Linter Rule: Enforce consistent right-trimming syntax

Rule: erb-right-trim

Description

This rule enforces the use of -%> for right-trimming ERB output tags (like <%= %>) instead of =%>.

Rationale

While =%> can be used for right-trimming whitespace in some ERB engines (like Erubi), it is an obscure and not well-defined syntax that lacks consistent support across most ERB implementations.

The -%> syntax is the standard, well-documented approach for right-trimming that is universally supported and consistent with left-trimming syntax (<%-). Using -%> ensures compatibility across different ERB engines, improves code clarity, and aligns with established Rails and ERB conventions.

Examples

✅ Good

<%= title -%>

<% if condition? %>
  <h1>Content</h1>
<% end %>

<% items.each do |item| %>
  <li><%= item -%></li>
<% end %>

🚫 Bad

<%= title =%>
Use `-%>` instead of `=%>` for right-trimming. The `=%>` syntax is obscure and not well-supported in most ERB engines. (erb-right-trim)


<% title =%>
Use `-%>` instead of `=%>` for right-trimming. The `=%>` syntax is obscure and not well-supported in most ERB engines. (erb-right-trim)


<% if true =%>
Use `-%>` instead of `=%>` for right-trimming. The `=%>` syntax is obscure and not well-supported in most ERB engines. (erb-right-trim)
  <h1>Content</h1>
<% end %>


<% items.each do |item| =%>
Use `-%>` instead of `=%>` for right-trimming. The `=%>` syntax is obscure and not well-supported in most ERB engines. (erb-right-trim)
  <li><%= item %></li>
<% end %>

References

• Inspiration: ERB Lint RightTrim rule