Add lang item for Future::Output

compiler/rustc_hir/src/lang_items.rs

@@ -238,6 +238,7 @@ language_item_table! {
     Iterator,                sym::iterator,            iterator_trait,             Target::Trait,          GenericRequirement::Exact(0);
     FusedIterator,           sym::fused_iterator,      fused_iterator_trait,       Target::Trait,          GenericRequirement::Exact(0);
     Future,                  sym::future_trait,        future_trait,               Target::Trait,          GenericRequirement::Exact(0);
+    FutureOutput,            sym::future_output,       future_output,              Target::AssocTy,        GenericRequirement::Exact(0);
     AsyncIterator,           sym::async_iterator,      async_iterator_trait,       Target::Trait,          GenericRequirement::Exact(0);
 
     CoroutineState,          sym::coroutine_state,     coroutine_state,            Target::Enum,           GenericRequirement::None;

compiler/rustc_hir_analysis/src/collect.rs

@@ -1478,7 +1478,7 @@ pub fn suggest_impl_trait<'tcx>(
         ),
         (
             infcx.tcx.lang_items().future_trait(),
-            infcx.tcx.get_diagnostic_item(sym::FutureOutput),
+            infcx.tcx.lang_items().future_output(),
             format_as_assoc,
         ),
         (

compiler/rustc_span/src/symbol.rs

@@ -210,7 +210,6 @@ symbols! {
         FsPermissions,
         FusedIterator,
         Future,
-        FutureOutput,
         GlobalAlloc,
         Hash,
         HashMap,
@@ -914,6 +913,7 @@ symbols! {
         fundamental,
         fused_iterator,
         future,
+        future_output,
         future_trait,
         gdb_script_file,
         ge,

compiler/rustc_trait_selection/src/solve/assembly/structural_traits.rs

@@ -454,12 +454,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<'tc
                     .rebind(ty::TraitRef::new(tcx, future_trait_def_id, [sig.output()]))
                     .upcast(tcx),
             ];
-            let future_output_def_id = tcx
-                .associated_items(future_trait_def_id)
-                .filter_by_name_unhygienic(sym::Output)
-                .next()
-                .unwrap()
-                .def_id;
+            let future_output_def_id = tcx.require_lang_item(LangItem::FutureOutput, None);
             let future_output_ty = Ty::new_projection(tcx, future_output_def_id, [sig.output()]);
             Ok((
                 bound_sig.rebind(AsyncCallableRelevantTypes {
@@ -510,12 +505,7 @@ pub(in crate::solve) fn extract_tupled_inputs_and_output_from_async_callable<'tc
                 );
             }
 
-            let future_output_def_id = tcx
-                .associated_items(future_trait_def_id)
-                .filter_by_name_unhygienic(sym::Output)
-                .next()
-                .unwrap()
-                .def_id;
+            let future_output_def_id = tcx.require_lang_item(LangItem::FutureOutput, None);
             let future_output_ty = Ty::new_projection(tcx, future_output_def_id, [sig.output()]);
             Ok((
                 bound_sig.rebind(AsyncCallableRelevantTypes {

compiler/rustc_trait_selection/src/traits/project.rs

@@ -1880,13 +1880,7 @@ fn confirm_async_closure_candidate<'cx, 'tcx>(
             let term = match item_name {
                 sym::CallOnceFuture | sym::CallRefFuture => sig.output(),
                 sym::Output => {
-                    let future_trait_def_id = tcx.require_lang_item(LangItem::Future, None);
-                    let future_output_def_id = tcx
-                        .associated_items(future_trait_def_id)
-                        .filter_by_name_unhygienic(sym::Output)
-                        .next()
-                        .unwrap()
-                        .def_id;
+                    let future_output_def_id = tcx.require_lang_item(LangItem::FutureOutput, None);
                     Ty::new_projection(tcx, future_output_def_id, [sig.output()])
                 }
                 name => bug!("no such associated type: {name}"),
@@ -1919,13 +1913,7 @@ fn confirm_async_closure_candidate<'cx, 'tcx>(
             let term = match item_name {
                 sym::CallOnceFuture | sym::CallRefFuture => sig.output(),
                 sym::Output => {
-                    let future_trait_def_id = tcx.require_lang_item(LangItem::Future, None);
-                    let future_output_def_id = tcx
-                        .associated_items(future_trait_def_id)
-                        .filter_by_name_unhygienic(sym::Output)
-                        .next()
-                        .unwrap()
-                        .def_id;
+                    let future_output_def_id = tcx.require_lang_item(LangItem::FutureOutput, None);
                     Ty::new_projection(tcx, future_output_def_id, [sig.output()])
                 }
                 name => bug!("no such associated type: {name}"),

library/core/src/future/future.rs

@@ -35,7 +35,7 @@ use crate::task::{Context, Poll};
 pub trait Future {
     /// The type of value produced on completion.
     #[stable(feature = "futures_api", since = "1.36.0")]
-    #[rustc_diagnostic_item = "FutureOutput"]
+    #[cfg_attr(not(bootstrap), lang = "future_output")]
     type Output;
 
     /// Attempt to resolve the future to a final value, registering