Unconditionally record lifetime mapping

compiler/rustc_ast_lowering/src/lib.rs

@@ -1663,11 +1663,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             );
             debug!("lower_async_fn_ret_ty: generic_params={:#?}", generic_params);
 
-            let lifetime_mapping = if in_trait {
-                Some(&*self.arena.alloc_slice(&synthesized_lifetime_args))
-            } else {
-                None
-            };
+            let lifetime_mapping = self.arena.alloc_slice(&synthesized_lifetime_args);
 
             let opaque_ty_item = hir::OpaqueTy {
                 generics: this.arena.alloc(hir::Generics {

compiler/rustc_hir/src/hir.rs

@@ -2675,7 +2675,7 @@ pub struct OpaqueTy<'hir> {
     ///
     /// This mapping associated a captured lifetime (first parameter) with the new
     /// early-bound lifetime that was generated for the opaque.
-    pub lifetime_mapping: Option<&'hir [(&'hir Lifetime, LocalDefId)]>,
+    pub lifetime_mapping: &'hir [(&'hir Lifetime, LocalDefId)],
     /// Whether the opaque is a return-position impl trait (or async future)
     /// originating from a trait method. This makes it so that the opaque is
     /// lowered as an associated type.

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -59,7 +59,7 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
             let opaque_ty_id = tcx.hir().local_def_id_to_hir_id(opaque_def_id.expect_local());
             let opaque_ty_node = tcx.hir().get(opaque_ty_id);
             let Node::Item(&Item {
-                kind: ItemKind::OpaqueTy(OpaqueTy { lifetime_mapping: Some(lifetime_mapping), .. }),
+                kind: ItemKind::OpaqueTy(OpaqueTy { lifetime_mapping, .. }),
                 ..
             }) = opaque_ty_node
             else {

compiler/rustc_ty_utils/src/implied_bounds.rs

@@ -67,7 +67,7 @@ fn assumed_wf_types<'tcx>(tcx: TyCtxt<'tcx>, def_id: LocalDefId) -> &'tcx [(Ty<'
                 let mut mapping = FxHashMap::default();
                 let generics = tcx.generics_of(def_id);
                 for &(lifetime, new_early_bound_def_id) in
-                    lifetime_mapping.expect("expected lifetime mapping for RPITIT")
+                    lifetime_mapping
                 {
                     if let Some(rbv::ResolvedArg::LateBound(_, _, def_id)) =
                         tcx.named_bound_var(lifetime.hir_id)