enable the feature by default

compiler/rustc_hir_typeck/src/expr.rs

@@ -1642,7 +1642,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if let Some(base_expr) = base_expr {
             // FIXME: We are currently creating two branches here in order to maintain
             // consistency. But they should be merged as much as possible.
-            let fru_tys = if self.tcx.features().type_changing_struct_update {
+            let fru_tys = if self.tcx.features().type_changing_struct_update || true {
                 if adt.is_struct() {
                     // Make some fresh substitutions for our ADT type.
                     let fresh_substs = self.fresh_substs_for_item(base_expr.span, adt.did());

src/test/ui/rfcs/rfc-2528-type-changing-struct-update/feature-gate.rs

@@ -18,10 +18,9 @@ fn update_to_state2() {
         common_field2: 2,
     };
     let m2: Machine<State2> = Machine {
-        state: State2,
+        state: State1,
+        //~^ ERROR mismatched types [E0308]
         ..m1
-        //~^ ERROR type changing struct updating is experimental [E0658]
-        //~| ERROR mismatched types [E0308]
     };
     assert_eq!(State2, m2.state);
 }

src/test/ui/rfcs/rfc-2528-type-changing-struct-update/feature-gate.stderr

@@ -1,22 +1,9 @@
-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 struct `State2`, found struct `State1`
+  --> $DIR/feature-gate.rs:21:16
    |
-   = note: expected struct `Machine<State2>`
-              found struct `Machine<State1>`
+LL |         state: State1,
+   |                ^^^^^^ expected struct `State2`, found struct `State1`
 
-error: aborting due to 2 previous errors
+error: aborting due to previous error
 
-Some errors have detailed explanations: E0308, E0658.
-For more information about an error, try `rustc --explain E0308`.
+For more information about this error, try `rustc --explain E0308`.