Deeply normalize when processing registered region obligations

Author: compiler-errors

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -20,6 +20,7 @@ use rustc_middle::ty::{
 };
 use rustc_middle::ty::{GenericParamDefKind, TyCtxt};
 use rustc_span::{Span, DUMMY_SP};
+use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::outlives_bounds::InferCtxtExt as _;
 use rustc_trait_selection::traits::{
@@ -380,7 +381,7 @@ fn compare_method_predicate_entailment<'tcx>(
         param_env,
         infcx.implied_bounds_tys(param_env, impl_m_def_id, wf_tys),
     );
-    let errors = infcx.resolve_regions(&outlives_env);
+    let errors = infcx.resolve_regions_normalizing_outlives_obligations(&outlives_env);
     if !errors.is_empty() {
         return Err(infcx
             .tainted_by_errors()

compiler/rustc_hir_analysis/src/check/compare_impl_item/refine.rs

@@ -8,6 +8,7 @@ use rustc_middle::ty::{
     self, Ty, TyCtxt, TypeFoldable, TypeFolder, TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
 use rustc_span::{Span, DUMMY_SP};
+use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::{
     elaborate, normalize_param_env_or_error, outlives_bounds::InferCtxtExt, ObligationCtxt,
 };
@@ -163,7 +164,7 @@ pub(super) fn check_refining_return_position_impl_trait_in_trait<'tcx>(
         param_env,
         infcx.implied_bounds_tys(param_env, impl_m.def_id.expect_local(), implied_wf_types),
     );
-    let errors = infcx.resolve_regions(&outlives_env);
+    let errors = infcx.resolve_regions_normalizing_outlives_obligations(&outlives_env);
     if !errors.is_empty() {
         tcx.sess.span_delayed_bug(
             DUMMY_SP,

compiler/rustc_hir_analysis/src/check/dropck.rs

@@ -8,6 +8,7 @@ use rustc_infer::infer::{RegionResolutionError, TyCtxtInferExt};
 use rustc_middle::ty::util::CheckRegions;
 use rustc_middle::ty::GenericArgsRef;
 use rustc_middle::ty::{self, TyCtxt};
+use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::{self, ObligationCtxt};
 
 use crate::errors;
@@ -169,7 +170,9 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
         return Err(guar.unwrap());
     }
 
-    let errors = ocx.infcx.resolve_regions(&OutlivesEnvironment::new(param_env));
+    let errors = ocx
+        .infcx
+        .resolve_regions_normalizing_outlives_obligations(&OutlivesEnvironment::new(param_env));
     if !errors.is_empty() {
         let mut guar = None;
         for error in errors {
@@ -184,6 +187,7 @@ fn ensure_drop_predicates_are_implied_by_item_defn<'tcx>(
                 RegionResolutionError::UpperBoundUniverseConflict(a, _, _, _, b) => {
                     format!("{b}: {a}", a = ty::Region::new_var(tcx, a))
                 }
+                RegionResolutionError::CannotNormalize(..) => todo!(),
             };
             guar = Some(
                 struct_span_err!(

compiler/rustc_hir_analysis/src/check/wfcheck.rs

@@ -23,6 +23,7 @@ use rustc_session::parse::feature_err;
 use rustc_span::symbol::{sym, Ident, Symbol};
 use rustc_span::{Span, DUMMY_SP};
 use rustc_target::spec::abi::Abi;
+use rustc_trait_selection::regions::InferCtxtRegionExt;
 use rustc_trait_selection::traits::error_reporting::TypeErrCtxtExt;
 use rustc_trait_selection::traits::misc::{
     type_allowed_to_implement_const_param_ty, ConstParamTyImplementationError,
@@ -725,7 +726,7 @@ fn resolve_regions_with_wf_tys<'tcx>(
 
     add_constraints(&infcx, region_bound_pairs);
 
-    let errors = infcx.resolve_regions(&outlives_environment);
+    let errors = infcx.resolve_regions_normalizing_outlives_obligations(&outlives_environment);
     debug!(?errors, "errors");
 
     // If we were able to prove that the type outlives the region without

compiler/rustc_infer/src/infer/error_reporting/mod.rs

@@ -511,6 +511,13 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
 
                         self.report_placeholder_failure(sup_origin, sub_r, sup_r).emit();
                     }
+
+                    RegionResolutionError::CannotNormalize(ty, origin) => {
+                        self.tcx
+                            .sess
+                            .struct_span_err(origin.span(), format!("cannot normalize `{ty}`"))
+                            .emit();
+                    }
                 }
             }
         }
@@ -552,7 +559,8 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             RegionResolutionError::GenericBoundFailure(..) => true,
             RegionResolutionError::ConcreteFailure(..)
             | RegionResolutionError::SubSupConflict(..)
-            | RegionResolutionError::UpperBoundUniverseConflict(..) => false,
+            | RegionResolutionError::UpperBoundUniverseConflict(..)
+            | RegionResolutionError::CannotNormalize(..) => false,
         };
 
         let mut errors = if errors.iter().all(|e| is_bound_failure(e)) {
@@ -567,6 +575,7 @@ impl<'tcx> TypeErrCtxt<'_, 'tcx> {
             RegionResolutionError::GenericBoundFailure(ref sro, _, _) => sro.span(),
             RegionResolutionError::SubSupConflict(_, ref rvo, _, _, _, _, _) => rvo.span(),
             RegionResolutionError::UpperBoundUniverseConflict(_, ref rvo, _, _, _) => rvo.span(),
+            RegionResolutionError::CannotNormalize(_, ref sro) => sro.span(),
         });
         errors
     }

compiler/rustc_infer/src/infer/lexical_region_resolve/mod.rs

@@ -98,6 +98,8 @@ pub enum RegionResolutionError<'tcx> {
         SubregionOrigin<'tcx>, // cause of the constraint
         Region<'tcx>,          // the placeholder `'b`
     ),
+
+    CannotNormalize(Ty<'tcx>, SubregionOrigin<'tcx>),
 }
 
 impl<'tcx> RegionResolutionError<'tcx> {
@@ -106,7 +108,8 @@ impl<'tcx> RegionResolutionError<'tcx> {
             RegionResolutionError::ConcreteFailure(origin, _, _)
             | RegionResolutionError::GenericBoundFailure(origin, _, _)
             | RegionResolutionError::SubSupConflict(_, _, origin, _, _, _, _)
-            | RegionResolutionError::UpperBoundUniverseConflict(_, _, _, origin, _) => origin,
+            | RegionResolutionError::UpperBoundUniverseConflict(_, _, _, origin, _)
+            | RegionResolutionError::CannotNormalize(_, origin) => origin,
         }
     }
 }

compiler/rustc_infer/src/infer/outlives/mod.rs

@@ -5,7 +5,7 @@ use super::{InferCtxt, RegionResolutionError};
 use crate::infer::free_regions::RegionRelations;
 use crate::infer::lexical_region_resolve;
 use rustc_middle::traits::query::OutlivesBound;
-use rustc_middle::ty;
+use rustc_middle::ty::{self, Ty};
 
 pub mod components;
 pub mod env;
@@ -41,12 +41,22 @@ impl<'tcx> InferCtxt<'tcx> {
     /// result. After this, no more unification operations should be
     /// done -- or the compiler will panic -- but it is legal to use
     /// `resolve_vars_if_possible` as well as `fully_resolve`.
+    ///
+    /// If you are in a crate that has access to `rustc_trai_selection`,
+    /// then it's probably better to use `resolve_regions_normalizing_outlives_obligations`,
+    /// which knows how to normalize registered region obligations.
     #[must_use]
     pub fn resolve_regions(
         &self,
         outlives_env: &OutlivesEnvironment<'tcx>,
+        deeply_normalize_ty: impl Fn(Ty<'tcx>) -> Result<Ty<'tcx>, Ty<'tcx>>,
     ) -> Vec<RegionResolutionError<'tcx>> {
-        self.process_registered_region_obligations(outlives_env);
+        match self.process_registered_region_obligations(outlives_env, deeply_normalize_ty) {
+            Ok(()) => {}
+            Err((ty, origin)) => {
+                return vec![RegionResolutionError::CannotNormalize(ty, origin)];
+            }
+        };
 
         let (var_infos, data) = {
             let mut inner = self.inner.borrow_mut();

compiler/rustc_infer/src/infer/outlives/obligations.rs

@@ -123,15 +123,19 @@ impl<'tcx> InferCtxt<'tcx> {
     /// flow of the inferencer. The key point is that it is
     /// invoked after all type-inference variables have been bound --
     /// right before lexical region resolution.
-    #[instrument(level = "debug", skip(self, outlives_env))]
-    pub fn process_registered_region_obligations(&self, outlives_env: &OutlivesEnvironment<'tcx>) {
+    #[instrument(level = "debug", skip(self, outlives_env, deeply_normalize_ty))]
+    pub fn process_registered_region_obligations<E>(
+        &self,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+        mut deeply_normalize_ty: impl FnMut(Ty<'tcx>) -> Result<Ty<'tcx>, E>,
+    ) -> Result<(), (E, SubregionOrigin<'tcx>)> {
         assert!(!self.in_snapshot(), "cannot process registered region obligations in a snapshot");
 
         let my_region_obligations = self.take_registered_region_obligations();
 
         for RegionObligation { sup_type, sub_region, origin } in my_region_obligations {
+            let sup_type = deeply_normalize_ty(sup_type).map_err(|e| (e, origin.clone()))?;
             debug!(?sup_type, ?sub_region, ?origin);
-            let sup_type = self.resolve_vars_if_possible(sup_type);
 
             let outlives = &mut TypeOutlives::new(
                 self,
@@ -143,6 +147,8 @@ impl<'tcx> InferCtxt<'tcx> {
             let category = origin.to_constraint_category();
             outlives.type_must_outlive(origin, sup_type, sub_region, category);
         }
+
+        Ok(())
     }
 }
 

compiler/rustc_trait_selection/src/lib.rs

@@ -39,6 +39,7 @@ extern crate smallvec;
 
 pub mod errors;
 pub mod infer;
+pub mod regions;
 pub mod solve;
 pub mod traits;
 

compiler/rustc_trait_selection/src/regions.rs

@@ -0,0 +1,31 @@
+use rustc_infer::infer::outlives::env::OutlivesEnvironment;
+use rustc_infer::infer::{InferCtxt, RegionResolutionError};
+use rustc_middle::traits::ObligationCause;
+
+pub trait InferCtxtRegionExt<'tcx> {
+    fn resolve_regions_normalizing_outlives_obligations(
+        &self,
+        outlives_env: &OutlivesEnvironment<'tcx>,
+    ) -> Vec<RegionResolutionError<'tcx>>;
+}
+
+impl<'tcx> InferCtxtRegionExt<'tcx> for InferCtxt<'tcx> {
+    fn resolve_regions_normalizing_outlives_obligations(
+        &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)
+            }
+        })
+    }
+}