Summary

I'd like to propose adding virtual workspace support to ruff-vscode by exporting a registerUriTranslator API — the same pattern Pylance already uses.

Problem

The extension currently declares virtualWorkspaces.supported: false. This blocks Ruff from providing linting/formatting in virtual workspace environments (GitHub Repositories, Microsoft Fabric notebooks, custom FileSystemProvider workspaces).

No Python linter or formatter currently supports virtual workspaces (see microsoft/vscode-python#21459).

Proposed approach

Ruff exports registerUriTranslator(), the VFS provider owns the cache.

This is the exact pattern Pylance uses. The VFS provider extension (which already maintains a disk cache for its own purposes) registers a translator with Ruff:

const ruff = vscode.extensions.getExtension('charliermarsh.ruff');
await ruff.activate();
ruff.exports.registerUriTranslator({
  translateToDisk(uri)    { /* virtual URI → cached file:// URI */ },
  translateToVirtual(uri) { /* file:// URI → virtual URI */ },
  clearTranslationCache() { /* invalidate */ }
});

On registration, Ruff restarts its language server with LSP middleware that calls the translator.

Key point addressing the copy-all-files concern: Ruff does NOT need to copy any files itself. The VFS provider already maintains a persistent disk cache (for Pylance integration, editor operations, etc.). Ruff simply plugs into that existing cache via the translator interface. The caching is lazy — only files that are actually opened/referenced get cached by the VFS provider.

Changes needed in ruff-vscode

1. package.json — set virtualWorkspaces.supported: true
2. New src/common/uriTranslator.ts — interface definitions + registerUriTranslator export
3. src/extension.ts — activate() returns the API; on registration triggers server restart
4. src/common/server.ts — configure LSP middleware when translator is registered
5. src/common/settings.ts / utilities.ts — handle non-file:// URI schemes

Zero changes needed in the Ruff binary — the native ruff server already speaks LSP and doesn't care about URI schemes.

Context

I work on the Microsoft Fabric Data Engineering VS Code extension which uses a custom VFS. We already register a URI translator with Pylance for Python IntelliSense. Adding the same integration for Ruff would give our users linting/formatting in virtual workspaces.

Environment

• Extension version: 2026.40.0
• Ruff version: Any (native server)