Stabilize the #[diagnostic] namespace and `#[diagnostic::on_unimple…

…mented]` 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
attribute 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: #111996

compiler/rustc_ast_passes/src/feature_gate.rs

@@ -209,14 +209,6 @@ 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

@@ -144,6 +144,8 @@ 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

@@ -436,8 +436,6 @@ 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/future/future.rs

@@ -28,10 +28,13 @@ use crate::task::{Context, Poll};
 #[must_use = "futures do nothing unless you `.await` or poll them"]
 #[stable(feature = "futures_api", since = "1.36.0")]
 #[lang = "future_trait"]
-#[diagnostic::on_unimplemented(
-    label = "`{Self}` is not a future",
-    message = "`{Self}` is not a future",
-    note = "{Self} must be a future or must implement `IntoFuture` to be awaited"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        label = "`{Self}` is not a future",
+        message = "`{Self}` is not a future",
+        note = "{Self} must be a future or must implement `IntoFuture` to be awaited"
+    )
 )]
 pub trait Future {
     /// The type of value produced on completion.

library/core/src/lib.rs

@@ -217,7 +217,6 @@
 #![feature(const_trait_impl)]
 #![feature(decl_macro)]
 #![feature(deprecated_suggestion)]
-#![feature(diagnostic_namespace)]
 #![feature(doc_cfg)]
 #![feature(doc_cfg_hide)]
 #![feature(doc_notable_trait)]

library/core/src/marker.rs

@@ -75,9 +75,12 @@ macro marker_impls {
 /// [ub]: ../../reference/behavior-considered-undefined.html
 #[stable(feature = "rust1", since = "1.0.0")]
 #[cfg_attr(not(test), rustc_diagnostic_item = "Send")]
-#[diagnostic::on_unimplemented(
-    message = "`{Self}` cannot be sent between threads safely",
-    label = "`{Self}` cannot be sent between threads safely"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "`{Self}` cannot be sent between threads safely",
+        label = "`{Self}` cannot be sent between threads safely"
+    )
 )]
 pub unsafe auto trait Send {
     // empty.
@@ -134,9 +137,12 @@ unsafe impl<T: Sync + ?Sized> Send for &T {}
 #[doc(alias = "?", alias = "?Sized")]
 #[stable(feature = "rust1", since = "1.0.0")]
 #[lang = "sized"]
-#[diagnostic::on_unimplemented(
-    message = "the size for values of type `{Self}` cannot be known at compilation time",
-    label = "doesn't have a size known at compile-time"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "the size for values of type `{Self}` cannot be known at compilation time",
+        label = "doesn't have a size known at compile-time"
+    )
 )]
 #[fundamental] // for Default, for example, which requires that `[T]: !Default` be evaluatable
 #[rustc_specialization_trait]
@@ -205,7 +211,10 @@ pub trait Unsize<T: ?Sized> {
 /// [RFC1445]: https://github.com/rust-lang/rfcs/blob/master/text/1445-restrict-constants-in-patterns.md
 /// [issue 63438]: https://github.com/rust-lang/rust/issues/63438
 #[unstable(feature = "structural_match", issue = "31434")]
-#[diagnostic::on_unimplemented(message = "the type `{Self}` does not `#[derive(PartialEq)]`")]
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(message = "the type `{Self}` does not `#[derive(PartialEq)]`")
+)]
 #[lang = "structural_peq"]
 pub trait StructuralPartialEq {
     // Empty.
@@ -273,7 +282,10 @@ marker_impls! {
 /// of the two derives (`#[derive(PartialEq)]` and `#[derive(Eq)]`) and check
 /// that both of them are present as part of structural-match checking.
 #[unstable(feature = "structural_match", issue = "31434")]
-#[diagnostic::on_unimplemented(message = "the type `{Self}` does not `#[derive(Eq)]`")]
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(message = "the type `{Self}` does not `#[derive(Eq)]`")
+)]
 #[lang = "structural_teq"]
 pub trait StructuralEq {
     // Empty.
@@ -964,9 +976,12 @@ marker_impls! {
 /// [section about `Unpin`]: crate::pin#unpin "pin module docs about unpin"
 /// [`unsafe`]: ../../std/keyword.unsafe.html "keyword unsafe"
 #[stable(feature = "pin", since = "1.33.0")]
-#[diagnostic::on_unimplemented(
-    note = "consider using the `pin!` macro\nconsider using `Box::pin` if you need to access the pinned value outside of the current scope",
-    message = "`{Self}` cannot be unpinned"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        note = "consider using the `pin!` macro\nconsider using `Box::pin` if you need to access the pinned value outside of the current scope",
+        message = "`{Self}` cannot be unpinned"
+    )
 )]
 #[lang = "unpin"]
 pub auto trait Unpin {}
@@ -1012,7 +1027,7 @@ pub trait Destruct {}
 /// for any user type.
 #[unstable(feature = "tuple_trait", issue = "none")]
 #[lang = "tuple_trait"]
-#[diagnostic::on_unimplemented(message = "`{Self}` is not a tuple")]
+#[cfg_attr(not(bootstrap), diagnostic::on_unimplemented(message = "`{Self}` is not a tuple"))]
 #[rustc_deny_explicit_impl(implement_via_object = false)]
 pub trait Tuple {}
 
@@ -1022,9 +1037,12 @@ pub trait Tuple {}
 /// `*const ()` automatically implement this trait.
 #[unstable(feature = "pointer_like_trait", issue = "none")]
 #[lang = "pointer_like"]
-#[diagnostic::on_unimplemented(
-    message = "`{Self}` needs to have the same ABI as a pointer",
-    label = "`{Self}` needs to be a pointer-like type"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "`{Self}` needs to have the same ABI as a pointer",
+        label = "`{Self}` needs to be a pointer-like type"
+    )
 )]
 pub trait PointerLike {}
 
@@ -1036,7 +1054,10 @@ pub trait PointerLike {}
 /// are `StructuralPartialEq`.
 #[lang = "const_param_ty"]
 #[unstable(feature = "adt_const_params", issue = "95174")]
-#[diagnostic::on_unimplemented(message = "`{Self}` can't be used as a const parameter type")]
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(message = "`{Self}` can't be used as a const parameter type")
+)]
 #[allow(multiple_supertrait_upcastable)]
 pub trait ConstParamTy: StructuralEq + StructuralPartialEq + Eq {}
 

library/core/src/ops/arith.rs

@@ -307,9 +307,12 @@ sub_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 /// ```
 #[lang = "mul"]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[diagnostic::on_unimplemented(
-    message = "cannot multiply `{Self}` by `{Rhs}`",
-    label = "no implementation for `{Self} * {Rhs}`"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "cannot multiply `{Self}` by `{Rhs}`",
+        label = "no implementation for `{Self} * {Rhs}`"
+    )
 )]
 #[doc(alias = "*")]
 pub trait Mul<Rhs = Self> {
@@ -441,9 +444,12 @@ mul_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 /// ```
 #[lang = "div"]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[diagnostic::on_unimplemented(
-    message = "cannot divide `{Self}` by `{Rhs}`",
-    label = "no implementation for `{Self} / {Rhs}`"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "cannot divide `{Self}` by `{Rhs}`",
+        label = "no implementation for `{Self} / {Rhs}`"
+    )
 )]
 #[doc(alias = "/")]
 pub trait Div<Rhs = Self> {
@@ -543,9 +549,12 @@ div_impl_float! { f32 f64 }
 /// ```
 #[lang = "rem"]
 #[stable(feature = "rust1", since = "1.0.0")]
-#[diagnostic::on_unimplemented(
-    message = "cannot calculate the remainder of `{Self}` divided by `{Rhs}`",
-    label = "no implementation for `{Self} % {Rhs}`"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "cannot calculate the remainder of `{Self}` divided by `{Rhs}`",
+        label = "no implementation for `{Self} % {Rhs}`"
+    )
 )]
 #[doc(alias = "%")]
 pub trait Rem<Rhs = Self> {
@@ -729,9 +738,12 @@ neg_impl! { isize i8 i16 i32 i64 i128 f32 f64 }
 /// ```
 #[lang = "add_assign"]
 #[stable(feature = "op_assign_traits", since = "1.8.0")]
-#[diagnostic::on_unimplemented(
-    message = "cannot add-assign `{Rhs}` to `{Self}`",
-    label = "no implementation for `{Self} += {Rhs}`"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "cannot add-assign `{Rhs}` to `{Self}`",
+        label = "no implementation for `{Self} += {Rhs}`"
+    )
 )]
 #[doc(alias = "+")]
 #[doc(alias = "+=")]
@@ -796,9 +808,12 @@ add_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 /// ```
 #[lang = "sub_assign"]
 #[stable(feature = "op_assign_traits", since = "1.8.0")]
-#[diagnostic::on_unimplemented(
-    message = "cannot subtract-assign `{Rhs}` from `{Self}`",
-    label = "no implementation for `{Self} -= {Rhs}`"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "cannot subtract-assign `{Rhs}` from `{Self}`",
+        label = "no implementation for `{Self} -= {Rhs}`"
+    )
 )]
 #[doc(alias = "-")]
 #[doc(alias = "-=")]
@@ -854,9 +869,12 @@ sub_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 /// ```
 #[lang = "mul_assign"]
 #[stable(feature = "op_assign_traits", since = "1.8.0")]
-#[diagnostic::on_unimplemented(
-    message = "cannot multiply-assign `{Self}` by `{Rhs}`",
-    label = "no implementation for `{Self} *= {Rhs}`"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "cannot multiply-assign `{Self}` by `{Rhs}`",
+        label = "no implementation for `{Self} *= {Rhs}`"
+    )
 )]
 #[doc(alias = "*")]
 #[doc(alias = "*=")]
@@ -912,9 +930,12 @@ mul_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 /// ```
 #[lang = "div_assign"]
 #[stable(feature = "op_assign_traits", since = "1.8.0")]
-#[diagnostic::on_unimplemented(
-    message = "cannot divide-assign `{Self}` by `{Rhs}`",
-    label = "no implementation for `{Self} /= {Rhs}`"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "cannot divide-assign `{Self}` by `{Rhs}`",
+        label = "no implementation for `{Self} /= {Rhs}`"
+    )
 )]
 #[doc(alias = "/")]
 #[doc(alias = "/=")]
@@ -973,9 +994,12 @@ div_assign_impl! { usize u8 u16 u32 u64 u128 isize i8 i16 i32 i64 i128 f32 f64 }
 /// ```
 #[lang = "rem_assign"]
 #[stable(feature = "op_assign_traits", since = "1.8.0")]
-#[diagnostic::on_unimplemented(
-    message = "cannot calculate and assign the remainder of `{Self}` divided by `{Rhs}`",
-    label = "no implementation for `{Self} %= {Rhs}`"
+#[cfg_attr(
+    not(bootstrap),
+    diagnostic::on_unimplemented(
+        message = "cannot calculate and assign the remainder of `{Self}` divided by `{Rhs}`",
+        label = "no implementation for `{Self} %= {Rhs}`"
+    )
 )]
 #[doc(alias = "%")]
 #[doc(alias = "%=")]