only erase param env regions where needed

Author: lcnr

compiler/rustc_middle/src/ty/util.rs

@@ -1107,7 +1107,7 @@ impl<'tcx> Ty<'tcx> {
                 // This doesn't depend on regions, so try to minimize distinct
                 // query keys used.
                 // If normalization fails, we just use `query_ty`.
-                let param_env = tcx.erase_regions(param_env);
+                debug_assert!(!param_env.has_infer());
                 let query_ty = tcx
                     .try_normalize_erasing_regions(param_env, query_ty)
                     .unwrap_or_else(|_| tcx.erase_regions(query_ty));

compiler/rustc_trait_selection/src/traits/query/dropck_outlives.rs

@@ -298,7 +298,7 @@ pub fn dtorck_constraint_for_ty_inner<'tcx>(
             // While we conservatively assume that all coroutines require drop
             // to avoid query cycles during MIR building, we can check the actual
             // witness during borrowck to avoid unnecessary liveness constraints.
-            if args.witness().needs_drop(tcx, param_env) {
+            if args.witness().needs_drop(tcx, tcx.erase_regions(param_env)) {
                 constraints.outlives.extend(args.upvar_tys().iter().map(ty::GenericArg::from));
                 constraints.outlives.push(args.resume_ty().into());
             }