error[E0658]: type changing struct updating is experimental
  --> $DIR/feature-gate.rs:22:11
   |
LL |         ..m1
   |           ^^
   |
   = note: see issue #86555 <https://github.com/rust-lang/rust/issues/86555> for more information
   = help: add `#![feature(type_changing_struct_update)]` to the crate attributes to enable

error[E0308]: mismatched types
  --> $DIR/feature-gate.rs:22:11
   |
LL |         ..m1
   |           ^^ expected `Machine<State2>`, found `Machine<State1>`
   |
   = note: expected struct `Machine<State2>`
              found struct `Machine<State1>`

error: aborting due to 2 previous errors

Some errors have detailed explanations: E0308, E0658.
For more information about an error, try `rustc --explain E0308`.