BoundaryML/baml · warning · LspError

Notification not supported: {0}

Error message

Notification not supported: {0}

What it means

LspError::NotificationNotSupported is produced when a notification method is received that this LSP server does not implement. thiserror formats it as 'Notification not supported: {method}'. It signals a capability negotiation or routing gap, not a protocol corruption.

Source

Thrown at baml_language/crates/baml_lsp/src/error.rs:13

//! The one LSP error type and its JSON-RPC code table.

use std::path::PathBuf;

/// Every failure a request or notification handler can report.
///
/// Serialized to the wire exclusively through [`LspError::to_response_error`];
/// the legacy `-32001 UnknownErrorCode` is never emitted.
#[derive(Debug, thiserror::Error)]
pub enum LspError {
    #[error("{0}")]
    NotificationExtractError(lsp_server::ExtractError<lsp_server::Notification>),
    #[error("Notification not supported: {0}")]
    NotificationNotSupported(String),
    #[error("{0}")]
    RequestExtractError(lsp_server::ExtractError<lsp_server::Request>),
    #[error("Request not supported: {0}")]
    RequestNotSupported(String),
    #[error("Failed to serialize request result: {0}")]
    RequestSerializeError(serde_json::Error),
    /// The client's sink is gone; nothing more can be delivered.
    #[error("Client closed")]
    ClientClosed,
    /// Bounded transport backpressure (LSP `RequestFailed`, `-32803`).
    #[error("LSP outbound sink is saturated")]
    OutboundSaturated,
    /// A frame larger than the transport limit (LSP `RequestFailed`,
    /// `-32803`).
    #[error("LSP outbound frame exceeds the transport limit")]
    OutboundOversized,
    #[error("Invalid command arguments for command: {command}: {message}")]

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Ignore or log-and-discard the unsupported notification if it is harmless
2. Update the server to handle the notification or stop advertising related capabilities
3. Fix client capability flags so it does not send notifications the server did not register

Example fix

// before: crash/propagate on unknown notification
return Err(LspError::NotificationNotSupported(method));
// after: log and continue
log::debug!("ignoring unsupported notification: {method}");
Ok(())

fn is_unsupported_notification(e: &LspError) -> Option<&str> {
    if let LspError::NotificationNotSupported(m) = e { Some(m) } else { None }
}

match result {
    Err(LspError::NotificationNotSupported(m)) => log::debug!("skipped notification {m}"),
    other => other?,
}

When it happens

Trigger: A client sends a notification whose method is not in the server's handled-method dispatch; the client enables a capability the server never advertised but sends notifications for anyway.

Common situations: Clients sending unsupported/$$ notifications, workspace/didChangeWatchedFiles without registration, or newer LSP notification types added after the server was written.

Related errors

• Request not supported: {0}
• {0}
• Failed to serialize request result: {0}
• no filesystem is attached to this server ({})
• Client closed

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/569e9bb4e6595f03. Report an issue: GitHub.