Auto merge of #39075 - est31:remove_reflect, r=nikomatsakis

Remove Reflect

PR for removing the `Reflect` trait. Opened so that a crater run can be done for testing the impact: #27749 (comment)

Fixes #27749

Author: bors

src/libcore/lib.rs

@@ -82,7 +82,6 @@
 #![feature(no_core)]
 #![feature(on_unimplemented)]
 #![feature(optin_builtin_traits)]
-#![feature(reflect)]
 #![feature(unwind_attributes)]
 #![feature(repr_simd, platform_intrinsics)]
 #![feature(rustc_attrs)]

src/libcore/marker.rs

@@ -553,59 +553,3 @@ mod impls {
     #[stable(feature = "rust1", since = "1.0.0")]
     unsafe impl<'a, T: Send + ?Sized> Send for &'a mut T {}
 }
-
-/// Types that can be reflected over.
-///
-/// By "reflection" we mean use of the [`Any`][any] trait, or related
-/// machinery such as [`TypeId`][typeid].
-///
-/// `Reflect` is implemented for all types. Its purpose is to ensure
-/// that when you write a generic function that will employ reflection,
-/// that must be reflected (no pun intended) in the generic bounds of
-/// that function.
-///
-/// ```
-/// #![feature(reflect_marker)]
-/// use std::marker::Reflect;
-/// use std::any::Any;
-///
-/// # #[allow(dead_code)]
-/// fn foo<T: Reflect + 'static>(x: &T) {
-///     let any: &Any = x;
-///     if any.is::<u32>() { println!("u32"); }
-/// }
-/// ```
-///
-/// Without the bound `T: Reflect`, `foo` would not typecheck. (As
-/// a matter of style, it would be preferable to write `T: Any`,
-/// because `T: Any` implies `T: Reflect` and `T: 'static`, but we
-/// use `Reflect` here for illustrative purposes.)
-///
-/// The `Reflect` bound serves to alert `foo`'s caller to the
-/// fact that `foo` may behave differently depending on whether
-/// `T` is `u32` or not. The ability for a caller to reason about what
-/// a function may do based solely on what generic bounds are declared
-/// is often called the "[parametricity property][param]". Despite the
-/// use of `Reflect`, Rust lacks true parametricity because a generic
-/// function can, at the very least, call [`mem::size_of`][size_of]
-/// without employing any trait bounds whatsoever.
-///
-/// [any]: ../any/trait.Any.html
-/// [typeid]: ../any/struct.TypeId.html
-/// [param]: http://en.wikipedia.org/wiki/Parametricity
-/// [size_of]: ../mem/fn.size_of.html
-#[rustc_reflect_like]
-#[unstable(feature = "reflect_marker",
-           reason = "requires RFC and more experience",
-           issue = "27749")]
-#[rustc_deprecated(since = "1.14.0", reason = "Specialization makes parametricity impossible")]
-#[rustc_on_unimplemented = "`{Self}` does not implement `Any`; \
-                            ensure all type parameters are bounded by `Any`"]
-pub trait Reflect {}
-
-#[unstable(feature = "reflect_marker",
-           reason = "requires RFC and more experience",
-           issue = "27749")]
-#[rustc_deprecated(since = "1.14.0", reason = "Specialization makes parametricity impossible")]
-#[allow(deprecated)]
-impl Reflect for .. { }

src/librustc/traits/select.rs

@@ -204,7 +204,6 @@ enum SelectionCandidate<'tcx> {
     ParamCandidate(ty::PolyTraitRef<'tcx>),
     ImplCandidate(DefId),
     DefaultImplCandidate(DefId),
-    DefaultImplObjectCandidate(DefId),
 
     /// This is a trait matching with a projected type as `Self`, and
     /// we found an applicable bound in the trait definition.
@@ -237,9 +236,6 @@ impl<'a, 'tcx> ty::Lift<'tcx> for SelectionCandidate<'a> {
             }
             ImplCandidate(def_id) => ImplCandidate(def_id),
             DefaultImplCandidate(def_id) => DefaultImplCandidate(def_id),
-            DefaultImplObjectCandidate(def_id) => {
-                DefaultImplObjectCandidate(def_id)
-            }
             ProjectionCandidate => ProjectionCandidate,
             FnPointerCandidate => FnPointerCandidate,
             ObjectCandidate => ObjectCandidate,
@@ -1431,17 +1427,9 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
             match self_ty.sty {
                 ty::TyDynamic(..) => {
                     // For object types, we don't know what the closed
-                    // over types are. For most traits, this means we
-                    // conservatively say nothing; a candidate may be
-                    // added by `assemble_candidates_from_object_ty`.
-                    // However, for the kind of magic reflect trait,
-                    // we consider it to be implemented even for
-                    // object types, because it just lets you reflect
-                    // onto the object type, not into the object's
-                    // interior.
-                    if self.tcx().has_attr(def_id, "rustc_reflect_like") {
-                        candidates.vec.push(DefaultImplObjectCandidate(def_id));
-                    }
+                    // over types are. This means we conservatively
+                    // say nothing; a candidate may be added by
+                    // `assemble_candidates_from_object_ty`.
                 }
                 ty::TyParam(..) |
                 ty::TyProjection(..) |
@@ -1671,7 +1659,6 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 FnPointerCandidate |
                 BuiltinObjectCandidate |
                 BuiltinUnsizeCandidate |
-                DefaultImplObjectCandidate(..) |
                 BuiltinCandidate { .. } => {
                     // We have a where-clause so don't go around looking
                     // for impls.
@@ -1998,11 +1985,6 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
                 Ok(VtableDefaultImpl(data))
             }
 
-            DefaultImplObjectCandidate(trait_def_id) => {
-                let data = self.confirm_default_impl_object_candidate(obligation, trait_def_id);
-                Ok(VtableDefaultImpl(data))
-            }
-
             ImplCandidate(impl_def_id) => {
                 Ok(VtableImpl(self.confirm_impl_candidate(obligation, impl_def_id)))
             }
@@ -2138,42 +2120,6 @@ impl<'cx, 'gcx, 'tcx> SelectionContext<'cx, 'gcx, 'tcx> {
         self.vtable_default_impl(obligation, trait_def_id, ty::Binder(types))
     }
 
-    fn confirm_default_impl_object_candidate(&mut self,
-                                             obligation: &TraitObligation<'tcx>,
-                                             trait_def_id: DefId)
-                                             -> VtableDefaultImplData<PredicateObligation<'tcx>>
-    {
-        debug!("confirm_default_impl_object_candidate({:?}, {:?})",
-               obligation,
-               trait_def_id);
-
-        assert!(self.tcx().has_attr(trait_def_id, "rustc_reflect_like"));
-
-        // OK to skip binder, it is reintroduced below
-        let self_ty = self.infcx.shallow_resolve(obligation.predicate.skip_binder().self_ty());
-        match self_ty.sty {
-            ty::TyDynamic(ref data, ..) => {
-                // OK to skip the binder, it is reintroduced below
-                let principal = data.principal().unwrap();
-                let input_types = principal.input_types();
-                let assoc_types = data.projection_bounds()
-                                      .map(|pb| pb.skip_binder().ty);
-                let all_types: Vec<_> = input_types.chain(assoc_types)
-                                                   .collect();
-
-                // reintroduce the two binding levels we skipped, then flatten into one
-                let all_types = ty::Binder(ty::Binder(all_types));
-                let all_types = self.tcx().flatten_late_bound_regions(&all_types);
-
-                self.vtable_default_impl(obligation, trait_def_id, all_types)
-            }
-            _ => {
-                bug!("asked to confirm default object implementation for non-object type: {:?}",
-                     self_ty);
-            }
-        }
-    }
-
     /// See `confirm_default_impl_candidate`
     fn vtable_default_impl(&mut self,
                            obligation: &TraitObligation<'tcx>,

src/libsyntax/feature_gate.rs

@@ -124,7 +124,6 @@ declare_features! (
     (active, advanced_slice_patterns, "1.0.0", Some(23121)),
     (active, box_syntax, "1.0.0", Some(27779)),
     (active, placement_in_syntax, "1.0.0", Some(27779)),
-    (active, reflect, "1.0.0", Some(27749)),
     (active, unboxed_closures, "1.0.0", Some(29625)),
 
     (active, allocator, "1.0.0", Some(27389)),
@@ -337,6 +336,7 @@ declare_features! (
     (removed, managed_boxes, "1.0.0", None),
     // Allows use of unary negate on unsigned integers, e.g. -e for e: u8
     (removed, negate_unsigned, "1.0.0", Some(29645)),
+    (removed, reflect, "1.0.0", Some(27749)),
     // A way to temporarily opt out of opt in copy. This will *never* be accepted.
     (removed, opt_out_copy, "1.0.0", None),
     (removed, quad_precision_float, "1.0.0", None),
@@ -734,10 +734,6 @@ pub const BUILTIN_ATTRIBUTES: &'static [(&'static str, AttributeType, AttributeG
                                         "unboxed_closures",
                                         "unboxed_closures are still evolving",
                                         cfg_fn!(unboxed_closures))),
-    ("rustc_reflect_like", Whitelisted, Gated(Stability::Unstable,
-                                              "reflect",
-                                              "defining reflective traits is still evolving",
-                                              cfg_fn!(reflect))),
 
     ("windows_subsystem", Whitelisted, Gated(Stability::Unstable,
                                              "windows_subsystem",

src/test/compile-fail/reflect-assoc.rs

@@ -167,7 +167,7 @@ pub fn check(path: &Path, bad: &mut bool) {
     // FIXME get this whitelist empty.
     let whitelist = vec![
         "abi_ptx", "simd", "macro_reexport",
-        "static_recursion", "reflect", "quote",
+        "static_recursion", "quote",
         "cfg_target_has_atomic", "staged_api", "const_indexing",
         "unboxed_closures", "stmt_expr_attributes",
         "cfg_target_thread_local", "unwind_attributes",