deprecate two columns alter

docs/changelog.rst

@@ -1,5 +1,6 @@
 0.6.0
 -----
+- deprecated `alter_column` comparing of columns. Just use explicit parameter change.
 - added option to define custom templates through option ``--templates_path`` and ``--templates_theme``, read more in :ref:`tutorial section <custom-templates>`
 - use Python logging for output, can be shut down by passing ``--disable_logging`` to :func:`migrate.versioning.shell.main`
 - `url` parameter can also be an :class:`Engine` instance (this usage is discouraged though sometimes necessary)

docs/changeset.rst

@@ -69,10 +69,12 @@ Given a standard SQLAlchemy table::
  assert col.nullable
  assert table.c.col3 is col
 
+.. warning:: 
+    Since version ``0.6.0`` passing column into alter is deprecated. Pass in explicit parameters instead.  
 
 .. note::
 
-	Since version ``0.6.0`` you can pass primary_key_name, index_name and unique_name to column.create method to issue ALTER TABLE ADD CONSTRAINT after changing the column. Note for multi columns constraints and other advanced configuration, check :ref:`constraint tutorial <constraint-tutorial>`.
+    Since version ``0.6.0`` you can pass primary_key_name, index_name and unique_name to column.create method to issue ALTER TABLE ADD CONSTRAINT after changing the column. Note for multi columns constraints and other advanced configuration, check :ref:`constraint tutorial <constraint-tutorial>`.
 
 .. _table-rename:
 

migrate/__init__.py

@@ -4,3 +4,6 @@
    :mod:`migrate.changeset` that allows to define database schema changes
    using Python.
 """
+
+class MigrateDeprecationWarning(DeprecationWarning):
+    """Warning for deprecated features in Migrate"""

migrate/changeset/schema.py

@@ -4,6 +4,7 @@
 from UserDict import DictMixin
 import sqlalchemy
 
+from migrate import MigrateDeprecationWarning
 from migrate.changeset import SQLA_06
 from migrate.changeset.exceptions import *
 from migrate.changeset.databases.visitor import (get_engine_visitor,
@@ -103,6 +104,10 @@ def alter_column(*p, **k):
     if 'engine' not in k:
         k['engine'] = k['table'].bind
 
+    # deprecation
+    if len(p) >= 2 and isinstance(p[1], sqlalchemy.Column):
+        raise MigrateDeprecationWarning("Alter column with comparing columns is deprecated. Just pass in parameters instead.")
+
     engine = k['engine']
     delta = ColumnDelta(*p, **k)