Auto merge of #55649 - scalexm:chalk-bound-ty, r=nikomatsakis

Use bound types in `librustc_traits`

r? @nikomatsakis
see the tests which now move the higher-ranked binders to the left in implied bound rules!

src/Cargo.lock

@@ -2419,6 +2419,7 @@ dependencies = [
  "log 0.4.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "rustc 0.0.0",
  "rustc_data_structures 0.0.0",
+ "rustc_target 0.0.0",
  "smallvec 0.6.5 (registry+https://github.com/rust-lang/crates.io-index)",
  "syntax 0.0.0",
  "syntax_pos 0.0.0",

src/librustc/infer/canonical/substitute.rs

@@ -80,6 +80,6 @@ where
             }
         };
 
-        tcx.replace_escaping_bound_vars(value, fld_r, fld_t)
+        tcx.replace_escaping_bound_vars(value, fld_r, fld_t).0
     }
 }

src/librustc/infer/higher_ranked/mod.rs

@@ -59,11 +59,11 @@ impl<'a, 'gcx, 'tcx> CombineFields<'a, 'gcx, 'tcx> {
             // with a fresh region variable. These region variables --
             // but no other pre-existing region variables -- can name
             // the placeholders.
-            let (a_prime, _) =
-                self.infcx.replace_late_bound_regions_with_fresh_var(
-                    span,
-                    HigherRankedType,
-                    a);
+            let (a_prime, _) = self.infcx.replace_bound_vars_with_fresh_vars(
+                span,
+                HigherRankedType,
+                a
+            );
 
             debug!("a_prime={:?}", a_prime);
             debug!("b_prime={:?}", b_prime);

src/librustc/infer/mod.rs

@@ -1328,18 +1328,18 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         self.report_and_explain_type_error(trace, &err)
     }
 
-    pub fn replace_late_bound_regions_with_fresh_var<T>(
+    pub fn replace_bound_vars_with_fresh_vars<T>(
         &self,
         span: Span,
         lbrct: LateBoundRegionConversionTime,
-        value: &ty::Binder<T>,
+        value: &ty::Binder<T>
     ) -> (T, BTreeMap<ty::BoundRegion, ty::Region<'tcx>>)
     where
-        T: TypeFoldable<'tcx>,
+        T: TypeFoldable<'tcx>
     {
-        self.tcx.replace_late_bound_regions(value, |br| {
-            self.next_region_var(LateBoundRegion(span, br, lbrct))
-        })
+        let fld_r = |br| self.next_region_var(LateBoundRegion(span, br, lbrct));
+        let fld_t = |_| self.next_ty_var(TypeVariableOrigin::MiscVariable(span));
+        self.tcx.replace_bound_vars(value, fld_r, fld_t)
     }
 
     /// Given a higher-ranked projection predicate like:

src/librustc/traits/error_reporting.rs

@@ -212,10 +212,11 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
             // cause I have no idea for a good error message.
             if let ty::Predicate::Projection(ref data) = predicate {
                 let mut selcx = SelectionContext::new(self);
-                let (data, _) = self.replace_late_bound_regions_with_fresh_var(
+                let (data, _) = self.replace_bound_vars_with_fresh_vars(
                     obligation.cause.span,
                     infer::LateBoundRegionConversionTime::HigherRankedType,
-                    data);
+                    data
+                );
                 let mut obligations = vec![];
                 let normalized_ty = super::normalize_projection_type(
                     &mut selcx,