tree 0b4e9f147c51d82b972dbcb523b9fbe69c8474e9
parent 72b8989a676d49507a16665ae534836d7121b9d1
author Mason Freed <masonf@chromium.org> 1667239329 -0700
committer Blink WPT Bot <blink-w3c-test-autoroller@chromium.org> 1667239881 -0700

Add support for streaming Declarative Shadow DOM

A new feature flag, StreamingDeclarativeShadowDOM, guards the new
behavior in this CL. When that flag is enabled, upon seeing the
*opening* `<template>` tag, the parser will attach a shadow root to
the `<template>`'s parent element. All subsequent template content will
then be parsed *directly* into that shadow root. The closing
`</template>` tag is then basically a no-op: there is no more moving
of template content into shadow roots and removal of the `<template>`
element. In this new mode, there is never an actual `<template>`
element placed into the DOM tree. There is a "placeholder" template
that gets added to the parser's stack of open elements, just to keep
track of the parsing mode appropriately.

If the StreamingDeclarativeShadowDOM flag is disabled, the "old"
behavior is retained, of attaching the shadow root at the closing
`</template>` tag. A virtual suite tests this the old non-streaming
behavior.

This approach follows the discussion on the HTML spec PR [1], and
the approach suggested by @rniwa [2].

[1] https://github.com/whatwg/html/pull/5465
[2] https://github.com/WebKit/WebKit/pull/4822

Bug: 1042130,1379513
Change-Id: Iab9c9c1a2eb49eaa8f1f7c928f2477977e92b49b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3967571
Reviewed-by: David Baron <dbaron@chromium.org>
Auto-Submit: Mason Freed <masonf@chromium.org>
Commit-Queue: Mason Freed <masonf@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1065551}