Introduce lambda combinations

As the ORM's combinatoric tests mostly use entities and
table metadata that's defined in fixtures, we can't use
@testing.combinations directly as it takes place at the
module level.   Instead we use lambdas, but to reduce
verbosity we use a code replacement so that the namespace
of the lambda can be provided at runtime rather than
module import time.

Change-Id: Ia63a510f9c1d08b055eef62cf047f1f427f0450c

3 files changed, 26 insertions, 2 deletions

diff --git a/lib/sqlalchemy/testing/__init__.py b/lib/sqlalchemy/testing/__init__.py
index a1f4b12ba..e7bb0a6a6 100644
--- a/lib/sqlalchemy/testing/__init__.py
+++ b/lib/sqlalchemy/testing/__init__.py
@@ -56,6 +56,7 @@ from .util import flag_combinations  # noqa
 from .util import force_drop_names  # noqa
 from .util import metadata_fixture  # noqa
 from .util import provide_metadata  # noqa
+from .util import resolve_lambda  # noqa
 from .util import rowset  # noqa
 from .util import run_as_contextmanager  # noqa
 from .util import teardown_events  # noqa
diff --git a/lib/sqlalchemy/testing/plugin/pytestplugin.py b/lib/sqlalchemy/testing/plugin/pytestplugin.py
index 44fccf28d..3e0630890 100644
--- a/lib/sqlalchemy/testing/plugin/pytestplugin.py
+++ b/lib/sqlalchemy/testing/plugin/pytestplugin.py
@@ -363,6 +363,7 @@ class PytestFixtureFunctions(plugin_base.FixtureFunctions):
                 for idx, char in enumerate(id_)
                 if char in _combination_id_fns
             ]
+
             arg_sets = [
                 pytest.param(
                     *_arg_getter(_filter_exclusions(arg))[1:],
@@ -370,14 +371,21 @@ class PytestFixtureFunctions(plugin_base.FixtureFunctions):
                         comb_fn(getter(arg)) for getter, comb_fn in fns
                     )
                 )
-                for arg in arg_sets
+                for arg in [
+                    (arg,) if not isinstance(arg, tuple) else arg
+                    for arg in arg_sets
+                ]
             ]
         else:
             # ensure using pytest.param so that even a 1-arg paramset
             # still needs to be a tuple.  otherwise paramtrize tries to
             # interpret a single arg differently than tuple arg
             arg_sets = [
-                pytest.param(*_filter_exclusions(arg)) for arg in arg_sets
+                pytest.param(*_filter_exclusions(arg))
+                for arg in [
+                    (arg,) if not isinstance(arg, tuple) else arg
+                    for arg in arg_sets
+                ]
             ]
 
         def decorate(fn):
diff --git a/lib/sqlalchemy/testing/util.py b/lib/sqlalchemy/testing/util.py
index 87c461fd2..dbe6a383d 100644
--- a/lib/sqlalchemy/testing/util.py
+++ b/lib/sqlalchemy/testing/util.py
@@ -261,6 +261,21 @@ def flag_combinations(*combinations):
     )
 
 
+def resolve_lambda(__fn, **kw):
+    """Given a no-arg lambda and a namespace, return a new lambda that
+    has all the values filled in.
+
+    This is used so that we can have module-level fixtures that
+    refer to instance-level variables using lambdas.
+
+    """
+
+    glb = dict(__fn.__globals__)
+    glb.update(kw)
+    new_fn = types.FunctionType(__fn.__code__, glb)
+    return new_fn()
+
+
 def metadata_fixture(ddl="function"):
     """Provide MetaData for a pytest fixture."""