Remove feature(dyn_compatible_for_dispatch) from the compiler

compiler/rustc_feature/src/removed.rs

@@ -100,6 +100,15 @@ declare_features! (
      Some("renamed to `doc_notable_trait`")),
     /// Allows using `#[unsafe_destructor_blind_to_params]` (RFC 1238).
     (removed, dropck_parametricity, "1.38.0", Some(28498), None),
+    /// Allows making `dyn Trait` well-formed even if `Trait` is not dyn compatible[^1].
+    /// In that case, `dyn Trait: Trait` does not hold. Moreover, coercions and
+    /// casts in safe Rust to `dyn Trait` for such a `Trait` is also forbidden.
+    ///
+    /// Renamed from `object_safe_for_dispatch`.
+    ///
+    /// [^1]: Formerly known as "object safe".
+    (removed, dyn_compatible_for_dispatch, "1.83.0", Some(43561),
+     Some("removed, not used heavily and represented additional complexity in dyn compatibility")),
     /// Uses generic effect parameters for ~const bounds
     (removed, effects, "1.84.0", Some(102090),
      Some("removed, redundant with `#![feature(const_trait_impl)]`")),

compiler/rustc_feature/src/unstable.rs

@@ -270,14 +270,6 @@ declare_features! (
     (unstable, doc_notable_trait, "1.52.0", Some(45040)),
     /// Allows using the `may_dangle` attribute (RFC 1327).
     (unstable, dropck_eyepatch, "1.10.0", Some(34761)),
-    /// Allows making `dyn Trait` well-formed even if `Trait` is not dyn compatible[^1].
-    /// In that case, `dyn Trait: Trait` does not hold. Moreover, coercions and
-    /// casts in safe Rust to `dyn Trait` for such a `Trait` is also forbidden.
-    ///
-    /// Renamed from `object_safe_for_dispatch`.
-    ///
-    /// [^1]: Formerly known as "object safe".
-    (unstable, dyn_compatible_for_dispatch, "1.83.0", Some(43561)),
     /// Allows using the `#[fundamental]` attribute.
     (unstable, fundamental, "1.0.0", Some(29635)),
     /// Allows using `#[link_name="llvm.*"]`.

compiler/rustc_hir_analysis/src/coherence/mod.rs

@@ -199,11 +199,7 @@ fn check_object_overlap<'tcx>(
 
         for component_def_id in component_def_ids {
             if !tcx.is_dyn_compatible(component_def_id) {
-                // Without the 'dyn_compatible_for_dispatch' feature this is an error
-                // which will be reported by wfcheck. Ignore it here.
-                // This is tested by `coherence-impl-trait-for-trait-dyn-compatible.rs`.
-                // With the feature enabled, the trait is not implemented automatically,
-                // so this is valid.
+                // This is a WF error tested by `coherence-impl-trait-for-trait-dyn-compatible.rs`.
             } else {
                 let mut supertrait_def_ids = elaborate::supertrait_def_ids(tcx, component_def_id);
                 if supertrait_def_ids

compiler/rustc_trait_selection/src/traits/dyn_compatibility.rs

@@ -538,10 +538,10 @@ fn receiver_for_self_ty<'tcx>(
 /// a pointer.
 ///
 /// In practice, we cannot use `dyn Trait` explicitly in the obligation because it would result in
-/// a new check that `Trait` is dyn-compatible, creating a cycle (until dyn_compatible_for_dispatch
-/// is stabilized, see tracking issue <https://github.com/rust-lang/rust/issues/43561>).
-/// Instead, we fudge a little by introducing a new type parameter `U` such that
+/// a new check that `Trait` is dyn-compatible, creating a cycle.
+/// Instead, we emulate a placeholder by introducing a new type parameter `U` such that
 /// `Self: Unsize<U>` and `U: Trait + ?Sized`, and use `U` in place of `dyn Trait`.
+///
 /// Written as a chalk-style query:
 /// ```ignore (not-rust)
 /// forall (U: Trait + ?Sized) {
@@ -572,8 +572,6 @@ fn receiver_is_dispatchable<'tcx>(
 
     // the type `U` in the query
     // use a bogus type parameter to mimic a forall(U) query using u32::MAX for now.
-    // FIXME(mikeyhew) this is a total hack. Once dyn_compatible_for_dispatch is stabilized, we can
-    // replace this with `dyn Trait`
     let unsized_self_ty: Ty<'tcx> =
         Ty::new_param(tcx, u32::MAX, rustc_span::sym::RustaceansAreAwesome);
 

compiler/rustc_trait_selection/src/traits/select/candidate_assembly.rs

@@ -859,13 +859,7 @@ impl<'cx, 'tcx> SelectionContext<'cx, 'tcx> {
                         }
 
                         if let Some(principal) = data.principal() {
-                            if !self.infcx.tcx.features().dyn_compatible_for_dispatch() {
-                                principal.with_self_ty(self.tcx(), self_ty)
-                            } else if self.tcx().is_dyn_compatible(principal.def_id()) {
-                                principal.with_self_ty(self.tcx(), self_ty)
-                            } else {
-                                return;
-                            }
+                            principal.with_self_ty(self.tcx(), self_ty)
                         } else {
                             // Only auto trait bounds exist.
                             return;

compiler/rustc_trait_selection/src/traits/wf.rs

@@ -904,19 +904,14 @@ impl<'a, 'tcx> TypeVisitor<TyCtxt<'tcx>> for WfPredicates<'a, 'tcx> {
                 // FIXME(#27579) RFC also considers adding trait
                 // obligations that don't refer to Self and
                 // checking those
-
-                let defer_to_coercion = tcx.features().dyn_compatible_for_dispatch();
-
-                if !defer_to_coercion {
-                    if let Some(principal) = data.principal_def_id() {
-                        self.out.push(traits::Obligation::with_depth(
-                            tcx,
-                            self.cause(ObligationCauseCode::WellFormed(None)),
-                            self.recursion_depth,
-                            self.param_env,
-                            ty::Binder::dummy(ty::PredicateKind::DynCompatible(principal)),
-                        ));
-                    }
+                if let Some(principal) = data.principal_def_id() {
+                    self.out.push(traits::Obligation::with_depth(
+                        tcx,
+                        self.cause(ObligationCauseCode::WellFormed(None)),
+                        self.recursion_depth,
+                        self.param_env,
+                        ty::Binder::dummy(ty::PredicateKind::DynCompatible(principal)),
+                    ));
                 }
             }
 

src/tools/tidy/src/issues.txt

@@ -3827,7 +3827,6 @@ ui/suggestions/issue-103646.rs
 ui/suggestions/issue-104086-suggest-let.rs
 ui/suggestions/issue-104287.rs
 ui/suggestions/issue-104327.rs
-ui/suggestions/issue-104328.rs
 ui/suggestions/issue-104961.rs
 ui/suggestions/issue-105226.rs
 ui/suggestions/issue-105494.rs

tests/ui/const-generics/issues/cg-in-dyn-issue-128176.rs

@@ -1,10 +1,7 @@
-//@ check-pass
-
 // Regression test for #128176. Previously we would call `type_of` on the `1` anon const
 // before the anon const had been lowered and had the `type_of` fed with a result.
 
 #![feature(generic_const_exprs)]
-#![feature(dyn_compatible_for_dispatch)]
 #![allow(incomplete_features)]
 
 trait X {
@@ -13,6 +10,7 @@ trait X {
 
 const _: () = {
     fn f2<'a>(arg: Box<dyn X<Y<1> = &'a ()>>) {}
+    //~^ ERROR the trait `X` is not dyn compatible
 };
 
 fn main() {}

tests/ui/const-generics/issues/cg-in-dyn-issue-128176.stderr

@@ -0,0 +1,19 @@
+error[E0038]: the trait `X` is not dyn compatible
+  --> $DIR/cg-in-dyn-issue-128176.rs:12:24
+   |
+LL |     fn f2<'a>(arg: Box<dyn X<Y<1> = &'a ()>>) {}
+   |                        ^^^^^^^^^^^^^^^^^^^^ `X` is not dyn compatible
+   |
+note: for a trait to be dyn compatible it needs to allow building a vtable
+      for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
+  --> $DIR/cg-in-dyn-issue-128176.rs:8:10
+   |
+LL | trait X {
+   |       - this trait is not dyn compatible...
+LL |     type Y<const N: i16>;
+   |          ^ ...because it contains the generic associated type `Y`
+   = help: consider moving `Y` to another trait
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0038`.

tests/ui/dyn-compatibility/associated-consts.rs

@@ -1,16 +1,12 @@
 // Check that we correctly prevent users from making trait objects
 // from traits with associated consts.
-//
-//@ revisions: curr dyn_compatible_for_dispatch
-
-#![cfg_attr(dyn_compatible_for_dispatch, feature(dyn_compatible_for_dispatch))]
 
 trait Bar {
     const X: usize;
 }
 
 fn make_bar<T:Bar>(t: &T) -> &dyn Bar {
-    //[curr]~^ ERROR E0038
+    //~^ ERROR E0038
     t
     //~^ ERROR E0038
 }

tests/ui/dyn-compatibility/generics.dyn_compatible_for_dispatch.stderr → tests/ui/dyn-compatibility/associated-consts.stderr

@@ -1,35 +1,34 @@
 error[E0038]: the trait `Bar` is not dyn compatible
-  --> $DIR/generics.rs:20:5
+  --> $DIR/associated-consts.rs:8:31
    |
-LL |     t
-   |     ^ `Bar` is not dyn compatible
+LL | fn make_bar<T:Bar>(t: &T) -> &dyn Bar {
+   |                               ^^^^^^^ `Bar` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
-  --> $DIR/generics.rs:10:8
+  --> $DIR/associated-consts.rs:5:11
    |
 LL | trait Bar {
    |       --- this trait is not dyn compatible...
-LL |     fn bar<T>(&self, t: T);
-   |        ^^^ ...because method `bar` has generic type parameters
-   = help: consider moving `bar` to another trait
-   = note: required for the cast from `&T` to `&dyn Bar`
+LL |     const X: usize;
+   |           ^ ...because it contains this associated `const`
+   = help: consider moving `X` to another trait
 
 error[E0038]: the trait `Bar` is not dyn compatible
-  --> $DIR/generics.rs:27:5
+  --> $DIR/associated-consts.rs:10:5
    |
-LL |     t as &dyn Bar
+LL |     t
    |     ^ `Bar` is not dyn compatible
    |
 note: for a trait to be dyn compatible it needs to allow building a vtable
       for more information, visit <https://doc.rust-lang.org/reference/items/traits.html#dyn-compatibility>
-  --> $DIR/generics.rs:10:8
+  --> $DIR/associated-consts.rs:5:11
    |
 LL | trait Bar {
    |       --- this trait is not dyn compatible...
-LL |     fn bar<T>(&self, t: T);
-   |        ^^^ ...because method `bar` has generic type parameters
-   = help: consider moving `bar` to another trait
+LL |     const X: usize;
+   |           ^ ...because it contains this associated `const`
+   = help: consider moving `X` to another trait
    = note: required for the cast from `&T` to `&dyn Bar`
 
 error: aborting due to 2 previous errors

tests/ui/dyn-compatibility/generics.rs

@@ -1,9 +1,6 @@
 // Check that we correctly prevent users from making trait objects
 // from traits with generic methods, unless `where Self : Sized` is
 // present.
-//@ revisions: curr dyn_compatible_for_dispatch
-
-#![cfg_attr(dyn_compatible_for_dispatch, feature(dyn_compatible_for_dispatch))]
 
 
 trait Bar {
@@ -16,18 +13,16 @@ trait Quux {
 }
 
 fn make_bar<T:Bar>(t: &T) -> &dyn Bar {
-    //[curr]~^ ERROR E0038
+    //~^ ERROR E0038
     t
-    //[dyn_compatible_for_dispatch]~^ ERROR E0038
-    //[curr]~^^ ERROR E0038
+    //~^ ERROR E0038
 }
 
 fn make_bar_explicit<T:Bar>(t: &T) -> &dyn Bar {
-    //[curr]~^ ERROR E0038
+    //~^ ERROR E0038
     t as &dyn Bar
-    //[dyn_compatible_for_dispatch]~^ ERROR E0038
-    //[curr]~^^ ERROR E0038
-    //[curr]~| ERROR E0038
+    //~^ ERROR E0038
+    //~| ERROR E0038
 }
 
 fn make_quux<T:Quux>(t: &T) -> &dyn Quux {