Stabilize `#[diagnostic::do_not_recommend]`

This commit seeks to stabilize the `#[diagnostic::do_not_recommend]`
attribute.
This attribute was first proposed as `#[do_not_recommend`] attribute in
RFC 2397 (https://github.com/rust-lang/rfcs/pull/2397). It gives the
crate authors the ability to not suggest to the compiler to not show
certain traits in it's error messages. With the presence of the
`#[diagnostic]` tool attribute namespace it was decided to move the
attribute there, as that lowers the amount of guarantees the compiler
needs to give about the exact way this influences error messages. It
turns the attribute into a hint which can be ignored. In addition to the
original proposed functionality this attribute now also hides the marked
trait in help messages ("This trait is implemented by: ").
The attribute does not accept any argument and can only be placed on
trait implementations. If it is placed somewhere else a lint warning is
emitted and the attribute is otherwise ignored. If an argument is
detected a lint warning is emitted and the argument is ignored. This
follows the rules outlined by the diagnostic namespace.

This attribute allows crates like diesel to improve their error messages
drastically. The most common example here is the following error
message:

```
error[E0277]: the trait bound `&str: Expression` is not satisfied
  --> /home/weiznich/Documents/rust/rust/tests/ui/diagnostic_namespace/do_not_recommend.rs:53:15
   |
LL |     SelectInt.check("bar");
   |               ^^^^^ the trait `Expression` is not implemented for `&str`, which is required by `&str: AsExpression<Integer>`
   |
   = help: the following other types implement trait `Expression`:
             Bound<T>
             SelectInt
note: required for `&str` to implement `AsExpression<Integer>`
  --> /home/weiznich/Documents/rust/rust/tests/ui/diagnostic_namespace/do_not_recommend.rs:26:13
   |
LL | impl<T, ST> AsExpression<ST> for T
   |             ^^^^^^^^^^^^^^^^     ^
LL | where
LL |     T: Expression<SqlType = ST>,
   |        ------------------------ unsatisfied trait bound introduced here
```

By applying the new attribute to the wild card trait implementation of
`AsExpression` for `T: Expression` the error message becomes:

```
error[E0277]: the trait bound `&str: AsExpression<Integer>` is not satisfied
  --> $DIR/as_expression.rs:55:15
   |
LL |     SelectInt.check("bar");
   |               ^^^^^ the trait `AsExpression<Integer>` is not implemented for `&str`
   |
   = help: the trait `AsExpression<Text>` is implemented for `&str`
   = help: for that trait implementation, expected `Text`, found `Integer`
```

which makes it much easier for users to understand that they are facing
a type mismatch.

Other explored example usages included

* This standard library error message: https://github.com/rust-lang/rust/pull/128008
* That bevy derived example:
https://github.com/rust-lang/rust/blob/e1f306899514ea80abc1d1c9f6a57762afb304a3/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.rs (No
more tuple pyramids)

Fixes #51992

41 files changed, 55 insertions, 235 deletions

diff --git a/compiler/rustc_feature/src/accepted.rs b/compiler/rustc_feature/src/accepted.rs
index 21fd11c1c5d..5a9b8c43e74 100644
--- a/compiler/rustc_feature/src/accepted.rs
+++ b/compiler/rustc_feature/src/accepted.rs
@@ -178,6 +178,8 @@ declare_features! (
     (accepted, destructuring_assignment, "1.59.0", Some(71126)),
     /// Allows using the `#[diagnostic]` attribute tool namespace
     (accepted, diagnostic_namespace, "1.78.0", Some(111996)),
+    /// Controls errors in trait implementations.
+    (accepted, do_not_recommend, "CURRENT_RUSTC_VERSION", Some(51992)),
     /// Allows `#[doc(alias = "...")]`.
     (accepted, doc_alias, "1.48.0", Some(50146)),
     /// Allows `..` in tuple (struct) patterns.
diff --git a/compiler/rustc_feature/src/builtin_attrs.rs b/compiler/rustc_feature/src/builtin_attrs.rs
index a065db7f7d0..4b9f62fa764 100644
--- a/compiler/rustc_feature/src/builtin_attrs.rs
+++ b/compiler/rustc_feature/src/builtin_attrs.rs
@@ -1187,10 +1187,9 @@ pub static BUILTIN_ATTRIBUTE_MAP: LazyLock<FxHashMap<Symbol, &BuiltinAttribute>>
         map
     });
 
-pub fn is_stable_diagnostic_attribute(sym: Symbol, features: &Features) -> bool {
+pub fn is_stable_diagnostic_attribute(sym: Symbol, _features: &Features) -> bool {
     match sym {
-        sym::on_unimplemented => true,
-        sym::do_not_recommend => features.do_not_recommend(),
+        sym::on_unimplemented | sym::do_not_recommend => true,
         _ => false,
     }
 }
diff --git a/compiler/rustc_feature/src/unstable.rs b/compiler/rustc_feature/src/unstable.rs
index 6570f9b565f..ebb07195a28 100644
--- a/compiler/rustc_feature/src/unstable.rs
+++ b/compiler/rustc_feature/src/unstable.rs
@@ -462,8 +462,6 @@ declare_features! (
     (unstable, deprecated_suggestion, "1.61.0", Some(94785)),
     /// Allows deref patterns.
     (incomplete, deref_patterns, "1.79.0", Some(87121)),
-    /// Controls errors in trait implementations.
-    (unstable, do_not_recommend, "1.67.0", Some(51992)),
     /// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.
     (unstable, doc_auto_cfg, "1.58.0", Some(43781)),
     /// Allows `#[doc(cfg(...))]`.
diff --git a/compiler/rustc_resolve/src/macros.rs b/compiler/rustc_resolve/src/macros.rs
index edee19c280a..b24e343c58d 100644
--- a/compiler/rustc_resolve/src/macros.rs
+++ b/compiler/rustc_resolve/src/macros.rs
@@ -689,8 +689,7 @@ impl<'ra, 'tcx> Resolver<'ra, 'tcx> {
             && let [namespace, attribute, ..] = &*path.segments
             && namespace.ident.name == sym::diagnostic
             && !(attribute.ident.name == sym::on_unimplemented
-                || (attribute.ident.name == sym::do_not_recommend
-                    && self.tcx.features().do_not_recommend()))
+                || attribute.ident.name == sym::do_not_recommend)
         {
             let distance =
                 edit_distance(attribute.ident.name.as_str(), sym::on_unimplemented.as_str(), 5);
diff --git a/library/core/src/lib.rs b/library/core/src/lib.rs
index 922866f95dc..18bd9bb8118 100644
--- a/library/core/src/lib.rs
+++ b/library/core/src/lib.rs
@@ -108,12 +108,12 @@
 // Library features:
 // tidy-alphabetical-start
 #![cfg_attr(bootstrap, feature(coverage_attribute))]
+#![cfg_attr(bootstrap, feature(do_not_recommend))]
 #![feature(array_ptr_get)]
 #![feature(asm_experimental_arch)]
 #![feature(const_eval_select)]
 #![feature(const_typed_swap)]
 #![feature(core_intrinsics)]
-#![feature(do_not_recommend)]
 #![feature(internal_impls_macro)]
 #![feature(ip)]
 #![feature(is_ascii_octdigit)]
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.current.stderr
index 5d0c1826411..28e7975c7a2 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.current.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.current.stderr
@@ -1,5 +1,5 @@
 error[E0277]: the trait bound `&str: AsExpression<Integer>` is not satisfied
-  --> $DIR/as_expression.rs:57:15
+  --> $DIR/as_expression.rs:55:15
    |
 LL |     SelectInt.check("bar");
    |               ^^^^^ the trait `AsExpression<Integer>` is not implemented for `&str`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.next.stderr
index 1e1eae852f9..1b76669ccb0 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.next.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.next.stderr
@@ -1,5 +1,5 @@
 error[E0277]: the trait bound `&str: AsExpression<<SelectInt as Expression>::SqlType>` is not satisfied
-  --> $DIR/as_expression.rs:57:21
+  --> $DIR/as_expression.rs:55:21
    |
 LL |     SelectInt.check("bar");
    |               ----- ^^^^^ the trait `AsExpression<<SelectInt as Expression>::SqlType>` is not implemented for `&str`
@@ -8,7 +8,7 @@ LL |     SelectInt.check("bar");
    |
    = help: the trait `AsExpression<Text>` is implemented for `&str`
 note: required by a bound in `Foo::check`
-  --> $DIR/as_expression.rs:48:12
+  --> $DIR/as_expression.rs:46:12
    |
 LL |     fn check<T>(&self, _: T) -> <T as AsExpression<<Self as Expression>::SqlType>>::Expression
    |        ----- required by a bound in this associated function
@@ -17,7 +17,7 @@ LL |         T: AsExpression<Self::SqlType>,
    |            ^^^^^^^^^^^^^^^^^^^^^^^^^^^ required by this bound in `Foo::check`
 
 error[E0277]: the trait bound `&str: AsExpression<Integer>` is not satisfied
-  --> $DIR/as_expression.rs:57:15
+  --> $DIR/as_expression.rs:55:15
    |
 LL |     SelectInt.check("bar");
    |               ^^^^^ the trait `AsExpression<Integer>` is not implemented for `&str`
@@ -27,7 +27,7 @@ LL |     SelectInt.check("bar");
    = help: for that trait implementation, expected `Text`, found `Integer`
 
 error[E0271]: type mismatch resolving `<SelectInt as Expression>::SqlType == Text`
-  --> $DIR/as_expression.rs:57:5
+  --> $DIR/as_expression.rs:55:5
    |
 LL |     SelectInt.check("bar");
    |     ^^^^^^^^^^^^^^^^^^^^^^ expected `Text`, found `Integer`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.rs b/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.rs
index 37b4429f694..583b3c4675a 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.rs
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/as_expression.rs
@@ -2,8 +2,6 @@
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
-#![feature(do_not_recommend)]
-
 pub trait Expression {
     type SqlType;
 }
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/do_not_apply_attribute_without_feature_flag.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/do_not_apply_attribute_without_feature_flag.current.stderr
deleted file mode 100644
index 660fc7d2171..00000000000
--- a/tests/ui/diagnostic_namespace/do_not_recommend/do_not_apply_attribute_without_feature_flag.current.stderr
+++ /dev/null
@@ -1,25 +0,0 @@
-error[E0277]: the trait bound `(): Foo` is not satisfied
-  --> $DIR/do_not_apply_attribute_without_feature_flag.rs:22:11
-   |
-LL |     check(());
-   |     ----- ^^ the trait `Foo` is not implemented for `()`
-   |     |
-   |     required by a bound introduced by this call
-   |
-   = help: the following other types implement trait `Foo`:
-             (A, B)
-             (A, B, C)
-             (A,)
-note: required by a bound in `check`
-  --> $DIR/do_not_apply_attribute_without_feature_flag.rs:19:18
-   |
-LL | fn check(a: impl Foo) {}
-   |                  ^^^ required by this bound in `check`
-help: use a unary tuple instead
-   |
-LL |     check(((),));
-   |           +  ++
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/do_not_apply_attribute_without_feature_flag.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/do_not_apply_attribute_without_feature_flag.next.stderr
deleted file mode 100644
index 1cd148186f1..00000000000
--- a/tests/ui/diagnostic_namespace/do_not_recommend/do_not_apply_attribute_without_feature_flag.next.stderr
+++ /dev/null
@@ -1,21 +0,0 @@
-error[E0277]: the trait bound `(): Foo` is not satisfied
-  --> $DIR/do_not_apply_attribute_without_feature_flag.rs:22:11
-   |
-LL |     check(());
-   |     ----- ^^ the trait `Foo` is not implemented for `()`
-   |     |
-   |     required by a bound introduced by this call
-   |
-   = help: the following other types implement trait `Foo`:
-             (A, B)
-             (A, B, C)
-             (A,)
-note: required by a bound in `check`
-  --> $DIR/do_not_apply_attribute_without_feature_flag.rs:19:18
-   |
-LL | fn check(a: impl Foo) {}
-   |                  ^^^ required by this bound in `check`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/do_not_apply_attribute_without_feature_flag.rs b/tests/ui/diagnostic_namespace/do_not_recommend/do_not_apply_attribute_without_feature_flag.rs
deleted file mode 100644
index 9c25069bc7d..00000000000
--- a/tests/ui/diagnostic_namespace/do_not_recommend/do_not_apply_attribute_without_feature_flag.rs
+++ /dev/null
@@ -1,24 +0,0 @@
-//@ revisions: current next
-//@ ignore-compare-mode-next-solver (explicit revisions)
-//@[next] compile-flags: -Znext-solver
-#![allow(unknown_or_malformed_diagnostic_attributes)]
-
-trait Foo {}
-
-#[diagnostic::do_not_recommend]
-impl<A> Foo for (A,) {}
-
-#[diagnostic::do_not_recommend]
-impl<A, B> Foo for (A, B) {}
-
-#[diagnostic::do_not_recommend]
-impl<A, B, C> Foo for (A, B, C) {}
-
-impl Foo for i32 {}
-
-fn check(a: impl Foo) {}
-
-fn main() {
-    check(());
-    //~^ ERROR the trait bound `(): Foo` is not satisfied
-}
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.current.stderr
index 3d004ca559e..47597a5d405 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.current.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.current.stderr
@@ -1,5 +1,5 @@
 warning: `#[diagnostic::do_not_recommend]` does not expect any arguments
-  --> $DIR/does_not_acccept_args.rs:12:1
+  --> $DIR/does_not_acccept_args.rs:10:1
    |
 LL | #[diagnostic::do_not_recommend(not_accepted)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -7,13 +7,13 @@ LL | #[diagnostic::do_not_recommend(not_accepted)]
    = note: `#[warn(unknown_or_malformed_diagnostic_attributes)]` on by default
 
 warning: `#[diagnostic::do_not_recommend]` does not expect any arguments
-  --> $DIR/does_not_acccept_args.rs:16:1
+  --> $DIR/does_not_acccept_args.rs:14:1
    |
 LL | #[diagnostic::do_not_recommend(not_accepted = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` does not expect any arguments
-  --> $DIR/does_not_acccept_args.rs:20:1
+  --> $DIR/does_not_acccept_args.rs:18:1
    |
 LL | #[diagnostic::do_not_recommend(not_accepted(42))]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.next.stderr
index 3d004ca559e..47597a5d405 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.next.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.next.stderr
@@ -1,5 +1,5 @@
 warning: `#[diagnostic::do_not_recommend]` does not expect any arguments
-  --> $DIR/does_not_acccept_args.rs:12:1
+  --> $DIR/does_not_acccept_args.rs:10:1
    |
 LL | #[diagnostic::do_not_recommend(not_accepted)]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -7,13 +7,13 @@ LL | #[diagnostic::do_not_recommend(not_accepted)]
    = note: `#[warn(unknown_or_malformed_diagnostic_attributes)]` on by default
 
 warning: `#[diagnostic::do_not_recommend]` does not expect any arguments
-  --> $DIR/does_not_acccept_args.rs:16:1
+  --> $DIR/does_not_acccept_args.rs:14:1
    |
 LL | #[diagnostic::do_not_recommend(not_accepted = "foo")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` does not expect any arguments
-  --> $DIR/does_not_acccept_args.rs:20:1
+  --> $DIR/does_not_acccept_args.rs:18:1
    |
 LL | #[diagnostic::do_not_recommend(not_accepted(42))]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.rs b/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.rs
index f3295546f34..eeff5e2e6e8 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.rs
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/does_not_acccept_args.rs
@@ -3,8 +3,6 @@
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
-#![feature(do_not_recommend)]
-
 trait Foo {}
 trait Bar {}
 trait Baz {}
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/feature-gate-do_not_recommend.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/feature-gate-do_not_recommend.current.stderr
deleted file mode 100644
index d1deaa6a006..00000000000
--- a/tests/ui/diagnostic_namespace/do_not_recommend/feature-gate-do_not_recommend.current.stderr
+++ /dev/null
@@ -1,15 +0,0 @@
-error[E0277]: the trait bound `u8: Bar` is not satisfied
-  --> $DIR/feature-gate-do_not_recommend.rs:18:11
-   |
-LL |     stuff(1u8);
-   |           ^^^ the trait `Bar` is not implemented for `u8`
-   |
-note: required by a bound in `stuff`
-  --> $DIR/feature-gate-do_not_recommend.rs:15:13
-   |
-LL | fn stuff<T: Bar>(_: T) {}
-   |             ^^^ required by this bound in `stuff`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/feature-gate-do_not_recommend.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/feature-gate-do_not_recommend.next.stderr
deleted file mode 100644
index 5bfcc60edc5..00000000000
--- a/tests/ui/diagnostic_namespace/do_not_recommend/feature-gate-do_not_recommend.next.stderr
+++ /dev/null
@@ -1,17 +0,0 @@
-error[E0277]: the trait bound `u8: Bar` is not satisfied
-  --> $DIR/feature-gate-do_not_recommend.rs:18:11
-   |
-LL |     stuff(1u8);
-   |     ----- ^^^ the trait `Bar` is not implemented for `u8`
-   |     |
-   |     required by a bound introduced by this call
-   |
-note: required by a bound in `stuff`
-  --> $DIR/feature-gate-do_not_recommend.rs:15:13
-   |
-LL | fn stuff<T: Bar>(_: T) {}
-   |             ^^^ required by this bound in `stuff`
-
-error: aborting due to 1 previous error
-
-For more information about this error, try `rustc --explain E0277`.
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/feature-gate-do_not_recommend.rs b/tests/ui/diagnostic_namespace/do_not_recommend/feature-gate-do_not_recommend.rs
deleted file mode 100644
index 4adce112f15..00000000000
--- a/tests/ui/diagnostic_namespace/do_not_recommend/feature-gate-do_not_recommend.rs
+++ /dev/null
@@ -1,20 +0,0 @@
-//@ revisions: current next
-//@ ignore-compare-mode-next-solver (explicit revisions)
-//@[next] compile-flags: -Znext-solver
-#![feature(do_not_recommend)]
-
-pub trait Foo {}
-
-impl Foo for i32 {}
-
-pub trait Bar {}
-
-#[diagnostic::do_not_recommend]
-impl<T: Foo> Bar for T {}
-
-fn stuff<T: Bar>(_: T) {}
-
-fn main() {
-    stuff(1u8);
-    //~^ the trait bound `u8: Bar` is not satisfied
-}
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.current.stderr
index 84ab0827ab6..0b0dac32b39 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.current.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.current.stderr
@@ -1,5 +1,5 @@
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:7:1
+  --> $DIR/incorrect-locations.rs:6:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -7,43 +7,43 @@ LL | #[diagnostic::do_not_recommend]
    = note: `#[warn(unknown_or_malformed_diagnostic_attributes)]` on by default
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:11:1
+  --> $DIR/incorrect-locations.rs:10:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:15:1
+  --> $DIR/incorrect-locations.rs:14:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:19:1
+  --> $DIR/incorrect-locations.rs:18:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:23:1
+  --> $DIR/incorrect-locations.rs:22:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:27:1
+  --> $DIR/incorrect-locations.rs:26:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:31:1
+  --> $DIR/incorrect-locations.rs:30:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:35:1
+  --> $DIR/incorrect-locations.rs:34:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.next.stderr
index 84ab0827ab6..0b0dac32b39 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.next.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.next.stderr
@@ -1,5 +1,5 @@
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:7:1
+  --> $DIR/incorrect-locations.rs:6:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -7,43 +7,43 @@ LL | #[diagnostic::do_not_recommend]
    = note: `#[warn(unknown_or_malformed_diagnostic_attributes)]` on by default
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:11:1
+  --> $DIR/incorrect-locations.rs:10:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:15:1
+  --> $DIR/incorrect-locations.rs:14:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:19:1
+  --> $DIR/incorrect-locations.rs:18:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:23:1
+  --> $DIR/incorrect-locations.rs:22:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:27:1
+  --> $DIR/incorrect-locations.rs:26:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:31:1
+  --> $DIR/incorrect-locations.rs:30:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
 warning: `#[diagnostic::do_not_recommend]` can only be placed on trait implementations
-  --> $DIR/incorrect-locations.rs:35:1
+  --> $DIR/incorrect-locations.rs:34:1
    |
 LL | #[diagnostic::do_not_recommend]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.rs b/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.rs
index daacf55ea79..014be580f61 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.rs
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/incorrect-locations.rs
@@ -2,7 +2,6 @@
 //@ revisions: current next
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
-#![feature(do_not_recommend)]
 
 #[diagnostic::do_not_recommend]
 //~^WARN `#[diagnostic::do_not_recommend]` can only be placed
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/nested.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/nested.current.stderr
index 2e08a679360..b14c68d6897 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/nested.current.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/nested.current.stderr
@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `(): Root` is not satisfied
-  --> $DIR/nested.rs:23:18
+  --> $DIR/nested.rs:21:18
    |
 LL |     needs_root::<()>();
    |                  ^^ the trait `Root` is not implemented for `()`
    |
 note: required by a bound in `needs_root`
-  --> $DIR/nested.rs:20:18
+  --> $DIR/nested.rs:18:18
    |
 LL | fn needs_root<T: Root>() {}
    |                  ^^^^ required by this bound in `needs_root`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/nested.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/nested.next.stderr
index 2e08a679360..b14c68d6897 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/nested.next.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/nested.next.stderr
@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `(): Root` is not satisfied
-  --> $DIR/nested.rs:23:18
+  --> $DIR/nested.rs:21:18
    |
 LL |     needs_root::<()>();
    |                  ^^ the trait `Root` is not implemented for `()`
    |
 note: required by a bound in `needs_root`
-  --> $DIR/nested.rs:20:18
+  --> $DIR/nested.rs:18:18
    |
 LL | fn needs_root<T: Root>() {}
    |                  ^^^^ required by this bound in `needs_root`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/nested.rs b/tests/ui/diagnostic_namespace/do_not_recommend/nested.rs
index d499cff9f56..6534157d1fb 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/nested.rs
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/nested.rs
@@ -2,8 +2,6 @@
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
-#![feature(do_not_recommend)]
-
 trait Root {}
 trait DontRecommend {}
 trait Other {}
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/simple.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/simple.current.stderr
index 729cb5694e2..884b13c17b8 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/simple.current.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/simple.current.stderr
@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `*mut (): Foo` is not satisfied
-  --> $DIR/simple.rs:17:17
+  --> $DIR/simple.rs:15:17
    |
 LL |     needs_foo::<*mut ()>();
    |                 ^^^^^^^ the trait `Foo` is not implemented for `*mut ()`
    |
 note: required by a bound in `needs_foo`
-  --> $DIR/simple.rs:12:17
+  --> $DIR/simple.rs:10:17
    |
 LL | fn needs_foo<T: Foo>() {}
    |                 ^^^ required by this bound in `needs_foo`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/simple.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/simple.next.stderr
index 729cb5694e2..884b13c17b8 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/simple.next.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/simple.next.stderr
@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `*mut (): Foo` is not satisfied
-  --> $DIR/simple.rs:17:17
+  --> $DIR/simple.rs:15:17
    |
 LL |     needs_foo::<*mut ()>();
    |                 ^^^^^^^ the trait `Foo` is not implemented for `*mut ()`
    |
 note: required by a bound in `needs_foo`
-  --> $DIR/simple.rs:12:17
+  --> $DIR/simple.rs:10:17
    |
 LL | fn needs_foo<T: Foo>() {}
    |                 ^^^ required by this bound in `needs_foo`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/simple.rs b/tests/ui/diagnostic_namespace/do_not_recommend/simple.rs
index 780649b009c..6bca2b724d2 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/simple.rs
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/simple.rs
@@ -2,8 +2,6 @@
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
-#![feature(do_not_recommend)]
-
 trait Foo {}
 
 #[diagnostic::do_not_recommend]
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/stacked.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/stacked.current.stderr
index 41a10a61e1d..d8605806395 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/stacked.current.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/stacked.current.stderr
@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `(): Root` is not satisfied
-  --> $DIR/stacked.rs:19:18
+  --> $DIR/stacked.rs:17:18
    |
 LL |     needs_root::<()>();
    |                  ^^ the trait `Root` is not implemented for `()`
    |
 note: required by a bound in `needs_root`
-  --> $DIR/stacked.rs:16:18
+  --> $DIR/stacked.rs:14:18
    |
 LL | fn needs_root<T: Root>() {}
    |                  ^^^^ required by this bound in `needs_root`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/stacked.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/stacked.next.stderr
index 41a10a61e1d..d8605806395 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/stacked.next.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/stacked.next.stderr
@@ -1,11 +1,11 @@
 error[E0277]: the trait bound `(): Root` is not satisfied
-  --> $DIR/stacked.rs:19:18
+  --> $DIR/stacked.rs:17:18
    |
 LL |     needs_root::<()>();
    |                  ^^ the trait `Root` is not implemented for `()`
    |
 note: required by a bound in `needs_root`
-  --> $DIR/stacked.rs:16:18
+  --> $DIR/stacked.rs:14:18
    |
 LL | fn needs_root<T: Root>() {}
    |                  ^^^^ required by this bound in `needs_root`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/stacked.rs b/tests/ui/diagnostic_namespace/do_not_recommend/stacked.rs
index fc355bdc4e2..842e04b9d90 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/stacked.rs
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/stacked.rs
@@ -2,8 +2,6 @@
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
-#![feature(do_not_recommend)]
-
 trait Root {}
 trait DontRecommend {}
 trait Other {}
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.current.stderr
index ca9a6ebc1c4..95ccbb92a89 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.current.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.current.stderr
@@ -1,5 +1,5 @@
 error[E0277]: the trait bound `(): Foo` is not satisfied
-  --> $DIR/supress_suggestions_in_help.rs:23:11
+  --> $DIR/supress_suggestions_in_help.rs:21:11
    |
 LL |     check(());
    |     ----- ^^ the trait `Foo` is not implemented for `()`
@@ -8,7 +8,7 @@ LL |     check(());
    |
    = help: the trait `Foo` is implemented for `i32`
 note: required by a bound in `check`
-  --> $DIR/supress_suggestions_in_help.rs:20:18
+  --> $DIR/supress_suggestions_in_help.rs:18:18
    |
 LL | fn check(a: impl Foo) {}
    |                  ^^^ required by this bound in `check`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.next.stderr
index ca9a6ebc1c4..95ccbb92a89 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.next.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.next.stderr
@@ -1,5 +1,5 @@
 error[E0277]: the trait bound `(): Foo` is not satisfied
-  --> $DIR/supress_suggestions_in_help.rs:23:11
+  --> $DIR/supress_suggestions_in_help.rs:21:11
    |
 LL |     check(());
    |     ----- ^^ the trait `Foo` is not implemented for `()`
@@ -8,7 +8,7 @@ LL |     check(());
    |
    = help: the trait `Foo` is implemented for `i32`
 note: required by a bound in `check`
-  --> $DIR/supress_suggestions_in_help.rs:20:18
+  --> $DIR/supress_suggestions_in_help.rs:18:18
    |
 LL | fn check(a: impl Foo) {}
    |                  ^^^ required by this bound in `check`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.rs b/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.rs
index ef6f255c351..2c7c1516123 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.rs
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/supress_suggestions_in_help.rs
@@ -2,8 +2,6 @@
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
-#![feature(do_not_recommend)]
-
 trait Foo {}
 
 #[diagnostic::do_not_recommend]
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.current.stderr
index bcede8a255f..b53febbb71a 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.current.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.current.stderr
@@ -1,11 +1,11 @@
 error[E0277]: Very important message!
-  --> $DIR/type_mismatch.rs:25:14
+  --> $DIR/type_mismatch.rs:23:14
    |
 LL |     verify::<u8>();
    |              ^^ the trait `TheImportantOne` is not implemented for `u8`
    |
 note: required by a bound in `verify`
-  --> $DIR/type_mismatch.rs:22:14
+  --> $DIR/type_mismatch.rs:20:14
    |
 LL | fn verify<T: TheImportantOne>() {}
    |              ^^^^^^^^^^^^^^^ required by this bound in `verify`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.next.stderr
index bcede8a255f..b53febbb71a 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.next.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.next.stderr
@@ -1,11 +1,11 @@
 error[E0277]: Very important message!
-  --> $DIR/type_mismatch.rs:25:14
+  --> $DIR/type_mismatch.rs:23:14
    |
 LL |     verify::<u8>();
    |              ^^ the trait `TheImportantOne` is not implemented for `u8`
    |
 note: required by a bound in `verify`
-  --> $DIR/type_mismatch.rs:22:14
+  --> $DIR/type_mismatch.rs:20:14
    |
 LL | fn verify<T: TheImportantOne>() {}
    |              ^^^^^^^^^^^^^^^ required by this bound in `verify`
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.rs b/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.rs
index d6721ccc848..7f30fdb06c7 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.rs
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/type_mismatch.rs
@@ -2,8 +2,6 @@
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
-#![feature(do_not_recommend)]
-
 #[diagnostic::on_unimplemented(message = "Very important message!")]
 trait TheImportantOne {}
 
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/unstable-feature.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/unstable-feature.current.stderr
deleted file mode 100644
index fdea9eacae1..00000000000
--- a/tests/ui/diagnostic_namespace/do_not_recommend/unstable-feature.current.stderr
+++ /dev/null
@@ -1,14 +0,0 @@
-error: unknown diagnostic attribute
-  --> $DIR/unstable-feature.rs:7:15
-   |
-LL | #[diagnostic::do_not_recommend]
-   |               ^^^^^^^^^^^^^^^^
-   |
-note: the lint level is defined here
-  --> $DIR/unstable-feature.rs:4:9
-   |
-LL | #![deny(unknown_or_malformed_diagnostic_attributes)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 1 previous error
-
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/unstable-feature.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/unstable-feature.next.stderr
deleted file mode 100644
index fdea9eacae1..00000000000
--- a/tests/ui/diagnostic_namespace/do_not_recommend/unstable-feature.next.stderr
+++ /dev/null
@@ -1,14 +0,0 @@
-error: unknown diagnostic attribute
-  --> $DIR/unstable-feature.rs:7:15
-   |
-LL | #[diagnostic::do_not_recommend]
-   |               ^^^^^^^^^^^^^^^^
-   |
-note: the lint level is defined here
-  --> $DIR/unstable-feature.rs:4:9
-   |
-LL | #![deny(unknown_or_malformed_diagnostic_attributes)]
-   |         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
-
-error: aborting due to 1 previous error
-
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/unstable-feature.rs b/tests/ui/diagnostic_namespace/do_not_recommend/unstable-feature.rs
deleted file mode 100644
index 7a67f67b67f..00000000000
--- a/tests/ui/diagnostic_namespace/do_not_recommend/unstable-feature.rs
+++ /dev/null
@@ -1,11 +0,0 @@
-//@ revisions: current next
-//@ ignore-compare-mode-next-solver (explicit revisions)
-//@[next] compile-flags: -Znext-solver
-#![deny(unknown_or_malformed_diagnostic_attributes)]
-trait Foo {}
-
-#[diagnostic::do_not_recommend]
-//~^ ERROR unknown diagnostic attribute [unknown_or_malformed_diagnostic_attributes]
-impl Foo for i32 {}
-
-fn main() {}
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.current.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.current.stderr
index c2874cf4594..a8429ff60f8 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.current.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.current.stderr
@@ -1,5 +1,5 @@
 error: lifetime may not live long enough
-  --> $DIR/with_lifetime.rs:19:5
+  --> $DIR/with_lifetime.rs:17:5
    |
 LL | fn foo<'a>(a: &'a ()) {
    |        -- lifetime `'a` defined here
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.next.stderr b/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.next.stderr
index c2874cf4594..a8429ff60f8 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.next.stderr
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.next.stderr
@@ -1,5 +1,5 @@
 error: lifetime may not live long enough
-  --> $DIR/with_lifetime.rs:19:5
+  --> $DIR/with_lifetime.rs:17:5
    |
 LL | fn foo<'a>(a: &'a ()) {
    |        -- lifetime `'a` defined here
diff --git a/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.rs b/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.rs
index 9aaf7f33ecd..6a67d83d5fe 100644
--- a/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.rs
+++ b/tests/ui/diagnostic_namespace/do_not_recommend/with_lifetime.rs
@@ -2,8 +2,6 @@
 //@ ignore-compare-mode-next-solver (explicit revisions)
 //@[next] compile-flags: -Znext-solver
 
-#![feature(do_not_recommend)]
-
 trait Root {}
 trait DontRecommend {}