DialectFunctionDispatcher does not support nesting of decorators

[Mike Bayer]

the DialectFunctionDispatcher doesn't support simple nesting of decorators, such as:

    @_init_connection_args.dispatch_for("mysql+mysqlconnector")
    @_init_connection_args.dispatch_for("mysql+mysqldb")
    def _init_connection_args(url, engine_args, **kw):
       # ...

Because the dispatch_for() decorator returns the dispatcher, and not the function (necessary so that the dispatcher remains available even decorating a same-named function), nesting above does not work automatically, you instead get a recursion overflow:

    File "/Users/classic/dev/redhat/openstack/oslo.db/oslo/db/sqlalchemy/utils.py", line 918, in __call__
      self._url_from_target(target), target, arg, kw)
    File "/Users/classic/dev/redhat/openstack/oslo.db/oslo/db/sqlalchemy/utils.py", line 955, in _dispatch_on
      return self._dispatch_on_db_driver(dbname, driver, arg, kw)
    File "/Users/classic/dev/redhat/openstack/oslo.db/oslo/db/sqlalchemy/utils.py", line 1009, in _dispatch_on_db_driver
      if self._invoke_fn(fn, arg, kw) is not None:
    File "/Users/classic/dev/redhat/openstack/oslo.db/oslo/db/sqlalchemy/utils.py", line 958, in _invoke_fn
      return fn(*arg, **kw)
    File "/Users/classic/dev/redhat/openstack/oslo.db/oslo/db/sqlalchemy/utils.py", line 918, in __call__
      self._url_from_target(target), target, arg, kw)
    File "/Users/classic/dev/redhat/openstack/oslo.db/oslo/db/sqlalchemy/utils.py", line 955, in _dispatch_on
      return self._dispatch_on_db_driver(dbname, driver, arg, kw)
    File "/Users/classic/dev/redhat/openstack/oslo.db/oslo/db/sqlalchemy/utils.py", line 1009, in _dispatch_on_db_driver

  The decorator should anticipate this condition and adapt for it.

[Davanum Srinivas (DIMS) (dims-v)]

Do we need to fix this in Mitaka zzzeek?

[Mike Bayer (zzzeek)]

this was fixed in 7a3e091c:

commit 7a3e091c1c9cc9ae6e34279c7c99c9989afd8894
Author: Mike Bayer <email address hidden>
Date: Wed Sep 24 15:04:53 2014 -0400

    Unwrap DialectFunctionDispatcher from itself.

    The DialectFunctionDispatcher.dispatch_for() decorator method
    necessarily returns the dispatcher itself and not the
    decorated function, so that the object can continue to be
    re-used even if the function name is the same as that of the
    dispatcher. In order to support a single function being
    wrapped by the dispatcher multiple times with different
    criteria, dispatch_for() will now check for the last function
    wrapped and use that.

    Change-Id: I331670d9b76ae30e7a666648e7e2d4c72641c9ff
    Closes-Bug: #1373568