Failed to start Vitest. Check the output for more details. Vitest WebSocket connection closed, cannot call RPC anymore.

[JohnCido]

Describe the bug

I did not make any changes to our Vitest installation or config in 2 months. We've also been using Proto tools alongside Vitest for quite some time and had no issue before. Today it suddenly won't start up. I have installed the latest VSCode 1.139.0. Wonder if that could be the source.

Expected behavior

It should start without any error.

Reproduction

I created an minimal project with the bun init and installed the vitest as dev dependency. Reload the window via F1, and the error showed up.

Output

[INFO 17:39:55] [v1.52.0] Vitest extension is activated because Vitest is installed or there is a Vite/Vitest config file in the workspace.
[INFO 17:39:55] [API] Using user root config: /Users/***/***/vitest.config.ts
[INFO 17:39:56] [API] Resolving configs: ***/vitest.config.ts
[17:39:56] [API] Spawning on-demand process...
[INFO 17:39:56] [API] Running Vitest v4.1.10 (***/vitest.config.ts) with "/Users/***/.proto/shims/node /Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/worker.js"
[17:39:58] [API] Vitest WebSocket connection closed, cannot call RPC anymore.
[17:39:58] [API] On-demand process finished in 2327ms
[Error 17:39:58] There were errors during config load.
[Error 17:39:58] [Error Error] [birpc] rpc is closed, cannot call "getFiles"
Error: [birpc] rpc is closed, cannot call "getFiles"
	at /Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/esm-219GbSo2.js:1:1011
	at Map.forEach (<anonymous>)
	at Proxy.b (/Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/esm-219GbSo2.js:1:974)
	at e.<anonymous> (/Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/extension.js:1:66879)
	at e.wrapper (node:events:639:12)
	at e.emit (node:events:526:24)
	at e.emitClose (/Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/esm-219GbSo2.js:1:29396)
	at Socket.X (/Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/esm-219GbSo2.js:1:39502)
	at Socket.emit (node:events:514:28)
	at TCP.<anonymous> (node:net:362:12)
[Error 17:39:59] Error: The extension could not load any config.
	at tn (/Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/extension.js:1:79360)
	at async lr._defineTestProfiles (/Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/extension.js:24:5481)
	at async lr.defineTestProfiles (/Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/extension.js:24:4769)
	at async lr.activate (/Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/extension.js:24:13636)
	at async sr (/Users/***/.vscode/extensions/vitest.explorer-1.52.0/dist/extension.js:24:3397)
	at async zb._activate (file:///Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/api/node/extensionHostProcess.js:164:16021)
	at async zb._waitForDepsThenActivate (file:///Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/api/node/extensionHostProcess.js:164:15963)
	at async zb._initialize (file:///Applications/Visual%20Studio%20Code.app/Contents/Resources/app/out/vs/workbench/api/node/extensionHostProcess.js:164:15330)

Extension Version

1.52.0

Vitest Version

4.1.10 in our monorepo, 5.0.1 in the test folder

Validations

• Check that you are using the latest version of the extension
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
• Check that this is a concrete bug. For Q&A open a GitHub Discussion or join our Discord Chat Server.
• The provided reproduction is a minimal reproducible example of the bug.

[Sector6759]

Same issue after installing VSCode 1.139.0.

[jay-zahiri]

Same prior to and after VSCode 1.139.0 update , but did update macOS to Golden Gate recently.

Edit: prior to 1.139.0 was a $PATH mismatch

[klairi-tas-monek]

For me it worked before installing 1.139, it stopped immediately after the upgrade.

[russray2008]

Look at #825. It is all related.

[mastry]

Opened #826 with a fix.

The mismatch is in V8's structured-clone format. VS Code 1.139's Electron (V8 15.0) writes format version 16, and Node 26.10 (V8 14.6) can only read up to 15. So the worker's first v8.deserialize of an RPC message throws. birpc swallows that error, the getFiles call never gets a reply, and the extension reports rpc is closed.

Until a release ships, a local workaround:

1. Open ~/.vscode/extensions/vitest.explorer-1.52.0/dist/.
2. In both worker.js and extension.js, find the serialize and deserialize expressions that check runtime===`node` (two per file) and replace that check with false.
3. Reload the window.

This forces JSON everywhere. The next extension update should overwrite the manual workaround.

[tobias-haenel]

this workaround in .vscode/settings.json works for my setup and might be helpful while we wait for the pull request to be merged:

"vitest.nodeExecutable": "/usr/share/code/code",
"vitest.nodeEnv": { "ELECTRON_RUN_AS_NODE": "1" }

[SameOldNick]

@tobias-haenel Worked for me. Just note for anyone else that "vitest.nodeExecutable" needs to be your VSCode executable (depends on what OS you're using and where you've installed it).