failing test demonstrating infinite updates

[gnoff]

This was.... fun?

So in a Next.js project there was an infinite updates issue causing a page to fail and unmount. After narrowing the scope of the problem as much as possible I was able to start to repro in a test case (see ReactDOMHooks-test.js)

There is a confluence of things happening

In StrictMode some effects are refired
In a SuspenseBoundary there is a OffscreenComponent fiber as a child fiber
DoubleInvoke-ing effects in Dev looks for whether there is a PlacementDEV flag or (critically) if the fiber is an OffscreenComponent.

This means that for every descendant of a SuspenseBoundary, you will double-invoke effects even on updates that happened after a Placement (In StrictMode of course)

So what is happening in this contrived test case is

a first layoutEffect is causing an immediate Sync render. there is also a passive effect queued to some non Sync lane.
a second layoutEffect is causing another immediate Sync render however b/c the passive effect is inside an OffscreenComponent it gets cleanedup and re-executed.

This effect has a setState but it cannot bail out of the update because there is pending work already on this fiber (from a previous run of the effect). It takes a few loops around but eventually there is an inifinite loop of setStates causing Sync renders causing setStates that cannot be bailed out, causing Sync renders...

At least I think...

The simple fix is probably to not always doubleinvoke with an OffscreenComponent child. I think that is wrong in the SuspenseBoundary case but maybe it makes sense for regular offscreen. I don't really know though

[sizebot]

Comparing: f0efa11...e9b2b5c

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.min.js	=	134.97 kB	134.97 kB	=	43.23 kB	43.23 kB
oss-experimental/react-dom/cjs/react-dom.production.min.js	=	141.64 kB	141.64 kB	=	45.20 kB	45.20 kB
facebook-www/ReactDOM-prod.classic.js	=	486.06 kB	486.06 kB	=	86.51 kB	86.51 kB
facebook-www/ReactDOM-prod.modern.js	=	471.34 kB	471.34 kB	=	84.29 kB	84.29 kB
facebook-www/ReactDOMForked-prod.classic.js	+0.09%	486.06 kB	486.50 kB	+0.15%	86.51 kB	86.64 kB

Significant size changes

Includes any change greater than 0.2%:

(No significant changes)

Generated by 🚫 dangerJS against e9b2b5c

[sammy-SC]

Fixed by #25203

@gnoff thanks for the report and great repro!