From 8fb8592fcf5637eb4bc04c1fced5e585b821d445 Mon Sep 17 00:00:00 2001
From: David Wengier <david.wengier@microsoft.com>
Date: Fri, 24 Dec 2021 16:14:27 +1100
Subject: [PATCH] Fix event hookup at the end of a document (#58477)

---
 .../EventHookup/EventHookupSessionManager.cs  | 24 +++++++++++++-
 ...HookupSessionManager_EventHookupSession.cs |  5 ++-
 .../EventHookupCommandHandlerTests.cs         | 31 +++++++++++++++++++
 3 files changed, 58 insertions(+), 2 deletions(-)

diff --git a/src/EditorFeatures/CSharp/EventHookup/EventHookupSessionManager.cs b/src/EditorFeatures/CSharp/EventHookup/EventHookupSessionManager.cs
index 570b58457add4..de8b8614f8726 100644
--- a/src/EditorFeatures/CSharp/EventHookup/EventHookupSessionManager.cs
+++ b/src/EditorFeatures/CSharp/EventHookup/EventHookupSessionManager.cs
@@ -50,7 +50,7 @@ internal void EventHookupFoundInSession(EventHookupSession analyzedSession)
             if (_toolTipPresenter == null &&
                 CurrentSession == analyzedSession &&
                 caretPoint.HasValue &&
-                analyzedSession.TrackingSpan.GetSpan(CurrentSession.TextView.TextSnapshot).Contains(caretPoint.Value))
+                IsCaretWithinSpanOrAtEnd(analyzedSession.TrackingSpan, analyzedSession.TextView.TextSnapshot, caretPoint.Value))
             {
                 // Create a tooltip presenter that stays alive, even when the user types, without tracking the mouse.
                 _toolTipPresenter = _toolTipService.CreatePresenter(analyzedSession.TextView,
@@ -80,6 +80,28 @@ internal void EventHookupFoundInSession(EventHookupSession analyzedSession)
             }
         }
 
+        private static bool IsCaretWithinSpanOrAtEnd(ITrackingSpan trackingSpan, ITextSnapshot textSnapshot, SnapshotPoint caretPoint)
+        {
+            var snapshotSpan = trackingSpan.GetSpan(textSnapshot);
+
+            // If the caret is within the span, then we want to show the tooltip
+            if (snapshotSpan.Contains(caretPoint))
+            {
+                return true;
+            }
+
+            // Otherwise if the span is empty, and at the end of the file, and the caret
+            // is also at the end of the file, then show the tooltip.
+            if (snapshotSpan.IsEmpty &&
+                snapshotSpan.Start.Position == caretPoint.Position &&
+                caretPoint.Position == textSnapshot.Length)
+            {
+                return true;
+            }
+
+            return false;
+        }
+
         internal void BeginSession(
             EventHookupCommandHandler eventHookupCommandHandler,
             ITextView textView,
diff --git a/src/EditorFeatures/CSharp/EventHookup/EventHookupSessionManager_EventHookupSession.cs b/src/EditorFeatures/CSharp/EventHookup/EventHookupSessionManager_EventHookupSession.cs
index e7f4f2bcbcfff..12dbd69c81d9e 100644
--- a/src/EditorFeatures/CSharp/EventHookup/EventHookupSessionManager_EventHookupSession.cs
+++ b/src/EditorFeatures/CSharp/EventHookup/EventHookupSessionManager_EventHookupSession.cs
@@ -114,7 +114,10 @@ public EventHookupSession(
                 {
                     var position = textView.GetCaretPoint(subjectBuffer).Value.Position;
                     _trackingPoint = textView.TextSnapshot.CreateTrackingPoint(position, PointTrackingMode.Negative);
-                    _trackingSpan = textView.TextSnapshot.CreateTrackingSpan(new Span(position, 1), SpanTrackingMode.EdgeInclusive);
+
+                    // If the caret is at the end of the document we just create an empty span
+                    var length = textView.TextSnapshot.Length > position + 1 ? 1 : 0;
+                    _trackingSpan = textView.TextSnapshot.CreateTrackingSpan(new Span(position, length), SpanTrackingMode.EdgeInclusive);
 
                     var asyncToken = asyncListener.BeginAsyncOperation(GetType().Name + ".Start");
 
diff --git a/src/EditorFeatures/CSharpTest/EventHookup/EventHookupCommandHandlerTests.cs b/src/EditorFeatures/CSharpTest/EventHookup/EventHookupCommandHandlerTests.cs
index 2cf1fe41ca81a..0d57db3ad040d 100644
--- a/src/EditorFeatures/CSharpTest/EventHookup/EventHookupCommandHandlerTests.cs
+++ b/src/EditorFeatures/CSharpTest/EventHookup/EventHookupCommandHandlerTests.cs
@@ -1042,6 +1042,37 @@ public async Task EventHookupInTopLevelCode()
 
 System.AppDomain.CurrentDomain.UnhandledException += CurrentDomain_UnhandledException;
 
+void CurrentDomain_UnhandledException(object sender, System.UnhandledExceptionEventArgs e)
+{
+    throw new System.NotImplementedException();
+}";
+            testState.AssertCodeIs(expectedCode);
+        }
+
+        [WpfFact, Trait(Traits.Feature, Traits.Features.EventHookup)]
+        public async Task EventHookupAtEndOfDocument()
+        {
+            var markup = @"
+
+System.AppDomain.CurrentDomain.UnhandledException +$$";
+            using var testState = EventHookupTestState.CreateTestState(markup);
+            testState.SendTypeChar('=');
+
+            await testState.WaitForAsynchronousOperationsAsync();
+            testState.AssertShowing("CurrentDomain_UnhandledException");
+
+            var expectedCode = @"
+
+System.AppDomain.CurrentDomain.UnhandledException +=";
+            testState.AssertCodeIs(expectedCode);
+
+            testState.SendTab();
+            await testState.WaitForAsynchronousOperationsAsync();
+
+            expectedCode = @"
+
+System.AppDomain.CurrentDomain.UnhandledException += CurrentDomain_UnhandledException;
+
 void CurrentDomain_UnhandledException(object sender, System.UnhandledExceptionEventArgs e)
 {
     throw new System.NotImplementedException();