[2.5.0-beta] Cannot import typescript types if importsNotUsedAsValues is not "remove"

[IanVS]

Describe the bug

The title is a little misleading, you cannot import types, but you can import type.

After #4279 began respecting tsconfig settings, I began getting errors from import statements which mixed value and types. I've narrowed it down to only happening when importsNotUsedAsValues is set to preserve or error.

So, for example, this has started to fail in my app:

import { useSelect, UseSelectProps } from 'downshift';

As a workaround, I can change it to:

import { useSelect } from 'downshift';
import type {UseSelectProps} from 'downshift';

But I think I should be able to mix them, right?

Note, this only happens in dev mode. Running yarn build && yarn serve does not throw an error in the console. Which makes me think this might be an esbuild bug, perhaps?

Reproduction

https://github.com/IanVS/vite/tree/ts-type-import

Clone my fork, checkout the ts-type-import branch, yarn, yarn build-vite, cd packages/playground/ts-import, yarn dev, and see the error in the browser console:

Uncaught SyntaxError: The requested module '/src/dep.ts' does not provide an export named 'Foo'

System Info

System:
    OS: macOS 11.4
    CPU: (16) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 1.07 GB / 32.00 GB
    Shell: 5.8 - /bin/zsh
  Binaries:
    Node: 16.4.0 - ~/.nvm/versions/node/v16.4.0/bin/node
    Yarn: 1.22.10 - ~/.nvm/versions/node/v16.4.0/bin/yarn
    npm: 7.19.0 - ~/.nvm/versions/node/v16.4.0/bin/npm
  Browsers:
    Brave Browser: 92.1.27.111
    Firefox: 90.0.2
    Safari: 14.1.1

Used Package Manager

npm

Logs

No response

Validations

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[sodatea]

I think it's a bug in esbuild.

[swandir]

Reported the problem upstream evanw/esbuild#1525

[quolpr]

There is a response in related esbuild issue:

TypeScript might be changing their behavior for this soon. See microsoft/TypeScript#43393 and microsoft/TypeScript#44619. I think the new behavior will be something like --importsNotUsedAsValues=preserve still does not preserve imports that aren't used as values, but you can additionally add --preserveValueImports to actually preserve unused imported values. We'll have to see what the behavior ends up being when the next version of TypeScript is released. When that happens, esbuild can be changed to do what that version of TypeScript does.

So, how the current issue can be solved right now for vite? It adds some pain to the current dev experience

[IanVS]

For now I've separated out my type imports from value imports. Honestly, I think it's cleaner and definitely more explicit that way anyway. But I agree it's not ideal to force devs to do that.

[swandir]

Another workaround is to set importsNotUsedAsValues to "remove"

[lgarron]

I wanted to evaluate Vite for https://github.com/cubing/cubing.js/ and it mostly worked like a charm, except for this.

My VSCode tooling mixes type imports with value imports by default, and Vite's interpretation of "importsNotUsedAsValues": "error" doesn't seem to match TypeScript's.

Another workaround is to set importsNotUsedAsValues to "remove"

This is very helpful to know, thanks! I'd love for Vite to match TypeScript semantics for "importsNotUsedAsValues": "error" before we consider a full switch, though.

(This thread suggests that it requires a fix in esbuild, but we have been using that successfully to build the codebase for quite a while. I'm guessing Vite is passing something that esbuild isn't picking up on its own?)

[swandir]

(This thread suggests that it requires a fix in esbuild, but we have been using that successfully to build the codebase for quite a while. I'm guessing Vite is passing something that esbuild isn't picking up on its own?)

Yes, this change seems to have been introduced in #4279
Before that vite wasn't passing importsNotUsedAsValues to esbuild

[jonlepage]

For now I've separated out my type imports from value imports. Honestly, I think it's cleaner and definitely more explicit that way anyway. But I agree it's not ideal to force devs to do that.

The issu is if you use Vscode as IDE , it become really panful for the workflow

When you fix a type, if the type are inside a value module, it will mix with the import value instead create a new import type !

Actually this issu give more handwork because i always need check how vscode add some types and move some types inside new files.
Sometime you just want keep some types inside a value module because it logique to see there and that types there removes some ambiguity in his use from the value module.

I hope we can get a fix

[dummdidumm]

Version 0.14 of ESBuild contains a change in behavior with regards to this setting. The behavior of importsNotUsedAsValues is now aligned with that of TypeScript. To get back the previous behavior the new flag by TS is also supported now: preserveValueImports. The flag does what its name says, all value (non-type) imports are preserved regardless of whether they are used or not. Also see the TS 4.5 announcement: https://devblogs.microsoft.com/typescript/announcing-typescript-4-5/#preserve-value-imports

Therefore I think this issue can be closed.

[Niputi]

@dummdidumm can be closed with vite 2.8 release with #5861 merged

[bluwy]

Closing as #5861 is merged