What causes "Internal error: path should not end with '/'" in windmill-labs/windmill?

Fix the code that builds RequiredDependency.path so it never appends a trailing '/' (e.g. `trim_end_matches('/')` when composing from URLs or directory joins)

windmill-labs/windmill · error

Internal error: path should not end with '/'

Error message

Internal error: path should not end with '/'

What it means

Before checking which dependencies are missing, `filter_to_missing` dedupes RequiredDependency entries and asserts an internal invariant: each dependency's install path must not end with '/'. A trailing slash would corrupt the `<path>.valid.windmill` marker lookup, so it fails fast as an internal construction bug rather than a user-facing problem.

Source

Thrown at backend/windmill-worker/src/universal_pkg_installer.rs:531

            let layers = graph.layers();
            (layers, Some((deps_map, nodes_display)))
        }
    };

    let mut name_ml = 0;
    let mut missing_keys: HashSet<String> = HashSet::new();
    let mut total_missing = 0;

    for layer in layers.iter_mut() {
        *layer = std::mem::take(layer)
            .into_iter()
            .unique_by(|rd| rd.path.clone())
            .collect();

        let mut missing = vec![];
        for rd in std::mem::take(layer) {
            if rd.path.ends_with("/") {
                anyhow::bail!("Internal error: path should not end with '/'")
            }
            if rd.display_name.len() > name_ml {
                name_ml = rd.display_name.len();
            }
            if tokio::fs::metadata(rd.path.clone() + ".valid.windmill")
                .await
                .is_err()
            {
                if let Some(key) = rd.path.rsplit('/').next() {
                    missing_keys.insert(key.to_string());
                }
                missing.push(rd);
            }
        }
        total_missing += missing.len();
        *layer = missing;
    }

View on GitHub (pinned to e474e8803c)

Solutions

Fix the code that builds RequiredDependency.path so it never appends a trailing '/' (e.g. `trim_end_matches('/')` when composing from URLs or directory joins)
Audit custom/patched executor or extension code that constructs dependency paths
If caused by a configured repository URL ending in '/', remove the trailing slash from the configuration

Example fix

// before
let path = format!("{repo_url}/{group}/{artifact}/{version}/");
// after
let path = format!("{}/{}/{artifact}/{version}", repo_url.trim_end_matches('/'));

Defensive patterns

Strategy: validation

Validate before calling

// guard before constructing/installing in custom code
assert!(!dep.path.ends_with('/'), "dependency path must not end with '/': {}", dep.path);

Type guard

fn valid_dep_path(rd: &RequiredDependency) -> bool {
    !rd.path.ends_with('/')
}

Prevention

Always trim trailing slashes when composing paths from URLs or user config
Add unit tests asserting constructed dependency paths have no trailing slash
Never join path components with separators on both sides of a concatenation

When it happens

Trigger: Any dependency install path reaching par_install_language_dependencies_all_at_once or _seq whose RequiredDependency.path was built with a trailing slash — a path-building bug in a language executor's dependency construction (e.g. `format!("{dir}/")`) or a trailing-slash URL leaking into the composed path.

Common situations: After customizing or extending a language executor's path-building code; a registry/mirror URL with a trailing slash used in path composition; hand-edited or plugin-generated dependency entries.

Related errors

AI-assisted analysis of windmill-labs/windmill@e474e8803c (2026-09-03). Data as JSON: /api/errors/77dd064f22f43c33. Report an issue: GitHub.