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| author | lcnr <rust@lcnr.de> | 2024-12-23 10:17:51 +0100 |
|---|---|---|
| committer | GitHub <noreply@github.com> | 2024-12-23 10:17:51 +0100 |
| commit | edd2a9bc392ec1c30f4d92d0e348e3d953e92837 (patch) | |
| tree | 07fddb4f8925bdf36c7b4586441b662dcba9aed0 | |
| parent | 444d0d765d8b6ad3f2618fcd4c0fa315cb7ccfff (diff) | |
| download | rust-edd2a9bc392ec1c30f4d92d0e348e3d953e92837.tar.gz rust-edd2a9bc392ec1c30f4d92d0e348e3d953e92837.zip | |
region-outlives propagation (#2169)
* region-outlives propagation * woops * gamer
| -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 |