• Replace ~const syntax with [const] conditionally const syntax in trait bounds (#1896, rust-lang/rust#139858)
• Support conditionally const impl Trait types (#1897)
• Reject polarity modifier and lifetime binder used in the same trait bound (#1899, rust-lang/rust#127054)
• Parse const trait bounds with bound lifetimes (#1902)
• Parse bound lifetimes with lifetime bounds (#1903)
• Allow type parameters and const parameters in trait bounds and generic closures (#1904, #1907, #1908, #1909)