Fix generateMetadata race condition

[ijjk]

This ensures we properly catch/handle generateMetadata errors during eager evaluating of nested generateMetadata functions in the tree. Previously if we eager evaluated a child metadata function that threw an error e.g. notFound() and but the parent metadata function took longer the thrown error would be an unhandled rejection causing the process to crash depending on the environment.

Fixes: NEXT-2588

Closes NEXT-2786

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	ijjk/next.js fix/metadata-promise-race	Change
buildDuration	13.7s	13.8s	N/A
buildDurationCached	7.4s	6.3s	N/A
nodeModulesSize	198 MB	198 MB	⚠️ +14.6 kB
nextStartRea..uration (ms)	438ms	438ms	✓

Client Bundles (main, webpack)

	vercel/next.js canary	ijjk/next.js fix/metadata-promise-race	Change
2453-HASH.js gzip	30.5 kB	30.5 kB	N/A
3304.HASH.js gzip	181 B	181 B	✓
3f784ff6-HASH.js gzip	53.7 kB	53.7 kB	N/A
8299-HASH.js gzip	5.04 kB	5.04 kB	N/A
framework-HASH.js gzip	45.2 kB	45.2 kB	✓
main-app-HASH.js gzip	242 B	242 B	✓
main-HASH.js gzip	32.2 kB	32.2 kB	N/A
webpack-HASH.js gzip	1.68 kB	1.68 kB	N/A
Overall change	45.6 kB	45.6 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	ijjk/next.js fix/metadata-promise-race	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	ijjk/next.js fix/metadata-promise-race	Change
_app-HASH.js gzip	196 B	197 B	N/A
_error-HASH.js gzip	184 B	184 B	✓
amp-HASH.js gzip	505 B	505 B	✓
css-HASH.js gzip	324 B	325 B	N/A
dynamic-HASH.js gzip	2.5 kB	2.5 kB	N/A
edge-ssr-HASH.js gzip	258 B	258 B	✓
head-HASH.js gzip	352 B	352 B	✓
hooks-HASH.js gzip	370 B	371 B	N/A
image-HASH.js gzip	4.21 kB	4.21 kB	✓
index-HASH.js gzip	259 B	259 B	✓
link-HASH.js gzip	2.67 kB	2.67 kB	N/A
routerDirect..HASH.js gzip	314 B	312 B	N/A
script-HASH.js gzip	386 B	386 B	✓
withRouter-HASH.js gzip	309 B	309 B	✓
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	6.57 kB	6.57 kB	✓

Client Build Manifests

	vercel/next.js canary	ijjk/next.js fix/metadata-promise-race	Change
_buildManifest.js gzip	481 B	484 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	ijjk/next.js fix/metadata-promise-race	Change
index.html gzip	530 B	529 B	N/A
link.html gzip	541 B	541 B	✓
withRouter.html gzip	524 B	523 B	N/A
Overall change	541 B	541 B	✓

Edge SSR bundle Size

	vercel/next.js canary	ijjk/next.js fix/metadata-promise-race	Change
edge-ssr.js gzip	95.1 kB	95.1 kB	N/A
page.js gzip	3.07 kB	3.07 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	ijjk/next.js fix/metadata-promise-race	Change
middleware-b..fest.js gzip	626 B	623 B	N/A
middleware-r..fest.js gzip	151 B	151 B	✓
middleware.js gzip	25.5 kB	25.5 kB	N/A
edge-runtime..pack.js gzip	839 B	839 B	✓
Overall change	990 B	990 B	✓

Next Runtimes

	vercel/next.js canary	ijjk/next.js fix/metadata-promise-race	Change
app-page-exp...dev.js gzip	171 kB	171 kB	N/A
app-page-exp..prod.js gzip	96.5 kB	96.6 kB	N/A
app-page-tur..prod.js gzip	98.3 kB	98.3 kB	N/A
app-page-tur..prod.js gzip	92.7 kB	92.8 kB	N/A
app-page.run...dev.js gzip	149 kB	149 kB	N/A
app-page.run..prod.js gzip	91.2 kB	91.3 kB	N/A
app-route-ex...dev.js gzip	21.3 kB	21.3 kB	✓
app-route-ex..prod.js gzip	15 kB	15 kB	✓
app-route-tu..prod.js gzip	15 kB	15 kB	✓
app-route-tu..prod.js gzip	14.8 kB	14.8 kB	✓
app-route.ru...dev.js gzip	21 kB	21 kB	✓
app-route.ru..prod.js gzip	14.8 kB	14.8 kB	✓
pages-api-tu..prod.js gzip	9.52 kB	9.52 kB	✓
pages-api.ru...dev.js gzip	9.8 kB	9.8 kB	✓
pages-api.ru..prod.js gzip	9.52 kB	9.52 kB	✓
pages-turbo...prod.js gzip	22.3 kB	22.3 kB	✓
pages.runtim...dev.js gzip	22.9 kB	22.9 kB	✓
pages.runtim..prod.js gzip	22.3 kB	22.3 kB	✓
server.runti..prod.js gzip	50.5 kB	50.5 kB	✓
Overall change	249 kB	249 kB	✓

build cache Overall increase ⚠️

	vercel/next.js canary	ijjk/next.js fix/metadata-promise-race	Change
0.pack gzip	1.56 MB	1.56 MB	⚠️ +1.17 kB
index.pack gzip	105 kB	105 kB	N/A
Overall change	1.56 MB	1.56 MB	⚠️ +1.17 kB

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Commit: aa3d795