Linter Rule: Prefer do ... end over { ... } for blocks that span multiple ERB tags

Rule: erb-prefer-do-end-blocks

Description

Disallow { ... } as the delimiters of a block that is opened in one ERB tag and closed in another.

<% @users.each { |user| %>
Avoid using `{ ... }` for a block that spans multiple ERB tags. Use `do ... end` instead. (erb-prefer-do-end-blocks)
  <p><%= user.name %></p>
<% } %>

Rationale

A block that spans ERB tags is a multi-line block, and do ... end is the convention for those in Ruby. In a template the argument is stronger than in plain Ruby: every other construct that wraps markup, like if, unless, case, or each with do, closes with <% end %>, so a lone <% } %> is the one closing tag that has to be read differently from the rest of the file.

The braces are also easy to lose. <% } %> is a single character of signal surrounded by ERB punctuation, and it looks the same whether it closes a block, a hash, or an interpolation, whereas <% end %> says what it does.

A brace block written entirely inside a single ERB tag is not reported. <%= @users.map { |user| user.name }.join(", ") %> stays on one line and reads fine, which is also what RuboCop's Style/BlockDelimiters prefers for single-line blocks.

Autofix

This rule provides an autofix that replaces { with do and the matching <% } %> with <% end %>:

<%= form_with(model: @user) { |form| %>
Avoid using `{ ... }` for a block that spans multiple ERB tags. Use `do ... end` instead. (erb-prefer-do-end-blocks)
  <%= form.submit %>
<% } %>

<%= form_with(model: @user) do |form| %>
  <%= form.submit %>
<% end %>

{ binds to the closest method call while do binds to the outermost one, so the fix is only safe when both are the same call. When they aren't, as in <% puts @users.map { |user| %> where the block belongs to map but a do would hand it to puts, the offense is still reported but the fix requires --fix-unsafely.

Examples

✅ Good

<% @users.each do |user| %>
  <p><%= user.name %></p>
<% end %>

<%= form_with(model: @user) do |form| %>
  <%= form.submit %>
<% end %>

<%= @users.map { |user| user.name }.join(", ") %>

🚫 Bad

<% @users.each { |user| %>
Avoid using `{ ... }` for a block that spans multiple ERB tags. Use `do ... end` instead. (erb-prefer-do-end-blocks)
  <p><%= user.name %></p>
<% } %>

<%= form_with(model: @user) { |form| %>
Avoid using `{ ... }` for a block that spans multiple ERB tags. Use `do ... end` instead. (erb-prefer-do-end-blocks)
  <%= form.submit %>
<% } %>

<% @users.each { %>
Avoid using `{ ... }` for a block that spans multiple ERB tags. Use `do ... end` instead. (erb-prefer-do-end-blocks)
  <p>Hello</p>
<% } %>

References

• RuboCop: Style/BlockDelimiters
• Ruby Style Guide: {...} vs do...end