Adjust for Variant returning itself as impl

Fixed bug where autogen comparison of a :class:`.Variant` datatype
would not compare to the dialect level type for the "default"
implementation of the :class:`.Variant`, returning the type as changed
between database and table metadata.

Change-Id: Ie94779ece9f1c768375cdbdc4124c98f9c11bb86
Fixes: #433

6 files changed, 60 insertions, 1 deletions

diff --git a/alembic/ddl/impl.py b/alembic/ddl/impl.py
index 0971c21..39558ab 100644
--- a/alembic/ddl/impl.py
+++ b/alembic/ddl/impl.py
@@ -240,6 +240,8 @@ class DefaultImpl(with_metaclass(ImplMeta)):
         metadata_type = metadata_column.type
 
         metadata_impl = metadata_type.dialect_impl(self.dialect)
+        if isinstance(metadata_impl, sqltypes.Variant):
+            metadata_impl = metadata_impl.impl.dialect_impl(self.dialect)
 
         # work around SQLAlchemy bug "stale value for type affinity"
         # fixed in 0.7.4
diff --git a/alembic/testing/requirements.py b/alembic/testing/requirements.py
index 4468ef2..3852772 100644
--- a/alembic/testing/requirements.py
+++ b/alembic/testing/requirements.py
@@ -154,6 +154,13 @@ class SuiteRequirements(Requirements):
         )
 
     @property
+    def sqlalchemy_1014(self):
+        return exclusions.skip_if(
+            lambda config: not util.sqla_1014,
+            "SQLAlchemy 1.0.14 or greater required"
+        )
+
+    @property
     def sqlalchemy_110(self):
         return exclusions.skip_if(
             lambda config: not util.sqla_110,
diff --git a/alembic/util/__init__.py b/alembic/util/__init__.py
index bb249dc..8a85736 100644
--- a/alembic/util/__init__.py
+++ b/alembic/util/__init__.py
@@ -8,7 +8,7 @@ from .pyfiles import (  # noqa
     pyc_file_from_path, load_python_file, edit)
 from .sqla_compat import (  # noqa
     sqla_07, sqla_079, sqla_08, sqla_083, sqla_084, sqla_09, sqla_092,
-    sqla_094, sqla_099, sqla_100, sqla_105, sqla_110, sqla_1010)
+    sqla_094, sqla_099, sqla_100, sqla_105, sqla_110, sqla_1010, sqla_1014)
 from .exc import CommandError
 
 
diff --git a/alembic/util/sqla_compat.py b/alembic/util/sqla_compat.py
index 57eacd5..e0507f8 100644
--- a/alembic/util/sqla_compat.py
+++ b/alembic/util/sqla_compat.py
@@ -30,6 +30,7 @@ sqla_100 = _vers >= (1, 0, 0)
 sqla_105 = _vers >= (1, 0, 5)
 sqla_1010 = _vers >= (1, 0, 10)
 sqla_110 = _vers >= (1, 1, 0)
+sqla_1014 = _vers >= (1, 0, 14)
 
 if sqla_08:
     from sqlalchemy.sql.expression import TextClause
diff --git a/docs/build/changelog.rst b/docs/build/changelog.rst
index 9a4b152..4b7a57d 100644
--- a/docs/build/changelog.rst
+++ b/docs/build/changelog.rst
@@ -7,6 +7,15 @@ Changelog
     :version: 0.9.3
     :released:
 
+    .. change:: 433
+      :tags: bug, autogenerate
+      :tickets: 433
+
+      Fixed bug where autogen comparison of a :class:`.Variant` datatype
+      would not compare to the dialect level type for the "default"
+      implementation of the :class:`.Variant`, returning the type as changed
+      between database and table metadata.
+
     .. change:: 431
       :tags: bug, tests
       :tickets: 431
diff --git a/tests/test_autogen_diffs.py b/tests/test_autogen_diffs.py
index 239e31f..39329cc 100644
--- a/tests/test_autogen_diffs.py
+++ b/tests/test_autogen_diffs.py
@@ -662,6 +662,46 @@ class CompareTypeSpecificityTest(TestBase):
         is_(impl.compare_type(Column('x', t2), Column('x', t3)), True)
 
 
+class AutogenerateVariantCompareTest(AutogenTest, TestBase):
+    __backend__ = True
+
+    # 1.0.13 and lower fail on Postgresql due to variant / bigserial issue
+    # #3739
+
+    __requires__ = ('sqlalchemy_1014', )
+
+    @classmethod
+    def _get_db_schema(cls):
+        m = MetaData()
+
+        Table('sometable', m,
+              Column(
+                  'id',
+                  BigInteger().with_variant(Integer, "sqlite"),
+                  primary_key=True),
+              Column('value', String(50)))
+        return m
+
+    @classmethod
+    def _get_model_schema(cls):
+        m = MetaData()
+
+        Table('sometable', m,
+              Column(
+                  'id',
+                  BigInteger().with_variant(Integer, "sqlite"),
+                  primary_key=True),
+              Column('value', String(50)))
+        return m
+
+    def test_variant_no_issue(self):
+        uo = ops.UpgradeOps(ops=[])
+        autogenerate._produce_net_changes(self.autogen_context, uo)
+
+        diffs = uo.as_diffs()
+        eq_(diffs, [])
+
+
 class AutogenerateCustomCompareTypeTest(AutogenTest, TestBase):
     __only_on__ = 'sqlite'