Expose Freeze trait again

library/core/src/marker.rs

@@ -810,15 +810,21 @@ pub trait DiscriminantKind {
     type Discriminant: Clone + Copy + Debug + Eq + PartialEq + Hash + Send + Sync + Unpin;
 }
 
-/// Compiler-internal trait used to determine whether a type contains
+/// Used to determine whether a type contains
 /// any `UnsafeCell` internally, but not through an indirection.
 /// This affects, for example, whether a `static` of that type is
 /// placed in read-only static memory or writable static memory.
+/// This can be used to declare that a constant with a generic type
+/// will not contain interior mutability, and subsequently allow
+/// placing the constant behind references.
 #[lang = "freeze"]
-pub(crate) unsafe auto trait Freeze {}
+#[unstable(feature = "freeze", issue = "60715")]
+pub unsafe auto trait Freeze {}
 
+#[unstable(feature = "freeze", issue = "60715")]
 impl<T: ?Sized> !Freeze for UnsafeCell<T> {}
 marker_impls! {
+    #[unstable(feature = "freeze", issue = "60715")]
     unsafe Freeze for
         {T: ?Sized} PhantomData<T>,
         {T: ?Sized} *const T,

tests/rustdoc/auto-trait-bounds-by-associated-type-50159.rs

@@ -9,7 +9,10 @@ pub trait Signal2 {
     type Item2;
 }
 
-impl<B, C> Signal2 for B where B: Signal<Item = C> {
+impl<B, C> Signal2 for B
+where
+    B: Signal<Item = C>,
+{
     type Item2 = C;
 }
 
@@ -17,7 +20,7 @@ impl<B, C> Signal2 for B where B: Signal<Item = C> {
 // @has - '//h3[@class="code-header"]' 'impl<B> Send for Switch<B>where <B as Signal>::Item: Send'
 // @has - '//h3[@class="code-header"]' 'impl<B> Sync for Switch<B>where <B as Signal>::Item: Sync'
 // @count - '//*[@id="implementations-list"]//*[@class="impl"]' 0
-// @count - '//*[@id="synthetic-implementations-list"]//*[@class="impl"]' 5
+// @count - '//*[@id="synthetic-implementations-list"]//*[@class="impl"]' 6
 pub struct Switch<B: Signal> {
     pub inner: <B as Signal2>::Item2,
 }

tests/rustdoc/empty-section.rs

@@ -1,6 +1,5 @@
 #![crate_name = "foo"]
-
+#![feature(negative_impls, freeze_impls, freeze)]
-#![feature(negative_impls)]
 
 pub struct Foo;
 
@@ -8,6 +7,7 @@
 // @!hasraw - 'Auto Trait Implementations'
 impl !Send for Foo {}
 impl !Sync for Foo {}
+impl !std::marker::Freeze for Foo {}
 impl !std::marker::Unpin for Foo {}
 impl !std::panic::RefUnwindSafe for Foo {}
 impl !std::panic::UnwindSafe for Foo {}

tests/rustdoc/synthetic_auto/basic.rs

@@ -2,7 +2,7 @@
 // @has - '//h3[@class="code-header"]' 'impl<T> Send for Foo<T>where T: Send'
 // @has - '//h3[@class="code-header"]' 'impl<T> Sync for Foo<T>where T: Sync'
 // @count - '//*[@id="implementations-list"]//*[@class="impl"]' 0
-// @count - '//*[@id="synthetic-implementations-list"]//*[@class="impl"]' 5
+// @count - '//*[@id="synthetic-implementations-list"]//*[@class="impl"]' 6
 pub struct Foo<T> {
     field: T,
 }

tests/rustdoc/synthetic_auto/manual.rs

@@ -6,7 +6,7 @@
 // 'impl<T> Send for Foo<T>'
 //
 // @count - '//*[@id="trait-implementations-list"]//*[@class="impl"]' 1
-// @count - '//*[@id="synthetic-implementations-list"]//*[@class="impl"]' 4
+// @count - '//*[@id="synthetic-implementations-list"]//*[@class="impl"]' 5
 pub struct Foo<T> {
     field: T,
 }

tests/ui/associated-consts/freeze.rs

@@ -0,0 +1,12 @@
+#![feature(freeze)]
+
+//@ check-pass
+
+use std::marker::Freeze;
+
+trait Trait<T: Freeze + 'static> {
+    const VALUE: T;
+    const VALUE_REF: &'static T = &Self::VALUE;
+}
+
+fn main() {}