fix: resolve error in deepimport

[zhangyuang]

Description

Mentioned #3039, there are only tryindex when no exports field. It will be error in below code.

Maybe there should tryindex again when no resolved or tryindex always.

// error
import Button from 'vant/lib/button'
// succeed
import Button from 'vant/lib/button/index.js'

Additional context

There is a reproduction

$ git clone git@github.com:zhangyuang/vite-ssr-error-require.git
$ git checkout bug/tryindex
$ yarn && yarn dev 

---

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[gluck]

Hi, the current behavior seems consistent with node resolver:

Welcome to Node.js v17.1.0.
Type ".help" for more information.
> require.resolve('vant/lib/button/index.js')
'/tmp/bar/node_modules/vant/lib/button/index.js'
> require.resolve('vant/lib/button')
Uncaught Error: Cannot find module '/tmp/bar/node_modules/vant/lib/button'
    at createEsmNotFoundErr (node:internal/modules/cjs/loader:954:15)
    at finalizeEsmResolution (node:internal/modules/cjs/loader:947:15)
    at resolveExports (node:internal/modules/cjs/loader:482:14)
    at Function.Module._findPath (node:internal/modules/cjs/loader:522:31)
    at Function.Module._resolveFilename (node:internal/modules/cjs/loader:919:27)
    at Function.resolve (node:internal/modules/cjs/helpers:108:19) {
  code: 'MODULE_NOT_FOUND',
  path: '/tmp/bar/node_modules/vant/package.json'
}

The spec may not be clear around whether an export mapping from ./lib/* to ./lib/* should resolve index.js but the implementation doesn't.

Retrying resolve with index lookup seems to defeat exports specs in many (other) ways.

My 2c.

[bluwy]

If @gluck confirmed this is intended behaviour by node, I think we should lean on that and not have this change. Unless we figure out the try index only if no exports field comment.

[zhangyuang]

Maybe it's vant bug ,let me take a look

[zhangyuang]

@bluwy Maybe we can fix the problem in vite layer? The kind of writing is frequent, some third-party ui library like antd, vant which use babel-plugin-import to transform below code

import { Button } from 'antd'

=> import Button from 'antd/lib/button'
import 'antd/lib/button/style'

not tryindex if has exports is not exactly in some case

[bluwy]

I don't think Vite should deviate from the spec as it's one of its philosophies. Re-reading try index only if no exports field now, I think it makes sense, since if we have an exports field, that should be respected no matter what.

But regarding vant, it looks like they're not correctly exporting the /lib. I don't see a trailing slash being in the spec, maybe something like:

"./lib/*": "./lib/*/index.js"

would work.

Re antd, they don't seem to be using exports.

[zhangyuang]

Ok, thanks a lot 😄