Extract rule: template-no-this-in-template-only-components

Author: NullVoxPopuli

README.md

@@ -262,6 +262,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | [template-no-positional-data-test-selectors](docs/rules/template-no-positional-data-test-selectors.md)             | disallow positional data-test-* params in curly invocations                  |    |    |    |
 | [template-no-potential-path-strings](docs/rules/template-no-potential-path-strings.md)                             | disallow potential path strings in attribute values                          |    |    |    |
 | [template-no-splattributes-with-class](docs/rules/template-no-splattributes-with-class.md)                         | disallow splattributes with class attribute                                  |    |    |    |
+| [template-no-this-in-template-only-components](docs/rules/template-no-this-in-template-only-components.md)         | disallow this in template-only components (gjs/gts)                          |    | 🔧 |    |
 | [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-this-in-template-only-components.md

@@ -0,0 +1,42 @@
+# ember/template-no-this-in-template-only-components
+
+🔧 This rule is automatically fixable by the [`--fix` CLI option](https://eslint.org/docs/latest/user-guide/command-line-interface#--fix).
+
+<!-- end auto-generated rule header -->
+
+There is no `this` context in template-tag (`<template>`) components that don't extend a class.
+
+## Rule Details
+
+In gjs/gts files with `<template>` tags, this rule flags all `this.*` path expressions and suggests converting them to named arguments (`@*`). The auto-fix replaces `this.foo` with `@foo` (except for built-in component properties like `elementId`, `tagName`, `ariaRole`, `class`, `classNames`, `classNameBindings`, `attributeBindings`, and `isVisible`, which are reported but not auto-fixed).
+
+## Examples
+
+This rule **forbids** the following:
+
+```gjs
+<template><h1>Hello {{this.name}}!</h1></template>
+```
+
+This rule **allows** the following:
+
+```gjs
+<template><h1>Hello {{@name}}!</h1></template>
+```
+
+The `--fix` option will convert to named arguments:
+
+```gjs
+<template><h1>Hello {{@name}}!</h1></template>
+```
+
+## Migration
+
+- use [ember-no-implicit-this-codemod](https://github.com/ember-codemods/ember-no-implicit-this-codemod)
+- [upgrade to Glimmer components](https://guides.emberjs.com/release/upgrading/current-edition/glimmer-components/), which don't allow ambiguous access
+  - classic components have [auto-reflection](https://github.com/emberjs/rfcs/blob/master/text/0276-named-args.md#motivation), and can use `this.myArgName` or `this.args.myArgNme` or `@myArgName` interchangeably
+
+## References
+
+- [Glimmer components](https://guides.emberjs.com/release/upgrading/current-edition/glimmer-components/)
+- [rfcs/named args](https://github.com/emberjs/rfcs/blob/master/text/0276-named-args.md#motivation)

lib/rules/template-no-this-in-template-only-components.js

@@ -0,0 +1,56 @@
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow this in template-only components (gjs/gts)',
+      category: 'Best Practices',
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-no-this-in-template-only-components.md',
+      templateMode: 'both',
+    },
+    fixable: 'code',
+    schema: [],
+    messages: {
+      noThis:
+        "Usage of 'this' in path '{{original}}' is not allowed in a template-only component. Use '{{fixed}}' if it is a named argument.",
+    },
+    originallyFrom: {
+      name: 'ember-template-lint',
+      rule: 'lib/rules/no-this-in-template-only-components.js',
+      docs: 'docs/rule/no-this-in-template-only-components.md',
+      tests: 'test/unit/rules/no-this-in-template-only-components-test.js',
+    },
+  },
+  create(context) {
+    // Properties that should not be auto-fixed (built-in component properties)
+    const BUILTIN_PROPERTIES = new Set([
+      'elementId',
+      'tagName',
+      'ariaRole',
+      'class',
+      'classNames',
+      'classNameBindings',
+      'attributeBindings',
+      'isVisible',
+    ]);
+
+    return {
+      GlimmerPathExpression(node) {
+        // In gjs/gts files with <template> tags, check for this.* usage
+        if (node.head?.type === 'ThisHead' && node.tail?.length > 0) {
+          const original = node.original;
+          const firstPart = node.tail[0];
+          const fixed = `@${node.tail.join('.')}`;
+          const canFix = !BUILTIN_PROPERTIES.has(firstPart);
+
+          context.report({
+            node,
+            messageId: 'noThis',
+            data: { original, fixed },
+            fix: canFix ? (fixer) => fixer.replaceText(node, fixed) : undefined,
+          });
+        }
+      },
+    };
+  },
+};

tests/lib/rules/template-no-this-in-template-only-components.js

@@ -0,0 +1,93 @@
+const rule = require('../../../lib/rules/template-no-this-in-template-only-components');
+const RuleTester = require('eslint').RuleTester;
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+ruleTester.run('template-no-this-in-template-only-components', rule, {
+  valid: [
+    '<template>{{@foo}}</template>',
+    '<template>{{welcome-page}}</template>',
+    '<template><WelcomePage /></template>',
+    '<template><MyComponent @prop={{can "edit" @model}} /></template>',
+    '<template>{{my-component model=model}}</template>',
+  ],
+  invalid: [
+    {
+      code: '<template>{{this.foo}}</template>',
+      output: '<template>{{@foo}}</template>',
+      errors: [{ messageId: 'noThis' }],
+    },
+
+    {
+      code: '<template>{{my-component model=this.model}}</template>',
+      output: '<template>{{my-component model=@model}}</template>',
+      errors: [{ messageId: 'noThis' }],
+    },
+    {
+      code: '<template>{{my-component action=(action this.myAction)}}</template>',
+      output: '<template>{{my-component action=(action @myAction)}}</template>',
+      errors: [{ messageId: 'noThis' }],
+    },
+    {
+      code: '<template><MyComponent @prop={{can "edit" this.model}} /></template>',
+      output: '<template><MyComponent @prop={{can "edit" @model}} /></template>',
+      errors: [{ messageId: 'noThis' }],
+    },
+    {
+      code: '<template>{{input id=(concat this.elementId "-username")}}</template>',
+      output: null,
+      errors: [{ messageId: 'noThis' }],
+    },
+  ],
+});
+
+const hbsRuleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser/hbs'),
+  parserOptions: {
+    ecmaVersion: 2022,
+    sourceType: 'module',
+  },
+});
+
+hbsRuleTester.run('template-no-this-in-template-only-components', rule, {
+  valid: [
+    '{{welcome-page}}',
+    '<WelcomePage />',
+    '<MyComponent @prop={{can "edit" @model}} />',
+    '{{my-component model=model}}',
+  ],
+  invalid: [
+    {
+      code: '{{my-component action=(action this.myAction)}}',
+      output: '{{my-component action=(action @myAction)}}',
+      errors: [
+        {
+          message:
+            "Usage of 'this' in path 'this.myAction' is not allowed in a template-only component. Use '@myAction' if it is a named argument.",
+        },
+      ],
+    },
+    {
+      code: '<MyComponent @prop={{can "edit" this.model}} />',
+      output: '<MyComponent @prop={{can "edit" @model}} />',
+      errors: [
+        {
+          message:
+            "Usage of 'this' in path 'this.model' is not allowed in a template-only component. Use '@model' if it is a named argument.",
+        },
+      ],
+    },
+    {
+      code: '{{input id=(concat this.elementId "-username")}}',
+      output: null,
+      errors: [
+        {
+          message:
+            "Usage of 'this' in path 'this.elementId' is not allowed in a template-only component. Use '@elementId' if it is a named argument.",
+        },
+      ],
+    },
+  ],
+});