[Fiber] Disable comments as containers in OSS

[gnoff]

3 years ago we partially disabled comment nodes as valid containers. Some unflagged support was left in due to legacy APIs like unmountComponentAtNode and unstable_renderSubtreeIntoContainer but these were since removed in React 19. This update flags the remaining uses of comments as containers.

[react-sizebot]

Comparing: 8bda715...ba621ee

Critical size changes

Includes critical production bundles, as well as any change greater than 2%:

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-stable/react-dom/cjs/react-dom.production.js	=	6.68 kB	6.68 kB	=	1.83 kB	1.83 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	516.76 kB	515.43 kB	=	92.22 kB	92.03 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.69 kB	6.69 kB	=	1.83 kB	1.83 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	559.79 kB	558.46 kB	=	99.50 kB	99.25 kB
facebook-www/ReactDOM-prod.classic.js	=	598.60 kB	597.95 kB	=	105.34 kB	105.26 kB
facebook-www/ReactDOM-prod.modern.js	=	589.03 kB	588.38 kB	=	103.79 kB	103.71 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
oss-experimental/react-dom/cjs/react-dom-profiling.profiling.js	=	615.30 kB	613.98 kB	=	108.19 kB	107.95 kB
oss-experimental/react-dom/cjs/react-dom-unstable_testing.production.js	=	574.52 kB	573.19 kB	=	103.06 kB	102.81 kB
oss-experimental/react-dom/cjs/react-dom-client.production.js	=	559.79 kB	558.46 kB	=	99.50 kB	99.25 kB
oss-stable/react-dom/cjs/react-dom-profiling.profiling.js	=	547.16 kB	545.83 kB	=	96.95 kB	96.72 kB
oss-stable-semver/react-dom/cjs/react-dom-profiling.profiling.js	=	547.03 kB	545.71 kB	=	96.92 kB	96.70 kB
oss-stable/react-dom/cjs/react-dom-client.production.js	=	516.76 kB	515.43 kB	=	92.22 kB	92.03 kB
oss-stable-semver/react-dom/cjs/react-dom-client.production.js	=	516.63 kB	515.30 kB	=	92.19 kB	92.00 kB
facebook-react-native/react-dom/cjs/ReactDOMProfiling-profiling.js	=	573.06 kB	571.50 kB	=	101.19 kB	100.92 kB
facebook-react-native/react-dom/cjs/ReactDOMClient-profiling.js	=	567.12 kB	565.56 kB	=	100.03 kB	99.76 kB
facebook-react-native/react-dom/cjs/ReactDOMProfiling-prod.js	=	547.79 kB	546.23 kB	=	97.38 kB	97.10 kB
facebook-react-native/react-dom/cjs/ReactDOMClient-prod.js	=	542.28 kB	540.73 kB	=	96.30 kB	96.02 kB

Generated by 🚫 dangerJS against cfaecb1

[eps1lon]

Test would be nice

[gnoff]

Test would be nice

we actually already do have them:

react/packages/react-dom/src/__tests__/ReactDOMRoot-test.js

Lines 401 to 414 in 8bda715

	// @gate disableCommentsAsDOMContainers
	it('errors if container is a comment node', () => {
	// This is an old feature used by www. Disabled in the open source build.
	const div = document.createElement('div');
	div.innerHTML = '<!-- react-mount-point-unstable -->';
	const commentNode = div.childNodes[0];
	expect(() => ReactDOMClient.createRoot(commentNode)).toThrow(
	'Target container is not a DOM element.',
	);
	expect(() => ReactDOMClient.hydrateRoot(commentNode)).toThrow(
	'Target container is not a DOM element.',
	);
	});

The only places the previously supported Comment container support would have been observable were in APIs we removed in React 19 so there really isn't anything new to test