eddyb's changes for DST coercions

+ lots of rebasing

src/liballoc/boxed.rs

@@ -62,6 +62,11 @@ use core::ops::{Deref, DerefMut};
 use core::ptr::{Unique};
 use core::raw::{TraitObject};
 
+#[cfg(not(stage0))] // SNAP c64d671
+use core::marker::Unsize;
+#[cfg(not(stage0))] // SNAP c64d671
+use core::ops::CoerceUnsized;
+
 /// A value that represents the heap. This is the default place that the `box`
 /// keyword allocates into when no place is supplied.
 ///
@@ -390,3 +395,6 @@ impl<'a,A,R> FnOnce<A> for Box<FnBox<A,Output=R>+Send+'a> {
         self.call_box(args)
     }
 }
+
+#[cfg(not(stage0))] // SNAP c64d671
+impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<Box<U>> for Box<T> {}

src/liballoc/rc.rs

@@ -173,9 +173,9 @@ use core::intrinsics::assume;
 use heap::deallocate;
 
 struct RcBox<T> {
-    value: T,
     strong: Cell<usize>,
-    weak: Cell<usize>
+    weak: Cell<usize>,
+    value: T
 }
 
 /// A reference-counted pointer type over an immutable value.

src/libcore/intrinsics.rs

@@ -193,6 +193,13 @@ extern "rust-intrinsic" {
     pub fn min_align_of<T>() -> usize;
     pub fn pref_align_of<T>() -> usize;
 
+    #[cfg(not(stage0))]
+    pub fn size_of_val<T: ?Sized>(_: &T) -> usize;
+    #[cfg(not(stage0))]
+    pub fn min_align_of_val<T: ?Sized>(_: &T) -> usize;
+    #[cfg(not(stage0))]
+    pub fn drop_in_place<T: ?Sized>(_: *mut T);
+
     /// Gets a static string slice containing the name of a type.
     pub fn type_name<T: ?Sized>() -> &'static str;
 

src/libcore/marker.rs

@@ -53,6 +53,14 @@ pub trait Sized {
     // Empty.
 }
 
+/// Types that can be "unsized" to a dynamically sized type.
+#[unstable(feature = "core")]
+#[cfg(not(stage0))] // SNAP c64d671
+#[lang="unsize"]
+pub trait Unsize<T> {
+    // Empty.
+}
+
 /// Types that can be copied by simply copying bits (i.e. `memcpy`).
 ///
 /// By default, variable bindings have 'move semantics.' In other

src/libcore/mem.rs

@@ -86,6 +86,22 @@ pub fn size_of<T>() -> usize {
     unsafe { intrinsics::size_of::<T>() }
 }
 
+/// Returns the size of the type that `val` points to in bytes.
+///
+/// # Examples
+///
+/// ```
+/// use std::mem;
+///
+/// assert_eq!(4, mem::size_of_val(&5i32));
+/// ```
+#[cfg(not(stage0))] // SNAP c64d671
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn size_of_val<T: ?Sized>(val: &T) -> usize {
+    unsafe { intrinsics::size_of_val(val) }
+}
+
 /// Returns the size of the type that `_val` points to in bytes.
 ///
 /// # Examples
@@ -95,6 +111,7 @@ pub fn size_of<T>() -> usize {
 ///
 /// assert_eq!(4, mem::size_of_val(&5i32));
 /// ```
+#[cfg(stage0)] // SNAP c64d671
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn size_of_val<T>(_val: &T) -> usize {
@@ -118,6 +135,22 @@ pub fn min_align_of<T>() -> usize {
     unsafe { intrinsics::min_align_of::<T>() }
 }
 
+/// Returns the ABI-required minimum alignment of the type of the value that `val` points to
+///
+/// # Examples
+///
+/// ```
+/// use std::mem;
+///
+/// assert_eq!(4, mem::min_align_of_val(&5i32));
+/// ```
+#[cfg(not(stage0))] // SNAP c64d671
+#[inline]
+#[stable(feature = "rust1", since = "1.0.0")]
+pub fn min_align_of_val<T: ?Sized>(val: &T) -> usize {
+    unsafe { intrinsics::min_align_of_val(val) }
+}
+
 /// Returns the ABI-required minimum alignment of the type of the value that `_val` points to
 ///
 /// # Examples
@@ -127,6 +160,7 @@ pub fn min_align_of<T>() -> usize {
 ///
 /// assert_eq!(4, mem::min_align_of_val(&5i32));
 /// ```
+#[cfg(stage0)] // SNAP c64d671
 #[inline]
 #[stable(feature = "rust1", since = "1.0.0")]
 pub fn min_align_of_val<T>(_val: &T) -> usize {

src/libcore/nonzero.rs

@@ -12,6 +12,8 @@
 
 use marker::Sized;
 use ops::Deref;
+#[cfg(not(stage0))] // SNAP c64d671
+use ops::CoerceUnsized;
 
 /// Unsafe trait to indicate what types are usable with the NonZero struct
 pub unsafe trait Zeroable {}
@@ -54,3 +56,6 @@ impl<T: Zeroable> Deref for NonZero<T> {
         inner
     }
 }
+
+#[cfg(not(stage0))] // SNAP c64d671
+impl<T: Zeroable+CoerceUnsized<U>, U: Zeroable> CoerceUnsized<NonZero<U>> for NonZero<T> {}

src/libcore/ops.rs

@@ -70,6 +70,9 @@
 use marker::Sized;
 use fmt;
 
+#[cfg(not(stage0))] // SNAP c64d671
+use marker::Unsize;
+
 /// The `Drop` trait is used to run some code when a value goes out of scope. This
 /// is sometimes called a 'destructor'.
 ///
@@ -1207,3 +1210,34 @@ mod impls {
         }
     }
 }
+
+/// Trait that indicates that this is a pointer or a wrapper for one,
+/// where unsizing can be performed on the pointee.
+#[unstable(feature = "core")]
+#[cfg(not(stage0))] // SNAP c64d671
+#[lang="coerce_unsized"]
+pub trait CoerceUnsized<T> {
+    // Empty.
+}
+
+#[cfg(not(stage0))] // SNAP c64d671
+impl<'a, T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<&'a mut U> for &'a mut T {}
+#[cfg(not(stage0))] // SNAP c64d671
+impl<'a, 'b: 'a, T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b mut T {}
+#[cfg(not(stage0))] // SNAP c64d671
+impl<'a, T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for &'a mut T {}
+#[cfg(not(stage0))] // SNAP c64d671
+impl<'a, T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for &'a mut T {}
+
+#[cfg(not(stage0))] // SNAP c64d671
+impl<'a, 'b: 'a, T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<&'a U> for &'b T {}
+#[cfg(not(stage0))] // SNAP c64d671
+impl<'a, T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for &'a T {}
+
+#[cfg(not(stage0))] // SNAP c64d671
+impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<*mut U> for *mut T {}
+#[cfg(not(stage0))] // SNAP c64d671
+impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *mut T {}
+
+#[cfg(not(stage0))] // SNAP c64d671
+impl<T: ?Sized+Unsize<U>, U: ?Sized> CoerceUnsized<*const U> for *const T {}

src/librustc/diagnostics.rs

@@ -807,6 +807,9 @@ register_diagnostics! {
     E0017,
     E0019,
     E0022,
+    E0038,
+    E0079, // enum variant: expected signed integer constant
+    E0080, // enum variant: constant evaluation error
     E0109,
     E0110,
     E0134,

src/librustc/metadata/common.rs

@@ -259,3 +259,5 @@ pub const tag_codemap_filemap: usize = 0xa2;
 pub const tag_item_super_predicates: usize = 0xa3;
 
 pub const tag_defaulted_trait: usize = 0xa4;
+
+pub const tag_impl_coerce_unsized_kind: usize = 0xa5;

src/librustc/metadata/csearch.rs

@@ -279,6 +279,14 @@ pub fn get_impl_polarity<'tcx>(tcx: &ty::ctxt<'tcx>,
     decoder::get_impl_polarity(&*cdata, def.node)
 }
 
+pub fn get_custom_coerce_unsized_kind<'tcx>(tcx: &ty::ctxt<'tcx>,
+                                            def: ast::DefId)
+                                            -> Option<ty::CustomCoerceUnsized> {
+    let cstore = &tcx.sess.cstore;
+    let cdata = cstore.get_crate_data(def.krate);
+    decoder::get_custom_coerce_unsized_kind(&*cdata, def.node)
+}
+
 // Given a def_id for an impl, return the trait it implements,
 // if there is one.
 pub fn get_impl_trait<'tcx>(tcx: &ty::ctxt<'tcx>,

src/librustc/metadata/decoder.rs

@@ -489,6 +489,16 @@ pub fn get_impl_polarity<'tcx>(cdata: Cmd,
     }
 }
 
+pub fn get_custom_coerce_unsized_kind<'tcx>(cdata: Cmd,
+                                            id: ast::NodeId)
+                                            -> Option<ty::CustomCoerceUnsized> {
+    let item_doc = lookup_item(id, cdata.data());
+    reader::maybe_get_doc(item_doc, tag_impl_coerce_unsized_kind).map(|kind_doc| {
+        let mut decoder = reader::Decoder::new(kind_doc);
+        Decodable::decode(&mut decoder).unwrap()
+    })
+}
+
 pub fn get_impl_trait<'tcx>(cdata: Cmd,
                             id: ast::NodeId,
                             tcx: &ty::ctxt<'tcx>)

src/librustc/metadata/encoder.rs

@@ -1219,6 +1219,16 @@ fn encode_info_for_item(ecx: &EncodeContext,
         encode_attributes(rbml_w, &item.attrs);
         encode_unsafety(rbml_w, unsafety);
         encode_polarity(rbml_w, polarity);
+
+        match tcx.custom_coerce_unsized_kinds.borrow().get(&local_def(item.id)) {
+            Some(&kind) => {
+                rbml_w.start_tag(tag_impl_coerce_unsized_kind);
+                kind.encode(rbml_w);
+                rbml_w.end_tag();
+            }
+            None => {}
+        }
+
         match ty.node {
             ast::TyPath(None, ref path) if path.segments.len() == 1 => {
                 let name = path.segments.last().unwrap().identifier.name;

src/librustc/middle/expr_use_visitor.rs

@@ -890,10 +890,6 @@ impl<'d,'t,'tcx,TYPER:mc::Typer<'tcx>> ExprUseVisitor<'d,'t,'tcx,TYPER> {
             }
         };
 
-        debug!("walk_autoref: expr.id={} cmt_base={}",
-               expr.id,
-               cmt_base.repr(self.tcx()));
-
         match *autoref {
             ty::AutoPtr(r, m) => {
                 self.delegate.borrow(expr.id,

src/librustc/middle/lang_items.rs

@@ -261,11 +261,14 @@ lets_do_this! {
 
     SendTraitLangItem,               "send",                    send_trait;
     SizedTraitLangItem,              "sized",                   sized_trait;
+    UnsizeTraitLangItem,             "unsize",                  unsize_trait;
     CopyTraitLangItem,               "copy",                    copy_trait;
     SyncTraitLangItem,               "sync",                    sync_trait;
 
     DropTraitLangItem,               "drop",                    drop_trait;
 
+    CoerceUnsizedTraitLangItem,      "coerce_unsized",          coerce_unsized_trait;
+
     AddTraitLangItem,                "add",                     add_trait;
     SubTraitLangItem,                "sub",                     sub_trait;
     MulTraitLangItem,                "mul",                     mul_trait;

src/librustc/middle/traits/error_reporting.rs

@@ -15,8 +15,12 @@ use super::{
     Obligation,
     ObligationCauseCode,
     OutputTypeParameterMismatch,
+    TraitNotObjectSafe,
     PredicateObligation,
     SelectionError,
+    ObjectSafetyViolation,
+    MethodViolationCode,
+    object_safety_violations,
 };
 
 use fmt_macros::{Parser, Piece, Position};
@@ -252,6 +256,54 @@ pub fn report_selection_error<'a, 'tcx>(infcx: &InferCtxt<'a, 'tcx>,
                     note_obligation_cause(infcx, obligation);
             }
         }
+
+        TraitNotObjectSafe(did) => {
+            span_err!(infcx.tcx.sess, obligation.cause.span, E0038,
+                "cannot convert to a trait object because trait `{}` is not object-safe",
+                ty::item_path_str(infcx.tcx, did));
+
+            for violation in object_safety_violations(infcx.tcx, did) {
+                match violation {
+                    ObjectSafetyViolation::SizedSelf => {
+                        infcx.tcx.sess.span_note(
+                            obligation.cause.span,
+                            "the trait cannot require that `Self : Sized`");
+                    }
+
+                    ObjectSafetyViolation::SupertraitSelf => {
+                        infcx.tcx.sess.span_note(
+                            obligation.cause.span,
+                            "the trait cannot use `Self` as a type parameter \
+                            in the supertrait listing");
+                    }
+
+                    ObjectSafetyViolation::Method(method,
+                            MethodViolationCode::StaticMethod) => {
+                        infcx.tcx.sess.span_note(
+                            obligation.cause.span,
+                            &format!("method `{}` has no receiver",
+                                    method.name.user_string(infcx.tcx)));
+                    }
+
+                    ObjectSafetyViolation::Method(method,
+                            MethodViolationCode::ReferencesSelf) => {
+                        infcx.tcx.sess.span_note(
+                            obligation.cause.span,
+                            &format!("method `{}` references the `Self` type \
+                                    in its arguments or return type",
+                                    method.name.user_string(infcx.tcx)));
+                    }
+
+                    ObjectSafetyViolation::Method(method,
+                            MethodViolationCode::Generic) => {
+                        infcx.tcx.sess.span_note(
+                            obligation.cause.span,
+                            &format!("method `{}` has generic type parameters",
+                                    method.name.user_string(infcx.tcx)));
+                    }
+                }
+            }
+        }
     }
 }
 
@@ -403,10 +455,6 @@ fn note_obligation_cause_code<'a, 'tcx, T>(infcx: &InferCtxt<'a, 'tcx>,
                        "only the last field of a struct or enum variant \
                        may have a dynamically sized type")
         }
-        ObligationCauseCode::ObjectSized => {
-            span_note!(tcx.sess, cause_span,
-                       "only sized types can be made into objects");
-        }
         ObligationCauseCode::SharedStatic => {
             span_note!(tcx.sess, cause_span,
                        "shared static variables must have a type that implements `Sync`");

src/librustc/middle/traits/mod.rs

@@ -28,6 +28,7 @@ use util::ppaux::Repr;
 
 pub use self::error_reporting::report_fulfillment_errors;
 pub use self::error_reporting::report_overflow_error;
+pub use self::error_reporting::report_selection_error;
 pub use self::error_reporting::suggest_new_overflow_limit;
 pub use self::coherence::orphan_check;
 pub use self::coherence::overlapping_impls;
@@ -48,6 +49,7 @@ pub use self::select::{MethodMatchedData}; // intentionally don't export variant
 pub use self::util::elaborate_predicates;
 pub use self::util::get_vtable_index_of_object_method;
 pub use self::util::trait_ref_for_builtin_bound;
+pub use self::util::predicate_for_trait_def;
 pub use self::util::supertraits;
 pub use self::util::Supertraits;
 pub use self::util::supertrait_def_ids;
@@ -121,9 +123,6 @@ pub enum ObligationCauseCode<'tcx> {
     // Types of fields (other than the last) in a struct must be sized.
     FieldSized,
 
-    // Only Sized types can be made into objects
-    ObjectSized,
-
     // static items must have `Sync` type
     SharedStatic,
 
@@ -159,6 +158,7 @@ pub enum SelectionError<'tcx> {
     OutputTypeParameterMismatch(ty::PolyTraitRef<'tcx>,
                                 ty::PolyTraitRef<'tcx>,
                                 ty::type_err<'tcx>),
+    TraitNotObjectSafe(ast::DefId),
 }
 
 pub struct FulfillmentError<'tcx> {
@@ -536,7 +536,9 @@ impl<'tcx, N> Vtable<'tcx, N> {
         }
     }
 
-    pub fn map_nested<M, F>(&self, op: F) -> Vtable<'tcx, M> where F: FnMut(&N) -> M {
+    pub fn map_nested<M, F>(&self, op: F) -> Vtable<'tcx, M> where
+        F: FnMut(&N) -> M,
+    {
         match *self {
             VtableImpl(ref i) => VtableImpl(i.map_nested(op)),
             VtableDefaultImpl(ref t) => VtableDefaultImpl(t.map_nested(op)),