, context);
 
-            return SymbolCompletionItem.Create(
+            var item = SymbolCompletionItem.Create(
                 displayText: displayAndInsertionText.Item1,
                 insertionText: displayAndInsertionText.Item2,
                 symbol: symbol,
                 contextPosition: context.Position,
-                descriptionPosition: position,
+                descriptionPosition: context.Position,
                 rules: CompletionItemRules.Default);
+
+            item = AddAdditionalProperties(item, symbol, context);
+            return item;
         }
 
+        protected abstract CompletionItem AddAdditionalProperties(
+            CompletionItem item, INamedTypeSymbol symbol, AbstractSyntaxContext context);
         protected abstract Task<AbstractSyntaxContext> CreateSyntaxContextAsync(
             Document document,
             SemanticModel semanticModel,

src/Features/VisualBasic/Portable/Completion/CompletionProviders/PartialTypeCompletionProvider.vb

@@ -13,6 +13,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Completion.Providers
     Partial Friend Class PartialTypeCompletionProvider
         Inherits AbstractPartialTypeCompletionProvider
 
+        Private Const InsertionTextOnOpenParen As String = NameOf(InsertionTextOnOpenParen)
+
         Private Shared ReadOnly _insertionTextFormatWithGenerics As SymbolDisplayFormat =
             New SymbolDisplayFormat(
                 globalNamespaceStyle:=SymbolDisplayGlobalNamespaceStyle.Omitted,
@@ -25,9 +27,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Completion.Providers
                     SymbolDisplayGenericsOptions.IncludeVariance Or
                     SymbolDisplayGenericsOptions.IncludeTypeConstraints)
 
-        Private Shared ReadOnly _insertionTextFormatWithoutGenerics As SymbolDisplayFormat =
-            _insertionTextFormatWithGenerics.WithGenericsOptions(SymbolDisplayGenericsOptions.None)
-
         Private Shared ReadOnly _displayTextFormat As SymbolDisplayFormat =
             _insertionTextFormatWithGenerics.RemoveMiscellaneousOptions(SymbolDisplayMiscellaneousOptions.EscapeKeywordIdentifiers)
 
@@ -50,19 +49,19 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Completion.Providers
             Return ValueTuple.Create(displayText, insertionText)
         End Function
 
+        Protected Overrides Function AddAdditionalProperties(item As CompletionItem, symbol As INamedTypeSymbol, context As AbstractSyntaxContext) As CompletionItem
+            Return item.AddProperty(InsertionTextOnOpenParen, symbol.Name.EscapeIdentifier())
+        End Function
+
         Public Overrides Async Function GetTextChangeAsync(document As Document, selectedItem As CompletionItem, ch As Char?, cancellationToken As CancellationToken) As Task(Of TextChange?)
             If ch = "("c Then
-                Dim symbols = Await SymbolCompletionItem.GetSymbolsAsync(selectedItem, document, cancellationToken).ConfigureAwait(False)
-                If symbols.Length > 0 Then
-                    Dim position = SymbolCompletionItem.GetContextPosition(selectedItem)
-                    Dim semanticModel = Await document.GetSemanticModelForSpanAsync(New TextSpan(position, 0), cancellationToken).ConfigureAwait(False)
-                    Dim insertionText = symbols(0).ToMinimalDisplayString(semanticModel, position, format:=_insertionTextFormatWithoutGenerics)
+                Dim insertionText As String = Nothing
+                If selectedItem.Properties.TryGetValue(InsertionTextOnOpenParen, insertionText) Then
                     Return New TextChange(selectedItem.Span, insertionText)
                 End If
             End If
 
             Return Await MyBase.GetTextChangeAsync(document, selectedItem, ch, cancellationToken).ConfigureAwait(False)
         End Function
-
     End Class
 End Namespace
\ No newline at end of file