Forced noExternal causes Vitest to fail with Astro components

[matthewp]

Describe the bug

This line that forces noExternal breaks testing Astro components because there are some CommonJS dependencies that can't be run through Vite's module loader.

vitest/packages/vitest/src/node/plugins/runnerTransform.ts

Line 146 in 1ec3a8b

environment.resolve.noExternal = true

Reproduction

https://github.com/HiDeoo/astro-6-vitest-repro

System Info

System:
    OS: macOS 15.6.1
    CPU: (10) arm64 Apple M1 Pro
    Memory: 769.50 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 22.21.1 - /Users/matthew/.volta/tools/image/node/22.21.1/bin/node
    Yarn: 1.22.19 - /Users/matthew/.volta/tools/image/yarn/1.22.19/bin/yarn
    npm: 10.9.4 - /Users/matthew/.volta/tools/image/node/22.21.1/bin/npm
    pnpm: 9.15.9 - /Users/matthew/Library/pnpm/pnpm
    bun: 1.2.20 - /Users/matthew/.bun/bin/bun
    Deno: 2.6.3 - /opt/homebrew/bin/deno
  Browsers:
    Brave Browser: 140.1.82.166
    Chrome: 143.0.7499.147
    Chrome Canary: 145.0.7592.0
    Firefox: 137.0.2
    Safari: 18.6
  npmPackages:
    vitest: ^4.0.16 => 4.0.16

Used Package Manager

pnpm

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• The provided reproduction is a minimal reproducible example of the bug.

[hi-ogawa]

@matthewp Do you know if the same or similiar setup worked on Vitest 3? There wasn't forced noExternal previously, but it was doing something similar underneath, so I expected it to fail. If it didn't, it might give some clue about the solution.

[hi-ogawa]

I just checked repro and I think I misunderstood the issue. The error happens during Astro's configureServer and ssr environment's rrunner.import("astro:app") and dependencies imported from there. https://github.com/withastro/astro/blob/76e7c321f75d33a47c6dc813a4dfbee57c51a90d/packages/astro/src/vite-plugin-astro-server/plugin.ts#L59

The stack trace with Error.stackTraceLimit = Infinity looks like this after I trimmed internal ModuleRunner stack:

ReferenceError: module is not defined
    at eval (/(root)/node_modules/.pnpm/cssesc@3.0.0/node_modules/cssesc/cssesc.js:110:1)
    at async eval (/(root)/node_modules/.pnpm/...//node_modules/astro/dist/runtime/server/transition.js:1:1)
    ...
    at async eval (/(root)/node_modules/.pnpm/...//node_modules/astro/dist/core/app/index.js:1:1)
    at async eval (virtual:astro:manifest:2:6)
    at async eval (astro:app:1:1)
    at async BasicMinimalPluginContext.configureServer (file:///(root)/node_modules/.pnpm/...//node_modules/astro/dist/vite-plugin-astro-server/plugin.js:45:49)
    at async _createServer (file:///(root)/node_modules/.pnpm/.../node_modules/vite/dist/node/chunks/config.js:25602:86)
    at async createViteServer (file:///(root)/node_modules/.pnpm/.../node_modules/vitest/dist/chunks/cli-api.BKg19Fvw.js:9815:17)
    at async createVitest (file:///(root)/node_modules/.pnpm/.../node_modules/vitest/dist/chunks/cli-api.BKg19Fvw.js:13119:17)
    at async prepareVitest (file:///(root)/node_modules/.pnpm/.../node_modules/vitest/dist/chunks/cli-api.BKg19Fvw.js:13481:14)
    at async startVitest (file:///(root)/node_modules/.pnpm/.../node_modules/vitest/dist/chunks/cli-api.BKg19Fvw.js:13427:14)
    at async start (file:///(root)/node_modules/.pnpm/.../node_modules/vitest/dist/chunks/cac.BGonGPac.js:1360:15)

Indeed, this is because of Vitest's noExternal: true. I thought there could be a similar issue for Vitest's own globalSetup etc. but they use Vitest's custom runner.import, so this doesn't happen. So, perhaps one solution could be to swap out the default runnable dev environment with Vitest's custom one, so Astro's environment.runner.import works similarly.

[matthewp]

Is that something Astro would need to do?

[hi-ogawa]

Is that something Astro would need to do?

@matthewp No, this likely needs to be handled on Vitest side since that's where special module runner for noExternal: true exists.

[matthewp]

@hi-ogawa did you reach any conclusion on this? This is blocking a Starlight release. Happy to send a PR if given some direction on what needs to be done here. Thank you.

[hi-ogawa]

@matthewp The plan is to overwrite Vite's server.environment.ssr.runner with Vitest's runner which handles external in a different way. This is ServerModuleRunner, for example:

vitest/packages/vitest/src/node/core.ts

Lines 242 to 248 in 2a60cf8

	this.runner = resolved.experimental.viteModuleRunner === false
	? new NativeModuleRunner(resolved.root)
	: new ServerModuleRunner(
	environment,
	this._fetcher,
	resolved,
	)

I dug in but I realized this can by still tricky because Astro needs server.environments.ssr.runner in configureServer, but Vitest finalizes internal structure during "post" configureServer and that's where Vitest's ServerModuleRunner becomes properly available.

Stepping back and trying to understand the background, can you explain whether your configureServer + runner.import is necessary for Astro component testing?

---

Also if not needed during configureServer, would runner.import needed during actual astro component test run?
For example, Astro's configureServer only runs when isRunnableDevEnvironment, so you can test it by swapping off with "non runnable environment", for example by:

// vitest.config.ts
import { getViteConfig } from "astro/config";
import { DevEnvironment } from "vite"

export default getViteConfig({
  environments: {
    ssr: {
      dev: {
        // overwrite default ssr environment with "non runnable" one
        createEnvironment(name, config, _context) {
          return new DevEnvironment(name, config, {
            hot: false,
          });
        },
      }
    }
  }
});

This works for the minimal repro at least https://stackblitz.com/edit/github-csxcwjt2?file=vitest.config.ts