Repair PG BIGSERIAL w/ TypeDecorator, Variant

Some of the dialect impl memoization for TypeDecorator
necessarily keeps the top-level TypeDecorator type
around, since a user-defined type will have bind and result
set processing behavior.  For both TypeDecorator and Variant,
PG dialect needs to ensure it's looking at the SQLAlchemy
type to check for SmallInteger / BigInteger.

Fixes: 3739
Change-Id: I2d45fb997f17c6272d6bb826a77d2dba665adae7
(cherry picked from commit 421fa6b8bf9f0c3c5041579c89ec405ce0f5e0b0)

3 files changed, 33 insertions, 1 deletions

diff --git a/doc/build/changelog/changelog_10.rst b/doc/build/changelog/changelog_10.rst
index a1e7d3678..7240e8e68 100644
--- a/doc/build/changelog/changelog_10.rst
+++ b/doc/build/changelog/changelog_10.rst
@@ -19,6 +19,16 @@
     :version: 1.0.14
 
     .. change::
+        :tags: bug, postgresql
+        :tickets: 3739
+        :versions: 1.1.0b3
+
+        Fixed bug whereby :class:`.TypeDecorator` and :class:`.Variant`
+        types were not deeply inspected enough by the Postgresql dialect
+        to determine if SMALLSERIAL or BIGSERIAL needed to be rendered
+        rather than SERIAL.
+
+    .. change::
         :tags: bug, sql
         :tickets: 3735
         :versions: 1.1.0b2
diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index 688ce9e1c..cc0f890dc 100644
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -1484,6 +1484,9 @@ class PGDDLCompiler(compiler.DDLCompiler):
 
         colspec = self.preparer.format_column(column)
         impl_type = column.type.dialect_impl(self.dialect)
+        if isinstance(impl_type, sqltypes.TypeDecorator):
+            impl_type = impl_type.impl
+
         if column.primary_key and \
             column is column.table._autoincrement_column and \
             (
diff --git a/test/dialect/postgresql/test_dialect.py b/test/dialect/postgresql/test_dialect.py
index c0e1819d6..9f7af8638 100644
--- a/test/dialect/postgresql/test_dialect.py
+++ b/test/dialect/postgresql/test_dialect.py
@@ -8,7 +8,7 @@ from sqlalchemy import testing
 import datetime
 from sqlalchemy import (
     Table, Column, select, MetaData, text, Integer, String, Sequence, Numeric,
-    DateTime, BigInteger, func, extract, SmallInteger)
+    DateTime, BigInteger, func, extract, SmallInteger, TypeDecorator)
 from sqlalchemy import exc, schema
 from sqlalchemy.dialects.postgresql import base as postgresql
 import logging
@@ -252,6 +252,15 @@ class MiscTest(fixtures.TestBase, AssertsExecutionResults, AssertsCompiledSQL):
         "postgresql >= 8.2", "requires standard_conforming_strings")
     def test_serial_integer(self):
 
+        class BITD(TypeDecorator):
+            impl = Integer
+
+            def load_dialect_impl(self, dialect):
+                if dialect.name == 'postgresql':
+                    return BigInteger()
+                else:
+                    return Integer()
+
         for version, type_, expected in [
             (None, Integer, 'SERIAL'),
             (None, BigInteger, 'BIGSERIAL'),
@@ -259,6 +268,16 @@ class MiscTest(fixtures.TestBase, AssertsExecutionResults, AssertsCompiledSQL):
             ((9, 2), SmallInteger, 'SMALLSERIAL'),
             (None, postgresql.INTEGER, 'SERIAL'),
             (None, postgresql.BIGINT, 'BIGSERIAL'),
+            (
+                None, Integer().with_variant(BigInteger(), 'postgresql'),
+                'BIGSERIAL'),
+            (
+                None, Integer().with_variant(postgresql.BIGINT, 'postgresql'),
+                'BIGSERIAL'),
+            (
+                (9, 2), Integer().with_variant(SmallInteger, 'postgresql'),
+                'SMALLSERIAL'),
+            (None, BITD(), 'BIGSERIAL')
         ]:
             m = MetaData()