cross-rs/cross · error

workspace_root can't end in `..`

Error message

workspace_root can't end in `..`

What it means

`docker_package_name` (src/docker/custom.rs:233) derives the default Docker image name from `metadata.workspace_root.file_name()`. `Path::file_name()` returns None when the path ends in `..`, a root, or is empty, so the code calls `expect("workspace_root can't end in `..`")` to fail fast with an explanatory message instead of silently producing a bad image name.

Solutions

1. Run cross from inside the project directory or pass a canonicalized manifest path (`realpath Cargo.toml`)
2. Ensure workspace_root resolves to a real directory name, not a `..` component
3. If invoking programmatically, canonicalize the path with `std::fs::canonicalize` before passing it

Example fix

// before
cross build --target x86_64-unknown-linux-musl  # run from /repo/sub/..
// after
cd /repo && cross build --target x86_64-unknown-linux-musl

let root = std::fs::canonicalize(&workspace_root)?;
assert!(root.file_name().is_some(), "workspace_root must end in a real directory name, not `..`");

fn has_file_name(p: &std::path::Path) -> bool { p.file_name().is_some() }

When it happens

Trigger: Calling cargo metadata / cross with a workspace_root PathBuf whose final component is `..` (e.g. `--manifest-path` or cwd resolving to `foo/..`), or an empty/root path from a corrupted metadata result.

Common situations: Running cross from or pointing at a path like `/path/to/project/..` (via shell `cd ..` composed paths, symlinks resolved oddly, or CARGO_MANIFEST_DIR set to a `..`-terminated path); building Docker images for the project then fails.

Related errors

• source is pointing to a directory instead of its contents
• artifact path does not start with , skipping
• Refusing to push without tag or branch. Specify a…
• unexpected progress type: expected plain, auto, or tty and…
• cannot make definite Image from unqualified PossibleImage

AI-assisted analysis of cross-rs/cross@8c1a8aa4b6 (2026-09-13). Data as JSON: /api/errors/4a872ac1c1aa854d. Report an issue: GitHub.

Appendix: source

Thrown at src/docker/custom.rs:233

        match self {
            Dockerfile::File { runs_with, .. } => runs_with,
            Dockerfile::Custom { runs_with, .. } => runs_with,
        }
    }
}

fn docker_package_name(metadata: &CargoMetadata) -> String {
    // a valid image name consists of the following:
    // - lowercase ASCII letters
    // - digits
    // - a period
    // - 1-2 underscores
    // - 1 or more hyphens (dashes)
    docker_tag_name(
        &metadata
            .workspace_root
            .file_name()
            .expect("workspace_root can't end in `..`")
            .to_string_lossy(),
    )
}

fn docker_tag_name(file_name: &str) -> String {
    // a valid image name consists of the following:
    // - lowercase ASCII letters
    // - digits
    // - a period
    // - 1-2 underscores
    // - 1 or more hyphens (dashes)
    let mut result = String::new();
    let mut consecutive_underscores = 0;
    for c in file_name.chars() {
        match c {
            'a'..='z' | '0'..='9' | '.' | '-' => {
                consecutive_underscores = 0;
                result.push(c);

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