On activation, Pyrefly silently writes disableLanguageServices = true to the user's
global VS Code settings for three named third-party extensions, without prompting
the user or notifying them in any way. These settings are never restored when
Pyrefly is deactivated or uninstalled, leaving those extensions permanently broken
until the user manually intervenes.

This has been verified by live reproduction on a real machine (see below).

Affected extensions

• detachhead.basedpyright
• codeium.windsurfpyright
• anysphere.cursorpyright

Source

lsp/src/extension-interop.ts:

export async function disableWindsurfPyrightIfInstalled() {
  const windsurfPyrightExtension = vscode.extensions.getExtension('codeium.windsurfpyright');
  if (windsurfPyrightExtension) {
    const config = vscode.workspace.getConfiguration('windsurfPyright');
    await config.update('disableLanguageServices', true, vscode.ConfigurationTarget.Global);
  }
}

export async function disableBasedPyrightIfInstalled() {
  const basedPyrightExtension = vscode.extensions.getExtension('detachhead.basedpyright');
  if (basedPyrightExtension) {
    const config = vscode.workspace.getConfiguration('basedpyright');
    await config.update('disableLanguageServices', true, vscode.ConfigurationTarget.Global);
  }
}

export async function disableCursorPyrightIfInstalled() {
  const cursorPyrightExtension = vscode.extensions.getExtension('anysphere.cursorpyright');
  if (cursorPyrightExtension) {
    const config = vscode.workspace.getConfiguration('cursorpyright');
    await config.update('disableLanguageServices', true, vscode.ConfigurationTarget.Global);
  }
}

These are called unconditionally in lsp/src/extension.ts on activation.

Relevant commits: 69985d1d, c0ab0d76, 72458900, 2fb5205a (December 8-9, 2025)

Why this is a problem

1. Silent global modification
ConfigurationTarget.Global writes to the user's global settings.json, affecting
every workspace on the machine. The user receives no notification, no prompt, no
indication this has occurred.

2. No cleanup on deactivation or uninstall
There is no corresponding deactivate() logic that restores these settings.
A user who installs Pyrefly, then uninstalls it, is left with basedpyright,
windsurfpyright, or cursorpyright silently broken — with no obvious cause.
They would need to know to manually find and delete these keys from their
global settings.json to restore functionality.

3. Targets extensions by publisher ID
This is not a generic "disable conflicting language servers" mechanism.
It hardcodes the extension IDs of specific named competitors and disables
them individually. The user has no opt-out.

Live reproduction

Reproduced independently on both VSCodium and stock VS Code 1.118.1.

Test 1 — VSCodium

Tested with detachhead.basedpyright installed.

~/.config/VSCodium/User/settings.json before installing Pyrefly:

{
    "python.languageServer": "Default"
}

After installing Pyrefly and opening a single Python file:

{
    "python.languageServer": "Default",
    "basedpyright.disableLanguageServices": true
}

After uninstalling Pyrefly:

{
    "python.languageServer": "Default",
    "basedpyright.disableLanguageServices": true
}

The key persists. basedpyright remains broken with no indication of why.

Test 2 — VS Code 1.118.1 (clean isolated profile)

To rule out any VSCodium-specific behaviour, reproduced on stock VS Code using a
completely clean profile (--user-data-dir /tmp/vscode-test-profile) with no prior
configuration.

settings.json before installing Pyrefly: file did not exist (empty profile)

After installing detachhead.basedpyright, then meta.pyrefly, and opening a single Python file:

{
    "python.languageServer": "None",
    "basedpyright.disableLanguageServices": true
}

Same result. The write happens on first Python file open regardless of editor or prior configuration.

Expected behavior

If Pyrefly needs exclusive access to Python language services to function correctly,
it should:

1. Ask the user before modifying settings owned by other extensions
2. Restore those settings in deactivate() when Pyrefly is disabled or uninstalled
3. Or at minimum, log what it changed so users can reverse it

Additional concern: forced Microsoft extension dependencies

package.json declares "extensionDependencies": ["ms-python.python"].

VSCodium and VS Code treat this as a hard bidirectional lock — installing Pyrefly
automatically installs:

• ms-python.python
• ms-python.debugpy
• ms-python.vscode-python-envs

Uninstalling any of those three also uninstalls Pyrefly.

The only thing ms-python.python is used for is querying the active Python interpreter
path for the optional "Run File / Run Test" CodeLens buttons. The core LSP features
(type checking, completions, hover, go-to-definition) run entirely through the
pyrefly binary and have no dependency on ms-python.python at all.

For users on VSCodium or other FOSS VS Code distributions who specifically avoid
Microsoft extensions, this is a significant and undisclosed side effect of installing
what is presented as an independent open source tool.

Steps to reproduce

1. Install detachhead.basedpyright and confirm it is working (completions, hover, etc.)
2. Install meta.pyrefly
3. Open a Python file (triggers Pyrefly activation)
4. Check your global settings.json — basedpyright.disableLanguageServices is now true
5. Uninstall meta.pyrefly
6. Observe that basedpyright.disableLanguageServices remains true — basedpyright
   is still broken with no indication of why