:released: June 25, 2019

 .. change::
     :tags: bug, sqlite, autogenerate, batch
     :tickets: 579

     SQLite server default reflection will ensure parenthesis are surrounding a
     column default expression that is detected as being a non-constant
     expression, such as a ``datetime()`` default, to accommodate for the
     requirement that SQL expressions have to be parenthesized when being sent
     as DDL.  Parenthesis are not added to constant expressions to allow for
     maximum cross-compatibility with other dialects and existing test suites
     (such as Alembic's), which necessarily entails scanning the expression to
     eliminate for constant numeric and string values. The logic is added to the
     two "reflection->DDL round trip" paths which are currently autogenerate and
     batch migration.  Within autogenerate, the logic is on the rendering side,
     whereas in batch the logic is installed as a column reflection hook.


 .. change::
     :tags: bug, sqlite, autogenerate
     :tickets: 579

     Improved SQLite server default comparison to accommodate for a ``text()``
     construct that added parenthesis directly vs. a construct that relied
     upon the SQLAlchemy SQLite dialect to render the parenthesis, as well
     as improved support for various forms of constant expressions such as
     values that are quoted vs. non-quoted.


 .. change::
     :tags: bug, autogenerate

     Fixed bug where the "literal_binds" flag was not being set when
     autogenerate would create a server default value, meaning server default
     comparisons would fail for functions that contained literal values.

 .. change::
    :tags: bug, mysql
    :tickets: 554

    Added support for MySQL "DROP CHECK", which is added as of MySQL 8.0.16,
    separate from MariaDB's "DROP CONSTRAINT" for CHECK constraints.  The MySQL
    Alembic implementation now checks for "MariaDB" in server_version_info to
    decide which one to use.



 .. change::
     :tags: bug, mysql, operations
     :tickets: 564

     Fixed issue where MySQL databases need to use CHANGE COLUMN when altering a
     server default of CURRENT_TIMESTAMP, NOW() and probably other functions
     that are only usable with DATETIME/TIMESTAMP columns.  While MariaDB
     supports both CHANGE and ALTER COLUMN in this case, MySQL databases only
     support CHANGE.  So the new logic is that if the server default change is
     against a DateTime-oriented column, the CHANGE format is used
     unconditionally, as in the vast majority of cases the server default is to
     be CURRENT_TIMESTAMP which may also be potentially bundled with an "ON
     UPDATE CURRENT_TIMESTAMP" directive, which SQLAlchemy does not currently
     support as a distinct field.  The fix addiionally improves the server
     default comparison logic when the "ON UPDATE" clause is present and
     there are parenthesis to be adjusted for as is the case on some MariaDB
     versions.



 .. change::
     :tags: bug, environment

     Warnings emitted by Alembic now include a default stack level of 2, and in
     some cases it's set to 3, in order to help warnings indicate more closely
     where they are originating from.  Pull request courtesy Ash Berlin-Taylor.


 .. change::
     :tags: bug, py3k
     :tickets: 563

     Replaced the Python compatbility routines for ``getargspec()`` with a fully
     vendored version based on ``getfullargspec()`` from Python 3.3.
     Originally, Python was emitting deprecation warnings for this function in
     Python 3.8 alphas.  While this change was reverted, it was observed that
     Python 3 implementations for ``getfullargspec()`` are an order of magnitude
     slower as of the 3.4 series where it was rewritten against ``Signature``.
     While Python plans to improve upon this situation, SQLAlchemy projects for
     now are using a simple replacement to avoid any future issues.


.. changelog::