From 7efa92fa47fd7870ec7b33a7a4636158e6227dcc Mon Sep 17 00:00:00 2001
From: NullVoxPopuli <199018+NullVoxPopuli@users.noreply.github.com>
Date: Wed, 18 Mar 2026 18:17:15 -0400
Subject: [PATCH 1/2] Extract rule: template-require-strict-mode

---
 README.md                                     |  1 +
 docs/rules/template-require-strict-mode.md    | 42 +++++++++++++
 lib/rules/template-require-strict-mode.js     | 45 +++++++++++++
 .../lib/rules/template-require-strict-mode.js | 63 +++++++++++++++++++
 4 files changed, 151 insertions(+)
 create mode 100644 docs/rules/template-require-strict-mode.md
 create mode 100644 lib/rules/template-require-strict-mode.js
 create mode 100644 tests/lib/rules/template-require-strict-mode.js

diff --git a/README.md b/README.md
index 515d97f416..61cc01f8ae 100644
--- a/README.md
+++ b/README.md
@@ -247,6 +247,7 @@ rules in templates can be disabled with eslint directives with mustache or html
 | [template-no-obsolete-elements](docs/rules/template-no-obsolete-elements.md)                                       | disallow obsolete HTML elements                                              |    |    |    |
 | [template-no-outlet-outside-routes](docs/rules/template-no-outlet-outside-routes.md)                               | disallow {{outlet}} outside of route templates                               |    |    |    |
 | [template-no-page-title-component](docs/rules/template-no-page-title-component.md)                                 | disallow usage of ember-page-title component                                 |    |    |    |
+| [template-require-strict-mode](docs/rules/template-require-strict-mode.md)                                         | require templates to be in strict mode                                       |    |    |    |
 | [template-require-valid-named-block-naming-format](docs/rules/template-require-valid-named-block-naming-format.md) | require valid named block naming format                                      |    | 🔧 |    |
 | [template-self-closing-void-elements](docs/rules/template-self-closing-void-elements.md)                           | require self-closing on void elements                                        |    | 🔧 |    |
 | [template-simple-modifiers](docs/rules/template-simple-modifiers.md)                                               | require simple modifier syntax                                               |    |    |    |
diff --git a/docs/rules/template-require-strict-mode.md b/docs/rules/template-require-strict-mode.md
new file mode 100644
index 0000000000..b54f2e5db0
--- /dev/null
+++ b/docs/rules/template-require-strict-mode.md
@@ -0,0 +1,42 @@
+# ember/template-require-strict-mode
+
+> **HBS Only**: This rule applies to classic `.hbs` template files only (loose mode). It is not relevant for `gjs`/`gts` files (strict mode), where these patterns cannot occur.
+
+<!-- end auto-generated rule header -->
+
+Require templates to be in strict mode.
+
+Templates should use the strict mode syntax (template tag format) rather than loose template files. Strict mode templates (`.gjs` / `.gts` files) provide better integration with JavaScript and type checking.
+
+## Examples
+
+This rule **forbids** the following:
+
+```hbs
+<div>
+  Hello World
+</div>
+```
+
+(in a `.hbs` file)
+
+This rule **allows** the following:
+
+```hbs
+Hello World
+```
+
+(in a `.gjs` or `.gts` file)
+
+## Why?
+
+Strict mode templates provide:
+
+- Better integration with JavaScript tooling
+- Type safety in TypeScript projects
+- Clearer component boundaries
+- Easier refactoring and navigation
+
+## References
+
+- [Ember.js Guides - Template Syntax](https://guides.emberjs.com/release/templates/syntax/)
diff --git a/lib/rules/template-require-strict-mode.js b/lib/rules/template-require-strict-mode.js
new file mode 100644
index 0000000000..64a0fb161a
--- /dev/null
+++ b/lib/rules/template-require-strict-mode.js
@@ -0,0 +1,45 @@
+const ERROR_MESSAGE =
+  'Templates are required to be in strict mode. Consider refactoring to template tag format.';
+
+/** @type {import('eslint').Rule.RuleModule} */
+module.exports = {
+  meta: {
+    type: 'suggestion',
+    docs: {
+      description: 'require templates to be in strict mode',
+      category: 'Best Practices',
+      recommended: false,
+      url: 'https://github.com/ember-cli/eslint-plugin-ember/tree/master/docs/rules/template-require-strict-mode.md',
+      templateMode: 'loose',
+    },
+    fixable: null,
+    schema: [],
+    messages: {},
+    originallyFrom: {
+      name: 'ember-template-lint',
+      rule: 'lib/rules/require-strict-mode.js',
+      docs: 'docs/rule/require-strict-mode.md',
+      tests: 'test/unit/rules/require-strict-mode-test.js',
+    },
+  },
+
+  create(context) {
+    return {
+      'GlimmerTemplate:exit'(node) {
+        // Check if the template is in strict mode
+        // Strict mode templates are in .gjs/.gts files
+        // Non-strict templates are in .hbs files
+
+        const filePath = context.getFilename ? context.getFilename() : context.filename;
+
+        // Only flag .hbs files as non-strict
+        if (filePath && filePath.endsWith('.hbs')) {
+          context.report({
+            node,
+            message: ERROR_MESSAGE,
+          });
+        }
+      },
+    };
+  },
+};
diff --git a/tests/lib/rules/template-require-strict-mode.js b/tests/lib/rules/template-require-strict-mode.js
new file mode 100644
index 0000000000..7c26f93ce8
--- /dev/null
+++ b/tests/lib/rules/template-require-strict-mode.js
@@ -0,0 +1,63 @@
+const rule = require('../../../lib/rules/template-require-strict-mode');
+const RuleTester = require('eslint').RuleTester;
+
+const ruleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser'),
+  parserOptions: { ecmaVersion: 2022, sourceType: 'module' },
+});
+
+ruleTester.run('template-require-strict-mode', rule, {
+  valid: [
+    {
+      filename: 'hello.gjs',
+      code: '<template>hello</template>',
+    },
+  ],
+  invalid: [
+    {
+      filename: 'hello.hbs',
+      code: '<template><div>hello</div></template>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Templates are required to be in strict mode. Consider refactoring to template tag format.',
+        },
+      ],
+    },
+
+    {
+      filename: 'hello.hbs',
+      code: `<template><div>
+  hello
+</div></template>`,
+      output: null,
+      errors: [
+        {
+          message:
+            'Templates are required to be in strict mode. Consider refactoring to template tag format.',
+        },
+      ],
+    },
+  ],
+});
+
+const hbsRuleTester = new RuleTester({
+  parser: require.resolve('ember-eslint-parser/hbs'),
+  parserOptions: {
+    ecmaVersion: 2022,
+    sourceType: 'module',
+  },
+});
+
+hbsRuleTester.run('template-require-strict-mode', rule, {
+  valid: [
+    '<template>hello</template>',
+    `import Component from '@glimmer/component';
+
+  export default class HelloComponent extends Component {
+    <template>hello</template>
+  }`,
+  ],
+  invalid: [],
+});

From 621c5f6c6c7eebc355890ab26667d2fc8a3e7199 Mon Sep 17 00:00:00 2001
From: NullVoxPopuli <199018+NullVoxPopuli@users.noreply.github.com>
Date: Thu, 19 Mar 2026 19:33:42 -0400
Subject: [PATCH 2/2] Sync with template-lint

---
 docs/rules/template-require-strict-mode.md    | 49 ++++++++++++-------
 lib/rules/template-require-strict-mode.js     | 15 +++---
 .../lib/rules/template-require-strict-mode.js | 25 ++++++----
 3 files changed, 55 insertions(+), 34 deletions(-)

diff --git a/docs/rules/template-require-strict-mode.md b/docs/rules/template-require-strict-mode.md
index b54f2e5db0..cf76e9def5 100644
--- a/docs/rules/template-require-strict-mode.md
+++ b/docs/rules/template-require-strict-mode.md
@@ -6,37 +6,52 @@
 
 Require templates to be in strict mode.
 
-Templates should use the strict mode syntax (template tag format) rather than loose template files. Strict mode templates (`.gjs` / `.gts` files) provide better integration with JavaScript and type checking.
+Ember's Polaris edition component authoring format is template tag, which makes
+templates follow "strict mode" semantics.
+
+This rule requires all templates to use strict mode (template tag). Effectively this
+means you may only have template content in `.gjs`/`.gts` files, not in `.hbs` or
+`.js`/`.ts`.
 
 ## Examples
 
 This rule **forbids** the following:
 
 ```hbs
-<div>
-  Hello World
-</div>
+// button.hbs
+<button>{{yield}}</button>
 ```
 
-(in a `.hbs` file)
-
-This rule **allows** the following:
+```js
+// button-test.js
+import { hbs } from 'ember-cli-htmlbars';
 
-```hbs
-Hello World
+test('it renders', async (assert) => {
+  await render(hbs`<Button>Ok</Button>`);
+  // ...
+});
 ```
 
-(in a `.gjs` or `.gts` file)
+This rule **allows** the following:
 
-## Why?
+```gjs
+// button.gjs
+<template>
+  <button>{{yield}}</button>
+</template>
+```
 
-Strict mode templates provide:
+```gjs
+// button-test.gjs
+import { Button } from 'ember-awesome-button';
 
-- Better integration with JavaScript tooling
-- Type safety in TypeScript projects
-- Clearer component boundaries
-- Easier refactoring and navigation
+test('it renders', async (assert) => {
+  await render(<template><Button>Ok</Button></template>);
+  // ..
+});
+```
 
 ## References
 
-- [Ember.js Guides - Template Syntax](https://guides.emberjs.com/release/templates/syntax/)
+- [Template Tag Guide](https://guides.emberjs.com/release/components/template-tag-format/)
+- [Strict Mode RFC](https://rfcs.emberjs.com/id/0496-handlebars-strict-mode/)
diff --git a/lib/rules/template-require-strict-mode.js b/lib/rules/template-require-strict-mode.js
index 64a0fb161a..9e6bfccb06 100644
--- a/lib/rules/template-require-strict-mode.js
+++ b/lib/rules/template-require-strict-mode.js
@@ -1,6 +1,10 @@
 const ERROR_MESSAGE =
   'Templates are required to be in strict mode. Consider refactoring to template tag format.';
 
+function isStrictModeFile(filePath) {
+  return filePath?.endsWith('.gjs') || filePath?.endsWith('.gts');
+}
+
 /** @type {import('eslint').Rule.RuleModule} */
 module.exports = {
   meta: {
@@ -24,16 +28,11 @@ module.exports = {
   },
 
   create(context) {
+    const filePath = context.getFilename ? context.getFilename() : context.filename;
+
     return {
       'GlimmerTemplate:exit'(node) {
-        // Check if the template is in strict mode
-        // Strict mode templates are in .gjs/.gts files
-        // Non-strict templates are in .hbs files
-
-        const filePath = context.getFilename ? context.getFilename() : context.filename;
-
-        // Only flag .hbs files as non-strict
-        if (filePath && filePath.endsWith('.hbs')) {
+        if (!isStrictModeFile(filePath)) {
           context.report({
             node,
             message: ERROR_MESSAGE,
diff --git a/tests/lib/rules/template-require-strict-mode.js b/tests/lib/rules/template-require-strict-mode.js
index 7c26f93ce8..994b573060 100644
--- a/tests/lib/rules/template-require-strict-mode.js
+++ b/tests/lib/rules/template-require-strict-mode.js
@@ -12,6 +12,10 @@ ruleTester.run('template-require-strict-mode', rule, {
       filename: 'hello.gjs',
       code: '<template>hello</template>',
     },
+    {
+      filename: 'hello.gts',
+      code: '<template>hello</template>',
+    },
   ],
   invalid: [
     {
@@ -25,7 +29,6 @@ ruleTester.run('template-require-strict-mode', rule, {
         },
       ],
     },
-
     {
       filename: 'hello.hbs',
       code: `<template><div>
@@ -51,13 +54,17 @@ const hbsRuleTester = new RuleTester({
 });
 
 hbsRuleTester.run('template-require-strict-mode', rule, {
-  valid: [
-    '<template>hello</template>',
-    `import Component from '@glimmer/component';
-
-  export default class HelloComponent extends Component {
-    <template>hello</template>
-  }`,
+  valid: [],
+  invalid: [
+    {
+      code: '<div>hello</div>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Templates are required to be in strict mode. Consider refactoring to template tag format.',
+        },
+      ],
+    },
   ],
-  invalid: [],
 });