Rollup merge of rust-lang#148641 - oli-obk:push-olzwqxsmnxmz, r=jackh726

Add a diagnostic attribute for special casing const bound errors for non-const impls

Somewhat of a follow-up to rust-lang#144194

My plan is to resolve

https://github.com/rust-lang/rust/blob/f4e19c68786211f3c3cf2593442629599678800a/compiler/rustc_hir_typeck/src/callee.rs#L907-913

but doing so without being able to mark impls the way I do in this PR wrould cause all nice diagnostics about for loops and pointer comparisons to just be a `*const u32 does not implement [const] PartialEq` errors.

Author: Zalathar

core/src/lib.rs

@@ -149,6 +149,7 @@
 #![feature(decl_macro)]
 #![feature(deprecated_suggestion)]
 #![feature(derive_const)]
+#![feature(diagnostic_on_const)]
 #![feature(doc_cfg)]
 #![feature(doc_notable_trait)]
 #![feature(extern_types)]

core/src/ptr/const_ptr.rs

@@ -1567,6 +1567,10 @@ impl<T, const N: usize> *const [T; N] {
 
 /// Pointer equality is by address, as produced by the [`<*const T>::addr`](pointer::addr) method.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<T: PointeeSized> PartialEq for *const T {
     #[inline]
     #[allow(ambiguous_wide_pointer_comparisons)]
@@ -1577,10 +1581,18 @@ impl<T: PointeeSized> PartialEq for *const T {
 
 /// Pointer equality is an equivalence relation.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<T: PointeeSized> Eq for *const T {}
 
 /// Pointer comparison is by address, as produced by the `[`<*const T>::addr`](pointer::addr)` method.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<T: PointeeSized> Ord for *const T {
     #[inline]
     #[allow(ambiguous_wide_pointer_comparisons)]
@@ -1597,6 +1609,10 @@ impl<T: PointeeSized> Ord for *const T {
 
 /// Pointer comparison is by address, as produced by the `[`<*const T>::addr`](pointer::addr)` method.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<T: PointeeSized> PartialOrd for *const T {
     #[inline]
     #[allow(ambiguous_wide_pointer_comparisons)]

core/src/ptr/mod.rs

@@ -2520,23 +2520,39 @@ pub fn hash<T: PointeeSized, S: hash::Hasher>(hashee: *const T, into: &mut S) {
 }
 
 #[stable(feature = "fnptr_impls", since = "1.4.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<F: FnPtr> PartialEq for F {
     #[inline]
     fn eq(&self, other: &Self) -> bool {
         self.addr() == other.addr()
     }
 }
 #[stable(feature = "fnptr_impls", since = "1.4.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<F: FnPtr> Eq for F {}
 
 #[stable(feature = "fnptr_impls", since = "1.4.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<F: FnPtr> PartialOrd for F {
     #[inline]
     fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
         self.addr().partial_cmp(&other.addr())
     }
 }
 #[stable(feature = "fnptr_impls", since = "1.4.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<F: FnPtr> Ord for F {
     #[inline]
     fn cmp(&self, other: &Self) -> Ordering {

core/src/ptr/mut_ptr.rs

@@ -2000,6 +2000,10 @@ impl<T, const N: usize> *mut [T; N] {
 
 /// Pointer equality is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<T: PointeeSized> PartialEq for *mut T {
     #[inline(always)]
     #[allow(ambiguous_wide_pointer_comparisons)]
@@ -2010,10 +2014,18 @@ impl<T: PointeeSized> PartialEq for *mut T {
 
 /// Pointer equality is an equivalence relation.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<T: PointeeSized> Eq for *mut T {}
 
 /// Pointer comparison is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<T: PointeeSized> Ord for *mut T {
     #[inline]
     #[allow(ambiguous_wide_pointer_comparisons)]
@@ -2030,6 +2042,10 @@ impl<T: PointeeSized> Ord for *mut T {
 
 /// Pointer comparison is by address, as produced by the [`<*mut T>::addr`](pointer::addr) method.
 #[stable(feature = "rust1", since = "1.0.0")]
+#[diagnostic::on_const(
+    message = "pointers cannot be reliably compared during const eval",
+    note = "see issue #53020 <https://github.com/rust-lang/rust/issues/53020> for more information"
+)]
 impl<T: PointeeSized> PartialOrd for *mut T {
     #[inline(always)]
     #[allow(ambiguous_wide_pointer_comparisons)]