Extract rule: template-no-capital-arguments

README.md

@@ -189,15 +189,16 @@ rules in templates can be disabled with eslint directives with mustache or html
 
 ### Best Practices
 
-| Name                                                                                                   | Description                                               | 💼 | 🔧 | 💡 |
-| :----------------------------------------------------------------------------------------------------- | :-------------------------------------------------------- | :- | :- | :- |
-| [template-builtin-component-arguments](docs/rules/template-builtin-component-arguments.md)             | disallow setting certain attributes on builtin components |    |    |    |
-| [template-no-action-modifiers](docs/rules/template-no-action-modifiers.md)                             | disallow usage of {{action}} modifiers                    |    |    |    |
-| [template-no-arguments-for-html-elements](docs/rules/template-no-arguments-for-html-elements.md)       | disallow @arguments on HTML elements                      |    |    |    |
-| [template-no-array-prototype-extensions](docs/rules/template-no-array-prototype-extensions.md)         | disallow usage of Ember Array prototype extensions        |    |    |    |
-| [template-no-block-params-for-html-elements](docs/rules/template-no-block-params-for-html-elements.md) | disallow block params on HTML elements                    |    |    |    |
-| [template-no-debugger](docs/rules/template-no-debugger.md)                                             | disallow {{debugger}} in templates                        |    |    |    |
-| [template-no-log](docs/rules/template-no-log.md)                                                       | disallow {{log}} in templates                             |    |    |    |
+| Name                                                                                                   | Description                                                     | 💼 | 🔧 | 💡 |
+| :----------------------------------------------------------------------------------------------------- | :-------------------------------------------------------------- | :- | :- | :- |
+| [template-builtin-component-arguments](docs/rules/template-builtin-component-arguments.md)             | disallow setting certain attributes on builtin components       |    |    |    |
+| [template-no-action-modifiers](docs/rules/template-no-action-modifiers.md)                             | disallow usage of {{action}} modifiers                          |    |    |    |
+| [template-no-arguments-for-html-elements](docs/rules/template-no-arguments-for-html-elements.md)       | disallow @arguments on HTML elements                            |    |    |    |
+| [template-no-array-prototype-extensions](docs/rules/template-no-array-prototype-extensions.md)         | disallow usage of Ember Array prototype extensions              |    |    |    |
+| [template-no-block-params-for-html-elements](docs/rules/template-no-block-params-for-html-elements.md) | disallow block params on HTML elements                          |    |    |    |
+| [template-no-capital-arguments](docs/rules/template-no-capital-arguments.md)                           | disallow capital arguments (use lowercase @arg instead of @Arg) |    |    |    |
+| [template-no-debugger](docs/rules/template-no-debugger.md)                                             | disallow {{debugger}} in templates                              |    |    |    |
+| [template-no-log](docs/rules/template-no-log.md)                                                       | disallow {{log}} in templates                                   |    |    |    |
 
 ### Components
 

docs/rules/template-no-capital-arguments.md

@@ -0,0 +1,43 @@
+# ember/template-no-capital-arguments
+
+<!-- end auto-generated rule header -->
+
+Disallow capital letters in argument names. Use lowercase argument names (e.g., `@arg` instead of `@Arg`).
+
+## Rule Details
+
+This rule enforces the convention that argument names should start with lowercase letters.
+
+## Examples
+
+Examples of **incorrect** code for this rule:
+
+```gjs
+<template>
+  <div>{{@Arg}}</div>
+</template>
+```
+
+```gjs
+<template>
+  <div>{{@MyArgument}}</div>
+</template>
+```
+
+Examples of **correct** code for this rule:
+
+```gjs
+<template>
+  <div>{{@arg}}</div>
+</template>
+```
+
+```gjs
+<template>
+  <div>{{@myArgument}}</div>
+</template>
+```
+
+## References
+
+- [Ember Style Guide](https://github.com/ember-cli/ember-styleguide)

lib/rules/template-no-capital-arguments.js

@@ -0,0 +1,47 @@
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow capital arguments (use lowercase @arg instead of @Arg)',
+      category: 'Best Practices',
+      recommended: false,
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-no-capital-arguments.md',
+    },
+    fixable: null,
+    schema: [],
+    messages: {
+      noCapitalArguments:
+        'Argument names should start with lowercase. Use @{{lowercase}} instead of @{{name}}.',
+    },
+    strictGjs: true,
+    strictGts: true,
+  },
+
+  create(context) {
+    function checkPath(node, path) {
+      if (!path || !path.head) {
+        return;
+      }
+
+      const name = path.head.name || path.head;
+      if (typeof name === 'string' && name.startsWith('@') && /^@[A-Z]/.test(name)) {
+        const lowercase = name.charAt(0) + name.charAt(1).toLowerCase() + name.slice(2);
+        context.report({
+          node,
+          messageId: 'noCapitalArguments',
+          data: {
+            name,
+            lowercase,
+          },
+        });
+      }
+    }
+
+    return {
+      GlimmerPathExpression(node) {
+        checkPath(node, node);
+      },
+    };
+  },
+};

tests/lib/rules/template-no-capital-arguments.js

@@ -0,0 +1,73 @@
+const { RuleTester } = require('eslint');
+const rule = require('../../../lib/rules/template-no-capital-arguments');
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+ruleTester.run('template-no-capital-arguments', rule, {
+  valid: [
+    {
+      filename: 'my-component.gjs',
+      code: `
+        import Component from '@glimmer/component';
+        export default class MyComponent extends Component {
+          <template>
+            <div>{{@arg}}</div>
+          </template>
+        }
+      `,
+      output: null,
+    },
+    {
+      filename: 'my-component.gjs',
+      code: `
+        import Component from '@glimmer/component';
+        export default class MyComponent extends Component {
+          <template>
+            <div>{{@myArgument}}</div>
+          </template>
+        }
+      `,
+      output: null,
+    },
+  ],
+
+  invalid: [
+    {
+      filename: 'my-component.gjs',
+      code: `
+        import Component from '@glimmer/component';
+        export default class MyComponent extends Component {
+          <template>
+            <div>{{@Arg}}</div>
+          </template>
+        }
+      `,
+      output: null,
+      errors: [
+        {
+          messageId: 'noCapitalArguments',
+        },
+      ],
+    },
+    {
+      filename: 'my-component.gjs',
+      code: `
+        import Component from '@glimmer/component';
+        export default class MyComponent extends Component {
+          <template>
+            <div>{{@MyArgument}}</div>
+          </template>
+        }
+      `,
+      output: null,
+      errors: [
+        {
+          messageId: 'noCapitalArguments',
+        },
+      ],
+    },
+  ],
+});