only normalize projections if they have inference variables in them

Author: compiler-errors

compiler/rustc_middle/src/ty/flags.rs

@@ -327,7 +327,13 @@ impl FlagComputation {
     }
 
     fn add_projection_ty(&mut self, projection_ty: ty::ProjectionTy<'_>) {
+        let old_outer_exclusive_binder =
+            std::mem::replace(&mut self.outer_exclusive_binder, ty::INNERMOST);
         self.add_substs(projection_ty.substs);
+        if self.outer_exclusive_binder > ty::INNERMOST {
+            self.add_flags(TypeFlags::HAS_LATE_IN_PROJECTION);
+        }
+        self.outer_exclusive_binder = self.outer_exclusive_binder.max(old_outer_exclusive_binder);
     }
 
     fn add_substs(&mut self, substs: &[GenericArg<'_>]) {

compiler/rustc_middle/src/ty/fold.rs

@@ -166,6 +166,14 @@ pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
     fn still_further_specializable(&self) -> bool {
         self.has_type_flags(TypeFlags::STILL_FURTHER_SPECIALIZABLE)
     }
+
+    // Indicates that this value has projection types which capture late-bound variables,
+    // which is a sign that the projection types within need further normalization. This
+    // is because we do not replace projections with inference variables when they capture
+    // late-bound variables.
+    fn has_late_bound_vars_in_projection(&self) -> bool {
+        self.has_type_flags(TypeFlags::HAS_LATE_IN_PROJECTION)
+    }
 }
 
 impl<'tcx> TypeFoldable<'tcx> for hir::Constness {

compiler/rustc_trait_selection/src/traits/fulfill.rs

@@ -357,7 +357,7 @@ impl<'a, 'b, 'tcx> FulfillProcessor<'a, 'b, 'tcx> {
 
         let infcx = self.selcx.infcx();
 
-        if obligation.predicate.has_projections() {
+        if obligation.predicate.has_late_bound_vars_in_projection() {
             let mut obligations = Vec::new();
             let predicate = crate::traits::project::try_normalize_with_depth_to(
                 self.selcx,

compiler/rustc_type_ir/src/lib.rs

@@ -107,6 +107,9 @@ bitflags! {
 
         /// Does this value have `InferConst::Fresh`?
         const HAS_CT_FRESH                = 1 << 19;
+
+        // Does this value have any late-bound vars in any projection type substs?
+        const HAS_LATE_IN_PROJECTION      = 1 << 20;
     }
 }