feat: new rule proposal: no-invalid-entity-351

[perpetual-cosmos]

• Addresses an existing open issue: New rule proposal: no-invalid-entity feature [FEATURE] New rule proposal: no-invalid-entity #351

---

Checklist

• Implemented the no-invalid-entity rule to disallow invalid HTML entities.
• Added tests for the rule in packages/eslint-plugin/tests/rules/no-invalid-entity.test.js.
• Added documentation for the rule in docs/rules/no-invalid-entity.md.
• Added entities.json data file to support entity validation.

Changes

• Added no-invalid-entity.js rule in packages/eslint-plugin/lib/rules/.
• Added tests in packages/eslint-plugin/tests/rules/no-invalid-entity.test.js.
• Added documentation in docs/rules/no-invalid-entity.md.
• Added entities.json in a new packages/eslint-plugin/lib/data folder.

Description

This PR introduces the no-invalid-entity rule to the @html-eslint/eslint-plugin package, addressing the feature request to prevent the use of invalid HTML entities in markup. The rule validates both named entities (e.g.,  ) and numeric entities (e.g.,  ) against a list of valid entities in entities.json.

##Note
While testing, I encountered a failure in the E2E test tests/e2e/index.test.js (e2e/robertakarobin) due to a mismatch in expected output. This failure is unrelated to the no-invalid-entity rule and may be due to formatting rules or test expectations. Should I attempt to resolve this issue before the PR is merged, or should I create a separate issue/PR for it?

##Thank You!
This is my first contribution to a project like this, and I want to thank the maintainers for their guidance and support throughout the process. It’s been a great learning experience, and I truly appreciate the opportunity to contribute to html-eslint. Thank you so much!

[Copilot]

Pull Request Overview

Adds a new ESLint rule no-invalid-entity to prevent invalid HTML entities in templates and text nodes

• Implements detection logic for named and numeric entities against a JSON data source
• Provides accompanying unit tests and integrates the rule into the plugin index
• Includes documentation with usage, though examples need correction

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 1 comment.

File	Description
packages/eslint-plugin/lib/rules/no-invalid-entity.js	Implements the rule to parse text nodes and report invalid entities
packages/eslint-plugin/tests/rules/no-invalid-entity.test.js	Adds basic unit tests for named entities; template tests are currently empty
packages/eslint-plugin/lib/rules/index.js	Imports and registers the new no-invalid-entity rule
docs/rules/no-invalid-entity.md	Adds documentation and examples for using the rule

Comments suppressed due to low confidence (3)

docs/rules/no-invalid-entity.md:28

• [nitpick] The 'Incorrect' and 'Correct' examples are identical, which can confuse readers. Update the incorrect sample to include an actual invalid entity (e.g., &nbsb;) so the difference is clear.

<p>&lt; &gt; &amp; &nbsp; &#160; &#xA0;</p>

packages/eslint-plugin/tests/rules/no-invalid-entity.test.js:9

• Add valid test cases for numeric entities (e.g.,   and  ) to ensure both decimal and hexadecimal references are covered.

{ code: "<p>&lt; &gt; &amp; &nbsp;</p>" }, // Valid entities

packages/eslint-plugin/tests/rules/no-invalid-entity.test.js:27

• The template parser tests are empty. Either add template-specific valid/invalid cases or remove this block if templates aren’t supported.

templateRuleTester.run("[template] no-invalid-entity", rule, {

[Copilot]

Hexadecimal entities (e.g.,  ) aren’t detected correctly because entityName begins with '#', so startsWith("x") is always false. Strip the leading # before testing, for example:

const raw = entityName.slice(1).toLowerCase();
const isHex = raw.startsWith('x');

Suggested change

	const isHex = entityName.startsWith("x");
	const numStr = isHex ? entityName.slice(2) : entityName.slice(1);
	const rawEntityName = entityName.slice(1).toLowerCase();
	const isHex = rawEntityName.startsWith("x");
	const numStr = isHex ? rawEntityName.slice(1) : rawEntityName;

[yeonjuan]

@perpetual-cosmos Thank you for your contribution. Can you please confirm that lint and format are okay before reviewing further?

• yarn run lint
• yarn run format

When viewed in CI, the following lint errors are occurring. This means that an improper whitespace string is present in the code during typing. (https://eslint.org/docs/latest/rules/no-irregular-whitespace)

/home/runner/work/html-eslint/html-eslint/packages/eslint-plugin/lib/rules/no-invalid-entity.js
Error:   59:40  error  Irregular whitespace not allowed  no-irregular-whitespace
Error:   70:42  error  Irregular whitespace not allowed  no-irregular-whitespace
Error:   70:47  error  Irregular whitespace not allowed  no-irregular-whitespace

[perpetual-cosmos]

Thanks for the heads-up! I've removed the irregular whitespace from the relevant lines and confirmed everything is clean now.
Ran yarn lint and yarn format — both pass ✅
I'm working on the other issues Copilot mentioned. Will update once they're resolved.

[yeonjuan]

Hi, @perpetual-cosmos Before I review the details, I’d like to check these two things first.

1. It seems formatting has not been applied. Please run yarn format in the project root directory and commit the changes.

2. The cspell CI is failing. Please add "nbnb" to the "words" field in .cspell.json.
   You can check the spelling with the yarn check:spell command.

[perpetual-cosmos]

Thank you for the guidance.

I've addressed both points:

Ran yarn format at the project root and committed the formatted changes.

Added "nbsb" to the "words" field in .cspell.json to resolve the spell check issue.

[yeonjuan]

Thank you for working on this, and sorry for the late review.
I've left some comments.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.31%. Comparing base (7c0dc9d) to head (57ae8e6).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #371      +/-   ##
==========================================
+ Coverage   98.29%   98.31%   +0.02%     
==========================================
  Files          79       80       +1     
  Lines        2517     2548      +31     
  Branches      687      695       +8     
==========================================
+ Hits         2474     2505      +31     
  Misses         43       43              

Flag	Coverage Δ
unittest	98.31% <100.00%> (+0.02%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
packages/eslint-plugin/lib/rules/index.js	100.00% <100.00%> (ø)
...kages/eslint-plugin/lib/rules/no-invalid-entity.js	100.00% <100.00%> (ø)

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[yeonjuan]

@perpetual-cosmos Thank you for contributing!