provide connectionfairy on initialize

This is so that dialect methods that are called within init
can assume the same argument structure as when they are called
in other places; we can nail down the type of object as well.

This change seems to mostly impact the isolation level routines
in the dialects, as these are called during initialize()
as well as on established connections.  these methods can now
assume a non-proxied DBAPI connection object in all cases,
as it is commonly required that attributes like ".autocommit"
are set on the object which don't work well in a proxied
situation.

Other changes:

* adds an interface for the "connectionfairy" concept
  called PoolProxiedConnection.
* Removes ``Connectable`` superclass of Connection.
  ``Connectable`` was originally meant to provide for the
  "method which accepts connection or engine" theme.  As this
  pattern  is greatly reduced in 2.0 and Engine no longer extends
  from it, the ``Connectable`` superclass doesnt serve any real
  purpose.

Leading from that, to set this in I also applied pep 484 annotations
to the Dialect base, and then in the interests of seeing some
of the typing information show up in my IDE did a little bit for Engine,
Connection and others.  I hope that it's feasible that we can
add annotations to specific classes and attributes ahead of when we
actually try to mass-populate the whole library.  This was
the original spirit of pep-484 that we can apply annotations
gradually.  I do of course want to try to do a mass-populate
although i think even in that case we will end up doing a lot
of manual work anyway (in particular for the changes here which
are distinct from what the stubs have).

Fixes: #7122
Change-Id: I5dd7fbff8a7ae520a81c165091af12a6a68826db

6 files changed, 45 insertions, 53 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/_psycopg_common.py b/lib/sqlalchemy/dialects/postgresql/_psycopg_common.py
index d82d5f009..a3a378947 100644
--- a/lib/sqlalchemy/dialects/postgresql/_psycopg_common.py
+++ b/lib/sqlalchemy/dialects/postgresql/_psycopg_common.py
@@ -150,7 +150,7 @@ class _PGDialect_common_psycopg(PGDialect):
             # requires that "dsn" be present as a blank string.
             return ([""], opts)
 
-    def get_isolation_level_values(self, dbapi_conn):
+    def get_isolation_level_values(self, dbapi_connection):
         return (
             "AUTOCOMMIT",
             "READ COMMITTED",
diff --git a/lib/sqlalchemy/dialects/postgresql/asyncpg.py b/lib/sqlalchemy/dialects/postgresql/asyncpg.py
index 1fdb46b6f..4951107bc 100644
--- a/lib/sqlalchemy/dialects/postgresql/asyncpg.py
+++ b/lib/sqlalchemy/dialects/postgresql/asyncpg.py
@@ -871,11 +871,11 @@ class PGDialect_asyncpg(PGDialect):
             "SERIALIZABLE": "serializable",
         }
 
-    def get_isolation_level_values(self, dbapi_conn):
+    def get_isolation_level_values(self, dbapi_connection):
         return list(self._isolation_lookup)
 
-    def set_isolation_level(self, connection, level):
-        connection.set_isolation_level(self._isolation_lookup[level])
+    def set_isolation_level(self, dbapi_connection, level):
+        dbapi_connection.set_isolation_level(self._isolation_lookup[level])
 
     def set_readonly(self, connection, value):
         connection.readonly = value
diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index d1d881dc3..614c84b56 100644
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -3251,17 +3251,17 @@ class PGDialect(default.DefaultDialect):
             "REPEATABLE READ",
         )
 
-    def set_isolation_level(self, connection, level):
-        cursor = connection.cursor()
+    def set_isolation_level(self, dbapi_connection, level):
+        cursor = dbapi_connection.cursor()
         cursor.execute(
             "SET SESSION CHARACTERISTICS AS TRANSACTION "
-            "ISOLATION LEVEL %s" % level
+            f"ISOLATION LEVEL {level}"
         )
         cursor.execute("COMMIT")
         cursor.close()
 
-    def get_isolation_level(self, connection):
-        cursor = connection.cursor()
+    def get_isolation_level(self, dbapi_connection):
+        cursor = dbapi_connection.cursor()
         cursor.execute("show transaction isolation level")
         val = cursor.fetchone()[0]
         cursor.close()
diff --git a/lib/sqlalchemy/dialects/postgresql/pg8000.py b/lib/sqlalchemy/dialects/postgresql/pg8000.py
index ede953195..1904a1ae1 100644
--- a/lib/sqlalchemy/dialects/postgresql/pg8000.py
+++ b/lib/sqlalchemy/dialects/postgresql/pg8000.py
@@ -446,7 +446,7 @@ class PGDialect_pg8000(PGDialect):
         # connection was closed normally
         return "connection is closed" in str(e)
 
-    def get_isolation_level_values(self, dbapi_conn):
+    def get_isolation_level_values(self, dbapi_connection):
         return (
             "AUTOCOMMIT",
             "READ COMMITTED",
@@ -455,21 +455,17 @@ class PGDialect_pg8000(PGDialect):
             "SERIALIZABLE",
         )
 
-    def set_isolation_level(self, connection, level):
+    def set_isolation_level(self, dbapi_connection, level):
         level = level.replace("_", " ")
 
-        # adjust for ConnectionFairy possibly being present
-        if hasattr(connection, "dbapi_connection"):
-            connection = connection.dbapi_connection
-
         if level == "AUTOCOMMIT":
-            connection.autocommit = True
+            dbapi_connection.autocommit = True
         else:
-            connection.autocommit = False
-            cursor = connection.cursor()
+            dbapi_connection.autocommit = False
+            cursor = dbapi_connection.cursor()
             cursor.execute(
                 "SET SESSION CHARACTERISTICS AS TRANSACTION "
-                "ISOLATION LEVEL %s" % level
+                f"ISOLATION LEVEL {level}"
             )
             cursor.execute("COMMIT")
             cursor.close()
@@ -516,13 +512,13 @@ class PGDialect_pg8000(PGDialect):
 
         return val == "on"
 
-    def set_client_encoding(self, connection, client_encoding):
-        # adjust for ConnectionFairy possibly being present
-        if hasattr(connection, "dbapi_connection"):
-            connection = connection.dbapi_connection
-
-        cursor = connection.cursor()
-        cursor.execute("SET CLIENT_ENCODING TO '" + client_encoding + "'")
+    def _set_client_encoding(self, dbapi_connection, client_encoding):
+        cursor = dbapi_connection.cursor()
+        cursor.execute(
+            f"""SET CLIENT_ENCODING TO '{
+            client_encoding.replace("'", "''")
+        }'"""
+        )
         cursor.execute("COMMIT")
         cursor.close()
 
@@ -556,7 +552,7 @@ class PGDialect_pg8000(PGDialect):
         if self.client_encoding is not None:
 
             def on_connect(conn):
-                self.set_client_encoding(conn, self.client_encoding)
+                self._set_client_encoding(conn, self.client_encoding)
 
             fns.append(on_connect)
 
diff --git a/lib/sqlalchemy/dialects/postgresql/psycopg.py b/lib/sqlalchemy/dialects/postgresql/psycopg.py
index c2017c975..4219b4fff 100644
--- a/lib/sqlalchemy/dialects/postgresql/psycopg.py
+++ b/lib/sqlalchemy/dialects/postgresql/psycopg.py
@@ -322,9 +322,6 @@ class PGDialect_psycopg(_PGDialect_common_psycopg):
         connection.isolation_level = isolation_level
 
     def get_isolation_level(self, dbapi_connection):
-        if hasattr(dbapi_connection, "dbapi_connection"):
-            dbapi_connection = dbapi_connection.dbapi_connection
-
         status_before = dbapi_connection.info.transaction_status
         value = super().get_isolation_level(dbapi_connection)
 
@@ -334,15 +331,14 @@ class PGDialect_psycopg(_PGDialect_common_psycopg):
             dbapi_connection.rollback()
         return value
 
-    def set_isolation_level(self, connection, level):
-        connection = getattr(connection, "dbapi_connection", connection)
+    def set_isolation_level(self, dbapi_connection, level):
         if level == "AUTOCOMMIT":
             self._do_isolation_level(
-                connection, autocommit=True, isolation_level=None
+                dbapi_connection, autocommit=True, isolation_level=None
             )
         else:
             self._do_isolation_level(
-                connection,
+                dbapi_connection,
                 autocommit=False,
                 isolation_level=self._isolation_lookup[level],
             )
diff --git a/lib/sqlalchemy/dialects/postgresql/psycopg2.py b/lib/sqlalchemy/dialects/postgresql/psycopg2.py
index 3d9f90a29..0bbad3257 100644
--- a/lib/sqlalchemy/dialects/postgresql/psycopg2.py
+++ b/lib/sqlalchemy/dialects/postgresql/psycopg2.py
@@ -597,7 +597,8 @@ class PGDialect_psycopg2(_PGDialect_common_psycopg):
         super(PGDialect_psycopg2, self).initialize(connection)
         self._has_native_hstore = (
             self.use_native_hstore
-            and self._hstore_oids(connection.connection) is not None
+            and self._hstore_oids(connection.connection.dbapi_connection)
+            is not None
         )
 
         # PGDialect.initialize() checks server version for <= 8.2 and sets
@@ -639,8 +640,8 @@ class PGDialect_psycopg2(_PGDialect_common_psycopg):
             "SERIALIZABLE": extensions.ISOLATION_LEVEL_SERIALIZABLE,
         }
 
-    def set_isolation_level(self, connection, level):
-        connection.set_isolation_level(self._isolation_lookup[level])
+    def set_isolation_level(self, dbapi_connection, level):
+        dbapi_connection.set_isolation_level(self._isolation_lookup[level])
 
     def set_readonly(self, connection, value):
         connection.readonly = value
@@ -660,47 +661,47 @@ class PGDialect_psycopg2(_PGDialect_common_psycopg):
         fns = []
         if self.client_encoding is not None:
 
-            def on_connect(conn):
-                conn.set_client_encoding(self.client_encoding)
+            def on_connect(dbapi_conn):
+                dbapi_conn.set_client_encoding(self.client_encoding)
 
             fns.append(on_connect)
 
         if self.dbapi and self.use_native_uuid:
 
-            def on_connect(conn):
-                extras.register_uuid(None, conn)
+            def on_connect(dbapi_conn):
+                extras.register_uuid(None, dbapi_conn)
 
             fns.append(on_connect)
 
         if self.dbapi and self.use_native_hstore:
 
-            def on_connect(conn):
-                hstore_oids = self._hstore_oids(conn)
+            def on_connect(dbapi_conn):
+                hstore_oids = self._hstore_oids(dbapi_conn)
                 if hstore_oids is not None:
                     oid, array_oid = hstore_oids
                     kw = {"oid": oid}
                     kw["array_oid"] = array_oid
-                    extras.register_hstore(conn, **kw)
+                    extras.register_hstore(dbapi_conn, **kw)
 
             fns.append(on_connect)
 
         if self.dbapi and self._json_deserializer:
 
-            def on_connect(conn):
+            def on_connect(dbapi_conn):
                 extras.register_default_json(
-                    conn, loads=self._json_deserializer
+                    dbapi_conn, loads=self._json_deserializer
                 )
                 extras.register_default_jsonb(
-                    conn, loads=self._json_deserializer
+                    dbapi_conn, loads=self._json_deserializer
                 )
 
             fns.append(on_connect)
 
         if fns:
 
-            def on_connect(conn):
+            def on_connect(dbapi_conn):
                 for fn in fns:
-                    fn(conn)
+                    fn(dbapi_conn)
 
             return on_connect
         else:
@@ -781,11 +782,10 @@ class PGDialect_psycopg2(_PGDialect_common_psycopg):
         )
 
     @util.memoized_instancemethod
-    def _hstore_oids(self, conn):
+    def _hstore_oids(self, dbapi_connection):
+
         extras = self._psycopg2_extras
-        if hasattr(conn, "dbapi_connection"):
-            conn = conn.dbapi_connection
-        oids = extras.HstoreAdapter.get_oids(conn)
+        oids = extras.HstoreAdapter.get_oids(dbapi_connection)
         if oids is not None and oids[0]:
             return oids[0:2]
         else: