Enable SQL Server testing and fix autogen issues

Fixed assorted autogenerate issues with SQL Server:

* ignore default reflected identity on primary_key columns
* improve server default comparison

Updated test_autogen_fks for modern levels of FK
capabilities

Change-Id: I94b815cedf90422ccd5ceceb765b07d772b505b7
Fixes: #787

3 files changed, 46 insertions, 2 deletions

diff --git a/alembic/ddl/impl.py b/alembic/ddl/impl.py
index 923fd8b..62692d2 100644
--- a/alembic/ddl/impl.py
+++ b/alembic/ddl/impl.py
@@ -555,7 +555,15 @@ class DefaultImpl(with_metaclass(ImplMeta)):
 
         diff.difference_update(self.identity_attrs_ignore)
 
-        return diff, ignored
+        # returns 3 values:
+        return (
+            # different identity attributes
+            diff,
+            # ignored identity attributes
+            ignored,
+            # if the two identity should be considered different
+            bool(diff) or bool(metadata_identity) != bool(inspector_identity),
+        )
 
 
 def _compare_identity_options(
diff --git a/alembic/ddl/mssql.py b/alembic/ddl/mssql.py
index 916011a..18e09f8 100644
--- a/alembic/ddl/mssql.py
+++ b/alembic/ddl/mssql.py
@@ -178,6 +178,42 @@ class MSSQLImpl(DefaultImpl):
             table_name, column, schema=schema, **kw
         )
 
+    def compare_server_default(
+        self,
+        inspector_column,
+        metadata_column,
+        rendered_metadata_default,
+        rendered_inspector_default,
+    ):
+        def clean(value):
+            if value is not None:
+                value = value.strip()
+                while value[0] == "(" and value[-1] == ")":
+                    value = value[1:-1]
+            return value
+
+        return clean(rendered_inspector_default) != clean(
+            rendered_metadata_default
+        )
+
+    def _compare_identity_default(self, metadata_identity, inspector_identity):
+        diff, ignored, is_alter = super(
+            MSSQLImpl, self
+        )._compare_identity_default(metadata_identity, inspector_identity)
+
+        if (
+            metadata_identity is None
+            and inspector_identity is not None
+            and not diff
+            and inspector_identity.column is not None
+            and inspector_identity.column.primary_key
+        ):
+            # mssql reflect primary keys with autoincrement as identity
+            # columns. if no different attributes are present ignore them
+            is_alter = False
+
+        return diff, ignored, is_alter
+
 
 class _ExecDropConstraint(Executable, ClauseElement):
     def __init__(self, tname, colname, type_, schema):
diff --git a/alembic/ddl/postgresql.py b/alembic/ddl/postgresql.py
index b8fdd99..6a2f007 100644
--- a/alembic/ddl/postgresql.py
+++ b/alembic/ddl/postgresql.py
@@ -319,7 +319,7 @@ def visit_identity_column(element, compiler, **kw):
         return text
     else:
         # alter identity
-        diff, _ = element.impl._compare_identity_default(
+        diff, _, _ = element.impl._compare_identity_default(
             element.default, element.existing_server_default
         )
         identity = element.default