Auto merge of #41349 - eddyb:ty-contents, r=nikomatsakis

rustc: replace TypeContents with two independent properties (is_freeze / needs_drop).

`InteriorUnsafe` / `interior_unsafe` was replaced with a private lang-item `Freeze` auto trait in libcore.

`OwnsDtor` / `needs_drop` was replaced with a specialized traversal that *doesn't* avoid caching results in case of a cycle, as the only cycles left can only occur in erroneous "types with infinite sizes", references and raw pointers not having destructors. Also, `Copy` is now checked at every step of the recursion.

r? @nikomatsakis

1 files changed, 17 insertions, 0 deletions

diff --git a/src/libcore/marker.rs b/src/libcore/marker.rs
index 393c01b0105..c0aa650a1e8 100644
--- a/src/libcore/marker.rs
+++ b/src/libcore/marker.rs
@@ -16,6 +16,7 @@
 
 #![stable(feature = "rust1", since = "1.0.0")]
 
+use cell::UnsafeCell;
 use cmp;
 use hash::Hash;
 use hash::Hasher;
@@ -553,3 +554,19 @@ mod impls {
     #[stable(feature = "rust1", since = "1.0.0")]
     unsafe impl<'a, T: Send + ?Sized> Send for &'a mut T {}
 }
+
+/// Compiler-internal trait 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.
+#[cfg_attr(not(stage0), lang = "freeze")]
+unsafe trait Freeze {}
+
+unsafe impl Freeze for .. {}
+
+impl<T: ?Sized> !Freeze for UnsafeCell<T> {}
+unsafe impl<T: ?Sized> Freeze for PhantomData<T> {}
+unsafe impl<T: ?Sized> Freeze for *const T {}
+unsafe impl<T: ?Sized> Freeze for *mut T {}
+unsafe impl<'a, T: ?Sized> Freeze for &'a T {}
+unsafe impl<'a, T: ?Sized> Freeze for &'a mut T {}