From c7c01777c03fe486d311974cd3afbae1d76fef58 Mon Sep 17 00:00:00 2001
From: NullVoxPopuli <199018+NullVoxPopuli@users.noreply.github.com>
Date: Tue, 10 Mar 2026 18:29:46 -0400
Subject: [PATCH] Extract rule: template-no-index-component-invocation

---
 README.md                                     |   1 +
 .../template-no-index-component-invocation.md |  61 +++++++
 .../template-no-index-component-invocation.js | 104 +++++++++++
 .../template-no-index-component-invocation.js | 168 ++++++++++++++++++
 4 files changed, 334 insertions(+)
 create mode 100644 docs/rules/template-no-index-component-invocation.md
 create mode 100644 lib/rules/template-no-index-component-invocation.js
 create mode 100644 tests/lib/rules/template-no-index-component-invocation.js

diff --git a/README.md b/README.md
index 5de51a02ff..de30c75deb 100644
--- a/README.md
+++ b/README.md
@@ -211,6 +211,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | [template-no-dynamic-subexpression-invocations](docs/rules/template-no-dynamic-subexpression-invocations.md) | disallow dynamic subexpression invocations                                   |    |    |    |
 | [template-no-element-event-actions](docs/rules/template-no-element-event-actions.md)                         | disallow element event actions (use {{on}} modifier instead)                 |    |    |    |
 | [template-no-implicit-this](docs/rules/template-no-implicit-this.md)                                         | require explicit `this` in property access                                   |    |    |    |
+| [template-no-index-component-invocation](docs/rules/template-no-index-component-invocation.md)               | disallow index component invocations                                         |    |    |    |
 | [template-no-inline-event-handlers](docs/rules/template-no-inline-event-handlers.md)                         | disallow DOM event handler attributes                                        |    |    |    |
 | [template-no-inline-styles](docs/rules/template-no-inline-styles.md)                                         | disallow inline styles                                                       |    |    |    |
 | [template-no-input-block](docs/rules/template-no-input-block.md)                                             | disallow block usage of {{input}} helper                                     |    |    |    |
diff --git a/docs/rules/template-no-index-component-invocation.md b/docs/rules/template-no-index-component-invocation.md
new file mode 100644
index 0000000000..88558f8139
--- /dev/null
+++ b/docs/rules/template-no-index-component-invocation.md
@@ -0,0 +1,61 @@
+# ember/template-no-index-component-invocation
+
+<!-- end auto-generated rule header -->
+
+Disallows invoking components using an explicit `/index` or `::Index` suffix.
+
+Components and Component Templates can be structured as `app/components/foo-bar/index.js` and
+`app/components/foo-bar/index.hbs`. This allows additional files related to the
+component (such as a `README.md` file) to be co-located on the filesystem.
+
+For template-only components, they can be either `app/components/foo-bar.hbs`
+or `app/components/foo-bar/index.hbs` without a corresponding JavaScript file.
+
+Similarly, for addons, templates can be placed inside `addon/components` with
+the same rules laid out above.
+
+In all of these case, if a template file is present in `app/components` or
+`addon/components`, it will take precedence over any corresponding template
+files in `app/templates`, the `layout` property on classic components, or a
+template with the same name that is made available with the resolver API.
+Instead of being resolved at runtime, a template in `app/components` will be
+associated with the component's JavaScript class at build time.
+
+## Examples
+
+This rule **forbids** the following:
+
+```gjs
+<template><Foo::Index /></template>
+```
+
+```gjs
+<template>{{component 'foo/index'}}</template>
+```
+
+```gjs
+<template>{{foo/index}}</template>
+```
+
+This rule **allows** the following:
+
+```gjs
+<template><Foo /></template>
+```
+
+```gjs
+<template>{{component 'foo'}}</template>
+```
+
+```gjs
+<template>{{foo}}</template>
+```
+
+## Migration
+
+- replace all `::Index>` to `>`
+- replace all `/index}}` to `}}`
+
+## References
+
+- [RFC #481](https://github.com/emberjs/rfcs/blob/master/text/0481-component-templates-co-location.md#high-level-design)
diff --git a/lib/rules/template-no-index-component-invocation.js b/lib/rules/template-no-index-component-invocation.js
new file mode 100644
index 0000000000..a3f71e98ec
--- /dev/null
+++ b/lib/rules/template-no-index-component-invocation.js
@@ -0,0 +1,104 @@
+/* eslint-disable complexity, eslint-plugin/prefer-placeholders, unicorn/explicit-length-check */
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'disallow index component invocations',
+      category: 'Best Practices',
+      recommended: false,
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-no-index-component-invocation.md',
+      templateMode: 'both',
+    },
+    fixable: null,
+    schema: [],
+    messages: {},
+    originallyFrom: {
+      name: 'ember-template-lint',
+      rule: 'lib/rules/no-index-component-invocation.js',
+      docs: 'docs/rule/no-index-component-invocation.md',
+      tests: 'test/unit/rules/no-index-component-invocation-test.js',
+    },
+  },
+
+  create(context) {
+    function lintIndexUsage(node) {
+      // Handle angle bracket components: <Foo::Index />
+      if (node.type === 'GlimmerElementNode') {
+        if (node.tag && node.tag.endsWith('::Index')) {
+          const invocation = `<${node.tag}`;
+          const replacement = `<${node.tag.replace('::Index', '')}`;
+
+          context.report({
+            node,
+            message: `Replace \`${invocation} ...\` to \`${replacement} ...\``,
+          });
+        }
+        return;
+      }
+
+      // Handle mustache and block statements: {{foo/index}} or {{#foo/index}}
+      if (node.type === 'GlimmerMustacheStatement' || node.type === 'GlimmerBlockStatement') {
+        if (
+          node.path &&
+          node.path.type === 'GlimmerPathExpression' &&
+          node.path.original &&
+          node.path.original.endsWith('/index')
+        ) {
+          const invocationPrefix = node.type === 'GlimmerBlockStatement' ? '{{#' : '{{';
+          const invocation = `${invocationPrefix}${node.path.original}`;
+          const replacement = `${invocationPrefix}${node.path.original.replace('/index', '')}`;
+
+          context.report({
+            node: node.path,
+            message: `Replace \`${invocation} ...\` to \`${replacement} ...\``,
+          });
+          return;
+        }
+      }
+
+      // Handle component helper: {{component "foo/index"}} or (component "foo/index")
+      if (
+        node.type === 'GlimmerMustacheStatement' ||
+        node.type === 'GlimmerBlockStatement' ||
+        node.type === 'GlimmerSubExpression'
+      ) {
+        const prefix =
+          node.type === 'GlimmerMustacheStatement'
+            ? '{{'
+            : node.type === 'GlimmerBlockStatement'
+              ? '{{#'
+              : '(';
+
+        if (
+          node.path &&
+          node.path.type === 'GlimmerPathExpression' &&
+          node.path.original === 'component' &&
+          node.params &&
+          node.params.length > 0 &&
+          node.params[0].type === 'GlimmerStringLiteral'
+        ) {
+          const componentName = node.params[0].value;
+
+          if (componentName.endsWith('/index')) {
+            const invocation = `${prefix}component "${componentName}"`;
+            const replacement = `${prefix}component "${componentName.replace('/index', '')}"`;
+
+            context.report({
+              node: node.params[0],
+              message: `Replace \`${invocation} ...\` to \`${replacement} ...\``,
+            });
+          }
+        }
+      }
+    }
+
+    return {
+      GlimmerElementNode: lintIndexUsage,
+      GlimmerMustacheStatement: lintIndexUsage,
+      GlimmerBlockStatement: lintIndexUsage,
+      GlimmerSubExpression: lintIndexUsage,
+    };
+  },
+};
+/* eslint-enable complexity, eslint-plugin/prefer-placeholders, unicorn/explicit-length-check */
diff --git a/tests/lib/rules/template-no-index-component-invocation.js b/tests/lib/rules/template-no-index-component-invocation.js
new file mode 100644
index 0000000000..f658d41093
--- /dev/null
+++ b/tests/lib/rules/template-no-index-component-invocation.js
@@ -0,0 +1,168 @@
+const rule = require('../../../lib/rules/template-no-index-component-invocation');
+const RuleTester = require('eslint').RuleTester;
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+ruleTester.run('template-no-index-component-invocation', rule, {
+  valid: [
+    '<template><Foo::Bar /></template>',
+    '<template><Foo::IndexItem /></template>',
+    '<template><Foo::MyIndex /></template>',
+    '<template><Foo::MyIndex></Foo::MyIndex></template>',
+    '<template>{{foo/index-item}}</template>',
+    '<template>{{foo/my-index}}</template>',
+    '<template>{{foo/bar}}</template>',
+    '<template>{{#foo/bar}}{{/foo/bar}}</template>',
+    '<template>{{component "foo/bar"}}</template>',
+    '<template>{{component "foo/my-index"}}</template>',
+    '<template>{{component "foo/index-item"}}</template>',
+    '<template>{{#component "foo/index-item"}}{{/component}}</template>',
+  ],
+  invalid: [
+    {
+      code: '<template>{{foo/index}}</template>',
+      output: null,
+      errors: [
+        {
+          message: 'Replace `{{foo/index ...` to `{{foo ...`',
+        },
+      ],
+    },
+    {
+      code: '<template>{{component "foo/index"}}</template>',
+      output: null,
+      errors: [
+        {
+          message: 'Replace `{{component "foo/index" ...` to `{{component "foo" ...`',
+        },
+      ],
+    },
+    {
+      code: '<template>{{#foo/index}}{{/foo/index}}</template>',
+      output: null,
+      errors: [
+        {
+          message: 'Replace `{{#foo/index ...` to `{{#foo ...`',
+        },
+      ],
+    },
+    {
+      code: '<template>{{#component "foo/index"}}{{/component}}</template>',
+      output: null,
+      errors: [
+        {
+          message: 'Replace `{{#component "foo/index" ...` to `{{#component "foo" ...`',
+        },
+      ],
+    },
+    {
+      code: '<template><Foo::Index /></template>',
+      output: null,
+      errors: [
+        {
+          message: 'Replace `<Foo::Index ...` to `<Foo ...`',
+        },
+      ],
+    },
+    {
+      code: '<template><Foo::Index></Foo::Index></template>',
+      output: null,
+      errors: [
+        {
+          message: 'Replace `<Foo::Index ...` to `<Foo ...`',
+        },
+      ],
+    },
+
+    {
+      code: '<template>{{foo/bar (component "foo/index")}}</template>',
+      output: null,
+      errors: [{ message: 'Replace `(component "foo/index" ...` to `(component "foo" ...`' }],
+    },
+    {
+      code: '<template>{{foo/bar name=(component "foo/index")}}</template>',
+      output: null,
+      errors: [{ message: 'Replace `(component "foo/index" ...` to `(component "foo" ...`' }],
+    },
+    {
+      code: '<template><Foo::Bar::Index /></template>',
+      output: null,
+      errors: [{ message: 'Replace `<Foo::Bar::Index ...` to `<Foo::Bar ...`' }],
+    },
+  ],
+});
+
+const hbsRuleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser/hbs'),
+  parserOptions: {
+    ecmaVersion: 2022,
+    sourceType: 'module',
+  },
+});
+
+hbsRuleTester.run('template-no-index-component-invocation', rule, {
+  valid: [
+    '<Foo::Bar />',
+    '<Foo::IndexItem />',
+    '<Foo::MyIndex />',
+    '<Foo::MyIndex></Foo::MyIndex>',
+    '{{foo/index-item}}',
+    '{{foo/my-index}}',
+    '{{foo/bar}}',
+    '{{#foo/bar}}{{/foo/bar}}',
+    '{{component "foo/bar"}}',
+    '{{component "foo/my-index"}}',
+    '{{component "foo/index-item"}}',
+    '{{#component "foo/index-item"}}{{/component}}',
+  ],
+  invalid: [
+    {
+      code: '{{foo/index}}',
+      output: null,
+      errors: [{ message: 'Replace `{{foo/index ...` to `{{foo ...`' }],
+    },
+    {
+      code: '{{component "foo/index"}}',
+      output: null,
+      errors: [{ message: 'Replace `{{component "foo/index" ...` to `{{component "foo" ...`' }],
+    },
+    {
+      code: '{{#foo/index}}{{/foo/index}}',
+      output: null,
+      errors: [{ message: 'Replace `{{#foo/index ...` to `{{#foo ...`' }],
+    },
+    {
+      code: '{{#component "foo/index"}}{{/component}}',
+      output: null,
+      errors: [{ message: 'Replace `{{#component "foo/index" ...` to `{{#component "foo" ...`' }],
+    },
+    {
+      code: '{{foo/bar (component "foo/index")}}',
+      output: null,
+      errors: [{ message: 'Replace `(component "foo/index" ...` to `(component "foo" ...`' }],
+    },
+    {
+      code: '{{foo/bar name=(component "foo/index")}}',
+      output: null,
+      errors: [{ message: 'Replace `(component "foo/index" ...` to `(component "foo" ...`' }],
+    },
+    {
+      code: '<Foo::Index />',
+      output: null,
+      errors: [{ message: 'Replace `<Foo::Index ...` to `<Foo ...`' }],
+    },
+    {
+      code: '<Foo::Bar::Index />',
+      output: null,
+      errors: [{ message: 'Replace `<Foo::Bar::Index ...` to `<Foo::Bar ...`' }],
+    },
+    {
+      code: '<Foo::Index></Foo::Index>',
+      output: null,
+      errors: [{ message: 'Replace `<Foo::Index ...` to `<Foo ...`' }],
+    },
+  ],
+});