Tree shaking for cross-module inlined enum values does not work

[shy-robin]

Describe the bug

I want to use const enums instead of enum to optimize transpiled code, but it only works in a single file. When I use ESM import/export syntax for cross-module inlining, it does not work.
I have tried to use rollup to implement this, and it can work. And now I want to know if this is a bug of Vite.

Reproduction

https://stackblitz.com/edit/vitejs-vite-7lxty9

Steps to reproduce

No response

System Info

System:
    OS: Linux 5.0 undefined
    CPU: (8) x64 Intel(R) Core(TM) i9-9880H CPU @ 2.30GHz
    Memory: 0 Bytes / 0 Bytes
    Shell: 1.0 - /bin/jsh
  Binaries:
    Node: 16.14.2 - /usr/local/bin/node
    Yarn: 1.22.10 - /usr/local/bin/yarn
    npm: 7.17.0 - /usr/local/bin/npm
  npmPackages:
    @vitejs/plugin-vue: ^3.1.2 => 3.1.2 
    vite: ^3.1.4 => 3.1.6

Used Package Manager

npm

Logs

No response

Validations

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• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
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• The provided reproduction is a minimal reproducible example of the bug.

[sapphi-red]

I have tried to use rollup to implement this, and it can work.

Would you provide a reproduction of this?

[shy-robin]

https://github.com/shy-robin/rollup-demo

[sapphi-red]

Thanks for the repro!

This does not work because of the limitation of isolatedModules: true. Vite uses esbuild's transform that only supports isolatedModules: true.

If you set typescript({ compilerOptions: { isolatedModules: true } }) in rollup repro, you can see the enum not inlined.

[shy-robin]

Thanks for your reply!
But it's not the key point. What I expect is that when I use ESM import/export syntax, const enum should be inlined by the use ofvite build. However, when I use rollup, const enum in cross-module such as using export const enum {} and then using import can be inlined.
I want to know if this is the problem of Vite.

[sapphi-red]

Ah, I got it.

Non cross-module enums are inlined because esbuild specially supports it (evanw/esbuild#128).
Cross-module enums inlining is supported by esbuild only when bundling. Vite uses transform that doesn't supported it.

To support cross-module enums inlining, the tool needs to know both:

1. TypeScript syntax
2. module graph

But in Vite, TypeScript syntax is processed by esbuild and module graph is handled by rollup. So it's not possible to support.

[shy-robin]

Cross-module enums inlining is supported by esbu

Thanks for your reply!
So for now, the method I can reduce the size of the output code is not use cross-module enums but replicate enums to another file. Right?

[sapphi-red]

I guess you could also use define + declare enum.

[shy-robin]

I guess you could also use define + declare enum.

emmm... Doesn't the type declaration file only work in the development process ?
I have tried to declare enum in a .d.ts file and use it in a .ts file, but enum doesn't be transpiled.

[sapphi-red]

You'll need to add define in the config.
https://vitejs.dev/config/shared-options.html#define

[shy-robin]

Oh, I got it. Thank you very much.