Auto merge of rust-lang#86943 - ptrojahn:suggest_derive, r=estebank

Suggest deriving traits if possible

This only applies to builtin derives as I don't think there is a
clean way to get the available derives in typeck.

Closes rust-lang#85851

Author: bors

core/src/cmp.rs

@@ -203,6 +203,7 @@ use self::Ordering::*;
     message = "can't compare `{Self}` with `{Rhs}`",
     label = "no implementation for `{Self} == {Rhs}`"
 )]
+#[rustc_diagnostic_item = "PartialEq"]
 pub trait PartialEq<Rhs: ?Sized = Self> {
     /// This method tests for `self` and `other` values to be equal, and is used
     /// by `==`.
@@ -269,6 +270,7 @@ pub macro PartialEq($item:item) {
 #[doc(alias = "==")]
 #[doc(alias = "!=")]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_diagnostic_item = "Eq"]
 pub trait Eq: PartialEq<Self> {
     // this method is used solely by #[deriving] to assert
     // that every component of a type implements #[deriving]
@@ -728,6 +730,7 @@ impl<T: Clone> Clone for Reverse<T> {
 #[doc(alias = "<=")]
 #[doc(alias = ">=")]
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_diagnostic_item = "Ord"]
 pub trait Ord: Eq + PartialOrd<Self> {
     /// This method returns an [`Ordering`] between `self` and `other`.
     ///
@@ -984,6 +987,7 @@ impl PartialOrd for Ordering {
     message = "can't compare `{Self}` with `{Rhs}`",
     label = "no implementation for `{Self} < {Rhs}` and `{Self} > {Rhs}`"
 )]
+#[rustc_diagnostic_item = "PartialOrd"]
 pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     /// This method returns an ordering between `self` and `other` values if one exists.
     ///

core/src/hash/mod.rs

@@ -157,6 +157,7 @@ mod sip;
 /// [`HashSet`]: ../../std/collections/struct.HashSet.html
 /// [`hash`]: Hash::hash
 #[stable(feature = "rust1", since = "1.0.0")]
+#[rustc_diagnostic_item = "Hash"]
 pub trait Hash {
     /// Feeds this value into the given [`Hasher`].
     ///

core/src/marker.rs

@@ -382,6 +382,7 @@ pub trait StructuralEq {
 // existing specializations on `Copy` that already exist in the standard
 // library, and there's no way to safely have this behavior right now.
 #[rustc_unsafe_specialization_marker]
+#[rustc_diagnostic_item = "Copy"]
 pub trait Copy: Clone {
     // Empty.
 }