Extract rule: template-no-splattributes-with-class

Author: NullVoxPopuli

README.md

@@ -256,6 +256,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | [template-no-obsolete-elements](docs/rules/template-no-obsolete-elements.md)                                       | disallow obsolete HTML elements                                              |    |    |    |
 | [template-no-outlet-outside-routes](docs/rules/template-no-outlet-outside-routes.md)                               | disallow {{outlet}} outside of route templates                               |    |    |    |
 | [template-no-page-title-component](docs/rules/template-no-page-title-component.md)                                 | disallow usage of ember-page-title component                                 |    |    |    |
+| [template-no-splattributes-with-class](docs/rules/template-no-splattributes-with-class.md)                         | disallow splattributes with class attribute                                  |    |    |    |
 | [template-no-trailing-spaces](docs/rules/template-no-trailing-spaces.md)                                           | disallow trailing whitespace at the end of lines in templates                |    | 🔧 |    |
 | [template-no-unavailable-this](docs/rules/template-no-unavailable-this.md)                                         | disallow `this` in templates that are not inside a class or function         |    |    |    |
 | [template-no-unnecessary-component-helper](docs/rules/template-no-unnecessary-component-helper.md)                 | disallow unnecessary component helper                                        |    | 🔧 |    |

docs/rules/template-no-splattributes-with-class.md

@@ -0,0 +1,53 @@
+# ember/template-no-splattributes-with-class
+
+<!-- end auto-generated rule header -->
+
+Disallow using `...attributes` with `class` attribute.
+
+When using `...attributes` (splattributes), any classes passed from the parent component will be automatically merged with the component's own classes. Adding a `class` attribute alongside `...attributes` can lead to confusion about which classes take precedence.
+
+## Examples
+
+This rule **forbids** the following:
+
+```gjs
+<template>
+  <div ...attributes class='foo'>
+    content
+  </div>
+</template>
+```
+
+```gjs
+<template>
+  <div class='foo' ...attributes>
+    content
+  </div>
+</template>
+```
+
+This rule **allows** the following:
+
+```gjs
+<template>
+  <div ...attributes>
+    content
+  </div>
+</template>
+```
+
+```gjs
+<template>
+  <div class='foo'>
+    content
+  </div>
+</template>
+```
+
+## Why?
+
+When using `...attributes`, classes are automatically merged from parent components. Using a `class` attribute alongside it creates confusion about which classes take precedence and can lead to unexpected styling behavior.
+
+## References
+
+- [Ember.js Guides - Splattributes](https://guides.emberjs.com/release/components/component-arguments-and-html-attributes/#toc_html-attributes)

lib/rules/template-no-splattributes-with-class.js

@@ -0,0 +1,41 @@
+const ERROR_MESSAGE =
+  'Using `...attributes` with `class` attribute is not allowed. Use `...attributes` alone to allow class merging.';
+
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow splattributes with class attribute',
+      category: 'Best Practices',
+      recommended: false,
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-no-splattributes-with-class.md',
+      templateMode: 'both',
+    },
+    fixable: null,
+    schema: [],
+    messages: {},
+    originallyFrom: {
+      name: 'ember-template-lint',
+      rule: 'lib/rules/no-splattributes-with-class.js',
+      docs: 'docs/rule/no-splattributes-with-class.md',
+      tests: 'test/unit/rules/no-splattributes-with-class-test.js',
+    },
+  },
+
+  create(context) {
+    return {
+      GlimmerElementNode(node) {
+        const hasSplattributes = node.attributes.some((attr) => attr.name === '...attributes');
+        const classAttribute = node.attributes.find((attr) => attr.name === 'class');
+
+        if (hasSplattributes && classAttribute) {
+          context.report({
+            node: classAttribute,
+            message: ERROR_MESSAGE,
+          });
+        }
+      },
+    };
+  },
+};

tests/lib/rules/template-no-splattributes-with-class.js

@@ -0,0 +1,103 @@
+const rule = require('../../../lib/rules/template-no-splattributes-with-class');
+const RuleTester = require('eslint').RuleTester;
+
+const ERROR_MESSAGE =
+  'Using `...attributes` with `class` attribute is not allowed. Use `...attributes` alone to allow class merging.';
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+ruleTester.run('template-no-splattributes-with-class', rule, {
+  valid: [
+    '<template><div ...attributes>content</div></template>',
+    '<template><div class="foo">content</div></template>',
+    '<template><div class="foo bar">content</div></template>',
+    '<template><div class={{foo}}>content</div></template>',
+    '<template><div class="foo {{bar}}">content</div></template>',
+  ],
+  invalid: [
+    {
+      code: '<template><div ...attributes class="foo">content</div></template>',
+      output: null,
+      errors: [{ message: ERROR_MESSAGE }],
+    },
+    {
+      code: '<template><div class="foo" ...attributes>content</div></template>',
+      output: null,
+      errors: [{ message: ERROR_MESSAGE }],
+    },
+    {
+      code: '<template><div ...attributes class={{foo}}>content</div></template>',
+      output: null,
+      errors: [{ message: ERROR_MESSAGE }],
+    },
+
+    {
+      code: '<template><div class="foo" ...attributes class="bar">content</div></template>',
+      output: null,
+      errors: [{ message: ERROR_MESSAGE }],
+    },
+  ],
+});
+
+const hbsRuleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser/hbs'),
+  parserOptions: {
+    ecmaVersion: 2022,
+    sourceType: 'module',
+  },
+});
+
+hbsRuleTester.run('template-no-splattributes-with-class', rule, {
+  valid: [
+    '<div ...attributes>content</div>',
+    '<div class="foo">content</div>',
+    '<div class="foo bar">content</div>',
+    '<div class={{foo}}>content</div>',
+    '<div class="foo {{bar}}">content</div>',
+  ],
+  invalid: [
+    {
+      code: '<div ...attributes class="foo">content</div>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Using `...attributes` with `class` attribute is not allowed. Use `...attributes` alone to allow class merging.',
+        },
+      ],
+    },
+    {
+      code: '<div class="foo" ...attributes>content</div>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Using `...attributes` with `class` attribute is not allowed. Use `...attributes` alone to allow class merging.',
+        },
+      ],
+    },
+    {
+      code: '<div ...attributes class={{foo}}>content</div>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Using `...attributes` with `class` attribute is not allowed. Use `...attributes` alone to allow class merging.',
+        },
+      ],
+    },
+    {
+      code: '<div class="foo" ...attributes class="bar">content</div>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Using `...attributes` with `class` attribute is not allowed. Use `...attributes` alone to allow class merging.',
+        },
+      ],
+    },
+  ],
+});