Linter Rule: Disallow Ruby literals in ERB without output

Rule: erb-no-unused-literals

Description

Disallow Ruby literal values inside ERB tags that do not produce output or side effects. Writing literals like <% "string" %> or <% 123 %> has no effect. The value is evaluated and discarded, making the line functionally useless.

This rule detects and warns about ERB tags containing:

• Literal strings
• Numeric values (integers, floats, rationals, imaginary)
• true and false
• nil
• Symbols
• Arrays, hashes, and ranges
• Regular expressions

Rationale

These expressions are evaluated but unused, they don't produce output (not <%= ... %>), and they don't perform side effects (no assignments, method calls, or control flow). They're likely accidental leftovers, debugging artifacts, or misunderstandings of ERB syntax.

Examples

✅ Good

<% if logged_in? %>
  <p>Welcome!</p>
<% end %>

<%= "Hello, #{user.name}" %>

🚫 Bad

<% "Logged in" %>
Avoid using silent ERB tags for literals. `"Logged in"` is evaluated but never used or output. (erb-no-unused-literals)

<% 42 %>
Avoid using silent ERB tags for literals. `42` is evaluated but never used or output. (erb-no-unused-literals)

<% true %>
Avoid using silent ERB tags for literals. `true` is evaluated but never used or output. (erb-no-unused-literals)

<% false %>
Avoid using silent ERB tags for literals. `false` is evaluated but never used or output. (erb-no-unused-literals)

<% nil %>
Avoid using silent ERB tags for literals. `nil` is evaluated but never used or output. (erb-no-unused-literals)

<% [:foo, :bar] %>
Avoid using silent ERB tags for literals. `[:foo, :bar]` is evaluated but never used or output. (erb-no-unused-literals)

<% /pattern/ %>
Avoid using silent ERB tags for literals. `/pattern/` is evaluated but never used or output. (erb-no-unused-literals)

<% { key: "value" } %>
Avoid using silent ERB tags for literals. `{ key: "value" }` is evaluated but never used or output. (erb-no-unused-literals)

<% :symbol %>
Avoid using silent ERB tags for literals. `:symbol` is evaluated but never used or output. (erb-no-unused-literals)

References

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