Merge pull request #2434 from NullVoxPopuli/nvp/template-lint-extract-rule-template-no-chained-this

Extract rule: template-no-chained-this

Author: NullVoxPopuli

README.md

@@ -198,6 +198,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | [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-chained-this](docs/rules/template-no-chained-this.md)                                     | disallow redundant `this.this` in templates                     |    | 🔧 |    |
 | [template-no-debugger](docs/rules/template-no-debugger.md)                                             | disallow {{debugger}} in templates                              |    |    |    |
 | [template-no-element-event-actions](docs/rules/template-no-element-event-actions.md)                   | disallow element event actions (use {{on}} modifier instead)    |    |    |    |
 | [template-no-log](docs/rules/template-no-log.md)                                                       | disallow {{log}} in templates                                   |    |    |    |

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

@@ -0,0 +1,102 @@
+# ember/template-no-chained-this
+
+🔧 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 -->
+
+Disallow redundant `this.this` in templates.
+
+Using `this.this.*` in templates is almost always a typo or copy/paste mistake. These patterns are misleading and result in unnecessary ambiguity about scope and component context.
+
+## Rule Details
+
+This rule disallows `this.this.*` patterns in templates (e.g., `{{this.this.foo}}` or `<this.this.Bar />`).
+
+## Examples
+
+### Incorrect ❌
+
+```gjs
+<template>
+  {{this.this.value}}
+</template>
+```
+
+```gjs
+<template>
+  {{#this.this.foo}}
+    some text
+  {{/this.this.foo}}
+</template>
+```
+
+```gjs
+<template>
+  {{helper value=this.this.foo}}
+</template>
+```
+
+```gjs
+<template>
+  <this.this.Component />
+</template>
+```
+
+```gjs
+<template>
+  {{component this.this.dynamicComponent}}
+</template>
+```
+
+### Correct ✅
+
+```gjs
+<template>
+  {{this.value}}
+</template>
+```
+
+```gjs
+<template>
+  <this.Component />
+</template>
+```
+
+```gjs
+<template>
+  {{component this.dynamicComponent}}
+</template>
+```
+
+```gjs
+<template>
+  {{@argName}}
+</template>
+```
+
+## Migration
+
+Remove the extra `this`:
+
+Before:
+
+```gjs
+<template>
+  {{this.this.foo}}
+  <this.this.bar />
+</template>
+```
+
+After:
+
+```gjs
+<template>
+  {{this.foo}}
+  <this.bar />
+</template>
+```
+
+## References
+
+- [Ember Guides - Glimmer Component Templates](https://guides.emberjs.com/release/upgrading/current-edition/glimmer-components/)
+- [Handlebars Strict Mode](https://github.com/emberjs/rfcs/blob/master/text/0496-handlebars-strict-mode.md)

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

@@ -0,0 +1,69 @@
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'problem',
+    docs: {
+      description: 'disallow redundant `this.this` in templates',
+      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: 'code',
+    schema: [],
+    messages: {
+      noChainedThis:
+        'this.this.* is not allowed in templates. This is likely a mistake — remove the redundant this.',
+    },
+  },
+
+  create(context) {
+    const sourceCode = context.sourceCode;
+
+    return {
+      GlimmerPathExpression(node) {
+        const text = sourceCode.getText(node);
+        if (!text.startsWith('this.this.')) {
+          return;
+        }
+
+        const fixed = text.replace('this.this.', 'this.');
+
+        context.report({
+          node,
+          messageId: 'noChainedThis',
+          fix(fixer) {
+            const fixes = [fixer.replaceText(node, fixed)];
+
+            // Block statements have a closing tag path that must match
+            const parent = node.parent;
+            if (parent?.type === 'GlimmerBlockStatement' && parent.path === node) {
+              const closingPathEnd = parent.range[1] - 2; // before '}}'
+              const closingPathStart = closingPathEnd - text.length;
+              fixes.push(fixer.replaceTextRange([closingPathStart, closingPathEnd], fixed));
+            }
+
+            return fixes;
+          },
+        });
+      },
+      GlimmerElementNode(node) {
+        if (!node.tag?.startsWith('this.this.')) {
+          return;
+        }
+
+        const fixedTag = node.tag.replace('this.this.', 'this.');
+
+        context.report({
+          node,
+          messageId: 'noChainedThis',
+          fix(fixer) {
+            // Replace the tag name after '<'
+            const openStart = node.range[0] + 1;
+            return fixer.replaceTextRange([openStart, openStart + node.tag.length], fixedTag);
+          },
+        });
+      },
+    };
+  },
+};

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

@@ -0,0 +1,51 @@
+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.value}}</template>',
+    '<template>{{this.thisvalue}}</template>',
+    '<template>{{@argName}}</template>',
+    '<template>{{this.user.name}}</template>',
+    '<template><this.Component /></template>',
+    '<template>{{component this.dynamicComponent}}</template>',
+  ],
+
+  invalid: [
+    {
+      code: '<template>{{this.this.value}}</template>',
+      output: '<template>{{this.value}}</template>',
+      errors: [{ messageId: 'noChainedThis' }],
+    },
+    {
+      code: '<template>{{helper value=this.this.foo}}</template>',
+      output: '<template>{{helper value=this.foo}}</template>',
+      errors: [{ messageId: 'noChainedThis' }],
+    },
+    {
+      code: '<template>{{#if this.this.condition}}true{{/if}}</template>',
+      output: '<template>{{#if this.condition}}true{{/if}}</template>',
+      errors: [{ messageId: 'noChainedThis' }],
+    },
+    {
+      code: '<template><this.this.Component /></template>',
+      output: '<template><this.Component /></template>',
+      errors: [{ messageId: 'noChainedThis' }],
+    },
+    {
+      code: '<template>{{#this.this.value}}woo{{/this.this.value}}</template>',
+      output: '<template>{{#this.value}}woo{{/this.value}}</template>',
+      errors: [{ messageId: 'noChainedThis' }],
+    },
+    {
+      code: '<template>{{component this.this.dynamicComponent}}</template>',
+      output: '<template>{{component this.dynamicComponent}}</template>',
+      errors: [{ messageId: 'noChainedThis' }],
+    },
+  ],
+});