Deeply normalize when processing registered region obligations

compiler/rustc_trait_selection/src/regions.rs

@@ -0,0 +1,37 @@
+use rustc_infer::infer::outlives::env::OutlivesEnvironment;
+use rustc_infer::infer::{InferCtxt, RegionResolutionError};
+use rustc_middle::traits::ObligationCause;
+
+pub trait InferCtxtRegionExt<'tcx> {
+    /// Resolve regions, using the deep normalizer to normalize any type-outlives
+    /// obligations in the process. This is in `rustc_trait_selection` because
+    /// we need to normalize.
+    ///
+    /// Prefer this method over `resolve_regions_with_normalize`, unless you are
+    /// doing something specific for normalization.
+    fn resolve_regions(
+        &self,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+    ) -> Vec<RegionResolutionError<'tcx>>;
+}
+
+impl<'tcx> InferCtxtRegionExt<'tcx> for InferCtxt<'tcx> {
+    fn resolve_regions(
+        &self,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+    ) -> Vec<RegionResolutionError<'tcx>> {
+        self.resolve_regions(outlives_env, |ty| {
+            let ty = self.resolve_vars_if_possible(ty);
+
+            if self.next_trait_solver() {
+                crate::solve::deeply_normalize(
+                    self.at(&ObligationCause::dummy(), outlives_env.param_env),
+                    ty,
+                )
+                .map_err(|_| ty)
+            } else {
+                Ok(ty)
+            }
+        })
+    }
+}