Add new Style/StringConcatenation cop

[fatkodima]

https://rubystyle.guide/#string-interpolation

# bad
email_with_name = user.name + ' <' + user.email + '>'

# good
email_with_name = "#{user.name} <#{user.email}>"

Closes #5067

1. Another good name for this cop, I think, is StringConcatenation.
2. Made it Safe: false, because there can be very rare cases where it can give false positives.
3. It may be also a good idea to add some config that indicates after which amount of terms to add an offense.

[marcandre]

Would be nice if the autocorrection dropped those (), or maybe should be done by another cop?

[marcandre]

Would be nice to drop these outer () too, but maybe a different cop should do this?

[marcandre]

Great PR (as usual 😆)

[bbatsov]

Another good name for this cop, I think, is StringConcatenation.

I think I like this name better. Might also be a good idea to have the ability to autocorrect using format, but that's not a big deal.

[fatkodima]

Changed name to Style/StringConcatenation.

Would be nice to drop these outer () too, but maybe a different cop should do this?

Yes, to not complicate the actual implementation and also this is needed in many other cops, so I think it should be better handled by a different cop (named like Style/RedundantParentheses, for example). I will try to create one in the future, if no one gets ahead of me.

[marcandre]

I think it should be better handled by a different cop (named like Style/RedundantParentheses, for example). I will try to create one in the future, if no one gets ahead of me.

Agreed. I created #8379 to be sure we don't forget 👍