zed-industries/zed · error

Cannot have two different hosts in debug configuration

Error message

Cannot have two different hosts in debug configuration

What it means

debugpy attach validation in Zed's Python adapter: when `request` is `"attach"` and both the task-level `tcp_connection` block already carry a `host` AND the adapter `config` object also has a `"host"` key, Zed cannot tell which host to dial and bails instead of guessing (python.rs:377). This guards against silently attaching to the wrong machine.

Source

Thrown at crates/dap_adapters/src/python.rs:377

                )
            })
            .unwrap_or_else(|| {
                (
                    config
                        .config
                        .get("port")
                        .and_then(|port| port.as_u64().map(|p| p as u16)),
                    config.config.get("host").and_then(|host| host.as_str()),
                )
            });

        let is_attach_with_connect = if config
            .config
            .get("request")
            .is_some_and(|val| val.as_str().is_some_and(|request| request == "attach"))
        {
            if tcp_connection.host.is_some() && config_host.is_some() {
                bail!("Cannot have two different hosts in debug configuration")
            } else if tcp_connection.port.is_some() && config_port.is_some() {
                bail!("Cannot have two different ports in debug configuration")
            }

            if let Some(hostname) = config_host {
                tcp_connection.host = Some(hostname.parse().context("invalid IP address")?);
            }
            tcp_connection.port = config_port;
            DebugpyLaunchMode::AttachWithConnect { host: config_host }
        } else {
            DebugpyLaunchMode::Normal
        };

        let (host, port, timeout) = crate::configure_tcp_connection(tcp_connection).await?;

        let python_path = if let Some(toolchain) = python_from_toolchain {
            Some(toolchain)
        } else {

View on GitHub (pinned to f4178619ac)

Solutions

1. Remove `host` from the `config` object and keep it only in `tcp_connection` (or the reverse) so exactly one source defines it.
2. For local debugpy attach, prefer `"tcp_connection": { "host": "127.0.0.1", "port": 5678 }` with `"request": "attach"` and no host inside config.

Example fix

// before (debug.json)
{
  "adapter": "Python",
  "request": "attach",
  "tcp_connection": { "host": "127.0.0.1", "port": 5678 },
  "config": { "host": "localhost", "port": 5678 }
}

// after
{
  "adapter": "Python",
  "request": "attach",
  "tcp_connection": { "host": "127.0.0.1", "port": 5678 },
  "config": { "request": "attach" }
}

// reject attach configs that define host in two places, before starting a session
let has_tcp_host = task.tcp_connection.as_ref().is_some_and(|t| t.host.is_some());
let has_config_host = task.config.get("request") == Some("attach") && task.config.get("host").is_some();
if has_tcp_host && has_config_host {
    return Err(anyhow!("remove `host` from either tcp_connection or config"));
}

fn defines_host_once(tcp: &Option<TcpConnection>, config: &serde_json::Value) -> bool {
    let in_tcp = tcp.as_ref().is_some_and(|t| t.host.is_some());
    let in_config = config.get("host").is_some_and(|v| !v.is_null());
    !(in_tcp && in_config)
}

Catch before session start and print both offending values (tcp_connection.host vs config.host) so the user sees the conflict instead of a generic failure.

When it happens

Trigger: A Zed debug task with `adapter: "Python"`, `tcp_connection: { "host": "127.0.0.1", "port": 5678 }`, and a `config` that also contains `"host": "localhost"` under an attach request. Both sources being non-null on an attach request is the exact trigger.

Common situations: Pasting a VS Code launch.json (which puts host/port inside the config) into a Zed debug configuration that already declares tcp_connection; incrementally migrating attach configs and leaving the old host key behind.

Related errors

• Cannot have two different ports in debug configuration
• debug config not found in mode: {mode}
• No process selected with config that contains {}
• Zed cannot determine how to run this debug scenario. `build`
• Expected exactly one context server configuration

AI-assisted analysis of zed-industries/zed@f4178619ac (2026-08-20). Data as JSON: /api/errors/2a5f8d9e0a21d7f4. Report an issue: GitHub.