Do not split assert conditions on multiple lines

[ovidiu-munteanu]

Black should not split conditions in assert statements over multiple lines unless necessary. Instead, it should split the assert error message over multiple lines.

Given a long assert statement such as this:

assert type(queryset) in (ModelBase, QuerySet), "You must specify a model or override the class 'queryset'."

Based on the current style black reformats it like this:

assert type(queryset) in (
    ModelBase,
    QuerySet,
), "You must specify a model or override the class 'queryset'."

Instead, I believe it would look much better if it were formatted like this:

assert type(queryset) in (ModelBase, QuerySet), (
    "You must specify a model or override the class 'queryset'."
)

[mk-pmb]

I think this boils down to predicting whether the items in the list will change in the future. Having them eachin one line helps reduce diff flickering, thus helps automatic versioning merges, and also (in some inferior editors) makes it easier to sort the list.

[rpkilby]

I think this boils down to predicting whether the items in the list will change in the future.

I think that's actually just coincidence. e.g., take this simple assert:

# input
assert False, 'safdlkafs lkasfljfas sadfljkklsadf asdfjl afsdljk sadfl kasdflkjsdflkj df sfd asdf'

# black
assert (
    False
), 'safdlkafs lkasfljfas sadfljkklsadf asdfjl afsdljk sadfl kasdflkjsdflkj df sfd asdf'

Note that black produces the preferred output when the message is sufficiently long:

# input
assert type(queryset) in (ModelBase, QuerySet), 'asdfkj aljkasdfljk df fdjklasdf fdjkafjkl dfakljafs djklasfldk sadfljkaf sdjklfdsa fdajklfadsljk afkjl aflskjjlakfsd asdjl'

# black
assert type(queryset) in (ModelBase, QuerySet), (
    'asdfkj aljkasdfljk df fdjklasdf fdjkafjkl dfakljafs djklasfldk sadfljkaf sdjklfdsa'
    ' fdajklfadsljk afkjl aflskjjlakfsd asdjl'
)

[miriaford]

Please see #1483 (my duplicate issue). I think the current behavior of Black is just incorrect.