`python_extension` is not expected to be combined with the i

Error message

`python_extension` is not expected to be combined with the initialization options as it's only set by the ty VS Code extension in the `workspace/configuration` request.

What it means

The `python_extension` server option is special: it is never part of initialization options and is only populated from the `workspace/configuration` request issued by the ty VS Code extension. Its `Combine` implementation (used to merge layered configuration) therefore panics if it is ever asked to combine, because that would mean someone put `python_extension` in the wrong configuration layer.

Source

Thrown at crates/ty_server/src/session/options.rs:526

impl Experimental {
    fn into_settings(self) -> ExperimentalSettings {
        // `use_uv` is resolved separately before project discovery because changing it requires
        // rebuilding every project database.
        let Self { use_uv: _ } = self;
        ExperimentalSettings {}
    }
}

#[derive(Clone, Debug, Serialize, Deserialize, Default, PartialEq, Eq)]
#[serde(rename_all = "camelCase")]
pub struct PythonExtension {
    active_environment: Option<ActiveEnvironment>,
}

impl Combine for PythonExtension {
    fn combine_with(&mut self, _other: Self) {
        panic!(
            "`python_extension` is not expected to be combined with the initialization options as \
            it's only set by the ty VS Code extension in the `workspace/configuration` request."
        );
    }
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
#[serde(rename_all = "camelCase")]
pub(crate) struct ActiveEnvironment {
    executable: PythonExecutable,
    #[deprecated]
    environment: Option<PythonEnvironment>,
    version: Option<EnvironmentVersion>,
}

#[derive(Clone, Debug, Serialize, Deserialize, PartialEq, Eq)]
#[serde(rename_all = "camelCase")]
pub(crate) struct EnvironmentVersion {

View on GitHub (pinned to 26f38c119c)

Solutions

Remove the `python_extension` key from your LSP initializationOptions.
Let the ty VS Code extension supply those settings via the `workspace/configuration` request instead of passing them at initialization.
Put only supported workspace settings (e.g. python path, interpreter) in initializationOptions.

Example fix

// before
initializationOptions = { python_extension: { activeEnvironment: "venv" } };
// after
initializationOptions = {}; // extension settings come via workspace/configuration

Defensive patterns

Strategy: validation

Validate before calling

// Client-side check before sending initializationOptions:
const forbidden = ['python_extension'];
for (const key of forbidden) {
  if (key in initializationOptions) {
    throw new Error(`${key} must come via workspace/configuration, not initializationOptions`);
  }
}

Prevention

Never place python_extension in initializationOptions.
Let the ty VS Code extension own that settings section via workspace/configuration.
Review LSP client configs (launch.json, nvim lspconfig) for stray server-only keys.

When it happens

Trigger: Sending a `python_extension` section inside `initializationOptions` when starting the ty LSP server, so the session tries to combine it with client/extension settings via `Combine::combine_with`.

Common situations: Users or client authors copying the extension's settings into initializationOptions in launch configurations (e.g. VS Code launch.json, Neovim LSP setup); misconfigured LSP client adapters passing all settings at init time.

Related errors

AI-assisted analysis of astral-sh/ruff@26f38c119c (2026-09-05). Data as JSON: /api/errors/938065069e3111d4. Report an issue: GitHub.