Improve error for missing default export in dynamic metadata routes

[huozhi]

Displaying hints of "missing default export" if you didn't properly export the default handler for og image

   ▲ Next.js 14.0.1-canary.2
   - Local:        http://localhost:3000

 ✓ Ready in 1089ms
 ✓ Compiled /opengraph-image/[[...__metadata_id__]]/route in 211ms (44 modules)
 ⨯ Error: Default export is missing in "/Users/huozhi/workspace/next.js/test/e2e/app-dir/metadata-dynam
ic-routes/app/opengraph-image.tsx"
    at eval (webpack:///app/opengraph-image.tsx?3407:11:1)
    at (app-metadata-route)/../../../../packages/next/dist/build/webpack/loaders/next-metadata-route-lo
ader.js?page=%2Fopengraph-image%2F%5B%5B...__metadata_id__%5D%5D%2Froute&isDynamic=1!./app/opengraph-im
age.tsx?__next_metadata_route__ (/Users/huozhi/workspace/next.js/test/e2e/app-dir/metadata-dynamic-rout
es/.next/server/app/opengraph-image/[[...__metadata_id__]]/route.js:362:1)
    at __webpack_require__ (/Users/huozhi/workspace/next.js/test/e2e/app-dir/metadata-dynamic-routes/.n
ext/server/webpack-runtime.js:33:42)

[ijjk]

Stats from current PR

Default Build

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js metadata/improve-error	Change
buildDuration	10.7s	10.6s	N/A
buildDurationCached	6.1s	6.2s	N/A
nodeModulesSize	175 MB	175 MB	⚠️ +1.94 kB
nextStartRea..uration (ms)	399ms	397ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	vercel/next.js metadata/improve-error	Change
199-HASH.js gzip	30 kB	30 kB	N/A
3f784ff6-HASH.js gzip	53.2 kB	53.2 kB	✓
99.HASH.js gzip	182 B	182 B	✓
framework-HASH.js gzip	45.5 kB	45.5 kB	✓
main-app-HASH.js gzip	254 B	251 B	N/A
main-HASH.js gzip	33.1 kB	33.1 kB	N/A
webpack-HASH.js gzip	1.75 kB	1.75 kB	N/A
Overall change	98.9 kB	98.9 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js metadata/improve-error	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js metadata/improve-error	Change
_app-HASH.js gzip	206 B	205 B	N/A
_error-HASH.js gzip	182 B	180 B	N/A
amp-HASH.js gzip	506 B	505 B	N/A
css-HASH.js gzip	322 B	323 B	N/A
dynamic-HASH.js gzip	2.59 kB	2.59 kB	✓
edge-ssr-HASH.js gzip	260 B	259 B	N/A
head-HASH.js gzip	350 B	350 B	✓
hooks-HASH.js gzip	369 B	369 B	✓
image-HASH.js gzip	4.38 kB	4.38 kB	N/A
index-HASH.js gzip	256 B	256 B	✓
link-HASH.js gzip	2.67 kB	2.67 kB	N/A
routerDirect..HASH.js gzip	316 B	318 B	N/A
script-HASH.js gzip	385 B	384 B	N/A
withRouter-HASH.js gzip	319 B	319 B	✓
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	3.99 kB	3.99 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js metadata/improve-error	Change
_buildManifest.js gzip	484 B	482 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js metadata/improve-error	Change
index.html gzip	527 B	529 B	N/A
link.html gzip	540 B	541 B	N/A
withRouter.html gzip	524 B	524 B	✓
Overall change	524 B	524 B	✓

Edge SSR bundle Size

	vercel/next.js canary	vercel/next.js metadata/improve-error	Change
edge-ssr.js gzip	96.1 kB	96.1 kB	N/A
page.js gzip	140 kB	140 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	vercel/next.js metadata/improve-error	Change
middleware-b..fest.js gzip	625 B	622 B	N/A
middleware-r..fest.js gzip	150 B	151 B	N/A
middleware.js gzip	23 kB	23 kB	N/A
edge-runtime..pack.js gzip	1.92 kB	1.92 kB	✓
Overall change	1.92 kB	1.92 kB	✓

Commit: e1304da

[ijjk]

Tests Passed

[feedthejim]

Should we fail at build time if we can?

[huozhi]

@feedthejim The PR is already doing that, the thrown error will bail the build