Fixing A and COOP_PREFERRED generics. WIP...

Author: peter-lyons-kehl

library/alloc/src/borrow.rs

@@ -11,7 +11,7 @@ use core::ops::{Add, AddAssign};
 #[stable(feature = "rust1", since = "1.0.0")]
 pub use core::borrow::{Borrow, BorrowMut};
 
-use crate::fmt;
+use crate::{fmt, DEFAULT_COOP_PREFERRED, alloc::Global};
 #[cfg(not(no_global_oom_handling))]
 use crate::string::String;
 
@@ -35,7 +35,11 @@ where
 /// from any borrow of a given type.
 #[cfg_attr(not(test), rustc_diagnostic_item = "ToOwned")]
 #[stable(feature = "rust1", since = "1.0.0")]
-pub trait ToOwned {
+#[allow(unused_braces)]
+pub trait ToOwned<const COOP_PREFERRED: bool = { DEFAULT_COOP_PREFERRED!() } >
+where
+    [(); core::alloc::co_alloc_metadata_num_slots_with_preference::<Global>(COOP_PREFERRED)]:,
+{
     /// The resulting type after obtaining ownership.
     #[stable(feature = "rust1", since = "1.0.0")]
     type Owned: Borrow<Self>;

library/alloc/src/str.rs

@@ -208,14 +208,17 @@ impl BorrowMut<str> for String {
 
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "rust1", since = "1.0.0")]
-impl ToOwned for str {
-    type Owned = String;
+impl<const COOP_PREFERRED: bool> ToOwned<COOP_PREFERRED> for str
+where
+    [(); core::alloc::co_alloc_metadata_num_slots_with_preference::<Global>(COOP_PREFERRED)]:,
+{
+    type Owned = String<COOP_PREFERRED>;
     #[inline]
-    fn to_owned(&self) -> String {
+    fn to_owned(&self) -> String<COOP_PREFERRED> {
         unsafe { String::from_utf8_unchecked(self.as_bytes().to_owned()) }
     }
 
-    fn clone_into(&self, target: &mut String) {
+    fn clone_into(&self, target: &mut String<COOP_PREFERRED>) {
         let mut b = mem::take(target).into_bytes();
         self.as_bytes().clone_into(&mut b);
         *target = unsafe { String::from_utf8_unchecked(b) }