Be resilient to the document being shorter than when it started when we get a...

Be resilient to the document being shorter than when it started when we get a completoin item description.

src/EditorFeatures/CSharpTest/Completion/CompletionProviders/SymbolCompletionProviderTests_NoInteractive.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.Linq;
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Completion;
 using Microsoft.CodeAnalysis.CSharp.Completion.Providers;
 using Microsoft.CodeAnalysis.Editor.CSharp.UnitTests.Completion.CompletionProviders;
 using Microsoft.CodeAnalysis.Editor.UnitTests.Workspaces;
+using Microsoft.VisualStudio.Text;
 using Roslyn.Test.Utilities;
 using Xunit;
 
@@ -320,5 +322,38 @@ class C { void M() { B.$$ } }
             await VerifyItemExistsAsync(code, "X");
             await VerifyItemExistsAsync(code, "Y");
         }
+
+        [WorkItem(209299, "https://devdiv.visualstudio.com/DevDiv/_workitems?id=209299")]
+        [Fact, Trait(Traits.Feature, Traits.Features.Completion)]
+        public async Task TestDescriptionWhenDocumentLengthChanges()
+        {
+            var code = @"using System;
+
+class C 
+{
+    string Property
+    {
+        get 
+        {
+            Console.$$";//, @"Beep"
+
+            using (var workspace = TestWorkspace.CreateCSharp(code))
+            {
+                var testDocument = workspace.Documents.Single();
+                var position = testDocument.CursorPosition.Value;
+
+                var document = workspace.CurrentSolution.GetDocument(testDocument.Id);
+                var service = CompletionService.GetService(document);
+                var completions = await service.GetCompletionsAsync(document, position);
+
+                var item = completions.Items.First(i => i.DisplayText == "Beep");
+                var edit = testDocument.GetTextBuffer().CreateEdit();
+                edit.Delete(Span.FromBounds(position - 10, position));
+                edit.Apply();
+
+                document = workspace.CurrentSolution.GetDocument(testDocument.Id);
+                var description = service.GetDescriptionAsync(document, item);
+            }
+        }
     }
 }

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

@@ -11,9 +11,10 @@ abstract class AbstractCrefCompletionProvider : CommonCompletionProvider
     {
         protected const string HideAdvancedMembers = nameof(HideAdvancedMembers);
 
-        protected override async Task<CompletionDescription> GetDescriptionWorkerAsync(Document document, CompletionItem item, CancellationToken cancellationToken)
+        protected override async Task<CompletionDescription> GetDescriptionWorkerAsync(
+            Document document, CompletionItem item, CancellationToken cancellationToken)
         {
-            var position = SymbolCompletionItem.GetContextPosition(item);
+            var position = await SymbolCompletionItem.GetContextPositionAsync(document, item, cancellationToken).ConfigureAwait(false);
 
             // What EditorBrowsable settings were we previously passed in (if it mattered)?
             bool hideAdvancedMembers = false;

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

@@ -108,7 +108,7 @@ private static int ComputeSymbolMatchPriority(ISymbol symbol)
         protected override async Task<CompletionDescription> GetDescriptionWorkerAsync(
             Document document, CompletionItem item, CancellationToken cancellationToken)
         {
-            var position = SymbolCompletionItem.GetContextPosition(item);
+            var position = await SymbolCompletionItem.GetContextPositionAsync(document, item, cancellationToken).ConfigureAwait(false);
             var name = SymbolCompletionItem.GetSymbolName(item);
             var kind = SymbolCompletionItem.GetKind(item);
             var relatedDocumentIds = document.Project.Solution.GetRelatedDocumentIds(document.Id).Concat(document.Id);

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

@@ -8,6 +8,7 @@
 using System.Threading.Tasks;
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Shared.Utilities;
+using Microsoft.CodeAnalysis.Text;
 
 namespace Microsoft.CodeAnalysis.Completion.Providers
 {
@@ -144,11 +145,12 @@ private static ISymbol DecodeSymbol(string id, Compilation compilation)
             return SymbolKey.Resolve(id, compilation).GetAnySymbol();
         }
 
-        public static async Task<CompletionDescription> GetDescriptionAsync(CompletionItem item, Document document, CancellationToken cancellationToken)
+        public static async Task<CompletionDescription> GetDescriptionAsync(
+            CompletionItem item, Document document, CancellationToken cancellationToken)
         {
             var workspace = document.Project.Solution.Workspace;
 
-            var position = GetDescriptionPosition(item);
+            var position = await GetDescriptionPositionAsync(document, item, cancellationToken).ConfigureAwait(false);
             if (position == -1)
             {
                 position = item.Span.Start;
@@ -214,11 +216,19 @@ public static SupportedPlatformData GetSupportedPlatforms(CompletionItem item, W
             return null;
         }
 
-        public static int GetContextPosition(CompletionItem item)
+        public static async Task<int> GetContextPositionAsync(
+            Document document, CompletionItem item, CancellationToken cancellationToken)
         {
-            if (item.Properties.TryGetValue("ContextPosition", out var text) && int.TryParse(text, out var number))
+            if (item.Properties.TryGetValue("ContextPosition", out var text) &&
+                int.TryParse(text, out var number))
             {
-                return number;
+                // We have no access to the editor at this layer.  So it's not 
+                // possible for us to map the original context position forward
+                // to the current position in the file.  So we need to cap the
+                // positoin to make sure it's within the bounds of the current
+                // text.
+                var sourceText = await document.GetTextAsync(cancellationToken).ConfigureAwait(false);
+                return Math.Min(number, sourceText.Length);
             }
             else
             {
@@ -226,10 +236,8 @@ public static int GetContextPosition(CompletionItem item)
             }
         }
 
-        public static int GetDescriptionPosition(CompletionItem item)
-        {
-            return GetContextPosition(item);
-        }
+        public static Task<int> GetDescriptionPositionAsync(Document document, CompletionItem item, CancellationToken cancellationToken)
+            => GetContextPositionAsync(document, item, cancellationToken);
 
         public static string GetInsertionText(CompletionItem item)
         {
@@ -293,11 +301,12 @@ internal static string GetSymbolName(CompletionItem item)
             return null;
         }
 
-        public static async Task<CompletionDescription> GetDescriptionAsync(CompletionItem item, ImmutableArray<ISymbol> symbols, Document document, SemanticModel semanticModel, CancellationToken cancellationToken)
+        public static async Task<CompletionDescription> GetDescriptionAsync(
+            CompletionItem item, ImmutableArray<ISymbol> symbols, Document document, SemanticModel semanticModel, CancellationToken cancellationToken)
         {
             var workspace = document.Project.Solution.Workspace;
 
-            var position = SymbolCompletionItem.GetDescriptionPosition(item);
+            var position = await SymbolCompletionItem.GetDescriptionPositionAsync(document, item, cancellationToken).ConfigureAwait(false);
             var supportedPlatforms = SymbolCompletionItem.GetSupportedPlatforms(item, workspace);
 
             var contextDocument = FindAppropriateDocumentForDescriptionContext(document, supportedPlatforms);