rust-lang/cargo · error · anyhow::Error

no timing data found in log

Error message

no timing data found in log

What it means

Inside prepare_context, `cargo report timings` collects timing records per build unit. When the log parses but contains zero units (error_if_no_units is true for the report path), it bails at timings.rs:351. Unlike the live `--timings` flag (which happily renders an empty report), the report command treats a unit-less log as corrupted/truncated, per rust-lang/cargo#17212.

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()

View on GitHub (pinned to 0e07a15537)

Solutions

1. Re-run a real build with `-Z build-analysis` that actually compiles units, then report against that session.
2. Use `cargo report sessions` to pick a session known to have done work.
3. If the log is corrupted, delete it from the log directory and regenerate.

Example fix

# before - report against an idle session
$ cargo report timings --id <idle-id>
error: no timing data found in log

# after - build something then report
$ cargo +nightly build -Z build-analysis
$ cargo +nightly report timings

# Heuristic: reject obviously empty/truncated logs (no timing records):
log="$1"
if ! grep -q '"kind"' "$log" 2>/dev/null; then
  echo "log has no build-unit records; rebuild with -Z build-analysis" >&2
  exit 1
fi
cargo report timings --id "$(basename "$log")"

When it happens

Trigger: Running `cargo report timings` against a log from a build that compiled nothing (e.g. `cargo test` with test=false and doctest=false), or a log that was truncated/corrupted mid-write.

Common situations: Pointing --id at an idle/no-op build session; cargo crashed mid-build leaving a partial log; log file manually edited.

Related errors

• no sessions found{context}
• no sessions found{context}
• no sessions found{context}
• artifact-dir was not locked

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/88f71d8ccccb82af.json. Report an issue: GitHub.