Account for class only having template tag in no-empty-glimmer-component-classes rule

lib/rules/no-empty-glimmer-component-classes.js

@@ -1,8 +1,11 @@
 'use strict';
 
 const { isGlimmerComponent } = require('../utils/ember');
+const { isClassPropertyOrPropertyDefinition } = require('../utils/types');
 
 const ERROR_MESSAGE = 'Do not create empty backing classes for Glimmer components.';
+const ERROR_MESSAGE_TEMPLATE_TAG =
+  'Do not create empty backing classes for Glimmer template tag only components.';
 
 //------------------------------------------------------------------------------
 // Rule Definition
@@ -23,12 +26,20 @@ module.exports = {
   },
 
   ERROR_MESSAGE,
+  ERROR_MESSAGE_TEMPLATE_TAG,
 
   create(context) {
     return {
       ClassDeclaration(node) {
         if (isGlimmerComponent(context, node) && !node.decorators && node.body.body.length === 0) {
           context.report({ node, message: ERROR_MESSAGE });
+        } else if (
+          isGlimmerComponent(context, node) &&
+          node.body.body.length === 1 &&
+          isClassPropertyOrPropertyDefinition(node.body.body[0]) &&
+          node.body.body[0].key?.callee?.name === '__GLIMMER_TEMPLATE'
+        ) {
+          context.report({ node, message: ERROR_MESSAGE_TEMPLATE_TAG });
         }
       },
     };

tests/lib/rules-preprocessor/gjs-gts-processor-test.js

@@ -102,6 +102,21 @@ const valid = [
 ];
 
 const invalid = [
+  {
+    filename: 'my-component.gjs',
+    code: `import Component from '@glimmer/component';
+    export default class Chris extends Component {
+      <template>Hello!</template>
+    }`,
+    errors: [
+      {
+        message: 'Do not create empty backing classes for Glimmer template tag only components.',
+        line: 2,
+        column: 20,
+        endColumn: 6,
+      },
+    ],
+  },
   {
     filename: 'my-component.gjs',
     code: `