Add `active_when` helper

We have the following pattern all over the codebase in views:

%li{ class: (klass == Gitlab::GitLogger ? 'active' : '') }

It'd be awesome if we could just do this, for example:

%li{ class: active_when(klass == Gitlab::GitLogger) }

The implementation couldn't be simpler:

def active_when(condition)
  'active' if condition
end

I'd love to take this up as a starter issue. Only thing I'd like to ask is how to best test this behavior?

@pawandubey Great! https://gitlab.com/gitlab-org/gitlab-ce/blob/master/spec/helpers/broadcast_messages_helper_spec.rb contains some really basic helper specs that should give you an idea of how to test a helper and our preferred style.

Also, as much as ApplicationHelper is a junk drawer already, I think this is a rare case of this helper actually belonging in that module.

@rspeicher Hi i'm new here, i would love take care of this issue, i don't know if @pawandubey still working on this, if not could you please assignee me to this issue?

Added ~307491 label

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@lchavez Hey Luis, I am almost done with this issue and will be making a PR by tomorrow. Sorry for the delay!

Reassigned to @pawandubey

Added Deliverable and removed ~307491 technical debt ~131895 labels

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I wonder if active_when should take a block instead of a value and become active_if { something } to resemble Array#delete_if better. Would this work?

@grzesiek What's the benefit there? The point of the helper as I saw it was just to clean up the frontend code a bit, and I think the block form is slightly dirtier.

@rspeicher Makes sense!

@pawandubey Any progress on this? Do you need help?

@rymai I am sorry for vanishing off the face of the internet. I am stuck with exams at the university for the next few days. I just have to make the PR but I need to clean up my commits. Is it acceptable if I delay it by a few days? I will make time for this by Dec 2nd.

@pawandubey That's ok, thanks for the heads up!

changed milestone to %8.16

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changed milestone to %8.17

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removed Deliverable label

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mentioned in merge request !9166 (merged)

closed via merge request !9166 (merged)

mentioned in merge request !14785