Dependency optimization does not work in SSR transform mode

[kherock]

Describe the bug

Vite lazily initializes the SSR deps optimizer when ViteDevServer.ssrLoadModule is called for the first time.

Vitest/vite-node does not seem to ever call this method, so the optimizer never ends up being initialized into the devSsrDepsOptimizerMap, which Vite uses to resolve the appropriate optimizer.

Reproduction

I'm currently running Vitest 0.34 with Vite 4, but I was able to recreate the issue with the latest Vitest and Vite 5:
https://stackblitz.com/edit/vitest-dev-vitest-1flfpv?file=test%2Fweb.test.ts

System Info

System:
    OS: macOS 13.6.3
    CPU: (10) arm64 Apple M1 Pro
    Memory: 103.50 MB / 16.00 GB
    Shell: 5.9 - /bin/zsh
  Binaries:
    Node: 20.10.0 - /opt/homebrew/bin/node
    Yarn: 1.22.19 - /opt/homebrew/bin/yarn
    npm: 10.2.3 - /opt/homebrew/bin/npm
    pnpm: 7.9.5 - /opt/homebrew/bin/pnpm
  Browsers:
    Chrome: 120.0.6099.199
    Edge: 120.0.2210.121
    Safari: 17.2.1
  npmPackages:
    @vitest/coverage-v8: ^0.34.6 => 0.34.6 
    vitest: ^0.34.6 => 0.34.6

Used Package Manager

npm

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

[hi-ogawa]

Interesting... I was also wondering how ssr.optimizeDeps (pre-bundling) is supposed to work (though my use case was directly using vite-node without Vitest).

As you mentioned, it looks like calling ssrLoadModule is necessary to trigger deps optimization. It's a very sketchy workaround, but doing so in a plugin seems to suffice for my use case:

import { defineConfig } from 'vite';

export default defineConfig({
  plugins: [
    {
      name: 'force-ssr-optimize-deps',
      configureServer(server) {
        return async () => {
          console.log('[ssrLoadModule to trigger ssr pre-bundling]');
          await server.ssrLoadModule('/dummy-module.js');
        };
      },
    },
  ],
});

I tested this on your repro as well though probably Vitest is supposed to handle this somehow eventually:

https://stackblitz.com/edit/vitest-dev-vitest-8wf26p?file=vite.config.ts

---

ssr.optimizeDeps is still experimental, so maybe it's worth providing a feedback here:

• Stabilizing deps optimization at build time (and SSR) vitejs/vite#13839

(EDIT: I made my own comment there based on my use case)

[patak-dev]

Created a PR to Vite to move the SSR dev optimization to the server init here. I think we should merge this for Vite 5.1:

• fix: init dev ssr optimizer on server init vitejs/vite#15561

[hi-ogawa]

I verified that Vite 5.1.0-beta.0 fixed the issue without hacky "force-ssr-optimize-deps'" plugin. I used npm's overrides in this stackblitz:
https://stackblitz.com/edit/vitest-dev-vitest-phpqaa?file=package.json

I also verified the fix in my project as well. Thanks @patak-dev!

[sheremet-va]

I think we can close this. Vitest doesn't support versions before 1.0, so the recommendation is to update to the latest version. You can also use a workaround provided by @hi-ogawa.