astral-sh/ruff · error

Could not diff paths

Error message

Could not diff paths

What it means

GitLab-format diagnostic rendering relativizes each path against the project root via pathdiff::diff_paths(&path, project_root).expect("Could not diff paths"). diff_paths returns None only when the paths have incompatible Windows prefixes (e.g. different drive letters), so the renderer panics in exactly that case.

Source

Thrown at crates/ruff_db/src/diagnostic/render/gitlab.rs:180

}

/// Generate a unique fingerprint to identify a violation.
fn fingerprint(diagnostic: &Diagnostic, project_path: &str, salt: u64) -> u64 {
    let mut hasher = DefaultHasher::new();

    salt.hash(&mut hasher);
    diagnostic.name().hash(&mut hasher);
    project_path.hash(&mut hasher);

    hasher.finish()
}

/// Convert an absolute path to be relative to the specified project root.
fn relativize_path_to<P: AsRef<Path>, R: AsRef<Path>>(path: P, project_root: R) -> String {
    format!(
        "{}",
        pathdiff::diff_paths(&path, project_root)
            .expect("Could not diff paths")
            .display()
    )
}

#[cfg(test)]
mod tests {
    use crate::diagnostic::{
        DiagnosticFormat,
        render::tests::{create_diagnostics, create_syntax_error_diagnostics},
    };

    const FINGERPRINT_FILTERS: [(&str, &str); 1] = [(
        r#""fingerprint": "[a-z0-9]+","#,
        r#""fingerprint": "<redacted>","#,
    )];

    #[test]
    fn output() {

View on GitHub (pinned to d1087a4b9e)

Solutions

1. Invoke ruff so files and project root share a drive; run from the same drive as the checked files
2. Pass file arguments relative to the project root instead of cross-drive absolute paths
3. If it still fires, report it - the renderer should fall back to the absolute path instead of panicking

Example fix

# before (panics: different drives)
ruff check --output-format gitlab D:\src\main.py  # run from C:\repo

# after (same drive, relative path)
cd D:\src && ruff check --output-format gitlab main.py

// Windows tooling: ensure inputs share the project root's drive before rendering
const { root } = require('path').parse(projectRoot);
if (path.parse(file).root !== root) { useAbsolutePathInstead(); }

When it happens

Trigger: Producing GitLab-format output where a diagnostic's file is on a different Windows drive than the project root - e.g. file D:\src\x.py with root C:\repo - so no relative path between them exists.

Common situations: Windows environments resolving dependencies or arguments across drives; UNC roots mixed with drive-letter paths; absolute cross-drive paths passed in include/files arguments.

Related errors

• Failed to convert path to URL: {}
• extra use-def data should have been retained
• Expected a Title
• unexpected annotation type: {annotation:?}
• Annotation range `{bigger:?}` is beyond the end of buffer `{

AI-assisted analysis of astral-sh/ruff@d1087a4b9e (2026-08-20). Data as JSON: /api/errors/4c8db99a47e3fe56. Report an issue: GitHub.