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Linter: Implement erb-prefer-do-end-blocks rule - #1973
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This pull request implements `erb-prefer-do-end-blocks`, a new rule that
flags a block opened with `{` in one ERB tag and closed with `<% } %>`
in another, and points at the `do ... end` form instead.
```erb
<% @users.each { |user| %>
<p><%= user.name %></p>
<% } %>
```
```
Avoid using `{ ... }` for a block that spans multiple ERB tags. Use `do ... end` instead.
```
A block that spans ERB tags is a multi-line block, and `do ... end` is
the typical 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, since `<% } %>` is a single character of
signal surrounded by ERB punctuation and looks the same whether it
closes a block, a hash, or an interpolation.
A brace block written entirely inside one ERB tag is not reported, so
`<%= @users.map { |user| user.name }.join(", ") %>` stays as it is.
#### Autofix
The rule is autocorrectable. The fix replaces `{` with `do` in the
opening tag and `}` with `end` in the closing tag, keeping trim markers
intact and inserting the missing space for `{|user|`:
```erb
<%= form_with(model: @user) { |form| %>
<%= form.submit %>
<% } %>
```
```erb
<%= form_with(model: @user) do |form| %>
<%= form.submit %>
<% end %>
```
Swapping the delimiters is not unconditionally safe, because `{` binds
to the closest method call while `do` binds to the outermost one. The
fix is marked safe only when both are the same call, which it checks on
the Prism node: the outermost node has to be a `CallNode` that owns the
block, after unwrapping an assignment so that `<% names = @users.map {
|user| %>` still qualifies.
```erb
<% puts @users.map { |user| %>
<p><%= user.name %></p>
<% } %>
```
Here the block belongs to `map`, but a `do` would hand it to `puts`, so
the offense is still reported while no autofix is offered.
joaoGabriel55
pushed a commit
to joaoGabriel55/herb
that referenced
this pull request
Aug 3, 2026
This pull request implements `erb-prefer-do-end-blocks`, a new rule that
flags a block opened with `{` in one ERB tag and closed with `<% } %>`
in another, and points at the `do ... end` form instead.
```erb
<% @users.each { |user| %>
<p><%= user.name %></p>
<% } %>
```
```
Avoid using `{ ... }` for a block that spans multiple ERB tags. Use `do ... end` instead.
```
A block that spans ERB tags is a multi-line block, and `do ... end` is
the typical 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, since `<% } %>` is a single character of
signal surrounded by ERB punctuation and looks the same whether it
closes a block, a hash, or an interpolation.
A brace block written entirely inside one ERB tag is not reported, so
`<%= @users.map { |user| user.name }.join(", ") %>` stays as it is.
#### Autofix
The rule is autocorrectable. The fix replaces `{` with `do` in the
opening tag and `}` with `end` in the closing tag, keeping trim markers
intact and inserting the missing space for `{|user|`:
```erb
<%= form_with(model: @user) { |form| %>
<%= form.submit %>
<% } %>
```
```erb
<%= form_with(model: @user) do |form| %>
<%= form.submit %>
<% end %>
```
Swapping the delimiters is not unconditionally safe, because `{` binds
to the closest method call while `do` binds to the outermost one. The
fix is marked safe only when both are the same call, which it checks on
the Prism node: the outermost node has to be a `CallNode` that owns the
block, after unwrapping an assignment so that `<% names = @users.map {
|user| %>` still qualifies.
```erb
<% puts @users.map { |user| %>
<p><%= user.name %></p>
<% } %>
```
Here the block belongs to `map`, but a `do` would hand it to `puts`, so
the offense is still reported while no autofix is offered.
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This pull request implements
erb-prefer-do-end-blocks, a new rule that flags a block opened with{in one ERB tag and closed with<% } %>in another, and points at thedo ... endform instead.A block that spans ERB tags is a multi-line block, and
do ... endis the typical 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, oreachwithdo, 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, since<% } %>is a single character of signal surrounded by ERB punctuation and looks the same whether it closes a block, a hash, or an interpolation.A brace block written entirely inside one ERB tag is not reported, so
<%= @users.map { |user| user.name }.join(", ") %>stays as it is.Autofix
The rule is autocorrectable. The fix replaces
{withdoin the opening tag and}withendin the closing tag, keeping trim markers intact and inserting the missing space for{|user|:Swapping the delimiters is not unconditionally safe, because
{binds to the closest method call whiledobinds to the outermost one. The fix is marked safe only when both are the same call, which it checks on the Prism node: the outermost node has to be aCallNodethat owns the block, after unwrapping an assignment so that<% names = @users.map { |user| %>still qualifies.Here the block belongs to
map, but adowould hand it toputs, so the offense is still reported while no autofix is offered.