merge self type and substs in trait_method

Author: oli-obk

compiler/rustc_mir_build/src/build/matches/test.rs

@@ -250,7 +250,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
                     let ref_str_ty = tcx.mk_imm_ref(re_erased, tcx.types.str_);
                     let ref_str = self.temp(ref_str_ty, test.span);
                     let deref = tcx.require_lang_item(LangItem::Deref, None);
-                    let method = trait_method(tcx, deref, sym::deref, ty, []);
+                    let method = trait_method(tcx, deref, sym::deref, [ty]);
                     let eq_block = self.cfg.start_new_block();
                     self.cfg.push_assign(block, source_info, ref_string, Rvalue::Ref(re_erased, BorrowKind::Shared, place));
                     self.cfg.terminate(
@@ -445,7 +445,7 @@ impl<'a, 'tcx> Builder<'a, 'tcx> {
         };
 
         let eq_def_id = self.tcx.require_lang_item(LangItem::PartialEq, Some(source_info.span));
-        let method = trait_method(self.tcx, eq_def_id, sym::eq, deref_ty, [deref_ty.into()]);
+        let method = trait_method(self.tcx, eq_def_id, sym::eq, [deref_ty, deref_ty]);
 
         let bool_ty = self.tcx.types.bool;
         let eq_result = self.temp(bool_ty, source_info.span);
@@ -837,10 +837,9 @@ fn trait_method<'tcx>(
     tcx: TyCtxt<'tcx>,
     trait_def_id: DefId,
     method_name: Symbol,
-    self_ty: Ty<'tcx>,
-    params: impl IntoIterator<Item = GenericArg<'tcx>, IntoIter: ExactSizeIterator>,
+    substs: impl IntoIterator<Item = impl Into<GenericArg<'tcx>>>,
 ) -> ConstantKind<'tcx> {
-    let substs = tcx.mk_substs_trait(self_ty, params);
+    let substs = tcx.mk_substs(substs.into_iter().map(Into::into));
 
     // The unhygienic comparison here is acceptable because this is only
     // used on known traits.