Linter Rule: Don't use children for case/when and case/in nodes

Rule: erb-no-case-node-children

Description

Disallow placing content or expressions directly between the opening <% case %> and the first <% when %> or <% in %> clause in an HTML+ERB template.

In Ruby and ERB, case expressions are intended to branch execution. Any content placed between the case and its when/in clauses is not executed as part of the branching logic, and may lead to confusion, orphaned output, or silent bugs.

Rationale

Including content directly inside a case block is likely unintended and often leads to unclear or broken rendering logic.

Most developers expect that nothing happens until the first when/in matches. Content in that location is often a copy/paste or indentation mistake and should be flagged to maintain clarity and correctness in templates.

This mirrors how case works in Ruby itself and helps avoid surprising output.

Examples

✅ Good

<% case variable %>
<% when "a" %>
  A
<% when "b" %>
  B
<% else %>
  C
<% end %>

🚫 Bad

<% case variable %>
Do not place `This content is outside of any when/in/else block!` between `<% case variable %>` and `<% when "a" %>`. Content here is not part of any branch and will not be rendered. (erb-no-case-node-children)
  This content is outside of any when/in/else block!
<% when "a" %>
  A
<% when "b" %>
  B
<% else %>
  C
<% end %>

References

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