Image Optimization API should 404 when loader is not default

[styfle]

We currently always accept requests to the new /_next/image endpoint, even when it should not be used.

Instead, we should check to see if the default loader is used as a signal to enable this API.

Other loaders (such as cloudinary) will not go through the Next.js API so there is no need to expose this, instead we 404.

• Analogous to [next] Image Optimization for default loader vercel#5321
• Related to [WIP] Next.js Image Component #18122

[ijjk]

Stats from current PR

Default Server Mode (Increase detected ⚠️)

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
buildDuration	13.1s	13s	-183ms
nodeModulesSize	91.3 MB	91.3 MB	⚠️ +440 B

Page Load Tests Overall increase ✓

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
/ failed reqs	0	0	✓
/ total time (seconds)	2.37	2.407	⚠️ +0.04
/ avg req/sec	1055.02	1038.74	⚠️ -16.28
/error-in-render failed reqs	0	0	✓
/error-in-render total time (seconds)	1.39	1.31	-0.08
/error-in-render avg req/sec	1798.98	1908.55	+109.57

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
677f882d2ed8..574c.js gzip	11.2 kB	11.2 kB	✓
framework.HASH.js gzip	39 kB	39 kB	✓
main-3dd37a4..54de.js gzip	7.34 kB	7.34 kB	✓
webpack-e067..f178.js gzip	751 B	751 B	✓
Overall change	58.3 kB	58.3 kB	✓

Client Bundles (main, webpack, commons) Modern

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
677f882d2ed8..dule.js gzip	7.02 kB	7.02 kB	✓
framework.HA..dule.js gzip	39 kB	39 kB	✓
main-082aff9..dule.js gzip	6.32 kB	6.32 kB	✓
webpack-07c5..dule.js gzip	751 B	751 B	✓
Overall change	53.1 kB	53.1 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
polyfills-4b..e242.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
_app-9a0b9e1..b37e.js gzip	1.28 kB	1.28 kB	✓
_error-ed1b0..8fbd.js gzip	3.44 kB	3.44 kB	✓
hooks-89731c..c609.js gzip	887 B	887 B	✓
index-17468f..5d83.js gzip	227 B	227 B	✓
link-41ceea0..6b62.js gzip	1.35 kB	1.35 kB	✓
routerDirect..924c.js gzip	284 B	284 B	✓
withRouter-7..c13d.js gzip	284 B	284 B	✓
Overall change	7.75 kB	7.75 kB	✓

Client Pages Modern

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
_app-75d3a82..dule.js gzip	625 B	625 B	✓
_error-4469a..dule.js gzip	2.29 kB	2.29 kB	✓
hooks-cbf13f..dule.js gzip	387 B	387 B	✓
index-b9a643..dule.js gzip	226 B	226 B	✓
link-2d41a89..dule.js gzip	1.31 kB	1.31 kB	✓
routerDirect..dule.js gzip	284 B	284 B	✓
withRouter-f..dule.js gzip	282 B	282 B	✓
Overall change	5.4 kB	5.4 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
_buildManifest.js gzip	323 B	323 B	✓
_buildManife..dule.js gzip	329 B	329 B	✓
Overall change	652 B	652 B	✓

Rendered Page Sizes

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
index.html gzip	1 kB	1 kB	✓
link.html gzip	1.01 kB	1.01 kB	✓
withRouter.html gzip	994 B	994 B	✓
Overall change	3 kB	3 kB	✓

---

Serverless Mode

General Overall increase ⚠️

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
buildDuration	14.4s	14.9s	⚠️ +447ms
nodeModulesSize	91.3 MB	91.3 MB	⚠️ +440 B

Client Bundles (main, webpack, commons)

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
677f882d2ed8..574c.js gzip	11.2 kB	11.2 kB	✓
framework.HASH.js gzip	39 kB	39 kB	✓
main-3dd37a4..54de.js gzip	7.34 kB	7.34 kB	✓
webpack-e067..f178.js gzip	751 B	751 B	✓
Overall change	58.3 kB	58.3 kB	✓

Client Bundles (main, webpack, commons) Modern

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
677f882d2ed8..dule.js gzip	7.02 kB	7.02 kB	✓
framework.HA..dule.js gzip	39 kB	39 kB	✓
main-082aff9..dule.js gzip	6.32 kB	6.32 kB	✓
webpack-07c5..dule.js gzip	751 B	751 B	✓
Overall change	53.1 kB	53.1 kB	✓

Legacy Client Bundles (polyfills)

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
polyfills-4b..e242.js gzip	31 kB	31 kB	✓
Overall change	31 kB	31 kB	✓

Client Pages

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
_app-9a0b9e1..b37e.js gzip	1.28 kB	1.28 kB	✓
_error-ed1b0..8fbd.js gzip	3.44 kB	3.44 kB	✓
hooks-89731c..c609.js gzip	887 B	887 B	✓
index-17468f..5d83.js gzip	227 B	227 B	✓
link-41ceea0..6b62.js gzip	1.35 kB	1.35 kB	✓
routerDirect..924c.js gzip	284 B	284 B	✓
withRouter-7..c13d.js gzip	284 B	284 B	✓
Overall change	7.75 kB	7.75 kB	✓

Client Pages Modern

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
_app-75d3a82..dule.js gzip	625 B	625 B	✓
_error-4469a..dule.js gzip	2.29 kB	2.29 kB	✓
hooks-cbf13f..dule.js gzip	387 B	387 B	✓
index-b9a643..dule.js gzip	226 B	226 B	✓
link-2d41a89..dule.js gzip	1.31 kB	1.31 kB	✓
routerDirect..dule.js gzip	284 B	284 B	✓
withRouter-f..dule.js gzip	282 B	282 B	✓
Overall change	5.4 kB	5.4 kB	✓

Client Build Manifests

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
_buildManifest.js gzip	323 B	323 B	✓
_buildManife..dule.js gzip	329 B	329 B	✓
Overall change	652 B	652 B	✓

Serverless bundles

	vercel/next.js canary	vercel/next.js api-image-loader-disable	Change
_error.js	1.06 MB	1.06 MB	✓
404.html	4.73 kB	4.73 kB	✓
hooks.html	3.92 kB	3.92 kB	✓
index.js	1.06 MB	1.06 MB	✓
link.js	1.1 MB	1.1 MB	✓
routerDirect.js	1.1 MB	1.1 MB	✓
withRouter.js	1.1 MB	1.1 MB	✓
Overall change	5.42 MB	5.42 MB	✓

Commit: b5d1bf1