astral-sh/uv · error · anyhow::Error

Failed to read

Error message

Failed to read `{}`: {}

What it means

Thrown in from_source_with_cache (crates/uv-requirements/src/specification.rs:298) when fs_err::tokio::read_to_string on a RequirementsSource::PyprojectToml fails with an io error other than NotFound (that kind gets error 46). The underlying error is appended, so the message distinguishes unreadable from missing files.

Solutions

1. Check the appended io error — for permissions, fix them (`chmod +r pyproject.toml` / `chown`)
2. If running in a container or CI, ensure the user running uv can read the file (inspect with `ls -l`)
3. Retry once if the file was transiently locked or being rewritten during the run

Example fix

# before
$ uv pip install -r pyproject.toml
Failed to read `pyproject.toml`: Permission denied (os error 13)
# after
$ chmod +r pyproject.toml
$ uv pip install -r pyproject.toml

match fs_err::tokio::read_to_string(&path).await {
    Ok(_) => { /* proceed with RequirementsSource::PyprojectToml(path) */ }
    Err(err) if err.kind() == std::io::ErrorKind::NotFound => { /* missing: handle separately */ }
    Err(err) => { /* surface permissions/io issue before calling uv */ }
}

match RequirementsSpecification::from_source(src, &client_builder).await {
    Err(err) if err.to_string().starts_with("Failed to read `") => {
        // inspect the trailing io error; fix perms or retry once after transient locks
    }
    spec => spec?,
}

When it happens

Trigger: Reading a pyproject.toml with no read permission (chmod 000, different owner), a directory passed where the file was expected, a file replaced/deleted between the existence check and the read (TOCTOU), or an OS-level io failure (disk, I/O) during `uv pip install -r pyproject.toml`.

Common situations: CI containers running as a non-root user against root-owned checkouts; Docker COPY losing permissions; editors or sync tools holding exclusive locks on Windows; flaky mounts.

Related errors

• The file ` ` appears to be a ` ` file, but overrides must…
• Cannot specify additional requirements alongside a…
• Cannot specify constraints with a `pylock.toml` file
• Cannot specify overrides with a `pylock.toml` file
• Cannot specify paths for groups with a `pylock.toml` file…

AI-assisted analysis of astral-sh/uv@f1a42680ff (2026-08-16). Data as JSON: /api/errors/fcef763238218193. Report an issue: GitHub.

Appendix: source

Thrown at crates/uv-requirements/src/specification.rs:298

                    RequirementsTxt::parse_with_cache(path, &*CWD, client_builder, cache).await?;

                if requirements_txt == RequirementsTxt::default() {
                    warn_user!(
                        "Requirements file `{}` does not contain any dependencies",
                        path.user_display()
                    );
                }

                Self::from_requirements_txt(requirements_txt)
            }
            RequirementsSource::PyprojectToml(path) => {
                let content = match fs_err::tokio::read_to_string(&path).await {
                    Ok(content) => content,
                    Err(err) if err.kind() == std::io::ErrorKind::NotFound => {
                        return Err(anyhow::anyhow!("File not found: `{}`", path.user_display()));
                    }
                    Err(err) => {
                        return Err(anyhow::anyhow!(
                            "Failed to read `{}`: {}",
                            path.user_display(),
                            err
                        ));
                    }
                };
                let pyproject_toml = PyProjectToml::from_toml(&content, path.user_display())
                    .with_context(|| format!("Failed to parse: `{}`", path.user_display()))?;

                Self {
                    source_trees: vec![SourceTree::PyProjectToml(path.clone(), pyproject_toml)],
                    ..Self::default()
                }
            }
            RequirementsSource::Pep723Script(path) => {
                let content = if let Some(content) = cache.get(path.as_path()) {
                    content.clone()
                } else {

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