NLL: complete transition from migrate to full NLL · Issue #57895 · rust-lang/rust (original) (raw)

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This is a tracking issue for the work items remaining for the NLL team before we can consider NLL stabilized across all editions (see also #43234).

Here is an outline of the steps we have identified.

Stage 1: Move all editions to NLL (NLL: turn on borrowck=migrate by default on 2015 edition #57804)
- Move Rust 2015 to borrowck=migrate
- Potential blockers:
  * NLL-sound bugs that affect migration mode (vs ones that only arise with #![feature(nll)] today)
  * Major diagnostic regressions that affect migration mode
Stage 2: Transition fully to NLL (NLL: turn off migration mode #58781)
- one currently opts into this via #![feature(nll)] or -Z borrowck=mir -Z two-phase-borrows)
- this causes NLL warnings (downgraded from errors) become errors again
  * possible intermediate steps
  * move to deny-by-default lints for the warnings
  * move 2018 to hard error on its own, leaving 2015 with downgrade-to-warnings
- It also gets rid of AST-region inference, causing some code to be accepted that is rejected by migrate mode.
- Potential blockers:
  * NLL-sound bugs that affect NLL mode without migration
  * Major diagnostic regressions
  * Two-phase borrows (2PB) question or other "unsettled questions" must have some conservative answer in place
  * Crater run showing no major crates fail in practice
Stage 3: remove old AST-borrowck (done in Rest In Peace, AST borrowck (2012-2019) #64790)