Enable F821

In Ia63a510f9c1d08b055eef62cf047f1f427f0450c we introduced
"lambda combinations" which use a bit of function closure inspection
in order to allow for testing combinations that make use of symbols that
come from test fixtures, or from the test itself.

Two problems.  One is that we can't use F821 flake8 rule without either
adding lots of noqas, skipping the file, or adding arguments to the
lambdas themselves that are then populated, which makes for a very
verbose system.  The other is that the system is already verbose
with all those lambdas and the magic in use is a non-explicit kind,
hence F821 reminds us that if we can improve upon this, we should.

So let's improve upon it by making it so that the "lambda" is just
once and up front for the whole thing, and let it accept the arguments
directly.   This still requires magic, because these test cases need
to resolve at test collection time, not test runtime.  But we will
instead substitute a namespace up front that can be coerced into
its desired form within the tests.

Additionally, there's a little bit of py2k compatible type annotations
present; f821 is checking these, so we have to add those imports
also using the TYPE_CHECKING boolean so they don't take place in
py2k.

Change-Id: Idb7e7a0c8af86d9ab133f548511306ef68cdba14

4 files changed, 25 insertions, 10 deletions

diff --git a/lib/sqlalchemy/sql/base.py b/lib/sqlalchemy/sql/base.py
index 60456223f..a7324c45f 100644
--- a/lib/sqlalchemy/sql/base.py
+++ b/lib/sqlalchemy/sql/base.py
@@ -19,9 +19,12 @@ from .visitors import ClauseVisitor
 from .. import exc
 from .. import util
 
-coercions = None  # type: types.ModuleType
-elements = None  # type: types.ModuleType
-type_api = None  # type: types.ModuleType
+if util.TYPE_CHECKING:
+    from types import ModuleType
+
+coercions = None  # type: ModuleType
+elements = None  # type: ModuleType
+type_api = None  # type: ModuleType
 
 PARSE_AUTOCOMMIT = util.symbol("PARSE_AUTOCOMMIT")
 NO_ARG = util.symbol("NO_ARG")
diff --git a/lib/sqlalchemy/sql/coercions.py b/lib/sqlalchemy/sql/coercions.py
index 12ec7c750..b3bf4e93b 100644
--- a/lib/sqlalchemy/sql/coercions.py
+++ b/lib/sqlalchemy/sql/coercions.py
@@ -17,10 +17,13 @@ from .. import inspection
 from .. import util
 from ..util import collections_abc
 
-elements = None  # type: types.ModuleType
-schema = None  # type: types.ModuleType
-selectable = None  # type: types.ModuleType
-sqltypes = None  # type: types.ModuleType
+if util.TYPE_CHECKING:
+    from types import ModuleType
+
+elements = None  # type: ModuleType
+schema = None  # type: ModuleType
+selectable = None  # type: ModuleType
+sqltypes = None  # type: ModuleType
 
 
 def _is_literal(element):
diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index d94d91b16..422eb6220 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -43,6 +43,11 @@ from .. import exc
 from .. import inspection
 from .. import util
 
+if util.TYPE_CHECKING:
+    from typing import Any
+    from typing import Optional
+    from typing import Union
+
 
 def collate(expression, collation):
     """Return the clause ``expression COLLATE collation``.
@@ -709,7 +714,7 @@ class ColumnElement(
     _alt_names = ()
 
     def self_group(self, against=None):
-        # type: (Module, Module, Optional[Any]) -> ClauseEleent
+        # type: (Optional[Any]) -> ClauseElement
         if (
             against in (operators.and_, operators.or_, operators._asbool)
             and self.type._type_affinity is type_api.BOOLEANTYPE._type_affinity
diff --git a/lib/sqlalchemy/sql/selectable.py b/lib/sqlalchemy/sql/selectable.py
index 8f5503db0..136c9f868 100644
--- a/lib/sqlalchemy/sql/selectable.py
+++ b/lib/sqlalchemy/sql/selectable.py
@@ -50,6 +50,10 @@ from .visitors import InternalTraversal
 from .. import exc
 from .. import util
 
+if util.TYPE_CHECKING:
+    from typing import Any
+    from typing import Optional
+
 
 class _OffsetLimitParam(BindParameter):
     @property
@@ -2096,7 +2100,7 @@ class SelectBase(
     _memoized_property = util.group_expirable_memoized_property()
 
     def _generate_fromclause_column_proxies(self, fromclause):
-        # type: (FromClause)
+        # type: (FromClause) -> None
         raise NotImplementedError()
 
     def _refresh_for_new_column(self, column):
@@ -2344,7 +2348,7 @@ class SelectStatementGrouping(GroupedElement, SelectBase):
     _is_select_container = True
 
     def __init__(self, element):
-        # type: (SelectBase)
+        # type: (SelectBase) -> None
         self.element = coercions.expect(roles.SelectStatementRole, element)
 
     @property