error[E0658]: return type notation is experimental
  --> $DIR/feature-gate-return_type_notation.rs:17:17
   |
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:17:17
   |
LL | fn foo<T: Trait<m(): Send>>() {}
   |                 ^--
   |                  |
   |                  help: remove these parentheses

error[E0220]: associated type `m` not found for `Trait`
  --> $DIR/feature-gate-return_type_notation.rs:17:17
   |
LL | fn foo<T: Trait<m(): Send>>() {}
   |                 ^ associated type `m` not found

error: aborting due to 3 previous errors

Some errors have detailed explanations: E0220, E0658.
For more information about an error, try `rustc --explain E0220`.