BUGFIX: template-no-yield-only — guard against native <template> as first HBS child

lib/rules/template-no-yield-only.js

@@ -37,8 +37,16 @@ module.exports = {
 
     return {
       GlimmerTemplate(node) {
+        // In GJS/GTS, `node.body` is a one-element list wrapping a
+        // `<template>` element whose `children` is the actual template
+        // content. In classic HBS, `node.body` is the template content
+        // directly. Require `body.length === 1` before descending so we
+        // don't mistake a native HTML `<template>` element that happens
+        // to be the first child of an HBS template for the GJS wrapper —
+        // e.g. `<template>{{yield}}</template>{{#each items}}…{{/each}}`
+        // would otherwise be wrongly flagged as yield-only.
         const templateNodes =
-          node.body[0] &&
+          node.body.length === 1 &&
           node.body[0].type === 'GlimmerElementNode' &&
           node.body[0].tag === 'template'
             ? node.body[0].children

tests/lib/rules/template-no-yield-only.js

@@ -9,6 +9,16 @@ const validHbs = [
   '<yield/>',
 ];
 
+// HBS-only cases: these use a native HTML `<template>` element as the first
+// child, which parses as a nested `<template>` in GJS/GTS (invalid syntax —
+// GJS reserves `<template>` for the module-level component wrapper).
+const validHbsOnly = [
+  // The rule must NOT descend into the native `<template>` and flag the
+  // inner `{{yield}}` as yield-only; the outer template has additional
+  // content (the `{{#each}}` block).
+  '<template>{{yield}}</template>{{#each items}}item{{/each}}',
+];
+
 const invalidHbs = [
   {
     code: '{{yield}}',
@@ -63,6 +73,6 @@ const hbsRuleTester = new RuleTester({
 });
 
 hbsRuleTester.run('template-no-yield-only', rule, {
-  valid: validHbs,
+  valid: [...validHbs, ...validHbsOnly],
   invalid: invalidHbs,
 });