Query: Distinct GroupBy fails for InMemory

[smitpatel]

Query

        [ConditionalFact]
        public virtual void Select_Distinct_GroupBy()
        {
            AssertQuery<Order>(
                os => os.Select(o => new { o.CustomerID, o.EmployeeID }).OrderBy(a => a.EmployeeID).Distinct().GroupBy(o => o.CustomerID),
                elementSorter: GroupingSorter<string, object>(),
                elementAsserter: GroupingAsserter<string, dynamic>(d => d.EmployeeID));
        }

Fails in assertion
Query Plan

Output from Microsoft.EntityFrameworkCore.Query.SimpleQueryInMemoryTest.Select_Distinct_GroupBy:
  Entity Framework Core 2.1.0-preview1 initialized 'NorthwindContext' using provider 'Microsoft.EntityFrameworkCore.InMemory' with options: SensitiveDataLoggingEnabled StoreName=Northwind 
  Compiling query model: 
  '(from Order o in DbSet<Order>
  order by [o].EmployeeID asc
  select new <>f__AnonymousType273<string, Nullable<int>>(
      [o].CustomerID, 
      [o].EmployeeID
  ))
  .Distinct()
  .GroupBy([o].CustomerID, new <>f__AnonymousType273`2(CustomerID = [o].CustomerID, EmployeeID = [o].EmployeeID))'
  Optimized query model: 
  '(from Order o in DbSet<Order>
  order by [o].EmployeeID asc
  select new <>f__AnonymousType273<string, Nullable<int>>(
      [o].CustomerID, 
      [o].EmployeeID
  ))
  .Distinct()
  .GroupBy([o].CustomerID, new <>f__AnonymousType273`2(CustomerID = [o].CustomerID, EmployeeID = [o].EmployeeID))'
  (QueryContext queryContext) => IEnumerable<IGrouping<string, <>f__AnonymousType273<string, Nullable<int>>>> _InterceptExceptions(
      source: IEnumerable<IGrouping<string, <>f__AnonymousType273<string, Nullable<int>>>> _GroupBy(
          source: IEnumerable<ValueBuffer> Distinct(IOrderedEnumerable<ValueBuffer> _OrderBy(
                  source: IEnumerable<ValueBuffer> ProjectionQuery(
                      queryContext: queryContext, 
                      entityType: EntityType: Order), 
                  expression: (ValueBuffer o) => Nullable<int> TryReadValue(o, 2, Order.EmployeeID), 
                  orderingDirection: Asc)), 
          keySelector: (ValueBuffer o) => string TryReadValue(o, 1, Order.CustomerID), 
          elementSelector: (ValueBuffer o) => new <>f__AnonymousType273<string, Nullable<int>>(
              string TryReadValue(o, 1, Order.CustomerID), 
              Nullable<int> TryReadValue(o, 2, Order.EmployeeID)
          )), 
      contextType: TestModels.Northwind.NorthwindContext, 
      logger: DiagnosticsLogger<Query>, 
      queryContext: queryContext)

The issue is Distinct is being applied on ValueBuffers which is not going work hence we generate duplicate entries in grouping. The root cause is we are optimizing away the selector in EntityQueryModelVisitor.VisitSelectClause to skip for GroupBy or All result operator. But we cannot do that if there are other result operators.

Disabling test for inmemory for now.