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

unexpectedly found multiple copies of crate

Error message

unexpectedly found multiple copies of crate `{dependency}` at `{source}`

What it means

Thrown by select_package when a path or git dependency query returns MORE than one Candidate summary. Path and git sources are expected to resolve to a single package; multiple candidates indicate the source directory holds several crates with colliding identity or the query matched more than expected. Cargo refuses to guess.

Solutions

1. Narrow the source to the specific member crate directory: `cargo add <name> --path ./member-dir`.
2. For git, specify the package explicitly: `cargo add <name> --git <url> <package>`.
3. Audit the source directory for duplicate Cargo.toml files and remove or restructure the collision.
4. Clear cargo's registry/path cache if you suspect stale duplicate summaries.

Example fix

// before
cargo add mycrate --path ./workspace-root
// after
cargo add mycrate --path ./workspace-root/crates/mycrate

// Detect multiple packages at a path/git source before adding.
use std::path::{Path, PathBuf};
fn member_count(dir: &Path) -> usize {
    glob::glob(&format!("{dir}/**/Cargo.toml"))
        .map(|it| it.filter_map(Result::ok).count())
        .unwrap_or(0)
}

When it happens

Trigger: Pointing `cargo add --path ./workspace-root` at a directory whose Cargo.toml is a virtual manifest with multiple members; a git source whose repo root contains several crates all matching the dependency query; a path source with multiple Cargo.toml files resolved by the query.

Common situations: Cloning a workspace repo and adding by root path instead of the member path; vendored directory containing both a library and a same-named binary crate; stale registry cache returning duplicate summaries for one source.

Related errors

• the crate ` ` could not be found at
• multiple packages found at
• all versions of crate
• can't checkout from ' ': you are in the offline mode ( )
• cannot add ` ` as a dependency to itself

AI-assisted analysis of rust-lang/cargo@98a09e7e7d (2026-08-11). Data as JSON: /api/errors/8c3bfe39de49b7db. Report an issue: GitHub.

Appendix: source

Thrown at src/ops/cargo_add/mod.rs:1051

                    anyhow::bail!("the crate `{dependency}` could not be found at `{source}`")
                }
                1 => {
                    let mut dep = Dependency::from(&possibilities[0]);
                    if let Some(reg_name) = dependency.registry.as_deref() {
                        dep = dep.set_registry(reg_name);
                    }
                    if let Some(Source::Path(PathSource { base, .. })) = dependency.source() {
                        if let Some(Source::Path(dep_src)) = &mut dep.source {
                            dep_src.base = base.clone();
                        }
                    }
                    Ok(dep)
                }
                _ => {
                    let source = dependency
                        .source()
                        .expect("source should be resolved before here");
                    anyhow::bail!(
                        "unexpectedly found multiple copies of crate `{dependency}` at `{source}`"
                    )
                }
            }
        }
    }
}

fn infer_package_for_git_source(
    mut packages: Vec<Package>,
    src: &dyn std::fmt::Display,
) -> CargoResult<Package> {
    let package = match packages.len() {
        0 => unreachable!(
            "this function should only be called with packages from `GitSource::read_packages` \
            and that call should error for us when there are no packages"
        ),
        1 => packages.pop().expect("match ensured element is present"),

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