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Zee
Zee

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Surprising behavior with Rails I18n Lazy Lookups and Partials

#help #rails #i18n

Rails i18n supports lazy lookup so that if you have a locales file shaped like this:

en:
 newsletter_cta:
   title: "Stay Up To Date With The Latest Happenings"

You can reference the value in newsletter_cta.title via t('.title') when in app/views/_newsletter_cta.html.erb

In many Rails applications, I extract partials to encapsulate components so any HTML/CSS oriented team member doesn't have to learn how to write helper methods when writing components; and so we don't wind up with copy-pasted code that would necessitate massive pain when upgrading or shifting the underlying UI framework.

Here's an example of a bootstrap section:

# app/views/application/_section.html.erb
<section class="section-wrap">
  <div class="container">
    <%= yield %>
  </div>
</section>

Which I can then use in other views, like this:

# app/views/_newsletter_cta.html.erb
<%= render "section" do %>
  <h2><%= t('newsletter_cta.title') %></h2>
  <%= render "cta-button", text: t('newsletter_cta.title') %> 
<% end %>

This works fine, so long as don't rely on lazy lookup and I hardcode the full lookup string for the translation.

However, as soon as I use lazy lookups the translation is not found.

# app/views/_newsletter_cta.html.erb 
<%= render "section" do %>
  <h2><%= t('.title') %></h2>
  <%= render "cta-button", text: t('.title') %> 
<% end %>

Tracing through to the translate method in ActionView::Helpers::TranslationHelper we see that it relies on a method named scope_key_by_partial which in turn, relies on an instance variable @virtual_path.

Do any of y'all know of a way to preserve the virtual path while using partials with blocks? Is there a gem somewhere that changes this behavior? I'm a bit surprised no one else has stumbled into this.

Top comments (4)

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yourivdlans profile image
Youri van der Lans •

I've also been running into this issue. But because I use the i18n-tasks gem to keep my localisation file in check I've chosen to write out the absolute path for a translation when using them within render blocks.

Basically what happens is as soon as you put a relative translation in a render block the path gets changed. In your example it would be: "application.section.title".

One way to approach this could be to pass the i18n scope of the view to the partial and use that when translating a key.

Something like:

<%= render "section", i18n_scope: @virtual_path.gsub(%r{/_?}, ".") do %>
  <h2><%= t('title', scope: i18n_scope) %></h2>
<% end %>

Note the removed dot before "title" indicating this is not a relative lookup.

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zspencer profile image
Zee •

I think landing on "Use absolute paths at all times with I18n" is great advice, especially since the lookup inference pattern is pretty unique to Rails.

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joshantbrown profile image
Josh Brown •

When you call render "section" what it seems actually happens is it treats the partial as a template, this changes the scope of execution and therefore changes where those translations are executed.

Instead you can explicitly render it as a partial by passing it as render partial: "section". However, partials don't allow you to pass blocks to them, instead you'll need to capture the content into a variable and pass it as a local:

<% content = capture do %>
  <!-- Your complex HTML/ERB code here -->
<% end %>

<%= render partial: "shared/section", locals: { content: content } %>
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Putting these in a helper tidies things up in the views:

module ApplicationHelper
  def section(&block)
    content = capture(&block)
    render partial: "shared/section", locals: { content: content }
  end
end
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Then in your view you can do:

<%= section do %>
  <h2><%= t('.title') %></h2>
<% end %>
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krebbl profile image
Marcus Krejpowicz •

In case somebody is looking for a workaround, here it is:

module ApplicationHelper
...
def render(*args, &block)
  if block
    vpath = instance_variable_get(:@virtual_path)
    super(*args) do |*kwargs|
      original_path = instance_variable_get(:@virtual_path)
      instance_variable_set(:@virtual_path, vpath)
      ret = capture(*kwargs, &block)
      instance_variable_set(:@virtual_path, original_path)
      ret
    end
  else
    super(*args, &block)
  end
end
...
end
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