Avoid ICE in trait without dyn lint

Do not attempt to provide an accurate suggestion for `impl Trait`
in bare trait types when linting. Instead, only do the object
safety check when an E0782 is already going to be emitted in the
2021 edition.

Fix #120241.

compiler/rustc_hir_analysis/src/astconv/lint.rs

@@ -132,7 +132,7 @@ fn maybe_lint_impl_trait(&self, self_ty: &hir::Ty<'_>, diag: &mut Diagnostic) ->
                     ],
                     Applicability::MachineApplicable,
                 );
-            } else if diag.is_error() && is_downgradable {
+            } else if is_downgradable {
                 // We'll emit the object safety error already, with a structured suggestion.
                 diag.downgrade_to_delayed_bug();
             }
@@ -158,7 +158,7 @@ fn maybe_lint_impl_trait(&self, self_ty: &hir::Ty<'_>, diag: &mut Diagnostic) ->
             }
             if !is_object_safe {
                 diag.note(format!("`{trait_name}` it is not object safe, so it can't be `dyn`"));
-                if diag.is_error() && is_downgradable {
+                if is_downgradable {
                     // We'll emit the object safety error already, with a structured suggestion.
                     diag.downgrade_to_delayed_bug();
                 }
@@ -241,9 +241,7 @@ pub(super) fn maybe_lint_bare_trait(&self, self_ty: &hir::Ty<'_>, in_path: bool)
             } else {
                 let msg = "trait objects without an explicit `dyn` are deprecated";
                 tcx.node_span_lint(BARE_TRAIT_OBJECTS, self_ty.hir_id, self_ty.span, msg, |lint| {
-                    if self_ty.span.can_be_used_for_suggestions()
-                        && !self.maybe_lint_impl_trait(self_ty, lint)
-                    {
+                    if self_ty.span.can_be_used_for_suggestions() {
                         lint.multipart_suggestion_verbose(
                             "use `dyn`",
                             sugg,

tests/ui/object-safety/avoid-ice-on-warning-2.new.stderr

@@ -0,0 +1,12 @@
+error[E0038]: the trait `Copy` cannot be made into an object
+  --> $DIR/avoid-ice-on-warning-2.rs:4:13
+   |
+LL | fn id<F>(f: Copy) -> usize {
+   |             ^^^^ `Copy` cannot be made into an object
+   |
+   = note: the trait cannot be made into an object because it requires `Self: Sized`
+   = 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>
+
+error: aborting due to 1 previous error
+
+For more information about this error, try `rustc --explain E0038`.

tests/ui/object-safety/avoid-ice-on-warning-2.old.stderr

@@ -1,43 +1,33 @@
 warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/avoid-ice-on-warning-2.rs:1:13
+  --> $DIR/avoid-ice-on-warning-2.rs:4:13
    |
 LL | fn id<F>(f: Copy) -> usize {
    |             ^^^^
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-   = note: `Copy` it is not object safe, so it can't be `dyn`
    = note: `#[warn(bare_trait_objects)]` on by default
-help: use a new generic type parameter, constrained by `Copy`
+help: use `dyn`
    |
-LL | fn id<F, T: Copy>(f: T) -> usize {
-   |        +++++++++     ~
-help: you can also use an opaque type, but users won't be able to specify the type parameter when calling the `fn`, having to rely exclusively on type inference
-   |
-LL | fn id<F>(f: impl Copy) -> usize {
-   |             ++++
+LL | fn id<F>(f: dyn Copy) -> usize {
+   |             +++
 
 warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/avoid-ice-on-warning-2.rs:1:13
+  --> $DIR/avoid-ice-on-warning-2.rs:4:13
    |
 LL | fn id<F>(f: Copy) -> usize {
    |             ^^^^
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-   = note: `Copy` it is not object safe, so it can't be `dyn`
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-help: use a new generic type parameter, constrained by `Copy`
+help: use `dyn`
    |
-LL | fn id<F, T: Copy>(f: T) -> usize {
-   |        +++++++++     ~
-help: you can also use an opaque type, but users won't be able to specify the type parameter when calling the `fn`, having to rely exclusively on type inference
-   |
-LL | fn id<F>(f: impl Copy) -> usize {
-   |             ++++
+LL | fn id<F>(f: dyn Copy) -> usize {
+   |             +++
 
 error[E0038]: the trait `Copy` cannot be made into an object
-  --> $DIR/avoid-ice-on-warning-2.rs:1:13
+  --> $DIR/avoid-ice-on-warning-2.rs:4:13
    |
 LL | fn id<F>(f: Copy) -> usize {
    |             ^^^^ `Copy` cannot be made into an object

tests/ui/object-safety/avoid-ice-on-warning-2.rs

@@ -1,9 +1,12 @@
+// revisions: old new
+//[old] edition:2015
+//[new] edition:2021
 fn id<F>(f: Copy) -> usize {
-//~^ WARN trait objects without an explicit `dyn` are deprecated
-//~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
-//~| WARN trait objects without an explicit `dyn` are deprecated
-//~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
-//~| ERROR the trait `Copy` cannot be made into an object
+//~^ ERROR the trait `Copy` cannot be made into an object
+//[old]~| WARN trait objects without an explicit `dyn` are deprecated
+//[old]~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+//[old]~| WARN trait objects without an explicit `dyn` are deprecated
+//[old]~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
     f()
 }
 fn main() {}

tests/ui/object-safety/avoid-ice-on-warning-3.new.stderr

@@ -0,0 +1,47 @@
+error[E0038]: the trait `A` cannot be made into an object
+  --> $DIR/avoid-ice-on-warning-3.rs:4:19
+   |
+LL | trait B { fn f(a: A) -> A; }
+   |                   ^ `A` 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/avoid-ice-on-warning-3.rs:12:14
+   |
+LL | trait A { fn g(b: B) -> B; }
+   |       -      ^ ...because associated function `g` has no `self` parameter
+   |       |
+   |       this trait cannot be made into an object...
+help: consider turning `g` into a method by giving it a `&self` argument
+   |
+LL | trait A { fn g(&self, b: B) -> B; }
+   |                ++++++
+help: alternatively, consider constraining `g` so it does not apply to trait objects
+   |
+LL | trait A { fn g(b: B) -> B where Self: Sized; }
+   |                           +++++++++++++++++
+
+error[E0038]: the trait `B` cannot be made into an object
+  --> $DIR/avoid-ice-on-warning-3.rs:12:19
+   |
+LL | trait A { fn g(b: B) -> B; }
+   |                   ^ `B` 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/avoid-ice-on-warning-3.rs:4:14
+   |
+LL | trait B { fn f(a: A) -> A; }
+   |       -      ^ ...because associated function `f` has no `self` parameter
+   |       |
+   |       this trait cannot be made into an object...
+help: consider turning `f` into a method by giving it a `&self` argument
+   |
+LL | trait B { fn f(&self, a: A) -> A; }
+   |                ++++++
+help: alternatively, consider constraining `f` so it does not apply to trait objects
+   |
+LL | trait B { fn f(a: A) -> A where Self: Sized; }
+   |                           +++++++++++++++++
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0038`.

tests/ui/object-safety/avoid-ice-on-warning-3.old.stderr

@@ -1,93 +1,78 @@
 warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/avoid-ice-on-warning-3.rs:9:19
+  --> $DIR/avoid-ice-on-warning-3.rs:4:19
    |
-LL | trait A { fn g(b: B) -> B; }
+LL | trait B { fn f(a: A) -> A; }
    |                   ^
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-   = note: `B` it is not object safe, so it can't be `dyn`
    = note: `#[warn(bare_trait_objects)]` on by default
-help: use a new generic type parameter, constrained by `B`
+help: use `dyn`
    |
-LL | trait A { fn g<T: B>(b: T) -> B; }
-   |               ++++++    ~
-help: you can also use an opaque type, but users won't be able to specify the type parameter when calling the `fn`, having to rely exclusively on type inference
-   |
-LL | trait A { fn g(b: impl B) -> B; }
-   |                   ++++
+LL | trait B { fn f(a: dyn A) -> A; }
+   |                   +++
 
 warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/avoid-ice-on-warning-3.rs:9:25
+  --> $DIR/avoid-ice-on-warning-3.rs:4:25
+   |
+LL | trait B { fn f(a: A) -> A; }
+   |                         ^
+   |
+   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+help: use `dyn`
+   |
+LL | trait B { fn f(a: A) -> dyn A; }
+   |                         +++
+
+warning: trait objects without an explicit `dyn` are deprecated
+  --> $DIR/avoid-ice-on-warning-3.rs:12:19
+   |
+LL | trait A { fn g(b: B) -> B; }
+   |                   ^
+   |
+   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+help: use `dyn`
+   |
+LL | trait A { fn g(b: dyn B) -> B; }
+   |                   +++
+
+warning: trait objects without an explicit `dyn` are deprecated
+  --> $DIR/avoid-ice-on-warning-3.rs:12:25
    |
 LL | trait A { fn g(b: B) -> B; }
    |                         ^
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-help: `B` is not object safe, use `impl B` to return an opaque type, as long as you return a single underlying type
+help: use `dyn`
    |
-LL | trait A { fn g(b: B) -> impl B; }
-   |                         ++++
+LL | trait A { fn g(b: B) -> dyn B; }
+   |                         +++
 
 warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/avoid-ice-on-warning-3.rs:1:19
+  --> $DIR/avoid-ice-on-warning-3.rs:4:19
    |
 LL | trait B { fn f(a: A) -> A; }
    |                   ^
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-   = note: `A` it is not object safe, so it can't be `dyn`
-help: use a new generic type parameter, constrained by `A`
-   |
-LL | trait B { fn f<T: A>(a: T) -> A; }
-   |               ++++++    ~
-help: you can also use an opaque type, but users won't be able to specify the type parameter when calling the `fn`, having to rely exclusively on type inference
-   |
-LL | trait B { fn f(a: impl A) -> A; }
-   |                   ++++
-
-warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/avoid-ice-on-warning-3.rs:1:25
-   |
-LL | trait B { fn f(a: A) -> A; }
-   |                         ^
-   |
-   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
-   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-help: `A` is not object safe, use `impl A` to return an opaque type, as long as you return a single underlying type
-   |
-LL | trait B { fn f(a: A) -> impl A; }
-   |                         ++++
-
-warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/avoid-ice-on-warning-3.rs:1:19
-   |
-LL | trait B { fn f(a: A) -> A; }
-   |                   ^
-   |
-   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
-   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-   = note: `A` it is not object safe, so it can't be `dyn`
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-help: use a new generic type parameter, constrained by `A`
+help: use `dyn`
    |
-LL | trait B { fn f<T: A>(a: T) -> A; }
-   |               ++++++    ~
-help: you can also use an opaque type, but users won't be able to specify the type parameter when calling the `fn`, having to rely exclusively on type inference
-   |
-LL | trait B { fn f(a: impl A) -> A; }
-   |                   ++++
+LL | trait B { fn f(a: dyn A) -> A; }
+   |                   +++
 
 error[E0038]: the trait `A` cannot be made into an object
-  --> $DIR/avoid-ice-on-warning-3.rs:1:19
+  --> $DIR/avoid-ice-on-warning-3.rs:4:19
    |
 LL | trait B { fn f(a: A) -> A; }
    |                   ^ `A` 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/avoid-ice-on-warning-3.rs:9:14
+  --> $DIR/avoid-ice-on-warning-3.rs:12:14
    |
 LL | trait A { fn g(b: B) -> B; }
    |       -      ^ ...because associated function `g` has no `self` parameter
@@ -103,32 +88,27 @@ LL | trait A { fn g(b: B) -> B where Self: Sized; }
    |                           +++++++++++++++++
 
 warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/avoid-ice-on-warning-3.rs:9:19
+  --> $DIR/avoid-ice-on-warning-3.rs:12:19
    |
 LL | trait A { fn g(b: B) -> B; }
    |                   ^
    |
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
-   = note: `B` it is not object safe, so it can't be `dyn`
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
-help: use a new generic type parameter, constrained by `B`
+help: use `dyn`
    |
-LL | trait A { fn g<T: B>(b: T) -> B; }
-   |               ++++++    ~
-help: you can also use an opaque type, but users won't be able to specify the type parameter when calling the `fn`, having to rely exclusively on type inference
-   |
-LL | trait A { fn g(b: impl B) -> B; }
-   |                   ++++
+LL | trait A { fn g(b: dyn B) -> B; }
+   |                   +++
 
 error[E0038]: the trait `B` cannot be made into an object
-  --> $DIR/avoid-ice-on-warning-3.rs:9:19
+  --> $DIR/avoid-ice-on-warning-3.rs:12:19
    |
 LL | trait A { fn g(b: B) -> B; }
    |                   ^ `B` 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/avoid-ice-on-warning-3.rs:1:14
+  --> $DIR/avoid-ice-on-warning-3.rs:4:14
    |
 LL | trait B { fn f(a: A) -> A; }
    |       -      ^ ...because associated function `f` has no `self` parameter

tests/ui/object-safety/avoid-ice-on-warning-3.rs

@@ -1,17 +1,20 @@
+// revisions: old new
+//[old] edition:2015
+//[new] edition:2021
 trait B { fn f(a: A) -> A; }
-//~^ WARN trait objects without an explicit `dyn` are deprecated
-//~| WARN trait objects without an explicit `dyn` are deprecated
-//~| WARN trait objects without an explicit `dyn` are deprecated
-//~| WARN this is accepted in the current edition
-//~| WARN this is accepted in the current edition
-//~| WARN this is accepted in the current edition
-//~| ERROR the trait `A` cannot be made into an object
+//~^ ERROR the trait `A` cannot be made into an object
+//[old]~| WARN trait objects without an explicit `dyn` are deprecated
+//[old]~| WARN trait objects without an explicit `dyn` are deprecated
+//[old]~| WARN trait objects without an explicit `dyn` are deprecated
+//[old]~| WARN this is accepted in the current edition
+//[old]~| WARN this is accepted in the current edition
+//[old]~| WARN this is accepted in the current edition
 trait A { fn g(b: B) -> B; }
-//~^ WARN trait objects without an explicit `dyn` are deprecated
-//~| WARN trait objects without an explicit `dyn` are deprecated
-//~| WARN trait objects without an explicit `dyn` are deprecated
-//~| WARN this is accepted in the current edition
-//~| WARN this is accepted in the current edition
-//~| WARN this is accepted in the current edition
-//~| ERROR the trait `B` cannot be made into an object
+//~^ ERROR the trait `B` cannot be made into an object
+//[old]~| WARN trait objects without an explicit `dyn` are deprecated
+//[old]~| WARN trait objects without an explicit `dyn` are deprecated
+//[old]~| WARN trait objects without an explicit `dyn` are deprecated
+//[old]~| WARN this is accepted in the current edition
+//[old]~| WARN this is accepted in the current edition
+//[old]~| WARN this is accepted in the current edition
 fn main() {}

tests/ui/object-safety/avoid-ice-on-warning.new.stderr

@@ -0,0 +1,15 @@
+error: return types are denoted using `->`
+  --> $DIR/avoid-ice-on-warning.rs:4:23
+   |
+LL | fn call_this<F>(f: F) : Fn(&str) + call_that {}
+   |                       ^ help: use `->` instead
+
+error[E0405]: cannot find trait `call_that` in this scope
+  --> $DIR/avoid-ice-on-warning.rs:4:36
+   |
+LL | fn call_this<F>(f: F) : Fn(&str) + call_that {}
+   |                                    ^^^^^^^^^ not found in this scope
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0405`.

tests/ui/object-safety/avoid-ice-on-warning.old.stderr

@@ -1,17 +1,17 @@
 error: return types are denoted using `->`
-  --> $DIR/avoid-ice-on-warning.rs:1:23
+  --> $DIR/avoid-ice-on-warning.rs:4:23
    |
 LL | fn call_this<F>(f: F) : Fn(&str) + call_that {}
    |                       ^ help: use `->` instead
 
 error[E0405]: cannot find trait `call_that` in this scope
-  --> $DIR/avoid-ice-on-warning.rs:1:36
+  --> $DIR/avoid-ice-on-warning.rs:4:36
    |
 LL | fn call_this<F>(f: F) : Fn(&str) + call_that {}
    |                                    ^^^^^^^^^ not found in this scope
 
 warning: trait objects without an explicit `dyn` are deprecated
-  --> $DIR/avoid-ice-on-warning.rs:1:25
+  --> $DIR/avoid-ice-on-warning.rs:4:25
    |
 LL | fn call_this<F>(f: F) : Fn(&str) + call_that {}
    |                         ^^^^^^^^^^^^^^^^^^^^
@@ -19,10 +19,10 @@ LL | fn call_this<F>(f: F) : Fn(&str) + call_that {}
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `#[warn(bare_trait_objects)]` on by default
-help: `Fn(&str) + call_that` is not object safe, use `impl Fn(&str) + call_that` to return an opaque type, as long as you return a single underlying type
+help: use `dyn`
    |
-LL | fn call_this<F>(f: F) : impl Fn(&str) + call_that {}
-   |                         ++++
+LL | fn call_this<F>(f: F) : dyn Fn(&str) + call_that {}
+   |                         +++
 
 error: aborting due to 2 previous errors; 1 warning emitted
 

tests/ui/object-safety/avoid-ice-on-warning.rs

@@ -1,6 +1,9 @@
+// revisions: old new
+//[old] edition:2015
+//[new] edition:2021
 fn call_this<F>(f: F) : Fn(&str) + call_that {}
 //~^ ERROR return types are denoted using `->`
 //~| ERROR cannot find trait `call_that` in this scope
-//~| WARN trait objects without an explicit `dyn` are deprecated
-//~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+//[old]~| WARN trait objects without an explicit `dyn` are deprecated
+//[old]~| WARN this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
 fn main() {}

tests/ui/object-safety/bare-trait-dont-suggest-dyn.fixed

@@ -1,9 +0,0 @@
-// run-rustfix
-#![deny(bare_trait_objects)]
-fn ord_prefer_dot(s: String) -> impl Ord {
-    //~^ ERROR the trait `Ord` cannot be made into an object
-    (s.starts_with("."), s)
-}
-fn main() {
-    let _ = ord_prefer_dot(String::new());
-}

tests/ui/object-safety/bare-trait-dont-suggest-dyn.new.fixed

@@ -0,0 +1,16 @@
+// revisions: old new
+//[old] edition:2015
+//[new] edition:2021
+//[new] run-rustfix
+// FIXME: the test suite tries to create a crate called `bare_trait_dont_suggest_dyn.new`
+#![crate_name="bare_trait_dont_suggest_dyn"]
+#![deny(bare_trait_objects)]
+fn ord_prefer_dot(s: String) -> impl Ord {
+    //~^ ERROR the trait `Ord` cannot be made into an object
+    //[old]~| ERROR trait objects without an explicit `dyn` are deprecated
+    //[old]~| WARNING this is accepted in the current edition (Rust 2015)
+    (s.starts_with("."), s)
+}
+fn main() {
+    let _ = ord_prefer_dot(String::new());
+}

tests/ui/object-safety/bare-trait-dont-suggest-dyn.new.stderr

@@ -1,5 +1,5 @@
 error[E0038]: the trait `Ord` cannot be made into an object
-  --> $DIR/bare-trait-dont-suggest-dyn.rs:3:33
+  --> $DIR/bare-trait-dont-suggest-dyn.rs:8:33
    |
 LL | fn ord_prefer_dot(s: String) -> Ord {
    |                                 ^^^ `Ord` cannot be made into an object

tests/ui/object-safety/bare-trait-dont-suggest-dyn.old.stderr

@@ -0,0 +1,39 @@
+error: trait objects without an explicit `dyn` are deprecated
+  --> $DIR/bare-trait-dont-suggest-dyn.rs:8:33
+   |
+LL | fn ord_prefer_dot(s: String) -> Ord {
+   |                                 ^^^
+   |
+   = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
+   = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
+note: the lint level is defined here
+  --> $DIR/bare-trait-dont-suggest-dyn.rs:7:9
+   |
+LL | #![deny(bare_trait_objects)]
+   |         ^^^^^^^^^^^^^^^^^^
+help: use `dyn`
+   |
+LL | fn ord_prefer_dot(s: String) -> dyn Ord {
+   |                                 +++
+
+error[E0038]: the trait `Ord` cannot be made into an object
+  --> $DIR/bare-trait-dont-suggest-dyn.rs:8:33
+   |
+LL | fn ord_prefer_dot(s: String) -> Ord {
+   |                                 ^^^ `Ord` 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>
+  --> $SRC_DIR/core/src/cmp.rs:LL:COL
+   |
+   = note: the trait cannot be made into an object because it uses `Self` as a type parameter
+  ::: $SRC_DIR/core/src/cmp.rs:LL:COL
+   |
+   = note: the trait cannot be made into an object because it uses `Self` as a type parameter
+help: consider using an opaque type instead
+   |
+LL | fn ord_prefer_dot(s: String) -> impl Ord {
+   |                                 ++++
+
+error: aborting due to 2 previous errors
+
+For more information about this error, try `rustc --explain E0038`.

tests/ui/object-safety/bare-trait-dont-suggest-dyn.rs

@@ -1,7 +1,14 @@
-// run-rustfix
+// revisions: old new
+//[old] edition:2015
+//[new] edition:2021
+//[new] run-rustfix
+// FIXME: the test suite tries to create a crate called `bare_trait_dont_suggest_dyn.new`
+#![crate_name="bare_trait_dont_suggest_dyn"]
 #![deny(bare_trait_objects)]
 fn ord_prefer_dot(s: String) -> Ord {
     //~^ ERROR the trait `Ord` cannot be made into an object
+    //[old]~| ERROR trait objects without an explicit `dyn` are deprecated
+    //[old]~| WARNING this is accepted in the current edition (Rust 2015)
     (s.starts_with("."), s)
 }
 fn main() {

tests/ui/traits/bound/not-on-bare-trait.stderr

@@ -7,18 +7,10 @@ LL | fn foo(_x: Foo + Send) {
    = warning: this is accepted in the current edition (Rust 2015) but is a hard error in Rust 2021!
    = note: for more information, see <https://doc.rust-lang.org/nightly/edition-guide/rust-2021/warnings-promoted-to-error.html>
    = note: `#[warn(bare_trait_objects)]` on by default
-help: use a new generic type parameter, constrained by `Foo + Send`
+help: use `dyn`
    |
-LL | fn foo<T: Foo + Send>(_x: T) {
-   |       +++++++++++++++     ~
-help: you can also use an opaque type, but users won't be able to specify the type parameter when calling the `fn`, having to rely exclusively on type inference
-   |
-LL | fn foo(_x: impl Foo + Send) {
-   |            ++++
-help: alternatively, use a trait object to accept any type that implements `Foo + Send`, accessing its methods at runtime using dynamic dispatch
-   |
-LL | fn foo(_x: &(dyn Foo + Send)) {
-   |            +++++           +
+LL | fn foo(_x: dyn Foo + Send) {
+   |            +++
 
 error[E0277]: the size for values of type `(dyn Foo + Send + 'static)` cannot be known at compilation time
   --> $DIR/not-on-bare-trait.rs:7:8