Rollup merge of #147184 - jdonszelmann:bevy-outlives-bound, r=lcnr

Fix the bevy implied bounds hack for the next solver

The diff is trivial, of course, and basically what you already suggested. Mostly dug around a bunch to learn. I hope this is roughly what you had in mind.

Fixes https://github.com/rust-lang/trait-system-refactor-initiative/issues/236.

r? `@lcnr`

2 files changed, 11 insertions, 1 deletions

diff --git a/compiler/rustc_infer/src/infer/outlives/obligations.rs b/compiler/rustc_infer/src/infer/outlives/obligations.rs
index b989d419057..a640dcb1b4e 100644
--- a/compiler/rustc_infer/src/infer/outlives/obligations.rs
+++ b/compiler/rustc_infer/src/infer/outlives/obligations.rs
@@ -170,6 +170,10 @@ impl<'tcx> InferCtxt<'tcx> {
         std::mem::take(&mut self.inner.borrow_mut().region_obligations)
     }
 
+    pub fn clone_registered_region_obligations(&self) -> Vec<TypeOutlivesConstraint<'tcx>> {
+        self.inner.borrow().region_obligations.clone()
+    }
+
     pub fn register_region_assumption(&self, assumption: ty::ArgOutlivesPredicate<'tcx>) {
         let mut inner = self.inner.borrow_mut();
         inner.undo_log.push(UndoLog::PushRegionAssumption);
diff --git a/compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs b/compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs
index 7540cbe3fd1..e55ffb4d5fd 100644
--- a/compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs
+++ b/compiler/rustc_trait_selection/src/traits/query/type_op/implied_outlives_bounds.rs
@@ -55,6 +55,12 @@ pub fn compute_implied_outlives_bounds_inner<'tcx>(
     span: Span,
     disable_implied_bounds_hack: bool,
 ) -> Result<Vec<OutlivesBound<'tcx>>, NoSolution> {
+    // Inside mir borrowck, each computation starts with an empty list.
+    assert!(
+        ocx.infcx.inner.borrow().region_obligations().is_empty(),
+        "compute_implied_outlives_bounds assumes region obligations are empty before starting"
+    );
+
     let normalize_ty = |ty| -> Result<_, NoSolution> {
         // We must normalize the type so we can compute the right outlives components.
         // for example, if we have some constrained param type like `T: Trait<Out = U>`,
@@ -143,7 +149,7 @@ pub fn compute_implied_outlives_bounds_inner<'tcx>(
         && ty.visit_with(&mut ContainsBevyParamSet { tcx: ocx.infcx.tcx }).is_break()
     {
         for TypeOutlivesConstraint { sup_type, sub_region, .. } in
-            ocx.infcx.take_registered_region_obligations()
+            ocx.infcx.clone_registered_region_obligations()
         {
             let mut components = smallvec![];
             push_outlives_components(ocx.infcx.tcx, sup_type, &mut components);