Use DroplessArena for variance inference

compiler/rustc_typeck/src/variance/mod.rs

@@ -4,7 +4,7 @@
 //! [rustc dev guide]: https://rustc-dev-guide.rust-lang.org/variance.html
 
 use hir::Node;
-use rustc_arena::TypedArena;
+use rustc_arena::DroplessArena;
 use rustc_hir as hir;
 use rustc_hir::def_id::{CrateNum, DefId, LOCAL_CRATE};
 use rustc_middle::ty::query::Providers;
@@ -32,8 +32,8 @@ pub fn provide(providers: &mut Providers) {
 
 fn crate_variances(tcx: TyCtxt<'_>, crate_num: CrateNum) -> CrateVariancesMap<'_> {
     assert_eq!(crate_num, LOCAL_CRATE);
-    let mut arena = TypedArena::default();
-    let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &mut arena);
+    let arena = DroplessArena::default();
+    let terms_cx = terms::determine_parameters_to_be_inferred(tcx, &arena);
     let constraints_cx = constraints::add_constraints_from_crate(terms_cx);
     solve::solve_constraints(constraints_cx)
 }

compiler/rustc_typeck/src/variance/terms.rs

@@ -9,7 +9,7 @@
 // `InferredIndex` is a newtype'd int representing the index of such
 // a variable.
 
-use rustc_arena::TypedArena;
+use rustc_arena::DroplessArena;
 use rustc_hir as hir;
 use rustc_hir::itemlikevisit::ItemLikeVisitor;
 use rustc_hir::HirIdMap;
@@ -47,7 +47,7 @@ impl<'a> fmt::Debug for VarianceTerm<'a> {
 
 pub struct TermsContext<'a, 'tcx> {
     pub tcx: TyCtxt<'tcx>,
-    pub arena: &'a TypedArena<VarianceTerm<'a>>,
+    pub arena: &'a DroplessArena,
 
     // For marker types, UnsafeCell, and other lang items where
     // variance is hardcoded, records the item-id and the hardcoded
@@ -64,7 +64,7 @@ pub struct TermsContext<'a, 'tcx> {
 
 pub fn determine_parameters_to_be_inferred<'a, 'tcx>(
     tcx: TyCtxt<'tcx>,
-    arena: &'a mut TypedArena<VarianceTerm<'a>>,
+    arena: &'a DroplessArena,
 ) -> TermsContext<'a, 'tcx> {
     let mut terms_cx = TermsContext {
         tcx,