enforce-locals-passed-to-a-partial.md

Enforce Locals Passed To A Partial

I have a big form partial (_form.html.erb) that is rendered by several different new and edit views. It's hard to tell at a glance, but the partial requires that blogmark and cancel_path are included as locals when it is rendered.

As of Rails 7.1, we now have a built-in way to enforce locals passed to a partial. We can add a magic comment at the top of the partial that specifies the locals:

<%# locals: (blogmark:, cancel_path:) -%>
<%= form_with(model: blogmark, local: true, class: "w-full max-w-3xl mb-8") do |form| %>
  <% ... %>
<% end %>

This particular ERB magic comment declares that blogmark and cancel_path are required locals.

So, what happens if I have a new.html.erb view that looks like this:

<h1>New Blogmark</h1>

<%= render 'blogmarks/form', blogmark: @blogmark %>

When I try to view the page, an error is raised:

Showing /Some/path/app/views/blogmarks/_form.html.erb where line # raised:

missing local: :cancel_path for app/views/blogmarks/_form.html.erb

Updating the render statement to include a cancel_path local fixes the issue.

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