feat(exporter): feature(trait_alias): only when feature(rustc)

frontend/exporter/src/lib.rs

@@ -1,8 +1,8 @@
-#![feature(trait_alias)]
 #![allow(rustdoc::private_intra_doc_links)]
 #![cfg_attr(feature = "rustc", feature(type_changing_struct_update))]
 #![cfg_attr(feature = "rustc", feature(macro_metavar_expr))]
 #![cfg_attr(feature = "rustc", feature(concat_idents))]
+#![cfg_attr(feature = "rustc", feature(trait_alias))]
 #![cfg_attr(feature = "rustc", feature(rustc_private))]
 
 macro_rules! cfg_feature_rustc {

frontend/exporter/src/state.rs

@@ -235,9 +235,14 @@ pub fn with_owner_id<'tcx, THIR, MIR>(
 }
 
 pub trait BaseState<'tcx> = HasBase<'tcx> + Clone + IsState<'tcx>;
+
 /// State of anything below a `owner_id`
 pub trait UnderOwnerState<'tcx> = BaseState<'tcx> + HasOwnerId;
 
+/// While translating expressions, we expect to always have a THIR
+/// body and an `owner_id` in the state
+pub trait ExprState<'tcx> = UnderOwnerState<'tcx> + HasThir<'tcx>;
+
 impl ImplInfos {
     fn from<'tcx>(base: Base<'tcx>, did: rustc_hir::def_id::DefId) -> Self {
         let tcx = base.tcx;

frontend/exporter/src/types/copied.rs

@@ -1322,11 +1322,6 @@ impl<'tcx, S: ExprState<'tcx>> SInto<S, Stmt> for rustc_middle::thir::StmtId {
     }
 }
 
-/// While translating expressions, we expect to always have a THIR
-/// body and an `owner_id` in the state
-#[cfg(feature = "rustc")]
-pub trait ExprState<'tcx> = UnderOwnerState<'tcx> + HasThir<'tcx>;
-
 #[cfg(feature = "rustc")]
 impl<'tcx, S: ExprState<'tcx>> SInto<S, Expr> for rustc_middle::thir::Expr<'tcx> {
     fn sinto(&self, s: &S) -> Expr {