Automatically detect workspace packages in uv add

[charliermarsh]

Summary

If the package isn't marked as workspace = true, locking will fail given:

let workspace_package_declared =
    // We require that when you use a package that's part of the workspace, ...
    !workspace.packages().contains_key(&requirement.name)
    // ... it must be declared as a workspace dependency (`workspace = true`), ...
    || matches!(
        source,
        Some(Source::Workspace {
            // By using toml, we technically support `workspace = false`.
            workspace: true,
            ..
        })
    )
    // ... except for recursive self-inclusion (extras that activate other extras), e.g.
    // `framework[machine_learning]` depends on `framework[cuda]`.
    || &requirement.name == project_name;
if !workspace_package_declared {
    return Err(LoweringError::UndeclaredWorkspacePackage);
}

Closes #4552.

[charliermarsh]

I am wondering why we require that workspace packages are marked as workspace if we enforce it here. Should we just do this automatically?

[ibraheemdev]

Should we error if you try to add a requirement with the same name from a different source? e.g. if you have a workspace member foo and run uv add git+https://github.com/bar/foo.

[charliermarsh]

That seems reasonable, yeah.

[charliermarsh]

Ahh, I think we already do that?

[charliermarsh]

I added a test and improved the error messages.

[konstin]

I am wondering why we require that workspace packages are marked as workspace if we enforce it here. Should we just do this automatically?

It ensures that you can see in a single pyproject.toml what source each requirements has (registry, url or workspace) and prevents accidentally using registry packages. I've copied this from cargo.