Polonius
Motivation
Polonius is an improved version of the borrow checker that resolves common limitations of the borrow checker and which is needed to support future patterns such as "lending iterators". Its model also prepares us for further improvements in the future.
The status quo
The next six months
- Land polonius on nightly
The "shiny future" we are working towards
Stable support for Polonius.
Design axioms
N/A
Ownership and other resources
Owner: lqd
Other support provided by Amanda Stjerna as part of her PhD.
Support needed from the project
We expect most support to be needed from the types team, for design, reviews, interactions with the trait solver, and so on. We expect Niko Matsakis, leading the polonius working group and design, to provide guidance and design time, and Michael Goulet and Matthew Jasper to help with reviews.
Outputs and milestones
Outputs
Nightly implementation of polonius that passes NLL problem case #3 and accepts lending iterators.
Performance should be reasonable enough that we can run the full test suite, do crater runs, and test it on CI, without significant slowdowns. We do not expect to be production-ready yet by then, and therefore the implementation would still be gated under a nightly -Z feature flag.
As our model is a superset of NLLs, we expect little to no diagnostics regressions, but improvements would probably still be needed for the new errors.
Milestones
| Milestone | Expected date |
|---|---|
| Factoring out higher-ranked concerns from the main path | TBD |
| Replace parts of the borrow checker with location-insensitive Polonius | TBD |
| Location-sensitive prototype on nightly | TBD |
| Verify full test suite/crater pass with location-sensitive Polonius | TBD |
| Location-sensitive pass on nightly, tested on CI | TBD |
Frequently asked questions
None yet.