Support :traits option on implicit association

[r7kamura]

If we want to specify traits in implicit associations, we have to use :factory option. This is not only a naming problem, but also redundant in implicit style, because when using :factory option, the main factory name must always be specified, so the same name must be written twice.

  user factory: [:user, :trait1, :trait2]
# ^^^^            ^^^^

To resolve this problem, I propose to allow :traits option on implicit associations in this Pull Request.

  user traits: [:trait1, :trait2]

[vburzynski]

I noticed this PR had been open for some time and took a look at it. Thanks for taking the time to submit it so long ago.

I liked the idea of not having to add in the redundant factory declaration just to declare some traits. I hesitated, however, at the idea of adding another special option in addition to the existing :factory one, as this would conflict with being able to override attributes named :traits. This all spurred me into digging into why the implicit syntax doesn't operate more like the explicit :association syntax. I think I found an alternate fix:

#1796

With that change, it should be possible to write your example as:

user :trait1, :trait2

quite similar to how the explicit syntax works:

association :user, :trait1, :trait2

...and made possible because static attributes were deprecated in factory_bot 4.11 and removed in 5.x.

As a result, I'm going to close this PR in favor of the other one. Thanks again for the contribution 😎