Make ToAsyncEnumerable() set the QueryStatistics.TotalResult

Note: TotalResult will not be available before enumeration of
the result started!

src/LinqTests/Operators/async_enumerable.cs

@@ -41,4 +41,31 @@ public async Task query_to_async_enumerable()
     }
 
     #endregion
+
+    [Fact]
+    public async Task query_to_async_enumerable_with_query_statistics()
+    {
+        var targets = Target.GenerateRandomData(20).ToArray();
+        await theStore.BulkInsertAsync(targets);
+
+        var ids = new List<Guid>();
+
+        var results = theSession.Query<Target>()
+            .Stats(out var stats)
+            .ToAsyncEnumerable();
+
+        stats.TotalResults.ShouldBe(0);
+
+        await foreach (var target in results)
+        {
+            stats.TotalResults.ShouldBe(20);
+            ids.Add(target.Id);
+        }
+
+        ids.Count.ShouldBe(20);
+        foreach (var target in targets)
+        {
+            ids.ShouldContain(target.Id);
+        }
+    }
 }

src/Marten/Linq/MartenLinqQueryProvider.cs

@@ -8,7 +8,6 @@
 using System.Threading.Tasks;
 using Marten.Exceptions;
 using Marten.Internal.Sessions;
-using Marten.Linq.Includes;
 using Marten.Linq.Parsing;
 using Marten.Linq.QueryHandlers;
 using Marten.Linq.Selectors;
@@ -153,7 +152,7 @@ public T ExecuteHandler<T>(IQueryHandler<T> handler)
 
 
     public async IAsyncEnumerable<T> ExecuteAsyncEnumerable<T>(Expression expression,
-        [EnumeratorCancellation] CancellationToken token)
+        MartenLinqQueryProvider martenProvider, [EnumeratorCancellation] CancellationToken token)
     {
         var parser = new LinqQueryParser(this, _session, expression);
         var statements = parser.BuildStatements();
@@ -166,8 +165,13 @@ public async IAsyncEnumerable<T> ExecuteAsyncEnumerable<T>(Expression expression
         var cmd = _session.BuildCommand(statement);
 
         await using var reader = await _session.ExecuteReaderAsync(cmd, token).ConfigureAwait(false);
+        var totalRowsColumnIndex = martenProvider.Statistics != null ? reader.GetOrdinal("total_rows") : -1;
         while (await reader.ReadAsync(token).ConfigureAwait(false))
         {
+            if (martenProvider.Statistics != null)
+            {
+                martenProvider.Statistics.TotalResults = await reader.GetFieldValueAsync<int>(totalRowsColumnIndex, token).ConfigureAwait(false);
+            }
             yield return await selector.ResolveAsync(reader, token).ConfigureAwait(false);
         }
     }

src/Marten/Linq/MartenLinqQueryable.cs

@@ -150,7 +150,7 @@ public async Task<IReadOnlyList<TResult>> ToListAsync<TResult>(CancellationToken
 
     public IAsyncEnumerable<T> ToAsyncEnumerable(CancellationToken token = default)
     {
-        return MartenProvider.ExecuteAsyncEnumerable<T>(Expression, token);
+        return MartenProvider.ExecuteAsyncEnumerable<T>(Expression, MartenProvider, token);
     }
 
     public Task<bool> AnyAsync(CancellationToken token)