rust-lang/cargo · error

failed to find rmeta

Error message

failed to find rmeta

What it means

While checking staleness, the fingerprint code selects the `.rmeta` output from a dependency's mtimes via `.find(...).expect("failed to find rmeta")` when `dep.only_requires_rmeta` is true. The dependency's outputs are expected to contain an `.rmeta` file; the panic means none of the recorded output paths has the `rmeta` extension.

Source

Thrown at src/compiler/fingerprint/mod.rs:1310

                | FsStatus::StaleDependency { .. }
                | FsStatus::StaleDepFingerprint { .. } => {
                    self.fs_status = FsStatus::StaleDepFingerprint {
                        unit: dep.fingerprint.index,
                    };
                    return Ok(());
                }
            };

            // If our dependency edge only requires the rmeta file to be present
            // then we only need to look at that one output file, otherwise we
            // need to consider all output files to see if we're out of date.
            let (dep_path, dep_mtime) = if dep.only_requires_rmeta {
                dep_mtimes
                    .iter()
                    .find(|(path, _mtime)| {
                        path.extension().and_then(|s| s.to_str()) == Some("rmeta")
                    })
                    .expect("failed to find rmeta")
            } else {
                match dep_mtimes.iter().max_by_key(|kv| kv.1) {
                    Some(dep_mtime) => dep_mtime,
                    // If our dependencies is up to date and has no filesystem
                    // interactions, then we can move on to the next dependency.
                    None => continue,
                }
            };
            debug!(
                "max dep mtime for {:?} is {:?} {}",
                pkg_root, dep_path, dep_mtime
            );

            // If the dependency is newer than our own output then it was
            // recompiled previously. We transitively become stale ourselves in
            // that case, so bail out.
            //
            // Note that this comparison should probably be `>=`, not `>`, but

View on GitHub (pinned to 0e07a15537)

Solutions

1. `cargo clean` and rebuild — missing `.rmeta` is almost always a stale/corrupt `target/`.
2. Ensure no external process deletes files under `target/` (antivirus, backup tools, IDE cleanup).
3. Free disk space if `target/` ran out of inodes/space mid-build.

Example fix

// before
let (dep_path, dep_mtime) = if dep.only_requires_rmeta {
    dep_mtimes
        .iter()
        .find(|(path, _mtime)| path.extension().and_then(|s| s.to_str()) == Some("rmeta"))
        .expect("failed to find rmeta")
};
// after
let (dep_path, dep_mtime) = if dep.only_requires_rmeta {
    dep_mtimes
        .iter()
        .find(|(path, _mtime)| path.extension().and_then(|s| s.to_str()) == Some("rmeta"))
        .ok_or_else(|| anyhow::anyhow!("dependency marked only_requires_rmeta has no .rmeta output"))?
};

// Confirm the target dir still contains .rmeta files before incremental rebuilds
fn has_rmeta(target_deps: &std::path::Path) -> bool {
    walkdir::WalkDir::new(target_deps).into_iter().filter_map(Result::ok)
        .any(|e| e.path().extension().and_then(|s| s.to_str()) == Some("rmeta"))
}

When it happens

Trigger: A dependency edge marked `only_requires_rmeta` whose compiled outputs were stripped of the `.rmeta` (e.g. it was built with a mode that emits only an rlib, or the file was deleted between Cargo recording it and the fingerprint check); pipelined compilation where the rmeta was never produced (rustc failed) but the unit was marked fresh.

Common situations: `cargo clean`/file deletion racing with a build; switching rustc versions without cleaning (rmeta emission rules changed); disk-full or antivirus quarantine removing `.rmeta` files from `target/`.

Related errors

• failed to find rmeta dep for pipelined dep
• output must exist after running
• artifact-dir was not locked
• required(true)
• a file should always have a parent

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/e5b5801936036f2b.json. Report an issue: GitHub.