Implement Open API Namespace Support

[nikomatsakis]

Metadata
Point of contact	@epage
Team(s)	cargo, compiler
Goal document	2025h1/open-namespaces

Summary

Navigate the cross-team design work to get RFC 3243 implemented.

Tasks and status

• Discussion and moral support (cargo, compiler )
• Compiler implementation ()
• Work through lingering cargo issues (@epage)

[nikomatsakis]

This issue is intended for status updates only.

For general questions or comments, please contact the owner(s) directly.

[epage]

Help wanted: this project goal needs a compiler developer to move forward.

[eholk]

@b-naber and I have been working on the rustc side of the implementation for this feature.

I merged rust-lang/rust#139647, which adds the unstables -Z namespaced-crates option to the compiler and enables parsing of externs like --extern foo::bar=libbar.rlib. @b-naber has led the resolver changes and has a draft PR up at rust-lang/rust#140271.

The implementation work has raised some new concerns about the overall direction, so work is ongoing to resolve those while continuing to make progress in the meantime.

[b-naber]

We have reached an agreement on the compiler implementation, and will implement it in the next 2-3 weeks hopefully.

[b-naber]

Chiming in for @epage here since further progress is still blocked on the compiler implementation. Unfortunately things have been moving more slowly than I had initially hoped. We have been doing some refactoring (rust-lang/rust#142547 and rust-lang/rust#144131) that allow us to introduce a new Scope for namespaced crates inside name resolution. There's a draft PR (rust-lang/rust#140271) that should be straightforward to adapt to the refactoring.