error[E0658]: return type notation is experimental
  --> $DIR/feature-gate-return_type_notation.rs:14:17
   |
LL | fn foo<T: Trait<m(): Send>>() {}
   |                 ^^^^^^^^^
   |
   = note: see issue #109417 <https://github.com/rust-lang/rust/issues/109417> for more information
   = help: add `#![feature(return_type_notation)]` to the crate attributes to enable

error: parenthesized generic arguments cannot be used in associated type constraints
  --> $DIR/feature-gate-return_type_notation.rs:14:17
   |
LL | fn foo<T: Trait<m(): Send>>() {}
   |                 ^--
   |                  |
   |                  help: remove these parentheses

error: expected type, found function
  --> $DIR/feature-gate-return_type_notation.rs:14:17
   |
LL | fn foo<T: Trait<m(): Send>>() {}
   |                 ^ unexpected function
   |
note: the associated function is defined here
  --> $DIR/feature-gate-return_type_notation.rs:10:5
   |
LL |     async fn m();
   |     ^^^^^^^^^^^^^

error: aborting due to 3 previous errors

For more information about this error, try `rustc --explain E0658`.