rust-lang/cargo · error

packages downloaded

Error message

packages downloaded

What it means

Invariant in the feature resolver: `has_any_proc_macro` does `self.package_set.get_one(package_id).expect("packages downloaded")`. By the time feature resolution runs, the package set should have all packages downloaded; `get_one` returning an error means a package is missing from the set.

Source

Thrown at src/resolver/features.rs:961

                    "{}/{:?} features mismatch\nresolve: {:?}\nnew: {:?}\n",
                    pkg_id,
                    dep_kind,
                    r_features,
                    features
                );
                found = true;
            }
        }
        if found {
            panic!("feature mismatch");
        }
    }

    /// Whether the given package has any proc macro target, including proc-macro examples.
    fn has_any_proc_macro(&self, package_id: PackageId) -> bool {
        self.package_set
            .get_one(package_id)
            .expect("packages downloaded")
            .proc_macro()
    }

    /// Whether the given package is a proc macro lib target.
    ///
    /// This is useful for checking if a dependency is a proc macro,
    /// as it is not possible to depend on a non-lib target as a proc-macro.
    fn has_proc_macro_lib(&self, package_id: PackageId) -> bool {
        self.package_set
            .get_one(package_id)
            .expect("packages downloaded")
            .library()
            .map(|lib| lib.proc_macro())
            .unwrap_or_default()
    }
}

View on GitHub (pinned to 0e07a15537)

Solutions

1. `cargo clean` and clear `~/.cargo/registry/cache` + `~/.cargo/git/checkouts`, then retry.
2. Check disk space and permissions on the cargo home directory.
3. Run with `CARGO_NET_RETRY=10` and `-v` to surface network failures hidden before the panic.
4. Verify `[patch]`/git deps resolve to a real crate: `cargo fetch -p <name>`.

// Ensure all packages are fetched before feature resolution.
for id in package_set.package_ids() {
    package_set.get_one(id)?; // surface download errors explicitly
}

When it happens

Trigger: Fires if the feature resolver queries a `package_id` that the `package_set` cannot provide — typically because downloads were incomplete, a source returned no data, or the package id is stale (mismatched with what was actually fetched).

Common situations: Interrupted/corrupted download cache; a `[patch]` or `[replace]` pointing at an empty source; a git dependency that fetched but produced no matching package; running cargo with concurrent cache mutations; disk-full / permission errors during download that were silently swallowed.

Related errors

• in the non-empty branch
• manifest validated
• We've already checked that there is exactly one.
• source ID should have valid URLs
• parent not currently active!?

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/897fe8d86fe31975.json. Report an issue: GitHub.