denoland/deno · error · AnyError

the argument '{previous}' cannot be used with '{name}'

Error message

the argument '{previous}' cannot be used with '{name}'

What it means

The `dcore` runtime binary (Deno's minimal core runner) accepts `--inspect`, `--inspect-brk` and `--inspect-wait`, but only one per invocation. The parser records the first seen in `seen_inspect_flag`; any subsequent `--inspect*` flag bails naming both the previous and the new flag. Each flag also accepts an optional `=host:port` value.

Source

Thrown at libs/dcore/src/main.rs:196

      None => Ok(None),
      Some(v) => v.parse::<SocketAddr>().map(Some).map_err(|e| {
        anyhow::anyhow!("invalid value '{v}' for '{flag}=<HOST_AND_PORT>': {e}")
      }),
    };

    for arg in args {
      let (name, value) = match arg.split_once('=') {
        Some((name, value)) => (name, Some(value)),
        None => (arg.as_str(), None),
      };
      match name {
        "-h" | "--help" => {
          println!("{USAGE}");
          return Ok(None);
        }
        "--inspect" | "--inspect-brk" | "--inspect-wait" => {
          if let Some(previous) = seen_inspect_flag {
            bail!("the argument '{previous}' cannot be used with '{name}'");
          }
          seen_inspect_flag = Some(match name {
            "--inspect" => "--inspect",
            "--inspect-brk" => "--inspect-brk",
            _ => "--inspect-wait",
          });
          let addr = parse_addr(name, value)?;
          match name {
            "--inspect" => out.inspect = Some(addr),
            "--inspect-wait" => out.inspect_wait = Some(addr),
            // `--inspect-brk` is accepted but not wired up to the inspector
            // server, matching the previous clap-based behavior.
            _ => {}
          }
        }
        "--strace-ops" => out.strace_ops = true,
        "--strace-ops-summary" => out.strace_ops_summary = true,
        "--v8-flags" => {

View on GitHub (pinned to 9ad36f7a2c)

Solutions

1. Keep exactly one inspector flag — prefer `--inspect-wait` for debugging (waits for the debugger before running user code) or plain `--inspect`.
2. Edit the launch config/alias so the flags are not stacked.
3. Run `dcore -h` to confirm the supported flag set.

Example fix

# before
dcore --inspect --inspect-brk app.js
# error: the argument '--inspect' cannot be used with '--inspect-brk'

# after: exactly one inspector flag
dcore --inspect-wait app.js

# reject stacked --inspect* flags before invoking dcore
n=0
for a in "$@"; do
  case "$a" in --inspect|--inspect-brk|--inspect-wait|--inspect=*|--inspect-brk=*|--inspect-wait=*) n=$((n+1));; esac
done
[ "$n" -gt 1 ] && { echo "only one --inspect* flag is allowed"; exit 2; }

When it happens

Trigger: Invoking dcore with two inspector flags in one command: `dcore --inspect --inspect-wait app.js`, `dcore --inspect-brk --inspect=127.0.0.1:9230 app.js`, or any other pairing of the three.

Common situations: Editor/IDE debug launch configs that append `--inspect` to a template that already contains `--inspect-brk`; copy-pasted commands combining 'break at start' and 'wait for debugger' variants.

Understand the failure class

Background: "mutually exclusive" flag errors: what "can't supply both nx and xx", "--raw is not compatible with -i" and "cannot be used with" mean, and how to fix them — this error's family across 29 libraries.

Related errors

• equal sign is needed when assigning values to '--v8-flags'
• unexpected argument '{name}' found
• unexpected argument '{arg}' found
• the following required arguments were not provided: <file_
• ERR_INSPECTOR_ALREADY_ACTIVATED

AI-assisted analysis of denoland/deno@9ad36f7a2c (2026-08-20). Data as JSON: /api/errors/7891ba12871d385b. Report an issue: GitHub.