Introduce language items for Arc and Rc.

This commit introduces language items for `Arc` and `Rc` so that types
can later be checked to be `Arc` or `Rc` in the NLL borrow checker. The
`lang` attribute is currently limited to `stage1` as it requires a
compiler built with knowledge of the expected language items.

Author: davidtwco

src/doc/unstable-book/src/language-features/lang-items.md

@@ -311,3 +311,5 @@ the source code.
   - `freeze`: `libcore/marker.rs`
   - `debug_trait`: `libcore/fmt/mod.rs`
   - `non_zero`: `libcore/nonzero.rs`
+  - `arc`: `liballoc/sync.rs`
+  - `rc`: `liballoc/rc.rs`

src/liballoc/rc.rs

@@ -282,6 +282,7 @@ struct RcBox<T: ?Sized> {
 /// type `T`.
 ///
 /// [get_mut]: #method.get_mut
+#[cfg_attr(all(not(stage0), not(test)), lang = "rc")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Rc<T: ?Sized> {
     ptr: NonNull<RcBox<T>>,

src/liballoc/sync.rs

@@ -199,6 +199,7 @@ const MAX_REFCOUNT: usize = (isize::MAX) as usize;
 /// counting in general.
 ///
 /// [rc_examples]: ../../std/rc/index.html#examples
+#[cfg_attr(all(not(stage0), not(test)), lang = "arc")]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub struct Arc<T: ?Sized> {
     ptr: NonNull<ArcInner<T>>,

src/librustc/middle/lang_items.rs

@@ -362,6 +362,9 @@ language_item_table! {
     AlignOffsetLangItem,             "align_offset",            align_offset_fn;
 
     TerminationTraitLangItem,        "termination",             termination;
+
+    Arc,                             "arc",                     arc;
+    Rc,                              "rc",                      rc;
 }
 
 impl<'a, 'tcx, 'gcx> TyCtxt<'a, 'tcx, 'gcx> {

src/librustc/ty/mod.rs

@@ -1694,9 +1694,13 @@ bitflags! {
         const IS_FUNDAMENTAL      = 1 << 2;
         const IS_UNION            = 1 << 3;
         const IS_BOX              = 1 << 4;
+        /// Indicates whether the type is an `Arc`.
+        const IS_ARC              = 1 << 5;
+        /// Indicates whether the type is an `Rc`.
+        const IS_RC               = 1 << 6;
         /// Indicates whether the variant list of this ADT is `#[non_exhaustive]`.
         /// (i.e., this flag is never set unless this ADT is an enum).
-        const IS_VARIANT_LIST_NON_EXHAUSTIVE   = 1 << 5;
+        const IS_VARIANT_LIST_NON_EXHAUSTIVE   = 1 << 7;
     }
 }
 
@@ -2016,6 +2020,12 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         if Some(did) == tcx.lang_items().owned_box() {
             flags = flags | AdtFlags::IS_BOX;
         }
+        if Some(did) == tcx.lang_items().arc() {
+            flags = flags | AdtFlags::IS_ARC;
+        }
+        if Some(did) == tcx.lang_items().rc() {
+            flags = flags | AdtFlags::IS_RC;
+        }
         if kind == AdtKind::Enum && tcx.has_attr(did, "non_exhaustive") {
             debug!("found non-exhaustive variant list for {:?}", did);
             flags = flags | AdtFlags::IS_VARIANT_LIST_NON_EXHAUSTIVE;
@@ -2094,6 +2104,16 @@ impl<'a, 'gcx, 'tcx> AdtDef {
         self.flags.intersects(AdtFlags::IS_PHANTOM_DATA)
     }
 
+    /// Returns `true` if this is `Arc<T>`.
+    pub fn is_arc(&self) -> bool {
+        self.flags.intersects(AdtFlags::IS_ARC)
+    }
+
+    /// Returns `true` if this is `Rc<T>`.
+    pub fn is_rc(&self) -> bool {
+        self.flags.intersects(AdtFlags::IS_RC)
+    }
+
     /// Returns true if this is Box<T>.
     #[inline]
     pub fn is_box(&self) -> bool {

src/librustc/ty/sty.rs

@@ -1598,6 +1598,22 @@ impl<'a, 'gcx, 'tcx> TyS<'tcx> {
         }
     }
 
+    /// Returns `true` if this type is an `Arc<T>`.
+    pub fn is_arc(&self) -> bool {
+        match self.sty {
+            Adt(def, _) => def.is_arc(),
+            _ => false,
+        }
+    }
+
+    /// Returns `true` if this type is an `Rc<T>`.
+    pub fn is_rc(&self) -> bool {
+        match self.sty {
+            Adt(def, _) => def.is_rc(),
+            _ => false,
+        }
+    }
+
     pub fn is_box(&self) -> bool {
         match self.sty {
             Adt(def, _) => def.is_box(),