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

couldn't find username

Error message

couldn't find username

What it means

In `github_fast_path`, after `url.path_segments()` succeeds, `pieces.next()` returned `None` for the username segment — i.e. the GitHub URL had a path like `github.com/` (empty). Like 162, this is an internal fast-path error: the doc comment says the function should never cause an actual failure and the caller logs the `Err` at `debug!` and falls back to a regular fetch. It is not normally surfaced.

Source

Thrown at src/sources/git/utils.rs:1653

                    debug!("github fast path is already a full commit hash {rev}");
                    return Ok(FastPathRev::NeedsFetch(oid));
                }
                rev
            } else {
                debug!("can't use github fast path with `rev = \"{}\"`", rev);
                return Ok(FastPathRev::Indeterminate);
            }
        }
    };

    // This expects GitHub urls in the form `github.com/user/repo` and nothing
    // else
    let mut pieces = url
        .path_segments()
        .ok_or_else(|| anyhow!("no path segments on url"))?;
    let username = pieces
        .next()
        .ok_or_else(|| anyhow!("couldn't find username"))?;
    let repository = pieces
        .next()
        .ok_or_else(|| anyhow!("couldn't find repository name"))?;
    if pieces.next().is_some() {
        anyhow::bail!("too many segments on URL");
    }

    // Trim off the `.git` from the repository, if present, since that's
    // optional for GitHub and won't work when we try to use the API as well.
    let repository = repository.strip_suffix(".git").unwrap_or(repository);

    let url = format!(
        "https://api.github.com/repos/{}/{}/commits/{}",
        username, repository, github_branch_name,
    );
    debug!("attempting GitHub fast path for {}", url);
    let mut request =
        Request::get(url).header(http::header::ACCEPT, "application/vnd.github.3.sha");

View on GitHub (pinned to 0e07a15537)

Solutions

1. Fix the dependency URL to include user and repo: `https://github.com/<user>/<repo>`.
2. No urgent action otherwise — Cargo falls back to a normal fetch automatically; investigate only if the fallback itself fails.

Example fix

# before
[dependencies]
foo = { git = "https://github.com" }

# after
foo = { git = "https://github.com/org/foo" }

// Same swallowed-fast-path pattern as 162.
match github_fast_path(repo, url, reference, gctx) {
    Ok(r) => r,
    Err(e) => { debug!("failed to check github {:?}", e); /* normal fetch */ }
}

When it happens

Trigger: A git source URL whose host is `github.com` but whose path is empty or only slashes (e.g. `https://github.com/`). Triggers only during the GitHub fast-path probe in `fetch()`.

Common situations: Typo'd git URL in `Cargo.toml` (`git = "https://github.com"` with no user/repo); a bad `insteadOf` rewrite stripping the path. Because the error is swallowed you typically only notice it as a subsequent real failure when the fallback fetch runs.

Related errors

• no path segments on url
• couldn't find repository name
• too many segments on URL
• invalid package name: `{url}` Use `cargo install --git {
• `{feature}` is unsupported when inferring the crate name, us

AI-assisted analysis of rust-lang/cargo@0e07a15537 (2026-08-06). Data as JSON: /data/errors/530c86dec2e75926.json. Report an issue: GitHub.