Stabilize the #[diagnostic] namespace and #[diagnostic::on_unimplemented] attribute

This PR stabilizes the `#[diagnostic]` attribute namespace and a minimal
option of the `#[diagnostic::on_unimplemented]` attribute.

The `#[diagnostic]` attribute namespace is meant to provide a home for
attributes that allow users to influence error messages emitted by the
compiler. The compiler is not guaranteed to use any of this hints,
however it should accept any (non-)existing attribute in this namespace
and potentially emit lint-warnings for unused attributes and options.
This is meant to allow discarding certain attributes/options in the
future to allow fundamental changes to the compiler without the need to
keep then non-meaningful options working.

The `#[diagnostic::on_unimplemented]` attribute is allowed to appear
on a trait definition. This allows crate authors to hint the compiler
to emit a specific error message if a certain trait is not implemented.
For the `#[diagnostic::on_unimplemented]` attribute the following
options are implemented:

* `message` which provides the text for the top level error message
* `label` which provides the text for the label shown inline in the
broken code in the error message
* `note` which provides additional notes.

The `note` option can appear several times, which results in several
note messages being emitted. If any of the other options appears several
times the first occurrence of the relevant option specifies the actually
used value. Any other occurrence generates an lint warning. For any
other non-existing option a lint-warning is generated.

All three options accept a text as argument. This text is allowed to
contain format parameters referring to generic argument or `Self` by
name via the `{Self}` or `{NameOfGenericArgument}` syntax. For any
non-existing argument a lint warning is generated.

Tracking issue: rust-lang#111996

Author: weiznich

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -203,14 +203,6 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
                 );
             }
         }
-        if !attr.is_doc_comment()
-            && let [seg, _] = attr.get_normal_item().path.segments.as_slice()
-            && seg.ident.name == sym::diagnostic
-            && !self.features.diagnostic_namespace
-        {
-            let msg = "`#[diagnostic]` attribute name space is experimental";
-            gate!(self, diagnostic_namespace, seg.ident.span, msg);
-        }
 
         // Emit errors for non-staged-api crates.
         if !self.features.staged_api {

compiler/rustc_feature/src/accepted.rs

@@ -146,6 +146,8 @@ declare_features! (
     (accepted, derive_default_enum, "1.62.0", Some(86985)),
     /// Allows the use of destructuring assignments.
     (accepted, destructuring_assignment, "1.59.0", Some(71126)),
+    /// Allows using the `#[diagnostic]` attribute tool namespace
+    (accepted, diagnostic_namespace, "CURRENT_RUSTC_VERSION", Some(111996)),
     /// Allows `#[doc(alias = "...")]`.
     (accepted, doc_alias, "1.48.0", Some(50146)),
     /// Allows `..` in tuple (struct) patterns.

compiler/rustc_feature/src/unstable.rs

@@ -434,8 +434,6 @@ declare_features! (
     (unstable, deprecated_safe, "1.61.0", Some(94978)),
     /// Allows having using `suggestion` in the `#[deprecated]` attribute.
     (unstable, deprecated_suggestion, "1.61.0", Some(94785)),
-    /// Allows using the `#[diagnostic]` attribute tool namespace
-    (unstable, diagnostic_namespace, "1.73.0", Some(111996)),
     /// Controls errors in trait implementations.
     (unstable, do_not_recommend, "1.67.0", Some(51992)),
     /// Tells rustdoc to automatically generate `#[doc(cfg(...))]`.

library/core/src/lib.rs

@@ -202,6 +202,7 @@
 //
 // Language features:
 // tidy-alphabetical-start
+#![cfg_attr(bootstrap, feature(diagnostic_namespace))]
 #![cfg_attr(bootstrap, feature(platform_intrinsics))]
 #![feature(abi_unadjusted)]
 #![feature(adt_const_params)]
@@ -223,7 +224,6 @@
 #![feature(const_trait_impl)]
 #![feature(decl_macro)]
 #![feature(deprecated_suggestion)]
-#![feature(diagnostic_namespace)]
 #![feature(doc_cfg)]
 #![feature(doc_cfg_hide)]
 #![feature(doc_notable_trait)]

src/doc/unstable-book/src/language-features/diagnostic-namespace.md

@@ -1,4 +1,3 @@
-#![feature(diagnostic_namespace)]
 //@ check-pass
 //@ aux-build:proc-macro-helper.rs
 

tests/ui/diagnostic_namespace/existing_proc_macros.rs

@@ -1,4 +1,3 @@
-#![feature(diagnostic_namespace)]
 //@ check-pass
 #[diagnostic::non_existing_attribute]
 //~^WARN unknown diagnostic attribute

tests/ui/diagnostic_namespace/feature-gate-diagnostic_namespace.rs

@@ -1,13 +1,13 @@
 warning: unknown diagnostic attribute
-  --> $DIR/non_existing_attributes_accepted.rs:3:15
+  --> $DIR/non_existing_attributes_accepted.rs:2:15
    |
 LL | #[diagnostic::non_existing_attribute]
    |               ^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(unknown_or_malformed_diagnostic_attributes)]` on by default
 
 warning: unknown diagnostic attribute
-  --> $DIR/non_existing_attributes_accepted.rs:8:15
+  --> $DIR/non_existing_attributes_accepted.rs:7:15
    |
 LL | #[diagnostic::non_existing_attribute(with_option = "foo")]
    |               ^^^^^^^^^^^^^^^^^^^^^^

tests/ui/diagnostic_namespace/feature-gate-diagnostic_namespace.stderr

@@ -1,5 +1,3 @@
-#![feature(diagnostic_namespace)]
-
 #[diagnostic::on_unimplemented(
     message = "Message",
     note = "Note",

tests/ui/diagnostic_namespace/non_existing_attributes_accepted.rs

@@ -1,5 +1,3 @@
-#![feature(diagnostic_namespace)]
-
 #[diagnostic::on_unimplemented(
     on(_Self = "&str"),
     //~^WARN malformed `on_unimplemented` attribute

tests/ui/diagnostic_namespace/non_existing_attributes_accepted.stderr

@@ -1,5 +1,3 @@
-#![feature(diagnostic_namespace)]
-
 #[diagnostic::on_unimplemented(unsupported = "foo")]
 //~^WARN malformed `on_unimplemented` attribute
 //~|WARN malformed `on_unimplemented` attribute

tests/ui/diagnostic_namespace/on_unimplemented/auxiliary/other.rs

@@ -1,61 +1,61 @@
 warning: `#[diagnostic::on_unimplemented]` can only be applied to trait definitions
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:8:1
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:6:1
    |
 LL | #[diagnostic::on_unimplemented(message = "Baz")]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = note: `#[warn(unknown_or_malformed_diagnostic_attributes)]` on by default
 
 warning: malformed `on_unimplemented` attribute
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:3:32
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:1:32
    |
 LL | #[diagnostic::on_unimplemented(unsupported = "foo")]
    |                                ^^^^^^^^^^^^^^^^^^^ invalid option found here
    |
    = help: only `message`, `note` and `label` are allowed as options
 
 warning: malformed `on_unimplemented` attribute
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:12:50
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:10:50
    |
 LL | #[diagnostic::on_unimplemented(message = "Boom", unsupported = "Bar")]
    |                                                  ^^^^^^^^^^^^^^^^^^^ invalid option found here
    |
    = help: only `message`, `note` and `label` are allowed as options
 
 warning: malformed `on_unimplemented` attribute
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:17:50
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:15:50
    |
 LL | #[diagnostic::on_unimplemented(message = "Boom", on(_Self = "i32", message = "whatever"))]
    |                                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid option found here
    |
    = help: only `message`, `note` and `label` are allowed as options
 
 warning: malformed `on_unimplemented` attribute
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:22:32
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:20:32
    |
 LL | #[diagnostic::on_unimplemented = "boom"]
    |                                ^^^^^^^^ invalid option found here
    |
    = help: only `message`, `note` and `label` are allowed as options
 
 warning: missing options for `on_unimplemented` attribute
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:26:1
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:24:1
    |
 LL | #[diagnostic::on_unimplemented]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: at least one of the `message`, `note` and `label` options are expected
 
 warning: there is no parameter `DoesNotExist` on trait `Test`
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:31:32
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:29:32
    |
 LL | #[diagnostic::on_unimplemented(message = "{DoesNotExist}")]
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
    |
    = help: expect either a generic argument name or `{Self}` as format argument
 
 warning: malformed `on_unimplemented` attribute
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:3:32
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:1:32
    |
 LL | #[diagnostic::on_unimplemented(unsupported = "foo")]
    |                                ^^^^^^^^^^^^^^^^^^^ invalid option found here
@@ -64,26 +64,26 @@ LL | #[diagnostic::on_unimplemented(unsupported = "foo")]
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0277]: the trait bound `i32: Foo` is not satisfied
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:43:14
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:41:14
    |
 LL |     take_foo(1_i32);
    |     -------- ^^^^^ the trait `Foo` is not implemented for `i32`
    |     |
    |     required by a bound introduced by this call
    |
 help: this trait has no implementations, consider adding one
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:6:1
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:4:1
    |
 LL | trait Foo {}
    | ^^^^^^^^^
 note: required by a bound in `take_foo`
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:36:21
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:34:21
    |
 LL | fn take_foo(_: impl Foo) {}
    |                     ^^^ required by this bound in `take_foo`
 
 warning: malformed `on_unimplemented` attribute
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:12:50
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:10:50
    |
 LL | #[diagnostic::on_unimplemented(message = "Boom", unsupported = "Bar")]
    |                                                  ^^^^^^^^^^^^^^^^^^^ invalid option found here
@@ -92,26 +92,26 @@ LL | #[diagnostic::on_unimplemented(message = "Boom", unsupported = "Bar")]
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0277]: Boom
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:45:14
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:43:14
    |
 LL |     take_baz(1_i32);
    |     -------- ^^^^^ the trait `Baz` is not implemented for `i32`
    |     |
    |     required by a bound introduced by this call
    |
 help: this trait has no implementations, consider adding one
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:15:1
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:13:1
    |
 LL | trait Baz {}
    | ^^^^^^^^^
 note: required by a bound in `take_baz`
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:37:21
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:35:21
    |
 LL | fn take_baz(_: impl Baz) {}
    |                     ^^^ required by this bound in `take_baz`
 
 warning: malformed `on_unimplemented` attribute
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:17:50
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:15:50
    |
 LL | #[diagnostic::on_unimplemented(message = "Boom", on(_Self = "i32", message = "whatever"))]
    |                                                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ invalid option found here
@@ -120,26 +120,26 @@ LL | #[diagnostic::on_unimplemented(message = "Boom", on(_Self = "i32", message
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0277]: Boom
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:47:15
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:45:15
    |
 LL |     take_boom(1_i32);
    |     --------- ^^^^^ the trait `Boom` is not implemented for `i32`
    |     |
    |     required by a bound introduced by this call
    |
 help: this trait has no implementations, consider adding one
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:20:1
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:18:1
    |
 LL | trait Boom {}
    | ^^^^^^^^^^
 note: required by a bound in `take_boom`
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:38:22
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:36:22
    |
 LL | fn take_boom(_: impl Boom) {}
    |                      ^^^^ required by this bound in `take_boom`
 
 warning: missing options for `on_unimplemented` attribute
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:26:1
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:24:1
    |
 LL | #[diagnostic::on_unimplemented]
    | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -148,26 +148,26 @@ LL | #[diagnostic::on_unimplemented]
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0277]: the trait bound `i32: Whatever` is not satisfied
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:49:19
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:47:19
    |
 LL |     take_whatever(1_i32);
    |     ------------- ^^^^^ the trait `Whatever` is not implemented for `i32`
    |     |
    |     required by a bound introduced by this call
    |
 help: this trait has no implementations, consider adding one
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:29:1
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:27:1
    |
 LL | trait Whatever {}
    | ^^^^^^^^^^^^^^
 note: required by a bound in `take_whatever`
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:39:26
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:37:26
    |
 LL | fn take_whatever(_: impl Whatever) {}
    |                          ^^^^^^^^ required by this bound in `take_whatever`
 
 warning: there is no parameter `DoesNotExist` on trait `Test`
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:31:32
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:29:32
    |
 LL | #[diagnostic::on_unimplemented(message = "{DoesNotExist}")]
    |                                ^^^^^^^^^^^^^^^^^^^^^^^^^^
@@ -176,20 +176,20 @@ LL | #[diagnostic::on_unimplemented(message = "{DoesNotExist}")]
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0277]: {DoesNotExist}
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:51:15
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:49:15
    |
 LL |     take_test(());
    |     --------- ^^ the trait `Test` is not implemented for `()`
    |     |
    |     required by a bound introduced by this call
    |
 help: this trait has no implementations, consider adding one
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:34:1
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:32:1
    |
 LL | trait Test {}
    | ^^^^^^^^^^
 note: required by a bound in `take_test`
-  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:40:22
+  --> $DIR/do_not_fail_parsing_on_invalid_options_1.rs:38:22
    |
 LL | fn take_test(_: impl Test) {}
    |                      ^^^^ required by this bound in `take_test`

tests/ui/diagnostic_namespace/on_unimplemented/do_not_accept_options_of_the_internal_rustc_attribute.rs

@@ -1,5 +1,3 @@
-#![feature(diagnostic_namespace)]
-
 #[diagnostic::on_unimplemented(
     if(Self = "()"),
     //~^WARN malformed `on_unimplemented` attribute

tests/ui/diagnostic_namespace/on_unimplemented/do_not_accept_options_of_the_internal_rustc_attribute.stderr

@@ -1,5 +1,5 @@
 warning: malformed `on_unimplemented` attribute
-  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:4:5
+  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:2:5
    |
 LL |     if(Self = "()"),
    |     ^^^^^^^^^^^^^^^ invalid option found here
@@ -8,7 +8,7 @@ LL |     if(Self = "()"),
    = note: `#[warn(unknown_or_malformed_diagnostic_attributes)]` on by default
 
 warning: `message` is ignored due to previous definition of `message`
-  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:10:32
+  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:8:32
    |
 LL |     message = "custom message",
    |     -------------------------- `message` is first declared here
@@ -17,7 +17,7 @@ LL | #[diagnostic::on_unimplemented(message = "fallback!!")]
    |                                ^^^^^^^^^^^^^^^^^^^^^^ `message` is already declared here
 
 warning: malformed `on_unimplemented` attribute
-  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:4:5
+  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:2:5
    |
 LL |     if(Self = "()"),
    |     ^^^^^^^^^^^^^^^ invalid option found here
@@ -26,7 +26,7 @@ LL |     if(Self = "()"),
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: `message` is ignored due to previous definition of `message`
-  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:10:32
+  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:8:32
    |
 LL |     message = "custom message",
    |     -------------------------- `message` is first declared here
@@ -37,7 +37,7 @@ LL | #[diagnostic::on_unimplemented(message = "fallback!!")]
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0277]: custom message
-  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:20:15
+  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:18:15
    |
 LL |     takes_foo(());
    |     --------- ^^ fallback label
@@ -48,12 +48,12 @@ LL |     takes_foo(());
    = note: custom note
    = note: fallback note
 help: this trait has no implementations, consider adding one
-  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:15:1
+  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:13:1
    |
 LL | trait Foo {}
    | ^^^^^^^^^
 note: required by a bound in `takes_foo`
-  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:17:22
+  --> $DIR/ignore_unsupported_options_and_continue_to_use_fallback.rs:15:22
    |
 LL | fn takes_foo(_: impl Foo) {}
    |                      ^^^ required by this bound in `takes_foo`

tests/ui/diagnostic_namespace/on_unimplemented/do_not_fail_parsing_on_invalid_options_1.rs

@@ -1,5 +1,3 @@
-#![feature(diagnostic_namespace)]
-
 #[diagnostic::on_unimplemented(message = "Foo", label = "Bar", note = "Baz", note = "Boom")]
 trait Foo {}
 

tests/ui/diagnostic_namespace/on_unimplemented/do_not_fail_parsing_on_invalid_options_1.stderr

@@ -1,5 +1,5 @@
 error[E0277]: Foo
-  --> $DIR/multiple_notes.rs:14:15
+  --> $DIR/multiple_notes.rs:12:15
    |
 LL |     takes_foo(());
    |     --------- ^^ Bar
@@ -10,18 +10,18 @@ LL |     takes_foo(());
    = note: Baz
    = note: Boom
 help: this trait has no implementations, consider adding one
-  --> $DIR/multiple_notes.rs:4:1
+  --> $DIR/multiple_notes.rs:2:1
    |
 LL | trait Foo {}
    | ^^^^^^^^^
 note: required by a bound in `takes_foo`
-  --> $DIR/multiple_notes.rs:10:22
+  --> $DIR/multiple_notes.rs:8:22
    |
 LL | fn takes_foo(_: impl Foo) {}
    |                      ^^^ required by this bound in `takes_foo`
 
 error[E0277]: Bar
-  --> $DIR/multiple_notes.rs:16:15
+  --> $DIR/multiple_notes.rs:14:15
    |
 LL |     takes_bar(());
    |     --------- ^^ Foo
@@ -32,12 +32,12 @@ LL |     takes_bar(());
    = note: Baz
    = note: Baz2
 help: this trait has no implementations, consider adding one
-  --> $DIR/multiple_notes.rs:8:1
+  --> $DIR/multiple_notes.rs:6:1
    |
 LL | trait Bar {}
    | ^^^^^^^^^
 note: required by a bound in `takes_bar`
-  --> $DIR/multiple_notes.rs:11:22
+  --> $DIR/multiple_notes.rs:9:22
    |
 LL | fn takes_bar(_: impl Bar) {}
    |                      ^^^ required by this bound in `takes_bar`

tests/ui/diagnostic_namespace/on_unimplemented/feature-gate-diagnostic_on_unimplemented.rs

@@ -1,5 +1,3 @@
-#![feature(diagnostic_namespace)]
-
 #[diagnostic::on_unimplemented(message = "Foo", label = "Bar", note = "Baz")]
 trait Foo {}
 

tests/ui/diagnostic_namespace/on_unimplemented/feature-gate-diagnostic_on_unimplemented.stderr

@@ -1,5 +1,5 @@
 error[E0277]: Foo
-  --> $DIR/on_unimplemented_simple.rs:9:15
+  --> $DIR/on_unimplemented_simple.rs:7:15
    |
 LL |     takes_foo(());
    |     --------- ^^ Bar
@@ -9,12 +9,12 @@ LL |     takes_foo(());
    = help: the trait `Foo` is not implemented for `()`
    = note: Baz
 help: this trait has no implementations, consider adding one
-  --> $DIR/on_unimplemented_simple.rs:4:1
+  --> $DIR/on_unimplemented_simple.rs:2:1
    |
 LL | trait Foo {}
    | ^^^^^^^^^
 note: required by a bound in `takes_foo`
-  --> $DIR/on_unimplemented_simple.rs:6:22
+  --> $DIR/on_unimplemented_simple.rs:4:22
    |
 LL | fn takes_foo(_: impl Foo) {}
    |                      ^^^ required by this bound in `takes_foo`

tests/ui/diagnostic_namespace/on_unimplemented/ignore_unsupported_options_and_continue_to_use_fallback.rs

@@ -1,5 +1,3 @@
-#![feature(diagnostic_namespace)]
-
 #[diagnostic::on_unimplemented(
     message = "first message",
     label = "first label",

tests/ui/diagnostic_namespace/on_unimplemented/ignore_unsupported_options_and_continue_to_use_fallback.stderr

@@ -1,5 +1,5 @@
 warning: `message` is ignored due to previous definition of `message`
-  --> $DIR/report_warning_on_duplicated_options.rs:9:5
+  --> $DIR/report_warning_on_duplicated_options.rs:7:5
    |
 LL |     message = "first message",
    |     ------------------------- `message` is first declared here
@@ -10,7 +10,7 @@ LL |     message = "second message",
    = note: `#[warn(unknown_or_malformed_diagnostic_attributes)]` on by default
 
 warning: `label` is ignored due to previous definition of `label`
-  --> $DIR/report_warning_on_duplicated_options.rs:12:5
+  --> $DIR/report_warning_on_duplicated_options.rs:10:5
    |
 LL |     label = "first label",
    |     --------------------- `label` is first declared here
@@ -19,7 +19,7 @@ LL |     label = "second label",
    |     ^^^^^^^^^^^^^^^^^^^^^^ `label` is already declared here
 
 warning: `message` is ignored due to previous definition of `message`
-  --> $DIR/report_warning_on_duplicated_options.rs:9:5
+  --> $DIR/report_warning_on_duplicated_options.rs:7:5
    |
 LL |     message = "first message",
    |     ------------------------- `message` is first declared here
@@ -30,7 +30,7 @@ LL |     message = "second message",
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 warning: `label` is ignored due to previous definition of `label`
-  --> $DIR/report_warning_on_duplicated_options.rs:12:5
+  --> $DIR/report_warning_on_duplicated_options.rs:10:5
    |
 LL |     label = "first label",
    |     --------------------- `label` is first declared here
@@ -41,7 +41,7 @@ LL |     label = "second label",
    = note: duplicate diagnostic emitted due to `-Z deduplicate-diagnostics=no`
 
 error[E0277]: first message
-  --> $DIR/report_warning_on_duplicated_options.rs:23:15
+  --> $DIR/report_warning_on_duplicated_options.rs:21:15
    |
 LL |     takes_foo(());
    |     --------- ^^ first label
@@ -52,12 +52,12 @@ LL |     takes_foo(());
    = note: custom note
    = note: second note
 help: this trait has no implementations, consider adding one
-  --> $DIR/report_warning_on_duplicated_options.rs:17:1
+  --> $DIR/report_warning_on_duplicated_options.rs:15:1
    |
 LL | trait Foo {}
    | ^^^^^^^^^
 note: required by a bound in `takes_foo`
-  --> $DIR/report_warning_on_duplicated_options.rs:20:22
+  --> $DIR/report_warning_on_duplicated_options.rs:18:22
    |
 LL | fn takes_foo(_: impl Foo) {}
    |                      ^^^ required by this bound in `takes_foo`

tests/ui/diagnostic_namespace/on_unimplemented/multiple_notes.rs

@@ -1,5 +1,3 @@
-#![feature(diagnostic_namespace)]
-
 #[diagnostic]
 //~^ERROR cannot find attribute `diagnostic` in this scope
 pub struct Bar;

tests/ui/diagnostic_namespace/on_unimplemented/multiple_notes.stderr

@@ -1,5 +1,5 @@
 error: cannot find attribute `diagnostic` in this scope
-  --> $DIR/requires_path.rs:3:3
+  --> $DIR/requires_path.rs:1:3
    |
 LL | #[diagnostic]
    |   ^^^^^^^^^^