This change is to pick the esm assets for RSC server layer and server rendering side, this is for production and development perf purpose, also to let them apply with the ESM related optimization such as tree-shaking, barrel files optimizations, etc.
We found a few packages that can't be optimized easily in bundling because we're using "main" field so the packages are not able to be tree-shaked, ending up with large bundle in the dist. This will change a lot for the bundling improvements as some packages are only having "main" and "module" field. So switching from CJS to ESM means better bundling, more optimization, and faster code.
#56501 was a precondition for this, as previously the bundling strategy was applied to some library but triggered the invalid hooks erroring.
### Other Monior Change
Previously we'll prefer to resolve CJS as there're 2 versions of react, using CJS assets will help let them pass by require-hook to use canary react for app router bundling assets. But now we changed the approach to bundling nextjs runtime and react packages. Now we dropped the condition that prefered to resolve CJS exports for externals, since if you're putting them in `serverComponentsExternalPackages`, they're not using the built-in react, so could potentially having trouble if any dependency is using react but excluded in bundles. So far we didn't see any report to this.
Closes NEXT-1286
Follow up for #50548
There're some packages like `aws-sdk-js-v3` which doesn't have a exports field yet:
```
"main": "./dist-cjs/index.js",
"types": "./dist-types/index.d.ts",
"module": "./dist-es/index.js",
```
This PR let u pick up by the js assets based on main fields, will prefer `"module"` field instead of `"main"`
Closes NEXT-1286
One potential risk is ESM dependencies that can't be bundled will cause
a build error. This also means that the `esmExternals` configuration
will be affected.
Closes#42249, closes#42588. Related: #1395.
## Bug
- [ ] Related issues linked using `fixes #number`
- [x] Integration tests added
- [ ] Errors have a helpful link attached, see `contributing.md`
## Feature
- [ ] Implements an existing feature request or RFC. Make sure the
feature request has been accepted for implementation before opening a
PR.
- [ ] Related issues linked using `fixes #number`
- [ ] Integration tests added
- [ ] Documentation added
- [ ] Telemetry added. In case of a feature if it's used or not.
- [ ] Errors have a helpful link attached, see `contributing.md`
## Documentation / Examples
- [ ] Make sure the linting passes by running `pnpm build && pnpm lint`
- [ ] The "examples guidelines" are followed from [our contributing
doc](https://github.com/vercel/next.js/blob/canary/contributing/examples/adding-examples.md)
Co-authored-by: kodiakhq[bot] <49736102+kodiakhq[bot]@users.noreply.github.com>
