Linter Rule: Disallow parser errors in HTML+ERB documents

Rule: parser-no-errors

Description

Report parser errors as linting offenses. This rule surfaces syntax errors, malformed HTML, and other parsing issues that prevent the document from being correctly parsed.

Rationale

Parser errors indicate fundamental structural problems in HTML+ERB documents that can lead to unexpected rendering behavior, accessibility issues, and maintenance difficulties. These errors should be fixed before addressing other linting concerns as they represent invalid markup that browsers may interpret inconsistently.

By surfacing parser errors through the linter, developers can catch these critical issues when running lint checks directly, without needing to switch to the language server or other tools.

Examples

✅ Good

html

<h2>Welcome to our site</h2>
<p>This is a paragraph with proper structure.</p>

<div class="container">
  <img src="image.jpg" alt="Description">
</div>

erb

<h2><%= @page.title %></h2>
<p><%= @page.description %></p>

<% if user_signed_in? %>
  <div class="user-section">
    <%= current_user.name %>
  </div>
<% end %>

🚫 Bad

html

<!-- Mismatched closing tag -->
<h2>Welcome to our site</h3>Opening tag `<h2>` at (2:1) closed with `</h3>` at (2:25). (`TAG_NAMES_MISMATCH_ERROR`) (parser-no-errors)

<!-- Unclosed element -->
<div>
  <p>This paragraph is never closed
</div>Opening tag `<p>` at (6:3) closed with `</div>` at (7:2). (`TAG_NAMES_MISMATCH_ERROR`) (parser-no-errors)

<!-- Missing opening tag -->
Some content
</div>Opening tag `<p>` at (6:3) closed with `</div>` at (11:2). (`TAG_NAMES_MISMATCH_ERROR`) (parser-no-errors)
Tag `<h2>` opened at (2:1) was never closed before the end of document. (`UNCLOSED_ELEMENT_ERROR`) (parser-no-errors)
Tag `<div>` opened at (5:1) was never closed before the end of document. (`UNCLOSED_ELEMENT_ERROR`) (parser-no-errors)
Tag `<p>` opened at (6:3) was never closed before the end of document. (`UNCLOSED_ELEMENT_ERROR`) (parser-no-errors)

erb

<!-- Invalid Ruby syntax in ERB -->
<%= 1 + %>expect_expression_after_operator: unexpected ';'; expected an expression after the operator (`RUBY_PARSE_ERROR`) (parser-no-errors)

<!-- Mismatched quotes -->
<div class="container'>Content</div>

<!-- Void element with closing tag -->
<img src="image.jpg" alt="Description"></img>Found `TOKEN_EOF` when expecting `TOKEN_HTML_TAG_END` at (8:45). (`UNEXPECTED_TOKEN_ERROR`) (parser-no-errors)
Found `TOKEN_EOF` when expecting `TOKEN_IDENTIFIER` at (8:45). (`UNEXPECTED_TOKEN_ERROR`) (parser-no-errors)
Found `TOKEN_EOF` when expecting `TOKEN_HTML_TAG_START_CLOSE` at (8:45). (`UNEXPECTED_TOKEN_ERROR`) (parser-no-errors)
`img` is a void element and should not be used as a closing tag. Use `<img>` or `<img />` instead of `</img>`. (`VOID_ELEMENT_CLOSING_TAG_ERROR`) (parser-no-errors)
Unescaped quote character in attribute value. Expected: `escaped quote (\') or different quote style (")`, found: `"`. (`UNEXPECTED_ERROR`) (parser-no-errors)
Opening tag `<div>` at (5:1) closed with `</>` at (8:45). (`TAG_NAMES_MISMATCH_ERROR`) (parser-no-errors)
Tag `<div>` opened at (5:1) was never closed before the end of document. (`UNCLOSED_ELEMENT_ERROR`) (parser-no-errors)

Error Types

This rule reports various parser error types:

UNCLOSED_ELEMENT_ERROR: Elements that are opened but never closed
MISSING_CLOSING_TAG_ERROR: Opening tags without matching closing tags
MISSING_OPENING_TAG_ERROR: Closing tags without matching opening tags
TAG_NAMES_MISMATCH_ERROR: Opening and closing tags with different names
QUOTES_MISMATCH_ERROR: Mismatched quotation marks in attributes
VOID_ELEMENT_CLOSING_TAG_ERROR: Void elements (like <img>) with closing tags
RUBY_PARSE_ERROR: Invalid Ruby syntax within ERB tags
UNEXPECTED_TOKEN_ERROR: Unexpected tokens during parsing
UNEXPECTED_ERROR: Other unexpected parsing issues

Linter Rule: Disallow parser errors in HTML+ERB documents ​

Description ​

Rationale ​

Examples ​

✅ Good ​

🚫 Bad ​

Error Types ​

References ​