Fix closing unpooled connection with transaction scope (#4964)

Fixes #4963

(cherry picked from commit bceb9e1)

src/Npgsql/NpgsqlConnection.cs

@@ -856,13 +856,10 @@ async Task CloseAsync(bool async)
 
                 connector.Connection = null;
 
-                // If pooled, close the connection and disconnect it from the resource manager but leave the
-                // connector in an enlisted pending list in the pool. If another connection is opened within
+                // Close the connection and disconnect it from the resource manager but leave the
+                // connector in an enlisted pending list in the data source. If another connection is opened within
                 // the same transaction scope, we will reuse this connector to avoid escalating to a distributed
                 // transaction
-                // If a *non-pooled* connection is being closed but is enlisted in an ongoing
-                // TransactionScope, we do nothing - simply detach the connector from the connection and leave
-                // it open. It will be closed when the TransactionScope is disposed.
                 _dataSource?.AddPendingEnlistedConnector(connector, EnlistedTransaction);
 
                 EnlistedTransaction = null;

src/Npgsql/UnpooledDataSource.cs

@@ -48,13 +48,4 @@ internal override void Return(NpgsqlConnector connector)
     }
 
     internal override void Clear() {}
-
-    internal override bool TryRentEnlistedPending(Transaction transaction, NpgsqlConnection connection,
-        [NotNullWhen(true)] out NpgsqlConnector? connector)
-    {
-        connector = null;
-        return false;
-    }
-
-    internal override bool TryRemovePendingEnlistedConnector(NpgsqlConnector connector, Transaction transaction) => false;
 }

test/Npgsql.Tests/DistributedTransactionTests.cs

@@ -111,37 +111,6 @@ public void Two_connections_with_failure()
         AssertNumberOfRows(adminConn, table, 0);
     }
 
-    [Test, IssueLink("https://github.com/npgsql/npgsql/issues/1737")]
-    public void Multiple_unpooled_connections_do_not_reuse()
-    {
-        var csb = new NpgsqlConnectionStringBuilder(ConnectionString)
-        {
-            Pooling = false,
-            Enlist = true
-        };
-
-        using var scope = new TransactionScope();
-
-        int processId;
-
-        using (var conn1 = OpenConnection(csb))
-        using (var cmd = new NpgsqlCommand("SELECT 1", conn1))
-        {
-            processId = conn1.ProcessID;
-            cmd.ExecuteNonQuery();
-        }
-
-        using (var conn2 = OpenConnection(csb))
-        using (var cmd = new NpgsqlCommand("SELECT 1", conn2))
-        {
-            // The connection reuse optimization isn't implemented for unpooled connections (though it could be)
-            Assert.That(conn2.ProcessID, Is.Not.EqualTo(processId));
-            cmd.ExecuteNonQuery();
-        }
-
-        scope.Complete();
-    }
-
     [Test(Description = "Transaction race, bool distributed")]
     [Explicit("Fails on Appveyor (https://ci.appveyor.com/project/roji/npgsql/build/3.3.0-250)")]
     public void Transaction_race([Values(false, true)] bool distributed)

test/Npgsql.Tests/SystemTransactionTests.cs

@@ -293,6 +293,29 @@ public void Single_unpooled_connection()
         scope.Complete();
     }
 
+    [Test, IssueLink("https://github.com/npgsql/npgsql/issues/4963")]
+    public void Single_unpooled_closed_connection()
+    {
+        var csb = new NpgsqlConnectionStringBuilder(ConnectionString)
+        {
+            Pooling = false,
+            Enlist = true
+        };
+        using var dataSource = NpgsqlDataSource.Create(csb);
+
+        using (var scope = new TransactionScope())
+        using (var conn = dataSource.OpenConnection())
+        using (var cmd = new NpgsqlCommand("SELECT 1", conn))
+        {
+            cmd.ExecuteNonQuery();
+            conn.Close();
+            Assert.That(dataSource.Statistics.Total, Is.EqualTo(1));
+            scope.Complete();
+        }
+
+        Assert.That(dataSource.Statistics.Total, Is.EqualTo(0));
+    }
+
     [Test]
     [IssueLink("https://github.com/npgsql/npgsql/issues/3863")]
     public void Break_connector_while_in_transaction_scope_with_rollback([Values] bool pooling)