Linter Rule: Disallow trailing whitespace at end of lines

Rule: erb-no-trailing-whitespace

Description

Disallow trailing whitespace (spaces, tabs, carriage returns, and other whitespace characters) at the end of lines in ERB templates.

Skipped Content

This rule does not flag trailing whitespace inside:

• <pre> - Preformatted text where whitespace is significant
• <textarea> - User input where whitespace may be intentional
• <script> - Treated as foreign content
• <style> - Treated as foreign content
• ERB tags (<% %>, <%= %>, <%# %>) - Ruby code where trailing whitespace could be significant (heredocs, string literals)

Rationale

Trailing whitespace is invisible and serves no purpose, but it can cause several issues:

• Creates unnecessary noise in diffs and pull requests
• Can trigger merge conflicts when different editors handle trailing whitespace differently
• Increases file size with characters that have no visual or functional effect
• Many editor configurations and linters in other languages flag trailing whitespace, so keeping templates clean maintains consistency across the project

Examples

✅ Good

<div>
  <p>Hello</p>
</div>

<%= content %>

<div>
  <h1>Title</h1>
</div>

🚫 Bad

<div>···
  <p>Hello</p>
</div>

<%= content %>·

Hello→→
World···

· represents a trailing space, → represents a trailing tab.

References

• Inspiration: ERB Lint TrailingWhitespace rule