fix: duplicate behavior for slotted content when no template is present

packages/@lwc/engine-server/src/__tests__/fixtures/slots-basic/implicit-no-template/light/expected.html

@@ -0,0 +1,4 @@
+<x-outer>
+  <x-inner>
+  </x-inner>
+</x-outer>

packages/@lwc/engine-server/src/__tests__/fixtures/slots-basic/implicit-no-template/light/index.js

@@ -0,0 +1,3 @@
+export const tagName = 'x-outer';
+export { default } from 'x/outer';
+export * from 'x/outer';

packages/@lwc/engine-server/src/__tests__/fixtures/slots-basic/implicit-no-template/light/modules/x/inner/inner.js

@@ -0,0 +1,5 @@
+import { LightningElement } from 'lwc';
+
+export default class extends LightningElement {
+    static renderMode = 'light';
+}

packages/@lwc/engine-server/src/__tests__/fixtures/slots-basic/implicit-no-template/light/modules/x/outer/outer.html

@@ -0,0 +1,6 @@
+<template lwc:render-mode="light">
+    <x-inner>
+        I am default slot
+        <div slot="foo">I am the foo slot</div>
+    </x-inner>
+</template>

packages/@lwc/engine-server/src/__tests__/fixtures/slots-basic/implicit-no-template/light/modules/x/outer/outer.js

@@ -0,0 +1,5 @@
+import { LightningElement } from 'lwc';
+
+export default class extends LightningElement {
+    static renderMode = 'light';
+}

packages/@lwc/engine-server/src/__tests__/fixtures/slots-basic/implicit-no-template/shadow/expected.html

@@ -0,0 +1,12 @@
+<x-outer>
+  <template shadowrootmode="open">
+    <x-inner>
+      <template shadowrootmode="open">
+      </template>
+      I am default slot
+      <div slot="foo">
+        I am the foo slot
+      </div>
+    </x-inner>
+  </template>
+</x-outer>

packages/@lwc/engine-server/src/__tests__/fixtures/slots-basic/implicit-no-template/shadow/index.js

@@ -0,0 +1,3 @@
+export const tagName = 'x-outer';
+export { default } from 'x/outer';
+export * from 'x/outer';

packages/@lwc/engine-server/src/__tests__/fixtures/slots-basic/implicit-no-template/shadow/modules/x/inner/inner.js

@@ -0,0 +1,3 @@
+import { LightningElement } from 'lwc';
+
+export default class extends LightningElement {}

packages/@lwc/engine-server/src/__tests__/fixtures/slots-basic/implicit-no-template/shadow/modules/x/outer/outer.html

@@ -0,0 +1,6 @@
+<template>
+    <x-inner>
+        I am default slot
+        <div slot="foo">I am the foo slot</div>
+    </x-inner>
+</template>

packages/@lwc/engine-server/src/__tests__/fixtures/slots-basic/implicit-no-template/shadow/modules/x/outer/outer.js

@@ -0,0 +1,3 @@
+import { LightningElement } from 'lwc';
+
+export default class extends LightningElement {}

packages/@lwc/ssr-runtime/src/render.ts

@@ -101,27 +101,33 @@ export function renderAttrsNoYield(
 }
 
 export function* fallbackTmpl(
-    _shadowSlottedContent: unknown,
+    shadowSlottedContent: AsyncGeneratorFunction,
     _lightSlottedContent: unknown,
     _scopedSlottedContent: unknown,
     Cmp: LightningElementConstructor,
-    _instance: unknown
+    instance: unknown
 ) {
     if (Cmp.renderMode !== 'light') {
-        yield '<template shadowrootmode="open"></template>';
+        yield `<template shadowrootmode="open"></template>`;
+        if (shadowSlottedContent) {
+            yield shadowSlottedContent(instance);
+        }
     }
 }
 
 export function fallbackTmplNoYield(
     emit: (segment: string) => void,
-    _shadowSlottedContent: unknown,
+    shadowSlottedContent: AsyncGeneratorFunction,
     _lightSlottedContent: unknown,
     _scopedSlottedContent: unknown,
     Cmp: LightningElementConstructor,
-    _instance: unknown
+    instance: unknown
 ) {
     if (Cmp.renderMode !== 'light') {
-        emit('<template shadowrootmode="open"></template>');
+        emit(`<template shadowrootmode="open"></template>`);
+        if (shadowSlottedContent) {
+            shadowSlottedContent(emit, instance);
+        }
     }
 }