Rubocop: Dynamic find by cop should observe TargetRailsVersion

[tedPen]

Expected behavior

The rails dynamic find_by cop should not flag code if the TargetRailsVersion is < ? (I can't find when this functionality changed).

Actual behavior

The dynamic find_by cop doesn't observe the TargetRailsVersion and flags these issues and even autocorrects them replacing them with invalid code. I realize that I can disable the cop but it makes more sense for TargetRailsVersion to work properly for this cop.

Steps to reproduce the problem

rails version 3.2.16 create a model and use a find_by_attribute call

RuboCop version

0.51.0 (using Parser 2.3.3.1, running on ruby 2.1.0 x86_64-linux)

[pocke]

https://github.com/bbatsov/rubocop/pull/4980#issuecomment-341291779
RuboCop does not support Rails 3.

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BTW, we can add a documentation for supported Rails versions probably.

[mikegee]

I think we will keep getting this issue for as long as folks run Rubocop on Rails 3 apps. (a.k.a. forever)

Ideally, the Rails cops would be extracted to another gem that depends on Rails 4+. Until then, maybe we should disable all the Rails cops if Rails <4 is detected?

I'm not convinced any documentation is going to prevent folks from being confused/upset initially. They might find the documentation after seeing the offense on their Rails 3 app and not open another issue, but it would be better if we got out ahead of this somehow.

[tedPen]

Adding this to the readme would be great for me especially since none of the other Rails cops have given me any trouble. We're running a supported version of ruby and there was no indication that Rails 3 would not be supported. We're also looking to upgrade to rails 4 later this year and I'm particularly motivated because of this issue.

Thanks for the response!