Lit SSR defer-hydration not being removed on subcomponent that do not have a node binding

[e111077]

Which package(s) are affected?

SSR (@lit-labs/ssr)

Description

When you SSR a component with a subcomponent in its shadowroot, lit-ssr will add defer-hydration to the element. The hydration step of Lit will then crawl the lit comment markers and remove that attribute on the component with a node marker.

Though, if there is no binding to a sub-component, and thus it does not have a node part marker, then lit hydration will never remove the defer-hydration attribute on the child.

Reproduction

live repro:
https://stackblitz.com/edit/node-jay1jm?file=index.html

useful commands in that repro are build to build the TS and gen-index to run lit-ssr to generate index.html

• create two lit elements
• place one of the elements in the shadow root of the other with no lit-bindings
• import the definition of the child component in the module of the parent element
• SSR the parent element onto a page
• load the javascript bundle for the parent element (and transitively the child element)
• See that defer-hydration has not been removed from the child element

Workaround

Place a dummy binding on the child element <my-second-element data-yolo=${swag}>

Is this a regression?

No or unsure. This never worked, or I haven't tried before.

Affected versions

Failing in lit@2.7.5 and @lit-labs/ssr@3.1.3

Browser/OS/Node environment

tested on: node 16+ and Chrome 113

[augustjk]

Looks like this might be regression from #3663
We should add back the lit-node marker for defined custom elements.

[e111077]

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