rust-lang/cargo · error

no timing data found in log

Error message

no timing data found in log

What it means

Thrown by `cargo report timings` when a timing log file contains no build units at all. Unlike `--timings` (which renders a report even for unit-less builds like an idle `cargo test`), `cargo report timings` treats an empty unit set as a corrupted or truncated log and errors out.

Solutions

1. Re-run the build with `--timings` to regenerate a fresh, complete timing log.
2. Verify the correct timing report directory is being read (check `target/cargo-timings/cargo-timing.html`).
3. Delete stale timing logs in `target/cargo-timings/` and rebuild.

Example fix

# Regenerate timing data
cargo build --timings
cargo report timings

use std::path::Path;
fn timing_log_has_units(timing_dir: &Path) -> Result<(), String> {
    let entries: Vec<_> = std::fs::read_dir(timing_dir).map_err(|e| e.to_string())?
        .filter_map(|e| e.ok()).collect();
    if entries.is_empty() {
        return Err("timing log directory is empty; re-run build with --timings".into());
    }
    Ok(())
}

When it happens

Trigger: Running `cargo report timings` pointing at a timing log (`timing/*`) directory or file that either is empty, was truncated, or came from a build that logged no timing entries.

Common situations: The timing log was partially deleted; the log is from a very old Cargo version with incompatible format; the build was interrupted before any units were recorded; the log directory is empty.

AI-assisted analysis of rust-lang/cargo@eb98b54bc9 (2026-08-11). Data as JSON: /api/errors/88f71d8ccccb82af. Report an issue: GitHub.

Appendix: source

Thrown at src/ops/cargo_report/timings.rs:351

                    e.get_mut().data.duration = elapsed;
                    e.get_mut().data.unblocked_units = unblocked;
                }
                Entry::Vacant(_) => {
                    tracing::warn!("unit {index} ended, but it has no start recorded");
                }
            },
            _ => {} // skip non-timing logs
        }
    }

    // A build can legitimately have no units at all, such as an idle
    // `cargo test` with `test = false` and `doctest = false`,
    // so `--timings` always renders its report.
    // `cargo report timings` instead treats a unit-less
    // log as corrupted or truncated and errors out.
    // See https://github.com/rust-lang/cargo/issues/17212.
    if error_if_no_units && units.is_empty() {
        anyhow::bail!("no timing data found in log");
    }

    ctx.root_units = {
        let mut root_map: IndexMap<_, Vec<_>> = IndexMap::default();
        for index in requested_units {
            let unit = &units[&index];
            // Pretty much like `workspace::Target::description_named`
            let target_desc = if unit.target.kind == "lib" {
                "lib".to_owned()
            } else if unit.target.kind == "build-script" {
                "build script".to_owned()
            } else {
                format!(r#" {} "{}""#, unit.target.name, unit.target.kind)
            };
            root_map.entry(index).or_default().push(target_desc);
        }
        root_map
            .into_iter()

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