Fix IndexVec::drain_enumerated

Author: compiler-errors

compiler/rustc_index/src/vec.rs

@@ -207,7 +207,12 @@ impl<I: Idx, T> IndexVec<I, T> {
         &'a mut self,
         range: R,
     ) -> impl Iterator<Item = (I, T)> + 'a {
-        self.raw.drain(range).enumerate().map(|(n, t)| (I::new(n), t))
+        let begin = match range.start_bound() {
+            std::ops::Bound::Included(i) => *i,
+            std::ops::Bound::Excluded(i) => i.checked_add(1).unwrap(),
+            std::ops::Bound::Unbounded => 0,
+        };
+        self.raw.drain(range).enumerate().map(move |(n, t)| (I::new(begin + n), t))
     }
 
     #[inline]

compiler/rustc_trait_selection/src/solve/trait_goals/structural_traits.rs

@@ -30,10 +30,7 @@ pub(super) fn instantiate_constituent_tys_for_auto_trait<'tcx>(
         | ty::Foreign(..)
         | ty::Alias(ty::Projection, ..)
         | ty::Bound(..)
-        | ty::Infer(ty::TyVar(_)) => {
-            // FIXME: Do we need to mark anything as ambiguous here? Yeah?
-            Err(NoSolution)
-        }
+        | ty::Infer(ty::TyVar(_)) => Err(NoSolution),
 
         ty::Infer(ty::FreshTy(_) | ty::FreshIntTy(_) | ty::FreshFloatTy(_)) => bug!(),
 
@@ -101,9 +98,8 @@ pub(super) fn instantiate_constituent_tys_for_sized_trait<'tcx>(
         | ty::Dynamic(..)
         | ty::Foreign(..)
         | ty::Alias(..)
-        | ty::Param(_) => Err(NoSolution),
-
-        ty::Infer(ty::TyVar(_)) => bug!("FIXME: ambiguous"),
+        | ty::Param(_)
+        | ty::Infer(ty::TyVar(_)) => Err(NoSolution),
 
         ty::Placeholder(..)
         | ty::Bound(..)
@@ -151,9 +147,8 @@ pub(super) fn instantiate_constituent_tys_for_copy_clone_trait<'tcx>(
         | ty::Ref(_, _, Mutability::Mut)
         | ty::Adt(_, _)
         | ty::Alias(_, _)
-        | ty::Param(_) => Err(NoSolution),
-
-        ty::Infer(ty::TyVar(_)) => bug!("FIXME: ambiguous"),
+        | ty::Param(_)
+        | ty::Infer(ty::TyVar(_)) => Err(NoSolution),
 
         ty::Placeholder(..)
         | ty::Bound(..)