Internal Tracking Issue for type system librarification

This is an internal tracking issue for the migration type system components into rustc_type_ir and rustc_next_trait_solver to be shared with RustAnalyzer and other users. See the dev-guide for more information.

This is mostly just a loose collection of things we should move into the shared library at some point. Please go to the the #t-types/trait-system-initiative zulip to discuss things and for mentoring opportunities. I will try to link to the relevant zulip topic for anything where it feels fairly clear what to do, while other migrations are less obvious or may interfere with work currently being done.

Specific work items

• Move methods on Region extension traits to be inherent instead, where possible
• uplift ty::Const similar to #154989
• move generalization into rustc_type_ir
• move solve/fullfil into rustc_next_trait_solver
• move the LowerUniverseFolder into rustc_type_ir
• move TypingEnv into rustc_type_ir

Long term goals

• partially move InferCtxt into rustc_type_ir
• uplift non-borrowck region handling

Implementation history

This list is very much incomplete, if you find any PRs which have been relevant here please DM @lcnr on zulip about them or add them yourself. Last updated on 2026.07.22

• @compiler-errors #138464 #137263 #129678 #127810 #127439 #127405 #127386 #127333 #126813 #126650 #126614 #126492 #125775 #125724 #125597 #125335 #125284 #125230 #125170 #125150 #125088 #125001 #124982 #121703 #120498 #118888 #118841 #117851 #117586 #117582 #117580 #117578 #117407 #117139 #117008 #116993 #116951 #116912 #116828
• @ChayimFriedman2 #156297 #156295 #155981 #155562 #155034 #149856 #147723 #146182 #146111 #145377
• @Jamesbarford #160986 #154989 #156956 #157695 #154709 #154270 #150271 #149535

Start with the dev-guide page on sharing crates with Rust Analyzer, then use the listed checklist and the #t-types/trait-system-initiative Zulip channel to find a clearly scoped, mentored item. Done means migrating one agreed type-system component into rustc_type_ir or rustc_next_trait_solver and recording the relevant work on this tracking issue.