[Sqlalchemy-tickets] Issue #4221: non-mapped declared_attr warning gets in the way; is of questionable value (zzzeek/sqlalchemy)

[Michael B. <iss...@bi...>]

New issue 4221: non-mapped declared_attr warning gets in the way; is of questionable value
https://bitbucket.org/zzzeek/sqlalchemy/issues/4221/non-mapped-declared_attr-warning-gets-in

Michael Bayer:

at http://docs.sqlalchemy.org/en/latest/orm/extensions/declarative/mixins.html#combining-table-mapper-arguments-from-multiple-mixins we document invoking `__table_args__` from a mixin.  if `@declared_attr` is used we get a warning:

```
#!python


from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.declarative import declared_attr

Base = declarative_base()


class Mixin(object):
    a = Column(Integer)

    @declared_attr
    def __table_args__(cls):
        return (UniqueConstraint("a"), )


class Baz(Base, Mixin):
    __tablename__ = 'baz'

    id = Column(Integer, primary_key=True)
    d = Column(Integer)

    @declared_attr
    def __table_args__(cls):
        ret = list(Mixin.__table_args__)
        ret.append(UniqueConstraint("d"))
        return tuple(ret)
```

    SAWarning: Unmanaged access of declarative attribute __table_args__ from non-mapped class Mixin

the thing we're guarding against here is the case in https://bitbucket.org/zzzeek/sqlalchemy/issues/3149/mixin_column-to-provide-more-context-for, which is already prevented here.

not clear what additional case we are guarding against here however we could also limit the warning only for names that aren't `__table_args__`, `__mapper_args__`, etc.