diff options
Diffstat (limited to 'src')
| -rw-r--r-- | src/doc/rustc-dev-guide/src/borrow_check/region_inference/closure_constraints.md | 6 |
1 files changed, 5 insertions, 1 deletions
diff --git a/src/doc/rustc-dev-guide/src/borrow_check/region_inference/closure_constraints.md b/src/doc/rustc-dev-guide/src/borrow_check/region_inference/closure_constraints.md index b4efd266191..be279b773cf 100644 --- a/src/doc/rustc-dev-guide/src/borrow_check/region_inference/closure_constraints.md +++ b/src/doc/rustc-dev-guide/src/borrow_check/region_inference/closure_constraints.md @@ -15,7 +15,11 @@ While borrow-checking a closure inside of `RegionInferenceContext::solve` we sep ### Region-outlive constraints -If we fail to prove a region-outlives constraint, we try to propagate it in `fn try_propagate_universal_region_error`. +If `RegionInferenceContext::check_universal_regions` fails to prove some outlives constraint `'longer_fr: 'shorter_fr`, we try to propagate it in `fn try_propagate_universal_region_error`. Both these universal regions are either local to the closure or an external region. + +In case `'longer_fr` is a local universal region, we search for the largest external region `'fr_minus` which is outlived by `'longer_fr`, i.e. `'longer_fr: 'fr_minus`. In case there are multiple such regions, we pick the `mutual_immediate_postdominator`: the fixpoint of repeatedly computing the GLB of all GLBs, see [TransitiveRelation::postdom_upper_bound](https://doc.rust-lang.org/nightly/nightly-rustc/rustc_data_structures/transitive_relation/struct.TransitiveRelation.html#method.postdom_upper_bound) for more details. + +If `'fr_minus` exists we require it to outlive all non-local upper bounds of `'shorter_fr`. There will always be at least one non-local upper bound `'static`. ### Type-outlive constraints |