Add generator lang-item

compiler/rustc_hir/src/lang_items.rs

@@ -268,6 +268,7 @@ language_item_table! {
     Future,                  sym::future_trait,        future_trait,               Target::Trait,          GenericRequirement::Exact(0);
     GeneratorState,          sym::generator_state,     gen_state,                  Target::Enum,           GenericRequirement::None;
     Generator,               sym::generator,           gen_trait,                  Target::Trait,          GenericRequirement::Minimum(1);
+    GeneratorReturn,         sym::generator_return,    generator_return,           Target::AssocTy,        GenericRequirement::None;
     Unpin,                   sym::unpin,               unpin_trait,                Target::Trait,          GenericRequirement::None;
     Pin,                     sym::pin,                 pin_type,                   Target::Struct,         GenericRequirement::None;
 

compiler/rustc_span/src/symbol.rs

@@ -678,6 +678,7 @@ symbols! {
         gen_future,
         gen_kill,
         generator,
+        generator_return,
         generator_state,
         generators,
         generic_arg_infer,

library/core/src/ops/generator.rs

@@ -82,6 +82,7 @@ pub trait Generator<R = ()> {
     /// `return` statement or implicitly as the last expression of a generator
     /// literal. For example futures would use this as `Result<T, E>` as it
     /// represents a completed future.
+    #[cfg_attr(not(bootstrap), lang = "generator_return")]
     type Return;
 
     /// Resumes the execution of this generator.