Extract rule: template-no-chained-this

Author: NullVoxPopuli

README.md

@@ -185,6 +185,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | Name                                                                                       | Description                                               | 💼 | 🔧 | 💡 |
 | :----------------------------------------------------------------------------------------- | :-------------------------------------------------------- | :- | :- | :- |
 | [template-builtin-component-arguments](docs/rules/template-builtin-component-arguments.md) | disallow setting certain attributes on builtin components |    |    |    |
+| [template-no-chained-this](docs/rules/template-no-chained-this.md)                         | disallow chained property access on this                  |    |    |    |
 | [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                             |    |    |    |
 

docs/rules/template-no-chained-this.md

@@ -0,0 +1,64 @@
+# ember/template-no-chained-this
+
+<!-- end auto-generated rule header -->
+
+💼 This rule is enabled in the following [configs](https://github.com/ember-cli/eslint-plugin-ember#-configurations): `strict-gjs`, `strict-gts`.
+
+Disallow chained property access on `this`.
+
+Accessing deeply nested properties through `this` (like `this.user.name`) in templates makes components harder to refactor and test. It also creates tight coupling between the template and the component's internal structure. Use local variables or computed properties instead.
+
+## Rule Details
+
+This rule disallows chaining property access on `this` in templates (e.g., `this.foo.bar`).
+
+## Examples
+
+### Incorrect ❌
+
+```gjs
+<template>
+  {{this.user.name}}
+</template>
+```
+
+```gjs
+<template>
+  {{this.model.user.firstName}}
+</template>
+```
+
+```gjs
+<template>
+  <div>{{this.data.items.length}}</div>
+</template>
+```
+
+### Correct ✅
+
+```gjs
+<template>
+  {{this.userName}}
+</template>
+```
+
+```gjs
+<template>
+  {{get this.user "name"}}
+</template>
+```
+
+```gjs
+<template>
+  {{userName}}
+</template>
+```
+
+## Related Rules
+
+- [template-no-implicit-this](./template-no-implicit-this.md)
+
+## References
+
+- [Ember Best Practices - Component Design](https://guides.emberjs.com/release/components/)
+- [eslint-plugin-ember: no-this-in-template-only-components](https://github.com/eslint-plugin-ember/eslint-plugin-ember/blob/master/docs/rule/no-this-in-template-only-components.md)

lib/rules/template-no-chained-this.js

@@ -0,0 +1,36 @@
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow chained property access on this',
+      category: 'Best Practices',
+      strictGjs: true,
+      strictGts: true,
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-no-chained-this.md',
+    },
+    fixable: null,
+    schema: [],
+    messages: {
+      noChainedThis:
+        'Do not chain property access on this ({{path}}). Use local variables or getters instead.',
+    },
+  },
+
+  create(context) {
+    return {
+      GlimmerPathExpression(node) {
+        // Check if this is a chained this path (this.foo.bar)
+        if (node.head && node.head.type === 'ThisHead' && node.parts && node.parts.length > 1) {
+          context.report({
+            node,
+            messageId: 'noChainedThis',
+            data: {
+              path: node.original,
+            },
+          });
+        }
+      },
+    };
+  },
+};

tests/lib/rules/template-no-chained-this.js

@@ -0,0 +1,52 @@
+const rule = require('../../../lib/rules/template-no-chained-this');
+const RuleTester = require('eslint').RuleTester;
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+ruleTester.run('template-no-chained-this', rule, {
+  valid: [
+    '<template>{{this.user}}</template>',
+    '<template>{{userName}}</template>',
+    '<template>{{@user}}</template>',
+    '<template>{{get this.user "name"}}</template>',
+  ],
+
+  invalid: [
+    {
+      code: '<template>{{this.user.name}}</template>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Do not chain property access on this (this.user.name). Use local variables or getters instead.',
+          type: 'GlimmerPathExpression',
+        },
+      ],
+    },
+    {
+      code: '<template>{{this.model.user.firstName}}</template>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Do not chain property access on this (this.model.user.firstName). Use local variables or getters instead.',
+          type: 'GlimmerPathExpression',
+        },
+      ],
+    },
+    {
+      code: '<template><div>{{this.data.items.length}}</div></template>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Do not chain property access on this (this.data.items.length). Use local variables or getters instead.',
+          type: 'GlimmerPathExpression',
+        },
+      ],
+    },
+  ],
+});