Linter Rule: Disallow sleep in ERB templates

Rule: erb-no-sleep

Description

This rule disallows calling sleep and Kernel.sleep in ERB templates.

Rationale

sleep blocks the thread that is rendering the response. Nothing is sent to the browser until the template finishes, so every second spent sleeping is a second added to the response time of every request that hits the template, and the worker handling it cannot serve anyone else in the meantime.

A sleep in a template is almost always left over from local work, such as demonstrating a loading state, reproducing a race condition, or waiting for something that has not finished yet. None of those need to happen in the template: artificial latency belongs in development-only middleware where it can be enabled and removed in one place, and work that takes time belongs in a background job.

sleep called on another receiver, such as client.sleep, is not reported, since that is an unrelated method that happens to share the name.

Examples

✅ Good

<%= render "products/list", products: @products %>

🚫 Bad

<% sleep 2 %>
Avoid using `sleep 2` in ERB templates. It blocks the thread rendering the response and delays the page for every request. Remove it, or move the delay outside of the template. (erb-no-sleep)

<% Kernel.sleep(0.5) %>
Avoid using `Kernel.sleep(0.5)` in ERB templates. It blocks the thread rendering the response and delays the page for every request. Remove it, or move the delay outside of the template. (erb-no-sleep)

<% @products.each do |product| %>
  <% sleep 0.1 %>
Avoid using `sleep 0.1` in ERB templates. It blocks the thread rendering the response and delays the page for every request. Remove it, or move the delay outside of the template. (erb-no-sleep)
  <%= product.name %>
<% end %>

References

• Kernel#sleep