Auto merge of rust-lang#96964 - oli-obk:const_trait_mvp, r=compiler-errors

Replace `#[default_method_body_is_const]` with `#[const_trait]`

pulled out of rust-lang#96077

related issues:  rust-lang#67792 and rust-lang#92158

cc `@fee1-dead`

This is groundwork to only allowing `impl const Trait` for traits that are marked with `#[const_trait]`. This is necessary to prevent adding a new default method from becoming a breaking change (as it could be a non-const fn).

Author: bors

core/src/clone.rs

@@ -107,6 +107,7 @@ use crate::marker::Destruct;
 #[lang = "clone"]
 #[rustc_diagnostic_item = "Clone"]
 #[rustc_trivial_field_reads]
+#[cfg_attr(not(bootstrap), const_trait)]
 pub trait Clone: Sized {
     /// Returns a copy of the value.
     ///
@@ -129,7 +130,7 @@ pub trait Clone: Sized {
     /// allocations.
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[default_method_body_is_const]
+    #[cfg_attr(bootstrap, default_method_body_is_const)]
     fn clone_from(&mut self, source: &Self)
     where
         Self: ~const Destruct,

core/src/cmp.rs

@@ -214,6 +214,7 @@ use self::Ordering::*;
         append_const_msg,
     )
 )]
+#[cfg_attr(not(bootstrap), const_trait)]
 #[rustc_diagnostic_item = "PartialEq"]
 pub trait PartialEq<Rhs: ?Sized = Self> {
     /// This method tests for `self` and `other` values to be equal, and is used
@@ -226,7 +227,7 @@ pub trait PartialEq<Rhs: ?Sized = Self> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[default_method_body_is_const]
+    #[cfg_attr(bootstrap, default_method_body_is_const)]
     fn ne(&self, other: &Rhs) -> bool {
         !self.eq(other)
     }
@@ -1053,6 +1054,7 @@ impl PartialOrd for Ordering {
         append_const_msg,
     )
 )]
+#[cfg_attr(not(bootstrap), const_trait)]
 #[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.
@@ -1096,7 +1098,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[default_method_body_is_const]
+    #[cfg_attr(bootstrap, default_method_body_is_const)]
     fn lt(&self, other: &Rhs) -> bool {
         matches!(self.partial_cmp(other), Some(Less))
     }
@@ -1116,7 +1118,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[default_method_body_is_const]
+    #[cfg_attr(bootstrap, default_method_body_is_const)]
     fn le(&self, other: &Rhs) -> bool {
         // Pattern `Some(Less | Eq)` optimizes worse than negating `None | Some(Greater)`.
         // FIXME: The root cause was fixed upstream in LLVM with:
@@ -1139,7 +1141,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[default_method_body_is_const]
+    #[cfg_attr(bootstrap, default_method_body_is_const)]
     fn gt(&self, other: &Rhs) -> bool {
         matches!(self.partial_cmp(other), Some(Greater))
     }
@@ -1159,7 +1161,7 @@ pub trait PartialOrd<Rhs: ?Sized = Self>: PartialEq<Rhs> {
     #[inline]
     #[must_use]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[default_method_body_is_const]
+    #[cfg_attr(bootstrap, default_method_body_is_const)]
     fn ge(&self, other: &Rhs) -> bool {
         matches!(self.partial_cmp(other), Some(Greater | Equal))
     }