Make WHERE_CLAUSES_OBJECT_SAFETY a regular object safety violation

compiler/rustc_lint_defs/src/builtin.rs

@@ -136,7 +136,6 @@ declare_lint_pass! {
         USELESS_DEPRECATED,
         WARNINGS,
         WASM_C_ABI,
-        WHERE_CLAUSES_OBJECT_SAFETY,
         WRITES_THROUGH_IMMUTABLE_POINTER,
         // tidy-alphabetical-end
     ]
@@ -2093,47 +2092,6 @@ declare_lint! {
     "detects labels that are never used"
 }
 
-declare_lint! {
-    /// The `where_clauses_object_safety` lint detects for [object safety] of
-    /// [where clauses].
-    ///
-    /// [object safety]: https://doc.rust-lang.org/reference/items/traits.html#object-safety
-    /// [where clauses]: https://doc.rust-lang.org/reference/items/generics.html#where-clauses
-    ///
-    /// ### Example
-    ///
-    /// ```rust,no_run
-    /// trait Trait {}
-    ///
-    /// trait X { fn foo(&self) where Self: Trait; }
-    ///
-    /// impl X for () { fn foo(&self) {} }
-    ///
-    /// impl Trait for dyn X {}
-    ///
-    /// // Segfault at opt-level 0, SIGILL otherwise.
-    /// pub fn main() { <dyn X as X>::foo(&()); }
-    /// ```
-    ///
-    /// {{produces}}
-    ///
-    /// ### Explanation
-    ///
-    /// The compiler previously allowed these object-unsafe bounds, which was
-    /// incorrect. This is a [future-incompatible] lint to transition this to
-    /// a hard error in the future. See [issue #51443] for more details.
-    ///
-    /// [issue #51443]: https://github.com/rust-lang/rust/issues/51443
-    /// [future-incompatible]: ../index.md#future-incompatible-lints
-    pub WHERE_CLAUSES_OBJECT_SAFETY,
-    Warn,
-    "checks the object safety of where clauses",
-    @future_incompatible = FutureIncompatibleInfo {
-        reason: FutureIncompatibilityReason::FutureReleaseErrorDontReportInDeps,
-        reference: "issue #51443 <https://github.com/rust-lang/rust/issues/51443>",
-    };
-}
-
 declare_lint! {
     /// The `proc_macro_derive_resolution_fallback` lint detects proc macro
     /// derives using inaccessible names from parent modules.

compiler/rustc_trait_selection/src/traits/object_safety.rs

@@ -13,7 +13,7 @@ use super::elaborate;
 use crate::infer::TyCtxtInferExt;
 use crate::traits::query::evaluate_obligation::InferCtxtExt;
 use crate::traits::{self, Obligation, ObligationCause};
-use rustc_errors::{FatalError, MultiSpan};
+use rustc_errors::FatalError;
 use rustc_hir as hir;
 use rustc_hir::def_id::DefId;
 use rustc_middle::query::Providers;
@@ -23,7 +23,6 @@ use rustc_middle::ty::{
 };
 use rustc_middle::ty::{GenericArg, GenericArgs};
 use rustc_middle::ty::{TypeVisitableExt, Upcast};
-use rustc_session::lint::builtin::WHERE_CLAUSES_OBJECT_SAFETY;
 use rustc_span::symbol::Symbol;
 use rustc_span::Span;
 use rustc_target::abi::Abi;
@@ -66,44 +65,13 @@ fn object_safety_violations(tcx: TyCtxt<'_>, trait_def_id: DefId) -> &'_ [Object
 }
 
 fn check_is_object_safe(tcx: TyCtxt<'_>, trait_def_id: DefId) -> bool {
-    let violations = tcx.object_safety_violations(trait_def_id);
-
-    if violations.is_empty() {
-        return true;
-    }
-
-    // If the trait contains any other violations, then let the error reporting path
-    // report it instead of emitting a warning here.
-    if violations.iter().all(|violation| {
-        matches!(
-            violation,
-            ObjectSafetyViolation::Method(_, MethodViolationCode::WhereClauseReferencesSelf, _)
-        )
-    }) {
-        for violation in violations {
-            if let ObjectSafetyViolation::Method(
-                _,
-                MethodViolationCode::WhereClauseReferencesSelf,
-                span,
-            ) = violation
-            {
-                lint_object_unsafe_trait(tcx, *span, trait_def_id, violation);
-            }
-        }
-        return true;
-    }
-
-    false
+    tcx.object_safety_violations(trait_def_id).is_empty()
 }
 
 /// We say a method is *vtable safe* if it can be invoked on a trait
 /// object. Note that object-safe traits can have some
 /// non-vtable-safe methods, so long as they require `Self: Sized` or
 /// otherwise ensure that they cannot be used when `Self = Trait`.
-///
-/// [`MethodViolationCode::WhereClauseReferencesSelf`] is considered object safe due to backwards
-/// compatibility, see <https://github.com/rust-lang/rust/issues/51443> and
-/// [`WHERE_CLAUSES_OBJECT_SAFETY`].
 pub fn is_vtable_safe_method(tcx: TyCtxt<'_>, trait_def_id: DefId, method: ty::AssocItem) -> bool {
     debug_assert!(tcx.generics_of(trait_def_id).has_self);
     debug!("is_vtable_safe_method({:?}, {:?})", trait_def_id, method);
@@ -112,9 +80,7 @@ pub fn is_vtable_safe_method(tcx: TyCtxt<'_>, trait_def_id: DefId, method: ty::A
         return false;
     }
 
-    virtual_call_violations_for_method(tcx, trait_def_id, method)
-        .iter()
-        .all(|v| matches!(v, MethodViolationCode::WhereClauseReferencesSelf))
+    virtual_call_violations_for_method(tcx, trait_def_id, method).is_empty()
 }
 
 fn object_safety_violations_for_trait(
@@ -163,47 +129,6 @@ fn object_safety_violations_for_trait(
     violations
 }
 
-/// Lint object-unsafe trait.
-fn lint_object_unsafe_trait(
-    tcx: TyCtxt<'_>,
-    span: Span,
-    trait_def_id: DefId,
-    violation: &ObjectSafetyViolation,
-) {
-    // Using `CRATE_NODE_ID` is wrong, but it's hard to get a more precise id.
-    // It's also hard to get a use site span, so we use the method definition span.
-    tcx.node_span_lint(WHERE_CLAUSES_OBJECT_SAFETY, hir::CRATE_HIR_ID, span, |err| {
-        err.primary_message(format!(
-            "the trait `{}` cannot be made into an object",
-            tcx.def_path_str(trait_def_id)
-        ));
-        let node = tcx.hir().get_if_local(trait_def_id);
-        let mut spans = MultiSpan::from_span(span);
-        if let Some(hir::Node::Item(item)) = node {
-            spans.push_span_label(item.ident.span, "this trait cannot be made into an object...");
-            spans.push_span_label(span, format!("...because {}", violation.error_msg()));
-        } else {
-            spans.push_span_label(
-                span,
-                format!(
-                    "the trait cannot be made into an object because {}",
-                    violation.error_msg()
-                ),
-            );
-        };
-        err.span_note(
-            spans,
-            "for a trait to be \"object safe\" it needs to allow building a vtable to allow the \
-                call to be resolvable dynamically; for more information visit \
-                <https://doc.rust-lang.org/reference/items/traits.html#object-safety>",
-        );
-        if node.is_some() {
-            // Only provide the help if its a local trait, otherwise it's not
-            violation.solution().add_to(err);
-        }
-    });
-}
-
 fn sized_trait_bound_spans<'tcx>(
     tcx: TyCtxt<'tcx>,
     bounds: hir::GenericBounds<'tcx>,

tests/ui/const-generics/generic_const_exprs/object-safety-err-where-bounds.rs

@@ -1,22 +1,21 @@
 #![feature(generic_const_exprs)]
 #![allow(incomplete_features)]
-#![deny(where_clauses_object_safety)]
 
 
 const fn bar<T: ?Sized>() -> usize { 7 }
 
 trait Foo {
     fn test(&self) where [u8; bar::<Self>()]: Sized;
-    //~^ ERROR the trait `Foo` cannot be made into an object
-    //~| WARN this was previously accepted by the compiler but is being phased out
 }
 
 impl Foo for () {
     fn test(&self) where [u8; bar::<Self>()]: Sized {}
 }
 
 fn use_dyn(v: &dyn Foo) {
+    //~^ ERROR the trait `Foo` cannot be made into an object
     v.test();
+    //~^ ERROR the trait `Foo` cannot be made into an object
 }
 
 fn main() {}

tests/ui/const-generics/generic_const_exprs/object-safety-err-where-bounds.stderr

@@ -1,24 +1,35 @@
-error: the trait `Foo` cannot be made into an object
-  --> $DIR/object-safety-err-where-bounds.rs:9:8
+error[E0038]: the trait `Foo` cannot be made into an object
+  --> $DIR/object-safety-err-where-bounds.rs:15:16
    |
-LL |     fn test(&self) where [u8; bar::<Self>()]: Sized;
-   |        ^^^^
+LL | fn use_dyn(v: &dyn Foo) {
+   |                ^^^^^^^ `Foo` cannot be made into an object
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #51443 <https://github.com/rust-lang/rust/issues/51443>
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
-  --> $DIR/object-safety-err-where-bounds.rs:9:8
+  --> $DIR/object-safety-err-where-bounds.rs:8:8
    |
 LL | trait Foo {
    |       --- this trait cannot be made into an object...
 LL |     fn test(&self) where [u8; bar::<Self>()]: Sized;
    |        ^^^^ ...because method `test` references the `Self` type in its `where` clause
    = help: consider moving `test` to another trait
-note: the lint level is defined here
-  --> $DIR/object-safety-err-where-bounds.rs:3:9
+   = help: only type `()` implements the trait, consider using it directly instead
+
+error[E0038]: the trait `Foo` cannot be made into an object
+  --> $DIR/object-safety-err-where-bounds.rs:17:5
+   |
+LL |     v.test();
+   |     ^^^^^^^^ `Foo` cannot be made into an object
+   |
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/object-safety-err-where-bounds.rs:8:8
    |
-LL | #![deny(where_clauses_object_safety)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+LL | trait Foo {
+   |       --- this trait cannot be made into an object...
+LL |     fn test(&self) where [u8; bar::<Self>()]: Sized;
+   |        ^^^^ ...because method `test` references the `Self` type in its `where` clause
+   = help: consider moving `test` to another trait
+   = help: only type `()` implements the trait, consider using it directly instead
 
-error: aborting due to 1 previous error
+error: aborting due to 2 previous errors
 
+For more information about this error, try `rustc --explain E0038`.

tests/ui/issues/issue-50781.rs

@@ -1,19 +1,19 @@
-#![deny(where_clauses_object_safety)]
-
 trait Trait {}
 
 trait X {
-    fn foo(&self) where Self: Trait; //~ ERROR the trait `X` cannot be made into an object
-    //~^ WARN this was previously accepted by the compiler but is being phased out
+    fn foo(&self) where Self: Trait;
 }
 
 impl X for () {
     fn foo(&self) {}
 }
 
 impl Trait for dyn X {}
+//~^ ERROR the trait `X` cannot be made into an object
 
 pub fn main() {
     // Check that this does not segfault.
     <dyn X as X>::foo(&());
+    //~^ ERROR the trait `X` cannot be made into an object
+    //~| ERROR the trait `X` cannot be made into an object
 }

tests/ui/issues/issue-50781.stderr

@@ -1,24 +1,52 @@
-error: the trait `X` cannot be made into an object
-  --> $DIR/issue-50781.rs:6:8
+error[E0038]: the trait `X` cannot be made into an object
+  --> $DIR/issue-50781.rs:11:16
    |
+LL | impl Trait for dyn X {}
+   |                ^^^^^ `X` cannot be made into an object
+   |
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/issue-50781.rs:4:8
+   |
+LL | trait X {
+   |       - this trait cannot be made into an object...
 LL |     fn foo(&self) where Self: Trait;
-   |        ^^^
+   |        ^^^ ...because method `foo` references the `Self` type in its `where` clause
+   = help: consider moving `foo` to another trait
+   = help: only type `()` implements the trait, consider using it directly instead
+
+error[E0038]: the trait `X` cannot be made into an object
+  --> $DIR/issue-50781.rs:16:23
+   |
+LL |     <dyn X as X>::foo(&());
+   |                       ^^^ `X` cannot be made into an object
    |
-   = warning: this was previously accepted by the compiler but is being phased out; it will become a hard error in a future release!
-   = note: for more information, see issue #51443 <https://github.com/rust-lang/rust/issues/51443>
 note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
-  --> $DIR/issue-50781.rs:6:8
+  --> $DIR/issue-50781.rs:4:8
    |
 LL | trait X {
    |       - this trait cannot be made into an object...
 LL |     fn foo(&self) where Self: Trait;
    |        ^^^ ...because method `foo` references the `Self` type in its `where` clause
    = help: consider moving `foo` to another trait
-note: the lint level is defined here
-  --> $DIR/issue-50781.rs:1:9
+   = help: only type `()` implements the trait, consider using it directly instead
+   = note: required for the cast from `&()` to `&dyn X`
+
+error[E0038]: the trait `X` cannot be made into an object
+  --> $DIR/issue-50781.rs:16:6
+   |
+LL |     <dyn X as X>::foo(&());
+   |      ^^^^^ `X` cannot be made into an object
    |
-LL | #![deny(where_clauses_object_safety)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^
+note: for a trait to be "object safe" it needs to allow building a vtable to allow the call to be resolvable dynamically; for more information visit <https://doc.rust-lang.org/reference/items/traits.html#object-safety>
+  --> $DIR/issue-50781.rs:4:8
+   |
+LL | trait X {
+   |       - this trait cannot be made into an object...
+LL |     fn foo(&self) where Self: Trait;
+   |        ^^^ ...because method `foo` references the `Self` type in its `where` clause
+   = help: consider moving `foo` to another trait
+   = help: only type `()` implements the trait, consider using it directly instead
 
-error: aborting due to 1 previous error
+error: aborting due to 3 previous errors
 
+For more information about this error, try `rustc --explain E0038`.

tests/ui/object-safety/issue-106247.rs

@@ -1,7 +1,5 @@
 //@ check-pass
 
-#![deny(where_clauses_object_safety)]
-
 pub trait Trait {
     fn method(&self) where Self: Sync;
 }

tests/ui/traits/vtable/vtable-vacant.rs

@@ -1,7 +1,6 @@
 //@ build-fail
 #![feature(rustc_attrs)]
 #![feature(negative_impls)]
-#![allow(where_clauses_object_safety)]
 
 // B --> A
 

tests/ui/traits/vtable/vtable-vacant.stderr

@@ -7,7 +7,7 @@ error: vtable entries for `<S as B>`: [
            Method(<S as B>::foo_b1),
            Vacant,
        ]
-  --> $DIR/vtable-vacant.rs:15:1
+  --> $DIR/vtable-vacant.rs:14:1
    |
 LL | trait B: A {
    | ^^^^^^^^^^