Don't instruct usage if no changes in use_package()

[malcolmbarrett]

If I do use_package("pre.existing.import", "Suggests"), use_dependency() warns me that no change will be made. However, how_to_use() doesn't know about this, so it still tells you how to use the given type.

This PR prevents use_package() and use_dev_package() from calling how_to_use() if no change has been made.

I thought to add a test for this little bug, but I don't know how to express the expectation "A warning, followed by no messages". Maybe just a snapshot test?

PS I actually don't understand the logic here, TBH. Why does usethis care if I'm shuffling dependencies around in the first place? And why does it let me move up the dependency ladder but not down?

[hadley]

A snapshot test would be perfect I think. And add a news bullet?

[malcolmbarrett]

Ok, style updated, test added, and news updated!

[jennybc]

PS I actually don't understand the logic here, TBH. Why does usethis care if I'm shuffling dependencies around in the first place? And why does it let me move up the dependency ladder but not down?

Just to provide some history, use_dependency() is sort of a nightmare to work on, i.e. deserving of a comment "you think you will be able to make this much better, but that's what the last person thought" 😅

[malcolmbarrett]

"you think you will be able to make this much better, but that's what the last person thought"

🤣 ok, I'll always use ten_foot_pole() when dealing with use_dependency()

[hadley]

Thanks!