Extract rule: template-require-strict-mode

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                                               |    |    |    |

docs/rules/template-require-strict-mode.md

@@ -0,0 +1,57 @@
+# 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.
+
+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
+// button.hbs
+<button>{{yield}}</button>
+```
+
+```js
+// button-test.js
+import { hbs } from 'ember-cli-htmlbars';
+
+test('it renders', async (assert) => {
+  await render(hbs`<Button>Ok</Button>`);
+  // ...
+});
+```
+
+This rule **allows** the following:
+
+```gjs
+// button.gjs
+<template>
+  <button>{{yield}}</button>
+</template>
+```
+
+```gjs
+// button-test.gjs
+import { Button } from 'ember-awesome-button';
+
+test('it renders', async (assert) => {
+  await render(<template><Button>Ok</Button></template>);
+  // ..
+});
+```
+
+## References
+
+- [Template Tag Guide](https://guides.emberjs.com/release/components/template-tag-format/)
+- [Strict Mode RFC](https://rfcs.emberjs.com/id/0496-handlebars-strict-mode/)

lib/rules/template-require-strict-mode.js

@@ -0,0 +1,44 @@
+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: {
+    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) {
+    const filePath = context.getFilename ? context.getFilename() : context.filename;
+
+    return {
+      'GlimmerTemplate:exit'(node) {
+        if (!isStrictModeFile(filePath)) {
+          context.report({
+            node,
+            message: ERROR_MESSAGE,
+          });
+        }
+      },
+    };
+  },
+};

tests/lib/rules/template-require-strict-mode.js

@@ -0,0 +1,70 @@
+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>',
+    },
+    {
+      filename: 'hello.gts',
+      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: [],
+  invalid: [
+    {
+      code: '<div>hello</div>',
+      output: null,
+      errors: [
+        {
+          message:
+            'Templates are required to be in strict mode. Consider refactoring to template tag format.',
+        },
+      ],
+    },
+  ],
+});