Linter Rule: Disallow class definitions in ERB templates

Rule: erb-no-class-definitions

Description

Disallow defining Ruby class structures inside ERB templates. View files should only contain rendering logic, not class definitions. Defining classes in ERB breaks separation of concerns and introduces maintainability risks.

Rationale

Defining classes inside a template:

• Pollutes the global or view namespace
• Makes behavior hard to test or reuse
• Cannot be autoloaded or organized conventionally
• Violates MVC boundaries in Rails
• May cause unpredictable behavior if the template is rendered multiple times

Templates are not an appropriate place for defining classes. Move them to helpers, models, or view objects.

Examples

✅ Good

# app/components/badge_component.rb
class BadgeComponent
  def render
    %(<span class="badge">NEW</span>).html_safe
  end
end

<%= BadgeComponent.new.render %>

🚫 Bad

<%
  class BadgeComponent
Avoid defining classes in ERB templates. Move this class to a model, helper, or view object. (erb-no-class-definitions)
    def render
Avoid defining methods in ERB templates. Move `render` to a helper, presenter, or view component. (erb-no-method-definitions)
      %(<span class="badge">NEW</span>).html_safe
Avoid using silent ERB tags for literals. `%(<span class="badge">NEW</span>)` is evaluated but never used or output. (erb-no-unused-literals)
    end
  end
%>

<%= BadgeComponent.new.render %>