### What
Optimizing the static generation for dynamic metadata routes
If you're not using `generateSitemaps()` or `generateSitemaps()`, you
don't need to change any file conventions.
If you're using multi sitemap routes, make sure the returned `id`
properties from `generateSitemaps()` don't need to contain `.xml`, since
we'll always append one for you.
Analyzing the exports of metadata routes and determine if we need to
make them as dynamic routes.
### Why
Previously, users are struggling with the multi routes of sitemap or
images.
For sitemap, the `.xml` extension in url doesn't get appended
consistently to the multi sitemap route between dev and prod.
For image routes, the generated image routes are always dynamic routes
which cannot get static optimized.
The reason is that we need to always generate a catch-all route (such as
`/icon/[[...id]]` to handle both single route case (e.g. without
`generateImageMetadata`, representing url `/icon`) or multi route (e.g.
with `generateImageMetadata`, representing url `/icon/[id]`), only
catch-all routes can do it. This approach fail the static optimization
and make mapping url pretty difficult as parsing the file to check the
module exports has to be done before it.
#### Benifits
For image routes urls, this approach could help on static generation
such as single `/opengraph-image` route can be treated as static, and
then it can get static optimized if possible.
**Before**: `/opengraph-image/[[...id]]` cannot be optimized
**After**: single route `/opengraph-image` and multi-route
`/opengraph-image/[id]` are both possible to be statically optimized
For sitemap, since we removed appending `.xml` for dynamic routes, it’s
hard for users to have `/sitemap.xml` url with dynamic route convention
`sitemap.js` . But users desire smooth migration and flexibility.
**Before**: In v15 rc we removed the `.xml` appending that `sitemap.js`
will generate url `/sitemap` makes users hard to migrate, as users need
to re-submit the new sitemap url.
**After**: Now we'll consistently generate the `.xml`. Single route will
become `/sitemap.xml`, and multi route will become `/sitemap/[id].xml`.
It's still better than v15 as the urls generation is consistent, no
difference between dev and prod.
Here's the url generation comparsion
#### Before
All the routes are dynamic which cannot be optimized, we only had a
hacky optimization for prodution build multi-routes sitemap routes
| | only default export | `export generateImageMetadata()` | `export
generateSitemaps()` |
| -- | -- | -- | -- |
| opengraph-image.js | /opengraph-image/[[...id]] |
/opengraph-image[[...id]]/ | /opengraph-image/[[...id]] |
| sitemap.js | /sitemap/[[...id]] | /sitemap/[[...id]] | dev:
`/sitemap/[[...id]]` prod: `/sitemap/[id]` |
#### After
Most of the single route will are to get statically optimized now, and
the multi-routes sitemap are able to get SSG now
| | only default export | `export generateImageMetadata()` | `export
generateSitemaps()` |
| -- | -- | -- | -- |
| opengraph-image.js | /opengraph-image | /opengraph-image/[id] | - |
| sitemap.js | /sitemap.xml | - | /sitemap/[id].xml |
Next.js will have less overhead of mapping urls, we can easily multiply
the urls generation simply based on file conventions.
x-ref: feedback from #65507Closes#66232
f893c18528