Fix: Throw an error for empty array return in generateStaticParams with output:export

[k-taro56]

Fixes #57038

What?

Added an error message when generateStaticParams returns an empty array with output:export.

Why?

To provide developers with clear feedback when generateStaticParams is not used correctly.

How?

Modified the condition checks around the use of generateStaticParams to include a check for an empty array and added a corresponding error message.

[dobrakmato]

Hey @timneutkens is there anything that needs to be done, before this can be merged? The error message is currently confusing. Also do you accept PRs implementing this functionality?

[ijjk]

Tests Passed

[ijjk]

Stats from current PR

Default Build (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	k-taro56/next.js fix-empty-gsp-return	Change
buildDuration	12.7s	12.8s	⚠️ +126ms
buildDurationCached	7.1s	6.1s	N/A
nodeModulesSize	200 MB	202 MB	⚠️ +2.14 MB
nextStartRea..uration (ms)	421ms	501ms	N/A

Client Bundles (main, webpack)

	vercel/next.js canary	k-taro56/next.js fix-empty-gsp-return	Change
193.HASH.js gzip	181 B	182 B	N/A
3f784ff6-HASH.js gzip	53.3 kB	53.3 kB	✓
433-HASH.js gzip	28.5 kB	28.5 kB	N/A
framework-HASH.js gzip	45.2 kB	45.2 kB	✓
main-app-HASH.js gzip	239 B	242 B	N/A
main-HASH.js gzip	31.7 kB	31.7 kB	N/A
webpack-HASH.js gzip	1.7 kB	1.7 kB	N/A
Overall change	98.5 kB	98.5 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	k-taro56/next.js fix-empty-gsp-return	Change
polyfills-HASH.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	k-taro56/next.js fix-empty-gsp-return	Change
_app-HASH.js gzip	194 B	195 B	N/A
_error-HASH.js gzip	183 B	181 B	N/A
amp-HASH.js gzip	504 B	502 B	N/A
css-HASH.js gzip	321 B	321 B	✓
dynamic-HASH.js gzip	2.5 kB	2.5 kB	N/A
edge-ssr-HASH.js gzip	255 B	253 B	N/A
head-HASH.js gzip	350 B	349 B	N/A
hooks-HASH.js gzip	369 B	369 B	✓
image-HASH.js gzip	4.28 kB	4.28 kB	N/A
index-HASH.js gzip	255 B	256 B	N/A
link-HASH.js gzip	2.61 kB	2.61 kB	✓
routerDirect..HASH.js gzip	312 B	311 B	N/A
script-HASH.js gzip	385 B	383 B	N/A
withRouter-HASH.js gzip	307 B	308 B	N/A
1afbb74e6ecf..834.css gzip	106 B	106 B	✓
Overall change	3.4 kB	3.4 kB	✓

Client Build Manifests

	vercel/next.js canary	k-taro56/next.js fix-empty-gsp-return	Change
_buildManifest.js gzip	483 B	484 B	N/A
Overall change	0 B	0 B	✓

Rendered Page Sizes

	vercel/next.js canary	k-taro56/next.js fix-empty-gsp-return	Change
index.html gzip	526 B	526 B	✓
link.html gzip	539 B	538 B	N/A
withRouter.html gzip	523 B	521 B	N/A
Overall change	526 B	526 B	✓

Edge SSR bundle Size

	vercel/next.js canary	k-taro56/next.js fix-empty-gsp-return	Change
edge-ssr.js gzip	93.8 kB	93.8 kB	N/A
page.js gzip	147 kB	147 kB	N/A
Overall change	0 B	0 B	✓

Middleware size

	vercel/next.js canary	k-taro56/next.js fix-empty-gsp-return	Change
middleware-b..fest.js gzip	626 B	623 B	N/A
middleware-r..fest.js gzip	151 B	151 B	✓
middleware.js gzip	37.4 kB	37.4 kB	N/A
edge-runtime..pack.js gzip	1.92 kB	1.92 kB	✓
Overall change	2.07 kB	2.07 kB	✓

Next Runtimes

	vercel/next.js canary	k-taro56/next.js fix-empty-gsp-return	Change
app-page-exp...dev.js gzip	169 kB	168 kB	N/A
app-page-exp..prod.js gzip	94.2 kB	94.2 kB	N/A
app-page-tur..prod.js gzip	94.9 kB	94.9 kB	N/A
app-page-tur..prod.js gzip	89.5 kB	89.4 kB	N/A
app-page.run...dev.js gzip	139 kB	138 kB	N/A
app-page.run..prod.js gzip	88.8 kB	88.7 kB	N/A
app-route-ex...dev.js gzip	24.1 kB	24.1 kB	N/A
app-route-ex..prod.js gzip	16.7 kB	16.7 kB	N/A
app-route-tu..prod.js gzip	16.7 kB	16.7 kB	N/A
app-route-tu..prod.js gzip	16.3 kB	16.3 kB	N/A
app-route.ru...dev.js gzip	23.5 kB	23.5 kB	N/A
app-route.ru..prod.js gzip	16.3 kB	16.3 kB	N/A
pages-api-tu..prod.js gzip	9.38 kB	9.38 kB	✓
pages-api.ru...dev.js gzip	9.65 kB	9.65 kB	✓
pages-api.ru..prod.js gzip	9.37 kB	9.37 kB	✓
pages-turbo...prod.js gzip	21.9 kB	21.9 kB	N/A
pages.runtim...dev.js gzip	22.6 kB	22.5 kB	N/A
pages.runtim..prod.js gzip	21.9 kB	21.9 kB	N/A
server.runti..prod.js gzip	49.4 kB	49.5 kB	N/A
Overall change	28.4 kB	28.4 kB	✓

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Commit: 47fcdd0

[styfle]

Thanks!

I pushed a change to fix it in next dev too

[barroudjo]

I think it's not a good idea to throw an error when generateStaticParams returns an empty array with output: export, maybe a warning, but it shouldn't crash.
For example when working with a CMS with a preview mode, we want to be able to preview the page in SSR, and build the site with output: export when that same page generateStaticParams returns an empty array (because the documents accessed in the page are not published yet, but are available in the preview mode).

[styfle]

@barroudjo Good point, the existing behavior doesn't account for dynamic data from a CMS.

I'll revert in PR #60831.

Instead of erroring, we should warn (and only in dev mode). Anyone want to create a new PR?