rust-lang/cargo · error

expect run ID in format…

Error message

expect run ID in format `20060724T012128000Z-<16-char-hex>`, got `{s}`

What it means

RunId::from_str expects the form `<timestamp>-<16-hex>`, e.g. `20060724T012128000Z-0123456789abcdef`. The first failure point is rsplit_once('-') returning None — the input contains no '-' separator at all, so it cannot be split into timestamp and hash.

Solutions

1. Regenerate the run id by letting Cargo produce it (it always emits the canonical form).
2. Ensure the value contains exactly one '-' separating a jiff-parseable timestamp from a 16-char hex suffix.

Example fix

# before
# CARGO_LOG_RUN_ID=20060724T012128000Z

# after
# CARGO_LOG_RUN_ID=20060724T012128000Z-0123456789abcdef

fn run_id_has_separator(s: &str) -> Result<(), String> {
    if s.rsplit_once('-').is_none() {
        return Err(format!("run id `{s}` missing '-' separator; expected <timestamp>-<16-hex>"));
    }
    Ok(())
}

fn run_id_shape_ok(s: &str) -> bool {
    s.rsplit_once('-').is_some()
}

When it happens

Trigger: Parsing a CARGO_LOG_RUN_ID (or equivalent) value that has no '-' separator, e.g. a bare timestamp, a bare hash, or a totally different string.

Common situations: Env var truncated by a shell quoting bug; a hand-typed run id; a tool writing only part of the id.

Related errors

• invalid url ` `: cannot-be-a-base-URLs are not supported
• sparse registry url must end in a slash `/
• Cannot specify both 'bin' and 'bin
• $CARGO not set
• config.json not found

AI-assisted analysis of rust-lang/cargo@eb98b54bc9 (2026-08-11). Data as JSON: /api/errors/f2b25c2535b02236. Report an issue: GitHub.

Appendix: source

Thrown at src/util/logger.rs:201

    }
}

impl std::fmt::Display for RunId {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        let hash = &self.hash;
        let timestamp = self.timestamp.strftime(Self::FORMAT);
        write!(f, "{timestamp}-{hash}")
    }
}

impl std::str::FromStr for RunId {
    type Err = anyhow::Error;

    fn from_str(s: &str) -> Result<Self, Self::Err> {
        let msg =
            || format!("expect run ID in format `20060724T012128000Z-<16-char-hex>`, got `{s}`");
        let Some((timestamp, hash)) = s.rsplit_once('-') else {
            anyhow::bail!(msg());
        };

        if hash.len() != 16 || !hash.chars().all(|c| c.is_ascii_hexdigit()) {
            anyhow::bail!(msg());
        }
        let timestamp = jiff::civil::DateTime::strptime(Self::FORMAT, timestamp)
            .and_then(|dt| dt.to_zoned(jiff::tz::TimeZone::UTC))
            .map(|zoned| zoned.timestamp())
            .with_context(msg)?;

        Ok(RunId {
            timestamp,
            hash: hash.into(),
        })
    }
}

#[cfg(test)]

View on GitHub (pinned to eb98b54bc9)