Test StrictEffects in react-dom

[eps1lon]

Working in render but broken in hydrateRoot.

[react-sizebot]

Comparing: 190cc99...044e6d4

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	=	6.66 kB	6.66 kB	+0.05%	1.82 kB	1.82 kB
oss-experimental/react-dom/cjs/react-dom.production.js	=	6.67 kB	6.67 kB	+0.05%	1.83 kB	1.83 kB
facebook-www/ReactDOM-prod.classic.js	=	591.11 kB	591.11 kB	=	103.94 kB	103.94 kB
facebook-www/ReactDOM-prod.modern.js	=	567.33 kB	567.33 kB	=	100.34 kB	100.34 kB
test_utils/ReactAllWarnings.js	Deleted	64.26 kB	0.00 kB	Deleted	16.02 kB	0.00 kB

Significant size changes

Includes any change greater than 0.2%:

Expand to show

Name	+/-	Base	Current	+/- gzip	Base gzip	Current gzip
test_utils/ReactAllWarnings.js	Deleted	64.26 kB	0.00 kB	Deleted	16.02 kB	0.00 kB

Generated by 🚫 dangerJS against 044e6d4

[eps1lon]

Uses mountChildFibers which has side-effect tracking disabled. Side-effect tracking sets the PlacementDEV flag. Since PlacementDEV is never set here, we never double invoke:

react/packages/react-reconciler/src/ReactFiberWorkLoop.js

Lines 3691 to 3701 in 94eed63

	if (fiber.flags & PlacementDEV) {
	setCurrentDebugFiberInDEV(fiber);
	if (isInStrictMode) {
	doubleInvokeEffectsOnFiber(
	root,
	fiber,
	(fiber.mode & NoStrictPassiveEffectsMode) === NoMode,
	);
	}
	resetCurrentDebugFiberInDEV();
	} else {

But then it's not clear yet why we need this flag at all. Shouldn't we double invoke regardless of whether something was placed?