rc.3 vitest browser mode issue with tslib

[LeonEck]

Command

test

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

rc.2

Description

In rc.3 when using vitest in browser mode and importing a decorator from a third party library, ng test fails with: TypeError: Cannot destructure property '__extends' of 'import_tslib.default' as it is undefined.
This was not an issue in rc.2

Minimal Reproduction

Minimal reproduction: https://github.com/LeonEck/test-tslib
Running ng test shows the described error.

Exception or Error

Your Environment

Angular CLI       : 21.0.0-rc.3
Angular           : 21.0.0-rc.2
Node.js           : 24.11.1
Package Manager   : npm 11.6.2
Operating System  : darwin arm64

┌───────────────────────────┬───────────────────┬───────────────────┐
│ Package                   │ Installed Version │ Requested Version │
├───────────────────────────┼───────────────────┼───────────────────┤
│ @angular/build            │ 21.0.0-rc.3       │ ^21.0.0-rc.3      │
│ @angular/cli              │ 21.0.0-rc.3       │ ^21.0.0-rc.3      │
│ @angular/common           │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/compiler         │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/compiler-cli     │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/core             │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/forms            │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/platform-browser │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ @angular/router           │ 21.0.0-rc.2       │ ^21.0.0-next.0    │
│ rxjs                      │ 7.8.2             │ ~7.8.0            │
│ typescript                │ 5.9.3             │ ~5.9.2            │
│ vitest                    │ 4.0.8             │ ^4.0.8            │
└───────────────────────────┴───────────────────┴───────────────────┘

Anything else relevant?

No response

[clydin]

You can workaround this temporarily with this custom config:

import { defineConfig } from 'vitest/config';

export default defineConfig({
  resolve: {
    conditions: ['module']
  }
});

A fix that will default this behavior is in progress.