Fix --no-emit-workspace with --all-packages on single-member workspaces

[zanieb]

Closes #18070

Fixes an issue where --no-emit-workspace --all-packages would incorrectly emit -e . (the workspace root) when the workspace contained only a single member at the root.

When a workspace contains a single member at the root, that member is not included in the lockfile's members set (it's empty). The --all-packages flag uses InstallTarget::Workspace, which returned None for project_name(). This meant include_package() had no way to identify the root project as a workspace member — neither the project_name check nor the members.contains() check could match it, so it passed through the --no-emit-workspace filter.

[konstin]

When a workspace contains a single member at the root, that member is not included in the lockfile's members set (it's empty).

Why is that, shouldn't we instead ensure that the members list is accurate?

[zanieb]

It's intentional behavior

uv/crates/uv/src/commands/project/lock_target.rs

Lines 151 to 156 in 50eb601

	// If this is a non-virtual project with a single member, we can omit it from the lockfile.
	// If any members are added or removed, it will inherently mismatch. If the member is
	// renamed, it will also mismatch.
	if members.len() == 1 && !workspace.is_non_project() {
	members.clear();
	}

and has been longstanding #6091

I don't think we should change it, since it'll churn lock files. If we see more problems, we can consider it.

[zanieb]

I think it's intended to avoid a noisy members manifest when you're not actually using a workspace.

[konstin]

That's a confusing edge case to do this on the Workspace level instead of the lockfile boundary.

[konstin]

Here we don't build the project, We should use uv_build for all new test packages, it's faster and uses no network for the cases where we do.