lit/lit

[labs/ssr] Remove deprecated `shadowroot` attribute from emitted DSD

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#4352 opened on Nov 1, 2023

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Description

Should this be an RFC?

  • This is not a substantial change

Which package is this a feature request for?

SSR (@lit-labs/ssr)

Description

Currently we include both the old shadowroot attribute and the new shadowrootmode attribute on <template> elements of the generated DSD.

Chromium was the only one that was supporting the shadowroot attribute. It began shipping streaming DSD with the new shadowrootmode attribute in Chromium 111 along with Webkit early this year. https://chromestatus.com/feature/5161240576393216 https://bugs.webkit.org/show_bug.cgi?id=249513

The non-standard shadowroot attribute has been marked deprecated since Chromium 112, to be removed in Chromium 119. https://chromestatus.com/feature/6239658726391808

The template shadowroot ponyfill was already updated to look for shadowrootmode instead of shadowroot here https://github.com/webcomponents/template-shadowroot/pull/43

Alternatives and Workarounds

n/a

Contributor guide

Tech stack
typescriptjavascripthtmlnodejs
Domain
backend
Issue type
refactor
DifficultyEstimated implementation difficulty for a new contributor, from 1 for very small changes to 5 for expert-level work.
2
Estimated timeA rough time range for an experienced contributor to investigate, implement, test, and prepare a pull request.
1-3 hours
Activity statusHow available the issue appears right now: fresh, active, stale, blocked, or waiting on maintainer input.
fresh
ClarityHow clearly the issue explains the expected change, acceptance criteria, and next step.
clear
Prerequisites
Lit SSRTypeScriptHTML templates
Newbie friendlinessA 1-100 score estimating how approachable this issue is for first-time contributors.
85
Research direction
Locate the file in the @lit labs/ssr package responsible for generating Declarative Shadow DOM (DSD) markup. This file currently outputs both the deprecated `shadowroot` attribute and the new `shadowrootmode` attribute on `<template>` elements. Remove the line or logic that adds `shadowroot`, and ensure only `shadowrootmode` is emitted. Update any associated tests to reflect this change. Reference the linked Chromium deprecation notices and the template shadowroot ponyfill PR for guidance.