Completion missing members of lambda parameter in fault tolerance case (#34312)

src/EditorFeatures/Test2/IntelliSense/CSharpCompletionCommandHandlerTests.vb

@@ -4651,6 +4651,239 @@ class C
             End Using
         End Function
 
+        Private Shared Function CreateThenIncludeTestCode(lambdaExpressionString As String, methodsDeclarationString As String) As XElement
+            Dim template = "<Document><![CDATA[
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Linq.Expressions;
+
+namespace ThenIncludeIntellisenseBug
+{
+    class Program
+    {
+        static void Main(string[] args)
+        {
+            var registrations = new List<Registration>().AsQueryable();
+            var reg = registrations.Include(r => r.Activities).ThenInclude([1]);
+        }
+    }
+
+    internal class Registration
+    {
+        public ICollection<Activity> Activities { get; set; }
+    }
+
+    public class Activity
+    {
+        public Task Task { get; set; }
+    }
+
+    public class Task
+    {
+        public string Name { get; set; }
+    }
+
+    public interface IIncludableQueryable<out TEntity, out TProperty> : IQueryable<TEntity>
+    {
+    }
+
+    public static class EntityFrameworkQuerybleExtensions
+    {
+        public static IIncludableQueryable<TEntity, TProperty> Include<TEntity, TProperty>(
+            this IQueryable<TEntity> source,
+            Expression<Func<TEntity, TProperty>> navigationPropertyPath)
+         where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }
+
+        [2]
+    }
+}]]></Document>"
+
+            Return XElement.Parse(template.Replace("[1]", lambdaExpressionString).Replace("[2]", methodsDeclarationString))
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenInclude(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateCSharpTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "b => b$$",
+                "
+    public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+        this IIncludableQueryable<TEntity, ICollection<TPreviousProperty>> source,
+        Expression<Func<TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }
+
+    public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+        this IIncludableQueryable<TEntity, TPreviousProperty> source,
+        Expression<Func<TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsContainAll({"Task", "FirstOrDefault"})
+            End Using
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenIncludeNoExpression(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateCSharpTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "b => b$$",
+                "
+        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+            this IIncludableQueryable<TEntity, ICollection<TPreviousProperty>> source,
+            Func<TPreviousProperty, TProperty> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }
+
+        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+            this IIncludableQueryable<TEntity, TPreviousProperty> source,
+            Func<TPreviousProperty, TProperty> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsContainAll({"Task", "FirstOrDefault"})
+            End Using
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenIncludeSecondArgument(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateCSharpTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "0, b => b$$",
+                "
+        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+            this IIncludableQueryable<TEntity, ICollection<TPreviousProperty>> source,
+            int a,
+            Expression<Func<TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }
+
+        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+            this IIncludableQueryable<TEntity, TPreviousProperty> source,
+            int a,
+            Expression<Func<TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsContainAll({"Task", "FirstOrDefault"})
+            End Using
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenIncludeSecondArgumentAndMultiArgumentLambda(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateCSharpTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "0, (a,b,c) => c$$)",
+                "
+        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+            this IIncludableQueryable<TEntity, ICollection<TPreviousProperty>> source,
+            int a,
+            Expression<Func<string, string, TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }
+
+        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+            this IIncludableQueryable<TEntity, TPreviousProperty> source,
+            int a,
+            Expression<Func<string, string, TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsContainAll({"Task", "FirstOrDefault"})
+            End Using
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenIncludeSecondArgumentNoOverlap(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateCSharpTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "b => b.Task, b =>b$$",
+                "
+        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+            this IIncludableQueryable<TEntity, ICollection<TPreviousProperty>> source,
+            Expression<Func<TPreviousProperty, TProperty>> navigationPropertyPath,
+            Expression<Func<TPreviousProperty, TProperty>> anotherNavigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }
+
+        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+            this IIncludableQueryable<TEntity, TPreviousProperty> source,
+            Expression<Func<TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }
+"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsDoNotContainAny({"FirstOrDefault"})
+                state.AssertCompletionItemsContainAll({"Task"})
+            End Using
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenIncludeSecondArgumentAndMultiArgumentLambdaWithNoLambdaOverlap(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateCSharpTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "0, (a,b,c) => c$$",
+                "
+        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+            this IIncludableQueryable<TEntity, ICollection<TPreviousProperty>> source,
+            int a,
+            Expression<Func<string, TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }
+
+        public static IIncludableQueryable<TEntity, TProperty> ThenInclude<TEntity, TPreviousProperty, TProperty>(
+            this IIncludableQueryable<TEntity, TPreviousProperty> source,
+            int a,
+            Expression<Func<string, string, TPreviousProperty, TProperty>> navigationPropertyPath) where TEntity : class
+        {
+            return default(IIncludableQueryable<TEntity, TProperty>);
+        }
+"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsContainAll({"FirstOrDefault"})
+                state.AssertCompletionItemsDoNotContainAny({"Task"})
+            End Using
+        End Function
+
         Private Class MultipleChangeCompletionProvider
             Inherits CompletionProvider
 

src/EditorFeatures/Test2/IntelliSense/VisualBasicCompletionCommandHandlerTests.vb

@@ -3143,6 +3143,231 @@ End Class
             End Using
         End Function
 
+        Private Shared Function CreateThenIncludeTestCode(lambdaExpressionString As String, methodsDeclarationString As String) As XElement
+            Dim template = "<Document><![CDATA[
+Imports System.Linq.Expressions
+
+Namespace ThenIncludeIntellisenseBug
+
+    Class Program
+        Shared Sub Main(args As String())
+            Dim registrations = New List(Of Registration)().AsQueryable()
+            Dim reg = registrations.Include(Function(r) r.Activities).ThenInclude([1])
+        End Sub
+    End Class
+
+    Friend Class Registration
+        Public Property Activities As ICollection(Of Activity)
+    End Class
+
+    Public Class Activity
+        Public Property Task As Task
+    End Class
+
+    Public Class Task
+        Public Property Name As String
+    End Class
+
+    Public Interface IIncludableQueryable(Of Out TEntity, Out TProperty)
+        Inherits IQueryable(Of TEntity)
+    End Interface
+
+    Public Module EntityFrameworkQuerybleExtensions
+        <System.Runtime.CompilerServices.Extension>
+        Public Function Include(Of TEntity, TProperty)(
+                                                      source As IQueryable(Of TEntity), 
+                                                      navigationPropertyPath As Expression(Of Func(Of TEntity, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function
+
+[2]
+
+    End Module
+End Namespace
+]]></Document>"
+
+            Return XElement.Parse(template.Replace("[1]", lambdaExpressionString).Replace("[2]", methodsDeclarationString))
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenInclude(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateVisualBasicTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "Function(b) b$$",
+                "
+        <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, ICollection(Of TPreviousProperty)), 
+                                                                             navigationPropertyPath As Expression(Of Func(Of TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function
+
+        <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, TPreviousProperty), 
+                                                                             navigationPropertyPath As Expression(Of Func(Of TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function
+"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsContainAll({"Task", "FirstOrDefault"})
+            End Using
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenIncludeNoExpression(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateVisualBasicTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "Function(b) b$$",
+                "
+        <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, ICollection(Of TPreviousProperty)), 
+                                                                             navigationPropertyPath As Func(Of TPreviousProperty, TProperty)) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function
+
+        <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, TPreviousProperty), 
+                                                                             navigationPropertyPath As Func(Of TPreviousProperty, TProperty)) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsContainAll({"Task", "FirstOrDefault"})
+            End Using
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenIncludeSecondArgument(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateVisualBasicTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "0, Function(b) b$$",
+                "
+        <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, ICollection(Of TPreviousProperty)), 
+                                                                             a as Integer,
+                                                                             navigationPropertyPath As Expression(Of Func(Of TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function
+
+        <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, TPreviousProperty),
+                                                                             a as Integer,
+                                                                             navigationPropertyPath As Expression(Of Func(Of TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function
+"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsContainAll({"Task", "FirstOrDefault"})
+            End Using
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenIncludeSecondArgumentAndMultiArgumentLambda(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateVisualBasicTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "0, Function(a, b, c) c$$",
+                "<System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, ICollection(Of TPreviousProperty)), 
+                                                                             a as Integer,
+                                                                             navigationPropertyPath As Expression(Of Func(Of string, string, TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function
+
+        <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, TPreviousProperty), 
+                                                                             a as Integer,
+                                                                             navigationPropertyPath As Expression(Of Func(Of string, string, TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsContainAll({"Task", "FirstOrDefault"})
+            End Using
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenIncludeSecondArgumentNoOverlap(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateVisualBasicTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "Function(b) b.Task, Function(b) b$$",
+                "        
+        <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, ICollection(Of TPreviousProperty)), 
+                                                                             navigationPropertyPath As Expression(Of Func(Of TPreviousProperty, TProperty)),
+                                                                             anotherNavigationPropertyPath As Expression(Of Func(Of TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function
+
+        <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, TPreviousProperty), 
+                                                                             navigationPropertyPath As Expression(Of Func(Of TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsDoNotContainAny({"FirstOrDefault"})
+                state.AssertCompletionItemsContainAll({"Task"})
+            End Using
+        End Function
+
+        <MemberData(NameOf(AllCompletionImplementations))>
+        <WpfTheory, Trait(Traits.Feature, Traits.Features.Completion)>
+        Public Async Function TestThenIncludeSecondArgumentAndMultiArgumentLambdaWithNoLambdaOverlap(completionImplementation As CompletionImplementation) As Task
+            Using state = TestStateFactory.CreateVisualBasicTestState(
+                completionImplementation,
+                CreateThenIncludeTestCode(
+                "0, Function(a, b, c) c$$",
+                "
+       <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, ICollection(Of TPreviousProperty)), 
+                                                                             a as Integer,
+                                                                             navigationPropertyPath As Expression(Of Func(Of string, TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function
+
+        <System.Runtime.CompilerServices.Extension>
+        Public Function ThenInclude(Of TEntity, TPreviousProperty, TProperty)(
+                                                                             source As IIncludableQueryable(Of TEntity, TPreviousProperty),
+                                                                             a as Integer,
+                                                                             navigationPropertyPath As Expression(Of Func(Of string, string, TPreviousProperty, TProperty))) As IIncludableQueryable(Of TEntity, TProperty)
+            Return Nothing
+        End Function
+"))
+
+                state.SendTypeChars(".")
+                Await state.AssertCompletionSession()
+                state.AssertCompletionItemsContainAll({"FirstOrDefault"})
+                state.AssertCompletionItemsDoNotContainAny({"Task"})
+            End Using
+        End Function
+
         <ExportLanguageService(GetType(ISnippetInfoService), LanguageNames.VisualBasic), System.Composition.Shared>
         Friend Class MockSnippetInfoService
             Implements ISnippetInfoService

src/Workspaces/CSharp/Portable/LanguageServices/CSharpSyntaxFactsService.cs

@@ -1431,8 +1431,8 @@ public bool IsCharacterLiteral(SyntaxToken token)
         public SeparatedSyntaxList<SyntaxNode> GetArgumentsOfInvocationExpression(SyntaxNode invocationExpression)
             => GetArgumentsOfArgumentList((invocationExpression as InvocationExpressionSyntax)?.ArgumentList);
 
-        public SeparatedSyntaxList<SyntaxNode> GetArgumentsOfObjectCreationExpression(SyntaxNode invocationExpression)
-            => GetArgumentsOfArgumentList((invocationExpression as ObjectCreationExpressionSyntax)?.ArgumentList);
+        public SeparatedSyntaxList<SyntaxNode> GetArgumentsOfObjectCreationExpression(SyntaxNode objectCreationExpression)
+            => GetArgumentsOfArgumentList((objectCreationExpression as ObjectCreationExpressionSyntax)?.ArgumentList);
 
         public SeparatedSyntaxList<SyntaxNode> GetArgumentsOfArgumentList(SyntaxNode argumentList)
             => (argumentList as BaseArgumentListSyntax)?.Arguments ?? default(SeparatedSyntaxList<SyntaxNode>);

src/Workspaces/CSharp/Portable/Recommendations/CSharpRecommendationServiceRunner.cs

@@ -386,6 +386,7 @@ private ImmutableArray<ISymbol> GetSymbolsOffOfConditionalReceiver(ExpressionSyn
             var excludeInstance = false;
             var excludeStatic = false;
             var symbol = leftHandBinding.GetAnySymbol();
+            ImmutableArray<ISymbol> symbols = default;
 
             if (symbol != null)
             {
@@ -448,6 +449,8 @@ private ImmutableArray<ISymbol> GetSymbolsOffOfConditionalReceiver(ExpressionSyn
 
                         excludeStatic = true;
 
+                        symbols = GetSymbols(parameter, originalExpression.SpanStart);
+
                         // case:
                         //    base.|
                         if (parameter.IsThis && !object.Equals(parameter.Type, container))
@@ -482,11 +485,14 @@ private ImmutableArray<ISymbol> GetSymbolsOffOfConditionalReceiver(ExpressionSyn
                 excludeStatic = false;
             }
 
-            var symbols = GetSymbols(
-                container,
-                position: originalExpression.SpanStart,
-                excludeInstance: excludeInstance,
-                useBaseReferenceAccessibility: useBaseReferenceAccessibility);
+            if (symbols.IsDefault)
+            {
+                symbols = GetSymbols(
+                    container,
+                    position: originalExpression.SpanStart,
+                    excludeInstance: excludeInstance,
+                    useBaseReferenceAccessibility: useBaseReferenceAccessibility);
+            }
 
             // If we're showing instance members, don't include nested types
             return excludeStatic

src/Workspaces/Core/Portable/Recommendations/AbstractRecommendationService.cs

@@ -6,6 +6,7 @@
 using System.Linq;
 using System.Threading;
 using System.Threading.Tasks;
+using Microsoft.CodeAnalysis.LanguageServices;
 using Microsoft.CodeAnalysis.Options;
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Shared.Extensions.ContextQuery;

src/Workspaces/Core/Portable/Recommendations/AbstractRecommendationServiceRunner.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.Immutable;
 using System.Linq;
+using System.Linq.Expressions;
 using System.Threading;
+using Microsoft.CodeAnalysis.LanguageServices;
+using Microsoft.CodeAnalysis.PooledObjects;
 using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Shared.Extensions.ContextQuery;
 
@@ -16,8 +20,8 @@ internal abstract class AbstractRecommendationServiceRunner<TSyntaxContext>
         protected readonly CancellationToken _cancellationToken;
 
         public AbstractRecommendationServiceRunner(
-            TSyntaxContext context, 
-            bool filterOutOfScopeLocals, 
+            TSyntaxContext context,
+            bool filterOutOfScopeLocals,
             CancellationToken cancellationToken)
         {
             _context = context;
@@ -27,6 +31,121 @@ internal abstract class AbstractRecommendationServiceRunner<TSyntaxContext>
 
         public abstract ImmutableArray<ISymbol> GetSymbols();
 
+        // This code is to help give intellisense in the following case: 
+        // query.Include(a => a.SomeProperty).ThenInclude(a => a.
+        // where there are more than one overloads of ThenInclude accepting different types of parameters.
+        protected ImmutableArray<ISymbol> GetSymbols(IParameterSymbol parameter, int position)
+        {
+            // Starting from a. in the example, looking for a => a.
+            if (!(parameter.ContainingSymbol is IMethodSymbol containingMethod &&
+                containingMethod.MethodKind == MethodKind.AnonymousFunction))
+            {
+                return default;
+            }
+
+            // Cannot proceed without DeclaringSyntaxReferences.
+            // We expect that there is a single DeclaringSyntaxReferences in the scenario.
+            // If anything changes on the compiler side, the approach should be revised.
+            if (containingMethod.DeclaringSyntaxReferences.Length != 1)
+            {
+                return default;
+            }
+
+            var syntaxFactsService = _context.Workspace.Services.GetLanguageServices(_context.SemanticModel.Language).GetService<ISyntaxFactsService>();
+
+            // Check that a => a. belongs to an invocation.
+            // Find its' ordinal in the invocation, e.g. ThenInclude(a => a.Something, a=> a.
+            var lambdaSyntax = containingMethod.DeclaringSyntaxReferences.Single().GetSyntax(_cancellationToken);
+            if (!(syntaxFactsService.IsAnonymousFunction(lambdaSyntax) &&
+                syntaxFactsService.IsArgument(lambdaSyntax.Parent) &&
+                syntaxFactsService.IsInvocationExpression(lambdaSyntax.Parent.Parent.Parent)))
+            {
+                return default;
+            }
+
+            var invocationExpression = lambdaSyntax.Parent.Parent.Parent;
+            var arguments = syntaxFactsService.GetArgumentsOfInvocationExpression(invocationExpression);
+            var ordinalInInvocation = arguments.IndexOf(lambdaSyntax.Parent);
+
+            var invocation = _context.SemanticModel.GetSymbolInfo(invocationExpression, _cancellationToken);
+            var candidateSymbols = invocation.GetAllSymbols();
+
+            // parameter.Ordinal is the ordinal within (a,b,c) => b.
+            // For candidate symbols of (a,b,c) => b., get types of all possible b.
+            var parameterTypeSymbols = GetTypeSymbols(candidateSymbols, ordinalInInvocation: ordinalInInvocation, ordinalInLambda: parameter.Ordinal);
+
+            // For each type of b., return all suitable members.
+            return parameterTypeSymbols
+                .SelectMany(parameterTypeSymbol => GetSymbols(parameterTypeSymbol, position, excludeInstance: false, useBaseReferenceAccessibility: false))
+                .ToImmutableArray();
+        }
+
+        /// <summary>
+        /// Tries to get a type of its' <paramref name="ordinalInLambda"/> lambda parameter of <paramref name="ordinalInInvocation"/> argument for each candidate symbol.
+        /// </summary>
+        /// <param name="candidateSymbols">symbols corresponding to <see cref="Expression{Func}"/> or <see cref="Func{some_args, TResult}"/>
+        /// Here, some_args can be multi-variables lambdas as well, e.g. f((a,b) => a+b, (a,b,c)=>a*b*c.Length)
+        /// </param>
+        /// <param name="ordinalInInvocation">ordinal of the arguments of function: (a,b) or (a,b,c) in the example above</param>
+        /// <param name="ordinalInLambda">ordinal of the lambda parameters, e.g. a, b or c.</param>
+        /// <returns></returns>
+        private ImmutableArray<ITypeSymbol> GetTypeSymbols(ImmutableArray<ISymbol> candidateSymbols, int ordinalInInvocation, int ordinalInLambda)
+        {
+            var expressionSymbol = _context.SemanticModel.Compilation.GetTypeByMetadataName(typeof(Expression<>).FullName);
+            var funcSymbol = _context.SemanticModel.Compilation.GetTypeByMetadataName(typeof(Func<>).FullName);
+            // We cannot help if semantic model is corrupted or incomplete (e.g. during solution loading) and those symbols are not loaded. 
+            // Just bail out.
+            if (expressionSymbol == null || funcSymbol == null)
+            {
+                return default;
+            }
+
+            var builder = ArrayBuilder<ITypeSymbol>.GetInstance();
+
+            foreach (var candidateSymbol in candidateSymbols)
+            {
+                if (candidateSymbol is IMethodSymbol method)
+                {
+                    if (method.Parameters.Length > ordinalInInvocation)
+                    {
+                        var methodParameterSymbool = method.Parameters[ordinalInInvocation];
+                        var type = methodParameterSymbool.Type;
+                        // If type is <see cref="Expression{TDelegate}"/>, ignore <see cref="Expression"/> and use TDelegate.
+                        if (type is INamedTypeSymbol expressionSymbolNamedTypeCandidate &&
+                            Equals(expressionSymbolNamedTypeCandidate.OriginalDefinition, expressionSymbol))
+                        {
+                            var allTypeArguments = type.GetAllTypeArguments();
+                            if (allTypeArguments.Length != 1)
+                            {
+                                continue;
+                            }
+
+                            type = allTypeArguments[0];
+                        }
+
+                        // If type is <see cref="Func{TSomeArguments, TResult}"/>, extract TSomeArguments 
+                        // and find the type of thee argument corresponding to the ordinal.
+                        if (type is INamedTypeSymbol funcSymbolNamedTypeCandidate &&
+                            Equals(funcSymbolNamedTypeCandidate.Name, funcSymbol.Name) &&
+                            Equals(funcSymbolNamedTypeCandidate.ContainingNamespace, funcSymbol.ContainingNamespace))
+                        {
+                            var allTypeArguments = type.GetAllTypeArguments();
+                            if (allTypeArguments.Length < ordinalInLambda)
+                            {
+                                continue;
+                            }
+
+                            type = allTypeArguments[ordinalInLambda];
+                        }
+
+                        builder.Add(type);
+                    }
+                }
+            }
+
+            return builder.ToImmutableAndFree().Distinct();
+        }
+
         protected ImmutableArray<ISymbol> GetSymbolsForNamespaceDeclarationNameContext<TNamespaceDeclarationSyntax>()
             where TNamespaceDeclarationSyntax : SyntaxNode
         {

src/Workspaces/VisualBasic/Portable/Recommendations/VisualBasicRecommendationServiceRunner.vb

@@ -12,7 +12,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
         Inherits AbstractRecommendationServiceRunner(Of VisualBasicSyntaxContext)
 
         Public Sub New(context As VisualBasicSyntaxContext, filterOutOfScopeLocals As Boolean, cancellationToken As CancellationToken)
-
             MyBase.New(context, filterOutOfScopeLocals, cancellationToken)
         End Sub
 
@@ -54,7 +53,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
         End Function
 
         Private Function IsWritableFieldOrLocal(symbol As ISymbol) As Boolean
-
             If symbol.Kind() = SymbolKind.Field Then
                 Dim field = DirectCast(symbol, IFieldSymbol)
                 Return Not field.IsReadOnly AndAlso Not field.IsConst
@@ -69,12 +67,10 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
         End Function
 
         Private Function GetSymbolsForGlobalStatementContext() As ImmutableArray(Of ISymbol)
-
             Return _context.SemanticModel.LookupSymbols(_context.TargetToken.Span.End)
         End Function
 
         Private Function GetUnqualifiedSymbolsForQueryIntoContext() As ImmutableArray(Of ISymbol)
-
             Dim symbols = _context.SemanticModel _
                 .LookupSymbols(_context.TargetToken.SpanStart, includeReducedExtensionMethods:=True)
 
@@ -89,7 +85,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
         End Function
 
         Private Function GetUnqualifiedSymbolsForRaiseEvent() As ImmutableArray(Of ISymbol)
-
             Dim containingType = _context.SemanticModel.GetEnclosingSymbol(_context.Position, _cancellationToken).ContainingType
 
             Return _context.SemanticModel _
@@ -98,13 +93,11 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
         End Function
 
         Private Function GetUnqualifiedSymbolsForType() As ImmutableArray(Of ISymbol)
-
             Dim symbols = _context.SemanticModel.LookupNamespacesAndTypes(_context.TargetToken.SpanStart)
             Return FilterToValidAccessibleSymbols(symbols)
         End Function
 
         Private Function GetUnqualifiedSymbolsForExpressionOrStatementContext() As ImmutableArray(Of ISymbol)
-
             Dim lookupPosition = _context.TargetToken.SpanStart
             If _context.FollowsEndOfStatement Then
                 lookupPosition = _context.Position
@@ -124,7 +117,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
             ' contexts, except within GetType
             If Not _context.TargetToken.IsKind(SyntaxKind.OpenParenToken) OrElse
                     Not _context.TargetToken.Parent.IsKind(SyntaxKind.GetTypeExpression) Then
-
                 symbols = symbols.WhereAsArray(Function(s) Not IsInEligibleDelegate(s))
             End If
 
@@ -133,7 +125,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
         End Function
 
         Private Function IsInEligibleDelegate(s As ISymbol) As Boolean
-
             If s.IsDelegateType() Then
                 Dim typeSymbol = DirectCast(s, ITypeSymbol)
                 Return typeSymbol.SpecialType <> SpecialType.System_Delegate
@@ -143,7 +134,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
         End Function
 
         Private Function GetSymbolsForQualifiedNameSyntax(node As QualifiedNameSyntax) As ImmutableArray(Of ISymbol)
-
             ' We're in a name-only context, since if we were an expression we'd be a
             ' MemberAccessExpressionSyntax. Thus, let's do other namespaces and types.
             Dim leftHandSymbolInfo = _context.SemanticModel.GetSymbolInfo(node.Left, _cancellationToken)
@@ -173,7 +163,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
         End Function
 
         Private Function GetSymbolsForMemberAccessExpression(node As MemberAccessExpressionSyntax) As ImmutableArray(Of ISymbol)
-
             Dim leftExpression = node.GetExpressionOfMemberAccessExpression(allowImplicitTarget:=True)
             If leftExpression Is Nothing Then
                 Return ImmutableArray(Of ISymbol).Empty
@@ -207,6 +196,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
             End If
 
             Dim couldBeMergedNamespace = False
+            Dim symbols As ImmutableArray(Of ISymbol) = Nothing
 
             If leftHandSymbolInfo.Symbol IsNot Nothing Then
 
@@ -231,6 +221,8 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
                             excludeShared = False
                         End If
 
+                        symbols = GetSymbols(parameter, node.SpanStart)
+
                         ' case:
                         '    MyBase.
                         If parameter.IsMe AndAlso parameter.Type IsNot container Then
@@ -281,15 +273,16 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
             End If
 
             Dim position = node.SpanStart
-            Dim symbols As ImmutableArray(Of ISymbol)
-            If couldBeMergedNamespace Then
-                symbols = leftHandSymbolInfo.CandidateSymbols _
+            If symbols.IsDefault Then
+                If couldBeMergedNamespace Then
+                    symbols = leftHandSymbolInfo.CandidateSymbols _
                     .OfType(Of INamespaceSymbol) _
                     .SelectMany(Function(n) LookupSymbolsInContainer(n, position, excludeInstance)) _
                     .ToImmutableArray()
-            Else
-                symbols = GetSymbols(
-                    container, position:=position, excludeInstance:=excludeInstance, useBaseReferenceAccessibility:=useBaseReferenceAccessibility)
+                Else
+                    symbols = GetSymbols(
+                        container, position:=position, excludeInstance:=excludeInstance, useBaseReferenceAccessibility:=useBaseReferenceAccessibility)
+                End If
             End If
 
             If excludeShared Then
@@ -349,7 +342,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
         End Function
 
         Private Function GetEnclosingCtor(node As MemberAccessExpressionSyntax) As IMethodSymbol
-
             Dim symbol = _context.SemanticModel.GetEnclosingSymbol(node.SpanStart, _cancellationToken)
 
             While symbol IsNot Nothing
@@ -363,7 +355,6 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
         End Function
 
         Private Function FilterToValidAccessibleSymbols(symbols As ImmutableArray(Of ISymbol)) As ImmutableArray(Of ISymbol)
-
             ' If this is an Inherits or Implements statement, we filter out symbols which do not recursively contain accessible, valid types.
             Dim inheritsContext = IsInheritsStatementContext(_context.TargetToken)
             Dim implementsContext = IsImplementsStatementContext(_context.TargetToken)
@@ -372,7 +363,7 @@ Namespace Microsoft.CodeAnalysis.VisualBasic.Recommendations
 
                 Dim typeBlock = _context.TargetToken.Parent?.FirstAncestorOrSelf(Of TypeBlockSyntax)()
                 If typeBlock IsNot Nothing Then
-                    Dim typeOrAssemblySymbol As ISymbol = _context.SemanticModel.GetDeclaredSymbol(typeBlock)
+                    Dim typeOrAssemblySymbol As ISymbol = _context.SemanticModel.GetDeclaredSymbol(typeBlock, _cancellationToken)
                     If typeOrAssemblySymbol Is Nothing Then
                         typeOrAssemblySymbol = _context.SemanticModel.Compilation.Assembly
                     End If