astral-sh/uv · error

Unnamed requirements are not allowed as constraints (found:

Error message

Unnamed requirements are not allowed as constraints (found: `{requirement}`)

What it means

Constraints in uv must be named requirements (e.g., `flask<2`), because a constraint only pins versions of an already-requested package. When a constraint source is parsed and an UnresolvedRequirement::Unnamed (a direct URL or file path requirement) is found, uv rejects it immediately during merging.

Source

Thrown at crates/uv-requirements/src/specification.rs:610

            spec.no_binary.extend(source.no_binary);
            spec.no_build.extend(source.no_build);
            spec.require_hashes |= source.require_hashes;
        }

        // Read all constraints, treating both requirements _and_ constraints as constraints.
        // Overrides are ignored.
        for source in constraints {
            let source = Self::from_source_with_cache(source, client_builder, &mut cache).await?;
            for entry in source.requirements {
                match entry.requirement {
                    UnresolvedRequirement::Named(requirement) => {
                        spec.constraints.push(NameRequirementSpecification {
                            requirement,
                            hashes: entry.hashes,
                        });
                    }
                    UnresolvedRequirement::Unnamed(requirement) => {
                        return Err(anyhow::anyhow!(
                            "Unnamed requirements are not allowed as constraints (found: `{requirement}`)"
                        ));
                    }
                }
            }
            spec.constraints.extend(source.constraints);

            if let Some(index_url) = source.index_url {
                if let Some(existing) = spec.index_url
                    && CanonicalUrl::new(index_url.url().clone())
                        != CanonicalUrl::new(existing.url().clone())
                {
                    return Err(anyhow::anyhow!(
                        "Multiple index URLs specified: `{existing}` vs. `{index_url}`",
                    ));
                }
                spec.index_url = Some(index_url);
            }

View on GitHub (pinned to f1a42680ff)

Solutions

1. Remove the unnamed (URL/path) entry named in the error from the constraints file — constraints cannot pin direct-URL packages.
2. If the direct-URL package must be pinned, move it to the main requirements source (it is already fully specified there) and constrain only named packages in the constraints file.
3. If you want the exact version of a local package, declare it in the requirements with its path and use constraints only for its transitive named dependencies.

Example fix

# before (constraints.txt)
numpy==1.26.4
./wheels/team-util-1.0-py3-none-any.whl
# after (constraints.txt)
numpy==1.26.4
# direct URL moved to requirements.txt instead

# Rust: reject unnamed requirements before passing a file as constraints
use uv_requirements::UnresolvedRequirement;

fn validate_constraints(reqs: &[RequirementEntry]) -> anyhow::Result<()> {
    for entry in reqs {
        if let UnresolvedRequirement::Unnamed(ref r) = entry.requirement {
            anyhow::bail!("unnamed requirement not allowed as constraint: {r}");
        }
    }
    Ok(())
}

fn is_named_constraint(entry: &RequirementEntry) -> bool {
    matches!(entry.requirement, UnresolvedRequirement::Named(_))
}

When it happens

Trigger: Running `uv pip compile -c constraints.txt` (or `uv lock` with a constraints file) where constraints.txt contains a line like `./libs/my-pkg.tar.gz`, `https://example.com/pkg.whl`, or a VCS URL; passing a URL requirement via `--constraint` directly.

Common situations: Reusing a full requirements.txt as a constraints file without pruning its URL entries; CI that generates constraints from a lock export that includes direct-URL dependencies; teams copy-pasting a private-package URL into the constraints file.

Related errors

• Unnamed requirements are not allowed as exclusions (found: `
• pip-compile's `--emit-options` is unsupported (try `--emit-b
• Extra names must start and end with a letter or digit and ma
• The file `{}` appears to be a `pylock.toml` file, but constr
• The file `{}` appears to be a TOML file, but constraints mus

AI-assisted analysis of astral-sh/uv@f1a42680ff (2026-08-16). Data as JSON: /api/errors/6d6afad73df231dd. Report an issue: GitHub.