Rollback if exception raised in with clause.

The previous code would only commit at the end of a with clause if an exception was raised, but
it did not perform a rollback like the documentation stated.  While this is harmless if you are
allocating new connections in a scope so the automatic close would roll it back, it would be a
disaster if you were using a manual connection pool and didn't roll back yourself.

src/connection.cpp

@@ -1281,15 +1281,19 @@ static PyObject* Connection_exit(PyObject* self, PyObject* args)
     // If an error has occurred, `args` will be a tuple of 3 values.  Otherwise it will be a tuple of 3 `None`s.
     I(PyTuple_Check(args));
 
-    if (cnxn->nAutoCommit == SQL_AUTOCOMMIT_OFF && PyTuple_GetItem(args, 0) == Py_None)
+    if (cnxn->nAutoCommit == SQL_AUTOCOMMIT_OFF)
     {
+        SQLSMALLINT CompletionType = (PyTuple_GetItem(args, 0) == Py_None) ? SQL_COMMIT : SQL_ROLLBACK;
         SQLRETURN ret;
         Py_BEGIN_ALLOW_THREADS
-        ret = SQLEndTran(SQL_HANDLE_DBC, cnxn->hdbc, SQL_COMMIT);
+        ret = SQLEndTran(SQL_HANDLE_DBC, cnxn->hdbc, CompletionType);
         Py_END_ALLOW_THREADS
 
         if (!SQL_SUCCEEDED(ret))
-            return RaiseErrorFromHandle("SQLEndTran(SQL_COMMIT)", cnxn->hdbc, SQL_NULL_HANDLE);
+        {
+            const char* szFunc = (CompletionType == SQL_COMMIT) ? "SQLEndTran(SQL_COMMIT)" : "SQLEndTran(SQL_ROLLBACK)";
+            return RaiseErrorFromHandle(szFunc, cnxn->hdbc, SQL_NULL_HANDLE);
+        }
     }
 
     Py_RETURN_NONE;

tests3/sqlservertests.py

@@ -1236,24 +1236,37 @@ def test_row_gtlt(self):
         rows.sort() # uses <
 
     def test_context_manager_success(self):
-
+        "Ensure `with` commits if an exception is not raised"
         self.cursor.execute("create table t1(n int)")
         self.cnxn.commit()
 
-        try:
-            with pyodbc.connect(self.connection_string) as cnxn:
-                cursor = cnxn.cursor()
-                cursor.execute("insert into t1 values (1)")
-        except Exception:
-            pass
-
-        cnxn = None
-        cursor = None
+        with self.cnxn:
+            self.cursor.execute("insert into t1 values (1)")
 
         rows = self.cursor.execute("select n from t1").fetchall()
         self.assertEquals(len(rows), 1)
         self.assertEquals(rows[0][0], 1)
 
+    def test_context_manager_failure(self):
+        "Ensure `with` rolls back if an exception is raised"
+        # We'll insert a row and commit it.  Then we'll insert another row followed by an
+        # exception.
+
+        self.cursor.execute("create table t1(n int)")
+        self.cursor.execute("insert into t1 values (1)")
+        self.cnxn.commit()
+
+        def _fail():
+            with self.cnxn:
+                self.cursor.execute("insert into t1 values (2)")
+                self.cursor.execute("delete from bogus")
+
+        self.assertRaises(pyodbc.Error, _fail)
+
+        self.cursor.execute("select max(n) from t1")
+        val = self.cursor.fetchval()
+        self.assertEqual(val, 1)
+
 
     def test_untyped_none(self):
         # From issue 129