Support context function argument as keyword

Today, when a user uses enginefacade reader/writer decorators
he/she is forced to pass the context argument as the
first positional argument. performing a decorated function
call with this argument passed as a keyword would lead to
an out of range exception.

This patch proposes to add support for the context argument
to be passed as a keyword argument in decorated functions.

e.g

@enginefacade.reader
def foo(context):
    ...

foo(context=ctxt)  <- will now be possible

Change-Id: Ief0b71bf9a7eb75935612431bdcc26d33bce852d

2 files changed, 17 insertions, 1 deletions

diff --git a/oslo_db/sqlalchemy/enginefacade.py b/oslo_db/sqlalchemy/enginefacade.py
index 1cfff15..28b8596 100644
--- a/oslo_db/sqlalchemy/enginefacade.py
+++ b/oslo_db/sqlalchemy/enginefacade.py
@@ -1003,10 +1003,13 @@ class _TransactionContextManager(object):
             context_index = 1
         else:
             context_index = 0
+        context_kw = argspec.args[context_index]
 
         @functools.wraps(fn)
         def wrapper(*args, **kwargs):
-            context = args[context_index]
+            context = kwargs.get(context_kw, None)
+            if not context:
+                context = args[context_index]
 
             with self._transaction_scope(context):
                 return fn(*args, **kwargs)
diff --git a/oslo_db/tests/sqlalchemy/test_enginefacade.py b/oslo_db/tests/sqlalchemy/test_enginefacade.py
index 12ccba6..5788fb3 100644
--- a/oslo_db/tests/sqlalchemy/test_enginefacade.py
+++ b/oslo_db/tests/sqlalchemy/test_enginefacade.py
@@ -519,6 +519,19 @@ class MockFacadeTest(oslo_test_base.BaseTestCase):
                 with self._assert_reader_session(makers) as session:
                     session.execute("test")
 
+    def test_session_reader_decorator_kwarg_call(self):
+        context = oslo_context.RequestContext()
+
+        @enginefacade.reader
+        def go(context):
+            context.session.execute("test")
+        go(context=context)
+
+        with self._assert_engines() as engines:
+            with self._assert_makers(engines) as makers:
+                with self._assert_reader_session(makers) as session:
+                    session.execute("test")
+
     def test_connection_reader_decorator(self):
         context = oslo_context.RequestContext()