Auto merge of #65671 - Centril:rollup-00glhmb, r=Centril

Rollup of 7 pull requests

Successful merges:

 - #62330 (Change untagged_unions to not allow union fields with drop)
 - #65092 (make is_power_of_two a const function)
 - #65621 (miri: add write_bytes method to Memory doing bounds-checks and supporting iterators)
 - #65647 (Remove unnecessary trait bounds and derivations)
 - #65653 (keep the root dir clean from debugging)
 - #65660 (Rename `ConstValue::Infer(InferConst::Canonical(..))` to `ConstValue::Bound(..)`)
 - #65663 (Fix typo from #65214)

Failed merges:

r? @ghost

.gitignore

@@ -1,6 +1,10 @@
-# This file should only ignore things that are generated during a build,
+# This file should only ignore things that are generated during a `x.py` build,
-# generated by common IDEs, and optional files controlled by the user
+# generated by common IDEs, and optional files controlled by the user that
-# that affect the build (such as config.toml).
+# affect the build (such as config.toml).
+# In particular, things like `mir_dump` should not be listed here; they are only
+# created during manual debugging and many people like to clean up instead of
+# having git ignore such leftovers. You can use `.git/info/exclude` to
+# configure your local ignore list.
 # FIXME: This needs cleanup.
 *~
 .#*
@@ -52,6 +56,4 @@ config.stamp
 Session.vim
 .cargo
 no_llvm_build
-# Generated when dumping Graphviz output for debugging:
+# Before adding new lines, see the comment at the top.
-/mir_dump/
-/*.dot

src/bootstrap/cache.rs

@@ -161,7 +161,7 @@ impl Ord for Interned<String> {
     }
 }
 
-struct TyIntern<T: Hash + Clone + Eq> {
+struct TyIntern<T: Clone + Eq> {
     items: Vec<T>,
     set: HashMap<T, Interned<T>>,
 }

src/doc/rustc/src/lints/listing/warn-by-default.md

@@ -596,30 +596,6 @@ warning: function cannot return without recursing
   |
 ```
 
-## unions-with-drop-fields
-
-This lint detects use of unions that contain fields with possibly non-trivial drop code. Some
-example code that triggers this lint:
-
-```rust
-#![feature(untagged_unions)]
-
-union U {
-    s: String,
-}
-```
-
-This will produce:
-
-```text
-warning: union contains a field with possibly non-trivial drop code, drop code of union fields is ignored when dropping the union
- --> src/main.rs:4:5
-  |
-4 |     s: String,
-  |     ^^^^^^^^^
-  |
-```
-
 ## unknown-lints
 
 This lint detects unrecognized lint attribute. Some

src/libcore/num/mod.rs

@@ -3757,8 +3757,8 @@ assert!(!10", stringify!($SelfT), ".is_power_of_two());", $EndFeature, "
 ```"),
             #[stable(feature = "rust1", since = "1.0.0")]
             #[inline]
-            pub fn is_power_of_two(self) -> bool {
+            pub const fn is_power_of_two(self) -> bool {
-                (self.wrapping_sub(1)) & self == 0 && !(self == 0)
+                self.count_ones() == 1
             }
         }
 

src/librustc/Cargo.toml

@@ -36,5 +36,5 @@ parking_lot = "0.9"
 byteorder = { version = "1.3" }
 chalk-engine = { version = "0.9.0", default-features=false }
 rustc_fs_util = { path = "../librustc_fs_util" }
-smallvec = { version = "0.6.7", features = ["union", "may_dangle"] }
+smallvec = { version = "0.6.8", features = ["union", "may_dangle"] }
 measureme = "0.3"

src/librustc/dep_graph/graph.rs

@@ -35,7 +35,7 @@ impl DepNodeIndex {
     pub const INVALID: DepNodeIndex = DepNodeIndex::MAX;
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(PartialEq)]
 pub enum DepNodeColor {
     Red,
     Green(DepNodeIndex)

src/librustc/hir/map/definitions.rs

@@ -599,7 +599,6 @@ macro_rules! define_global_metadata_kind {
     (pub enum GlobalMetaDataKind {
         $($variant:ident),*
     }) => (
-        #[derive(Clone, Copy, Debug, Hash, RustcEncodable, RustcDecodable)]
         pub enum GlobalMetaDataKind {
             $($variant),*
         }

src/librustc/hir/mod.rs

@@ -1077,7 +1077,7 @@ impl Mutability {
     }
 }
 
-#[derive(Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Hash, HashStable)]
+#[derive(Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, HashStable)]
 pub enum BinOpKind {
     /// The `+` operator (addition).
     Add,
@@ -1211,7 +1211,7 @@ impl Into<ast::BinOpKind> for BinOpKind {
 
 pub type BinOp = Spanned<BinOpKind>;
 
-#[derive(Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Hash, HashStable)]
+#[derive(Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, HashStable)]
 pub enum UnOp {
     /// The `*` operator (deferencing).
     UnDeref,
@@ -1388,8 +1388,7 @@ impl Body {
 }
 
 /// The type of source expression that caused this generator to be created.
-#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, HashStable,
+#[derive(Clone, PartialEq, Eq, HashStable, RustcEncodable, RustcDecodable, Debug, Copy)]
-         RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
 pub enum GeneratorKind {
     /// An explicit `async` block or the body of an async function.
     Async(AsyncGeneratorKind),
@@ -1412,8 +1411,7 @@ impl fmt::Display for GeneratorKind {
 ///
 /// This helps error messages but is also used to drive coercions in
 /// type-checking (see #60424).
-#[derive(Clone, PartialEq, Eq, PartialOrd, Ord, HashStable,
+#[derive(Clone, PartialEq, Eq, HashStable, RustcEncodable, RustcDecodable, Debug, Copy)]
-         RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
 pub enum AsyncGeneratorKind {
     /// An explicit `async` block written by the user.
     Block,

src/librustc/hir/ptr.rs

@@ -11,7 +11,7 @@ use rustc_serialize::{Encodable, Decodable, Encoder, Decoder};
 
 use rustc_data_structures::stable_hasher::{StableHasher, HashStable};
 /// An owned smart pointer.
-#[derive(Hash, PartialEq, Eq)]
+#[derive(PartialEq, Eq)]
 pub struct P<T: ?Sized> {
     ptr: Box<T>
 }

src/librustc/infer/canonical/canonicalizer.rs

@@ -468,7 +468,7 @@ impl<'cx, 'tcx> TypeFolder<'tcx> for Canonicalizer<'cx, 'tcx> {
             ConstValue::Infer(InferConst::Fresh(_)) => {
                 bug!("encountered a fresh const during canonicalization")
             }
-            ConstValue::Infer(InferConst::Canonical(debruijn, _)) => {
+            ConstValue::Bound(debruijn, _) => {
                 if debruijn >= self.binder_index {
                     bug!("escaping bound type during canonicalization")
                 } else {
@@ -700,7 +700,7 @@ impl<'cx, 'tcx> Canonicalizer<'cx, 'tcx> {
             let var = self.canonical_var(info, const_var.into());
             self.tcx().mk_const(
                 ty::Const {
-                    val: ConstValue::Infer(InferConst::Canonical(self.binder_index, var.into())),
+                    val: ConstValue::Bound(self.binder_index, var.into()),
                     ty: self.fold_ty(const_var.ty),
                 }
             )

src/librustc/infer/canonical/mod.rs

@@ -33,7 +33,7 @@ use std::ops::Index;
 use syntax::source_map::Span;
 use crate::ty::fold::TypeFoldable;
 use crate::ty::subst::GenericArg;
-use crate::ty::{self, BoundVar, InferConst, Lift, List, Region, TyCtxt};
+use crate::ty::{self, BoundVar, Lift, List, Region, TyCtxt};
 
 mod canonicalizer;
 
@@ -73,7 +73,7 @@ pub struct CanonicalVarValues<'tcx> {
 /// various parts of it with canonical variables. This struct stores
 /// those replaced bits to remember for when we process the query
 /// result.
-#[derive(Clone, Debug, PartialEq, Eq, Hash, RustcDecodable, RustcEncodable)]
+#[derive(Clone, Debug)]
 pub struct OriginalQueryValues<'tcx> {
     /// Map from the universes that appear in the query to the
     /// universes in the caller context. For the time being, we only
@@ -510,9 +510,7 @@ impl<'tcx> CanonicalVarValues<'tcx> {
                     GenericArgKind::Const(ct) => {
                         tcx.mk_const(ty::Const {
                             ty: ct.ty,
-                            val: ConstValue::Infer(
+                            val: ConstValue::Bound(ty::INNERMOST, ty::BoundVar::from_u32(i)),
-                                InferConst::Canonical(ty::INNERMOST, ty::BoundVar::from_u32(i))
-                            ),
                         }).into()
                     }
                 })

src/librustc/infer/canonical/query_response.rs

@@ -26,7 +26,7 @@ use crate::traits::TraitEngine;
 use crate::traits::{Obligation, ObligationCause, PredicateObligation};
 use crate::ty::fold::TypeFoldable;
 use crate::ty::subst::{GenericArg, GenericArgKind};
-use crate::ty::{self, BoundVar, InferConst, Ty, TyCtxt};
+use crate::ty::{self, BoundVar, Ty, TyCtxt};
 use crate::util::captures::Captures;
 
 impl<'tcx> InferCtxtBuilder<'tcx> {
@@ -493,10 +493,7 @@ impl<'cx, 'tcx> InferCtxt<'cx, 'tcx> {
                     }
                 }
                 GenericArgKind::Const(result_value) => {
-                    if let ty::Const {
+                    if let ty::Const { val: ConstValue::Bound(debrujin, b), .. } = result_value {
-                        val: ConstValue::Infer(InferConst::Canonical(debrujin, b)),
-                        ..
-                    } = result_value {
                         // ...in which case we would set `canonical_vars[0]` to `Some(const X)`.
 
                         // We only allow a `ty::INNERMOST` index in substitutions.

src/librustc/infer/combine.rs

@@ -53,7 +53,7 @@ pub struct CombineFields<'infcx, 'tcx> {
     pub obligations: PredicateObligations<'tcx>,
 }
 
-#[derive(Copy, Clone, Eq, PartialEq, Hash, Debug)]
+#[derive(Copy, Clone, Debug)]
 pub enum RelationDir {
     SubtypeOf, SupertypeOf, EqTo
 }

src/librustc/infer/freshen.rs

@@ -252,7 +252,7 @@ impl<'a, 'tcx> TypeFolder<'tcx> for TypeFreshener<'a, 'tcx> {
                 return ct;
             }
 
-            ConstValue::Infer(ty::InferConst::Canonical(..)) |
+            ConstValue::Bound(..) |
             ConstValue::Placeholder(_) => {
                 bug!("unexpected const {:?}", ct)
             }

src/librustc/infer/mod.rs

@@ -407,7 +407,7 @@ pub enum RegionVariableOrigin {
     NLL(NLLRegionVariableOrigin),
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Copy, Clone, Debug)]
 pub enum NLLRegionVariableOrigin {
     /// During NLL region processing, we create variables for free
     /// regions that we encounter in the function signature and

src/librustc/infer/nll_relate/mod.rs

@@ -27,12 +27,12 @@ use crate::ty::error::TypeError;
 use crate::ty::fold::{TypeFoldable, TypeVisitor};
 use crate::ty::relate::{self, Relate, RelateResult, TypeRelation};
 use crate::ty::subst::GenericArg;
-use crate::ty::{self, Ty, TyCtxt, InferConst};
+use crate::ty::{self, Ty, TyCtxt};
 use crate::mir::interpret::ConstValue;
 use rustc_data_structures::fx::FxHashMap;
 use std::fmt::Debug;
 
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(PartialEq)]
 pub enum NormalizationStrategy {
     Lazy,
     Eager,
@@ -618,7 +618,7 @@ where
         a: &'tcx ty::Const<'tcx>,
         b: &'tcx ty::Const<'tcx>,
     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
-        if let ty::Const { val: ConstValue::Infer(InferConst::Canonical(_, _)), .. } = a {
+        if let ty::Const { val: ConstValue::Bound(..), .. } = a {
             // FIXME(const_generics): I'm unsure how this branch should actually be handled,
             // so this is probably not correct.
             self.infcx.super_combine_consts(self, a, b)
@@ -993,7 +993,7 @@ where
     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
         debug!("TypeGeneralizer::consts(a={:?})", a);
 
-        if let ty::Const { val: ConstValue::Infer(InferConst::Canonical(_, _)), .. } = a {
+        if let ty::Const { val: ConstValue::Bound(..), .. } = a {
             bug!(
                 "unexpected inference variable encountered in NLL generalization: {:?}",
                 a

src/librustc/infer/region_constraints/mod.rs

@@ -116,7 +116,7 @@ pub struct RegionConstraintData<'tcx> {
 }
 
 /// Represents a constraint that influences the inference process.
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, PartialOrd, Ord)]
+#[derive(Clone, Copy, PartialEq, Eq, Debug, PartialOrd, Ord)]
 pub enum Constraint<'tcx> {
     /// A region variable is a subregion of another.
     VarSubVar(RegionVid, RegionVid),

src/librustc/lib.rs

@@ -43,6 +43,7 @@
 #![feature(nll)]
 #![feature(non_exhaustive)]
 #![feature(optin_builtin_traits)]
+#![feature(option_expect_none)]
 #![feature(range_is_empty)]
 #![feature(slice_patterns)]
 #![feature(specialization)]

src/librustc/middle/cstore.rs

@@ -117,7 +117,7 @@ pub struct NativeLibrary {
     pub wasm_import_module: Option<Symbol>,
 }
 
-#[derive(Clone, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Clone, RustcEncodable, RustcDecodable, HashStable)]
 pub struct ForeignModule {
     pub foreign_items: Vec<DefId>,
     pub def_id: DefId,

src/librustc/middle/mem_categorization.rs

@@ -102,7 +102,7 @@ pub struct Upvar {
 }
 
 // different kinds of pointers:
-#[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+#[derive(Clone, Copy, Debug, PartialEq)]
 pub enum PointerKind<'tcx> {
     /// `Box<T>`
     Unique,
@@ -116,7 +116,7 @@ pub enum PointerKind<'tcx> {
 
 // We use the term "interior" to mean "something reachable from the
 // base without a pointer dereference", e.g., a field
-#[derive(Clone, Copy, PartialEq, Eq, Hash)]
+#[derive(Clone, PartialEq)]
 pub enum InteriorKind {
     InteriorField(FieldIndex),
     InteriorElement(InteriorOffsetKind),
@@ -139,13 +139,13 @@ impl Hash for FieldIndex {
     }
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, PartialEq)]
 pub enum InteriorOffsetKind {
     Index,   // e.g., `array_expr[index_expr]`
     Pattern, // e.g., `fn foo([_, a, _, _]: [A; 4]) { ... }`
 }
 
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, Copy, PartialEq, Debug)]
 pub enum MutabilityCategory {
     McImmutable, // Immutable.
     McDeclared,  // Directly declared as mutable.

src/librustc/middle/stability.rs

@@ -25,7 +25,7 @@ use crate::util::nodemap::{FxHashSet, FxHashMap};
 use std::mem::replace;
 use std::cmp::Ordering;
 
-#[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Clone, Copy, Debug, Eq, Hash)]
+#[derive(PartialEq, Clone, Copy, Debug)]
 pub enum StabilityLevel {
     Unstable,
     Stable,

src/librustc/mir/interpret/allocation.rs

@@ -245,6 +245,8 @@ impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
     /// as a slice.
     ///
     /// It is the caller's responsibility to check bounds and alignment beforehand.
+    /// Most likely, you want to use the `PlaceTy` and `OperandTy`-based methods
+    /// on `InterpCx` instead.
     #[inline]
     pub fn get_bytes(
         &self,
@@ -275,6 +277,8 @@ impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
     /// so be sure to actually put data there!
     ///
     /// It is the caller's responsibility to check bounds and alignment beforehand.
+    /// Most likely, you want to use the `PlaceTy` and `OperandTy`-based methods
+    /// on `InterpCx` instead.
     pub fn get_bytes_mut(
         &mut self,
         cx: &impl HasDataLayout,
@@ -297,6 +301,8 @@ impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
 impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
     /// Reads bytes until a `0` is encountered. Will error if the end of the allocation is reached
     /// before a `0` is found.
+    ///
+    /// Most likely, you want to call `Memory::read_c_str` instead of this method.
     pub fn read_c_str(
         &self,
         cx: &impl HasDataLayout,
@@ -342,33 +348,22 @@ impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
     /// Writes `src` to the memory starting at `ptr.offset`.
     ///
     /// It is the caller's responsibility to check bounds and alignment beforehand.
+    /// Most likely, you want to call `Memory::write_bytes` instead of this method.
     pub fn write_bytes(
         &mut self,
         cx: &impl HasDataLayout,
         ptr: Pointer<Tag>,
-        src: &[u8],
+        src: impl IntoIterator<Item=u8, IntoIter: iter::ExactSizeIterator>,
     ) -> InterpResult<'tcx>
     {
+        let mut src = src.into_iter();
         let bytes = self.get_bytes_mut(cx, ptr, Size::from_bytes(src.len() as u64))?;
-        bytes.clone_from_slice(src);
+        // `zip` would stop when the first iterator ends; we want to definitely
-        Ok(())
+        // cover all of `bytes`.
-    }
+        for dest in bytes {
-
+            *dest = src.next().expect("iterator was shorter than it said it would be");
-    /// Sets `count` bytes starting at `ptr.offset` with `val`. Basically `memset`.
-    ///
-    /// It is the caller's responsibility to check bounds and alignment beforehand.
-    pub fn write_repeat(
-        &mut self,
-        cx: &impl HasDataLayout,
-        ptr: Pointer<Tag>,
-        val: u8,
-        count: Size
-    ) -> InterpResult<'tcx>
-    {
-        let bytes = self.get_bytes_mut(cx, ptr, count)?;
-        for b in bytes {
-            *b = val;
         }
+        src.next().expect_none("iterator was longer than it said it would be");
         Ok(())
     }
 
@@ -380,6 +375,7 @@ impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
     ///   pointers being valid for ZSTs.
     ///
     /// It is the caller's responsibility to check bounds and alignment beforehand.
+    /// Most likely, you want to call `InterpCx::read_scalar` instead of this method.
     pub fn read_scalar(
         &self,
         cx: &impl HasDataLayout,
@@ -418,6 +414,7 @@ impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
     /// Reads a pointer-sized scalar.
     ///
     /// It is the caller's responsibility to check bounds and alignment beforehand.
+    /// Most likely, you want to call `InterpCx::read_scalar` instead of this method.
     pub fn read_ptr_sized(
         &self,
         cx: &impl HasDataLayout,
@@ -435,6 +432,7 @@ impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
     ///   pointers being valid for ZSTs.
     ///
     /// It is the caller's responsibility to check bounds and alignment beforehand.
+    /// Most likely, you want to call `InterpCx::write_scalar` instead of this method.
     pub fn write_scalar(
         &mut self,
         cx: &impl HasDataLayout,
@@ -477,6 +475,7 @@ impl<'tcx, Tag: Copy, Extra: AllocationExtra<Tag>> Allocation<Tag, Extra> {
     /// Writes a pointer-sized scalar.
     ///
     /// It is the caller's responsibility to check bounds and alignment beforehand.
+    /// Most likely, you want to call `InterpCx::write_scalar` instead of this method.
     pub fn write_ptr_sized(
         &mut self,
         cx: &impl HasDataLayout,

src/librustc/mir/interpret/value.rs

@@ -5,11 +5,12 @@ use rustc_apfloat::{Float, ieee::{Double, Single}};
 use crate::ty::{Ty, InferConst, ParamConst, layout::{HasDataLayout, Size}, subst::SubstsRef};
 use crate::ty::PlaceholderConst;
 use crate::hir::def_id::DefId;
+use crate::ty::{BoundVar, DebruijnIndex};
 
 use super::{InterpResult, Pointer, PointerArithmetic, Allocation, AllocId, sign_extend, truncate};
 
 /// Represents the result of a raw const operation, pre-validation.
-#[derive(Copy, Clone, Debug, Eq, PartialEq, RustcEncodable, RustcDecodable, Hash, HashStable)]
+#[derive(Clone, HashStable)]
 pub struct RawConst<'tcx> {
     // the value lives here, at offset 0, and that allocation definitely is a `AllocKind::Memory`
     // (so you can use `AllocMap::unwrap_memory`).
@@ -28,6 +29,9 @@ pub enum ConstValue<'tcx> {
     /// Infer the value of the const.
     Infer(InferConst<'tcx>),
 
+    /// Bound const variable, used only when preparing a trait query.
+    Bound(DebruijnIndex, BoundVar),
+
     /// A placeholder const - universally quantified higher-ranked const.
     Placeholder(PlaceholderConst),
 
@@ -66,8 +70,9 @@ impl<'tcx> ConstValue<'tcx> {
         match *self {
             ConstValue::Param(_) |
             ConstValue::Infer(_) |
+            ConstValue::Bound(..) |
             ConstValue::Placeholder(_) |
-            ConstValue::ByRef{ .. } |
+            ConstValue::ByRef { .. } |
             ConstValue::Unevaluated(..) |
             ConstValue::Slice { .. } => None,
             ConstValue::Scalar(val) => Some(val),
@@ -487,7 +492,7 @@ impl<Tag> From<Pointer<Tag>> for Scalar<Tag> {
     }
 }
 
-#[derive(Clone, Copy, Eq, PartialEq, Ord, PartialOrd, Hash, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Copy, Eq, PartialEq, RustcEncodable, RustcDecodable)]
 pub enum ScalarMaybeUndef<Tag = (), Id = AllocId> {
     Scalar(Scalar<Tag, Id>),
     Undef,

src/librustc/mir/mod.rs

@@ -468,7 +468,7 @@ impl<T: Decodable> rustc_serialize::UseSpecializedDecodable for ClearCrossCrate<
 /// Grouped information about the source code origin of a MIR entity.
 /// Intended to be inspected by diagnostics and debuginfo.
 /// Most passes can work with it as a whole, within a single function.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, HashStable)]
+#[derive(Copy, Clone, Debug, PartialEq, RustcEncodable, RustcDecodable, HashStable)]
 pub struct SourceInfo {
     /// The source span for the AST pertaining to this MIR entity.
     pub span: Span,
@@ -608,7 +608,7 @@ pub enum LocalKind {
     ReturnPointer,
 }
 
-#[derive(Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
 pub struct VarBindingForm<'tcx> {
     /// Is variable bound via `x`, `mut x`, `ref x`, or `ref mut x`?
     pub binding_mode: ty::BindingMode,
@@ -630,7 +630,7 @@ pub struct VarBindingForm<'tcx> {
     pub pat_span: Span,
 }
 
-#[derive(Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable)]
 pub enum BindingForm<'tcx> {
     /// This is a binding for a non-`self` binding, or a `self` that has an explicit type.
     Var(VarBindingForm<'tcx>),
@@ -641,7 +641,7 @@ pub enum BindingForm<'tcx> {
 }
 
 /// Represents what type of implicit self a function has, if any.
-#[derive(Clone, Copy, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
+#[derive(Clone, Copy, PartialEq, Debug, RustcEncodable, RustcDecodable)]
 pub enum ImplicitSelfKind {
     /// Represents a `fn x(self);`.
     Imm,
@@ -2392,7 +2392,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
 /// this does not necessarily mean that they are "==" in Rust -- in
 /// particular one must be wary of `NaN`!
 
-#[derive(Copy, Clone, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, HashStable)]
 pub struct Constant<'tcx> {
     pub span: Span,
 
@@ -2438,7 +2438,7 @@ pub struct Constant<'tcx> {
 /// The first will lead to the constraint `w: &'1 str` (for some
 /// inferred region `'1`). The second will lead to the constraint `w:
 /// &'static str`.
-#[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable)]
 pub struct UserTypeProjections {
     pub(crate) contents: Vec<(UserTypeProjection, Span)>,
 }
@@ -2515,7 +2515,7 @@ impl<'tcx> UserTypeProjections {
 /// * `let (x, _): T = ...` -- here, the `projs` vector would contain
 ///   `field[0]` (aka `.0`), indicating that the type of `s` is
 ///   determined by finding the type of the `.0` field from `T`.
-#[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable)]
 pub struct UserTypeProjection {
     pub base: UserTypeAnnotationIndex,
     pub projs: Vec<ProjectionKind>,
@@ -2724,7 +2724,7 @@ impl Location {
     }
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, HashStable)]
 pub enum UnsafetyViolationKind {
     General,
     /// Permitted both in `const fn`s and regular `fn`s.
@@ -2733,7 +2733,7 @@ pub enum UnsafetyViolationKind {
     BorrowPacked(hir::HirId),
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Copy, Clone, PartialEq, RustcEncodable, RustcDecodable, HashStable)]
 pub struct UnsafetyViolation {
     pub source_info: SourceInfo,
     pub description: InternedString,
@@ -2741,7 +2741,7 @@ pub struct UnsafetyViolation {
     pub kind: UnsafetyViolationKind,
 }
 
-#[derive(Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Clone, RustcEncodable, RustcDecodable, HashStable)]
 pub struct UnsafetyCheckResult {
     /// Violations that are propagated *upwards* from this function.
     pub violations: Lrc<[UnsafetyViolation]>,

src/librustc/mir/mono.rs

@@ -15,7 +15,7 @@ use std::fmt;
 use std::hash::Hash;
 
 /// Describes how a monomorphization will be instantiated in object files.
-#[derive(PartialEq, Eq, Clone, Copy, Debug, Hash)]
+#[derive(PartialEq)]
 pub enum InstantiationMode {
     /// There will be exactly one instance of the given MonoItem. It will have
     /// external linkage so that it can be linked to from other codegen units.
@@ -251,7 +251,7 @@ pub struct CodegenUnit<'tcx> {
     size_estimate: Option<usize>,
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable)]
+#[derive(Copy, Clone, PartialEq, Debug, RustcEncodable, RustcDecodable)]
 pub enum Linkage {
     External,
     AvailableExternally,
@@ -280,7 +280,7 @@ impl_stable_hash_for!(enum self::Linkage {
     Common
 });
 
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Copy, Clone, PartialEq, Debug)]
 pub enum Visibility {
     Default,
     Hidden,

src/librustc/mir/visit.rs

@@ -947,7 +947,7 @@ impl<'tcx> MirVisitable<'tcx> for Option<Terminator<'tcx>> {
 
 /// Extra information passed to `visit_ty` and friends to give context
 /// about where the type etc appears.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Debug)]
 pub enum TyContext {
     LocalDecl {
         /// The index of the local variable we are visiting.

src/librustc/session/config.rs

@@ -62,7 +62,7 @@ impl_stable_hash_via_hash!(OptLevel);
 
 /// This is what the `LtoCli` values get mapped to after resolving defaults and
 /// and taking other command line options into account.
-#[derive(Clone, Copy, PartialEq, Hash, Debug)]
+#[derive(Clone, PartialEq)]
 pub enum Lto {
     /// Don't do any LTO whatsoever
     No,
@@ -296,10 +296,10 @@ impl OutputTypes {
 /// Use tree-based collections to cheaply get a deterministic `Hash` implementation.
 /// *Do not* switch `BTreeMap` or `BTreeSet` out for an unsorted container type! That
 /// would break dependency tracking for command-line arguments.
-#[derive(Clone, Hash)]
+#[derive(Clone)]
 pub struct Externs(BTreeMap<String, ExternEntry>);
 
-#[derive(Clone, Hash, Eq, PartialEq, Ord, PartialOrd, Debug, Default)]
+#[derive(Clone, Debug, Default)]
 pub struct ExternEntry {
     pub locations: BTreeSet<Option<String>>,
     pub is_private_dep: bool
@@ -459,7 +459,7 @@ pub enum PrintRequest {
     NativeStaticLibs,
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[derive(Copy, Clone)]
 pub enum BorrowckMode {
     Mir,
     Migrate,

src/librustc/session/search_paths.rs

@@ -1,5 +1,4 @@
 use std::path::{Path, PathBuf};
-use rustc_macros::HashStable;
 use crate::session::{early_error, config};
 use crate::session::filesearch::make_target_lib_path;
 
@@ -10,7 +9,7 @@ pub struct SearchPath {
     pub files: Vec<PathBuf>,
 }
 
-#[derive(Eq, PartialEq, Clone, Copy, Debug, PartialOrd, Ord, Hash, HashStable)]
+#[derive(PartialEq, Clone, Copy, Debug, HashStable)]
 pub enum PathKind {
     Native,
     Crate,

src/librustc/traits/query/mod.rs

@@ -40,7 +40,7 @@ pub type CanonicalTypeOpProvePredicateGoal<'tcx> =
 pub type CanonicalTypeOpNormalizeGoal<'tcx, T> =
     Canonical<'tcx, ty::ParamEnvAnd<'tcx, type_op::normalize::Normalize<T>>>;
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Clone, Debug)]
 pub struct NoSolution;
 
 pub type Fallible<T> = Result<T, NoSolution>;

src/librustc/traits/query/type_op/implied_outlives_bounds.rs

@@ -3,7 +3,7 @@ use crate::traits::query::outlives_bounds::OutlivesBound;
 use crate::traits::query::Fallible;
 use crate::ty::{ParamEnvAnd, Ty, TyCtxt};
 
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Clone, Debug)]
 pub struct ImpliedOutlivesBounds<'tcx> {
     pub ty: Ty<'tcx>,
 }

src/librustc/ty/binding.rs

@@ -2,7 +2,7 @@ use crate::hir::BindingAnnotation::*;
 use crate::hir::BindingAnnotation;
 use crate::hir::Mutability;
 
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
+#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Copy)]
 pub enum BindingMode {
     BindByReference(Mutability),
     BindByValue(Mutability),

src/librustc/ty/context.rs

@@ -827,7 +827,7 @@ rustc_index::newtype_index! {
 pub type CanonicalUserTypeAnnotations<'tcx> =
     IndexVec<UserTypeAnnotationIndex, CanonicalUserTypeAnnotation<'tcx>>;
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Clone, Debug, RustcEncodable, RustcDecodable, HashStable)]
 pub struct CanonicalUserTypeAnnotation<'tcx> {
     pub user_ty: CanonicalUserType<'tcx>,
     pub span: Span,
@@ -882,7 +882,7 @@ impl CanonicalUserType<'tcx> {
                         },
 
                         GenericArgKind::Const(ct) => match ct.val {
-                            ConstValue::Infer(InferConst::Canonical(debruijn, b)) => {
+                            ConstValue::Bound(debruijn, b) => {
                                 // We only allow a `ty::INNERMOST` index in substitutions.
                                 assert_eq!(debruijn, ty::INNERMOST);
                                 cvar == b
@@ -899,7 +899,7 @@ impl CanonicalUserType<'tcx> {
 /// A user-given type annotation attached to a constant. These arise
 /// from constants that are named via paths, like `Foo::<A>::new` and
 /// so forth.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Copy, Clone, Debug, PartialEq, RustcEncodable, RustcDecodable, HashStable)]
 pub enum UserType<'tcx> {
     Ty(Ty<'tcx>),
 

src/librustc/ty/error.rs

@@ -51,7 +51,6 @@ pub enum TypeError<'tcx> {
     IntrinsicCast,
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, PartialEq, Eq, Hash, Debug, Copy)]
 pub enum UnconstrainedNumeric {
     UnconstrainedFloat,
     UnconstrainedInt,

src/librustc/ty/fast_reject.rs

@@ -19,7 +19,7 @@ pub type SimplifiedType = SimplifiedTypeGen<DefId>;
 /// the non-stable but fast to construct DefId-version is the better choice.
 #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash, PartialOrd, Ord, RustcEncodable, RustcDecodable)]
 pub enum SimplifiedTypeGen<D>
-    where D: Copy + Debug + Ord + Eq + Hash
+    where D: Copy + Debug + Ord + Eq
 {
     BoolSimplifiedType,
     CharSimplifiedType,
@@ -123,10 +123,10 @@ pub fn simplify_type(
     }
 }
 
-impl<D: Copy + Debug + Ord + Eq + Hash> SimplifiedTypeGen<D> {
+impl<D: Copy + Debug + Ord + Eq> SimplifiedTypeGen<D> {
     pub fn map_def<U, F>(self, map: F) -> SimplifiedTypeGen<U>
         where F: Fn(D) -> U,
-              U: Copy + Debug + Ord + Eq + Hash,
+              U: Copy + Debug + Ord + Eq,
     {
         match self {
             BoolSimplifiedType => BoolSimplifiedType,
@@ -155,7 +155,7 @@ impl<D: Copy + Debug + Ord + Eq + Hash> SimplifiedTypeGen<D> {
 
 impl<'a, D> HashStable<StableHashingContext<'a>> for SimplifiedTypeGen<D>
 where
-    D: Copy + Debug + Ord + Eq + Hash + HashStable<StableHashingContext<'a>>,
+    D: Copy + Debug + Ord + Eq + HashStable<StableHashingContext<'a>>,
 {
     fn hash_stable(&self, hcx: &mut StableHashingContext<'a>, hasher: &mut StableHasher) {
         mem::discriminant(self).hash_stable(hcx, hasher);

src/librustc/ty/flags.rs

@@ -240,10 +240,10 @@ impl FlagComputation {
                 self.add_flags(TypeFlags::HAS_FREE_LOCAL_NAMES | TypeFlags::HAS_CT_INFER);
                 match infer {
                     InferConst::Fresh(_) => {}
-                    InferConst::Canonical(debruijn, _) => self.add_binder(debruijn),
                     InferConst::Var(_) => self.add_flags(TypeFlags::KEEP_IN_LOCAL_TCX),
                 }
             }
+            ConstValue::Bound(debruijn, _) => self.add_binder(debruijn),
             ConstValue::Param(_) => {
                 self.add_flags(TypeFlags::HAS_FREE_LOCAL_NAMES | TypeFlags::HAS_PARAMS);
             }

src/librustc/ty/fold.rs

@@ -521,10 +521,7 @@ impl<'a, 'tcx> TypeFolder<'tcx> for BoundVarReplacer<'a, 'tcx> {
     }
 
     fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
-        if let ty::Const {
+        if let ty::Const { val: ConstValue::Bound(debruijn, bound_const), ty } = *ct {
-            val: ConstValue::Infer(ty::InferConst::Canonical(debruijn, bound_const)),
-            ty,
-        } = *ct {
             if debruijn == self.current_index {
                 let fld_c = &mut self.fld_c;
                 let ct = fld_c(bound_const, ty);
@@ -570,7 +567,10 @@ impl<'tcx> TyCtxt<'tcx> {
         // identity for bound types and consts
         let fld_t = |bound_ty| self.mk_ty(ty::Bound(ty::INNERMOST, bound_ty));
         let fld_c = |bound_ct, ty| {
-            self.mk_const_infer(ty::InferConst::Canonical(ty::INNERMOST, bound_ct), ty)
+            self.mk_const(ty::Const {
+                val: ConstValue::Bound(ty::INNERMOST, bound_ct),
+                ty,
+            })
         };
         self.replace_escaping_bound_vars(value.skip_binder(), fld_r, fld_t, fld_c)
     }
@@ -721,7 +721,6 @@ impl<'tcx> TyCtxt<'tcx> {
 // vars. See comment on `shift_vars_through_binders` method in
 // `subst.rs` for more details.
 
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 enum Direction {
     In,
     Out,
@@ -802,10 +801,7 @@ impl TypeFolder<'tcx> for Shifter<'tcx> {
     }
 
     fn fold_const(&mut self, ct: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
-        if let ty::Const {
+        if let ty::Const { val: ConstValue::Bound(debruijn, bound_ct), ty } = *ct {
-            val: ConstValue::Infer(ty::InferConst::Canonical(debruijn, bound_const)),
-            ty,
-        } = *ct {
             if self.amount == 0 || debruijn < self.current_index {
                 ct
             } else {
@@ -816,7 +812,10 @@ impl TypeFolder<'tcx> for Shifter<'tcx> {
                         debruijn.shifted_out(self.amount)
                     }
                 };
-                self.tcx.mk_const_infer(ty::InferConst::Canonical(debruijn, bound_const), ty)
+                self.tcx.mk_const(ty::Const {
+                    val: ConstValue::Bound(debruijn, bound_ct),
+                    ty,
+                })
             }
         } else {
             ct.super_fold_with(self)
@@ -920,8 +919,7 @@ impl<'tcx> TypeVisitor<'tcx> for HasEscapingVarsVisitor {
         // const, as it has types/regions embedded in a lot of other
         // places.
         match ct.val {
-            ConstValue::Infer(ty::InferConst::Canonical(debruijn, _))
+            ConstValue::Bound(debruijn, _) if debruijn >= self.outer_index => true,
-                if debruijn >= self.outer_index => true,
             _ => ct.super_visit_with(self),
         }
     }

src/librustc/ty/mod.rs

@@ -159,7 +159,7 @@ impl AssocItemContainer {
 /// The "header" of an impl is everything outside the body: a Self type, a trait
 /// ref (in the case of a trait impl), and a set of predicates (from the
 /// bounds / where-clauses).
-#[derive(Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, Debug)]
 pub struct ImplHeader<'tcx> {
     pub impl_def_id: DefId,
     pub self_ty: Ty<'tcx>,
@@ -195,7 +195,7 @@ pub struct AssocItem {
     pub method_has_self_argument: bool,
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Copy, Clone, PartialEq, Debug, HashStable)]
 pub enum AssocKind {
     Const,
     Method,
@@ -331,7 +331,7 @@ impl Visibility {
     }
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, RustcDecodable, RustcEncodable, Hash, HashStable)]
+#[derive(Copy, Clone, PartialEq, RustcDecodable, RustcEncodable, HashStable)]
 pub enum Variance {
     Covariant,      // T<A> <: T<B> iff A <: B -- e.g., function return type
     Invariant,      // T<A> <: T<B> iff B == A -- e.g., type of mutable cell
@@ -752,7 +752,7 @@ pub struct UpvarId {
     pub closure_expr_id: LocalDefId,
 }
 
-#[derive(Clone, PartialEq, Eq, Hash, Debug, RustcEncodable, RustcDecodable, Copy, HashStable)]
+#[derive(Clone, PartialEq, Debug, RustcEncodable, RustcDecodable, Copy, HashStable)]
 pub enum BorrowKind {
     /// Data must be immutable and is aliasable.
     ImmBorrow,

src/librustc/ty/query/keys.rs

@@ -8,14 +8,12 @@ use crate::ty::subst::SubstsRef;
 use crate::ty::fast_reject::SimplifiedType;
 use crate::mir;
 
-use std::fmt::Debug;
-use std::hash::Hash;
 use syntax_pos::{Span, DUMMY_SP};
 use syntax_pos::symbol::InternedString;
 
 /// The `Key` trait controls what types can legally be used as the key
 /// for a query.
-pub(super) trait Key: Clone + Hash + Eq + Debug {
+pub(super) trait Key {
     /// Given an instance of this key, what crate is it referring to?
     /// This is used to find the provider.
     fn query_crate(&self) -> CrateNum;
@@ -201,10 +199,7 @@ impl Key for InternedString {
 
 /// Canonical query goals correspond to abstract trait operations that
 /// are not tied to any crate in particular.
-impl<'tcx, T> Key for Canonical<'tcx, T>
+impl<'tcx, T> Key for Canonical<'tcx, T> {
-where
-    T: Debug + Hash + Clone + Eq,
-{
     fn query_crate(&self) -> CrateNum {
         LOCAL_CRATE
     }

src/librustc/ty/query/plumbing.rs

@@ -801,7 +801,7 @@ macro_rules! define_queries_inner {
         }
 
         #[allow(nonstandard_style)]
-        #[derive(Clone, Copy, Debug, PartialEq, Eq, Hash)]
+        #[derive(Clone, Copy)]
         pub enum QueryName {
             $($name),*
         }
@@ -819,7 +819,7 @@ macro_rules! define_queries_inner {
         }
 
         #[allow(nonstandard_style)]
-        #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+        #[derive(Clone, Debug)]
         pub enum Query<$tcx> {
             $($(#[$attr])* $name($K)),*
         }

src/librustc/ty/structural_impls.rs

@@ -1379,27 +1379,23 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx ty::Const<'tcx> {
 impl<'tcx> TypeFoldable<'tcx> for ConstValue<'tcx> {
     fn super_fold_with<F: TypeFolder<'tcx>>(&self, folder: &mut F) -> Self {
         match *self {
-            ConstValue::ByRef { alloc, offset } =>
-                ConstValue::ByRef { alloc, offset },
             ConstValue::Infer(ic) => ConstValue::Infer(ic.fold_with(folder)),
             ConstValue::Param(p) => ConstValue::Param(p.fold_with(folder)),
-            ConstValue::Placeholder(p) => ConstValue::Placeholder(p),
-            ConstValue::Scalar(a) => ConstValue::Scalar(a),
-            ConstValue::Slice { data, start, end } => ConstValue::Slice { data, start, end },
             ConstValue::Unevaluated(did, substs)
                 => ConstValue::Unevaluated(did, substs.fold_with(folder)),
+            ConstValue::ByRef { .. } | ConstValue::Bound(..) | ConstValue::Placeholder(..)
+            | ConstValue::Scalar(..) | ConstValue::Slice { .. } => *self,
+
         }
     }
 
     fn super_visit_with<V: TypeVisitor<'tcx>>(&self, visitor: &mut V) -> bool {
         match *self {
-            ConstValue::ByRef { .. } => false,
             ConstValue::Infer(ic) => ic.visit_with(visitor),
             ConstValue::Param(p) => p.visit_with(visitor),
-            ConstValue::Placeholder(_) => false,
-            ConstValue::Scalar(_) => false,
-            ConstValue::Slice { .. } => false,
             ConstValue::Unevaluated(_, substs) => substs.visit_with(visitor),
+            ConstValue::ByRef { .. } | ConstValue::Bound(..) | ConstValue::Placeholder(_)
+            | ConstValue::Scalar(_) | ConstValue::Slice { .. } => false,
         }
     }
 }

src/librustc/ty/sty.rs

@@ -304,8 +304,7 @@ static_assert_size!(TyKind<'_>, 24);
 /// type parameters is similar, but the role of CK and CS are
 /// different. CK represents the "yield type" and CS represents the
 /// "return type" of the generator.
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug,
+#[derive(Copy, Clone, Debug)]
-         RustcEncodable, RustcDecodable, HashStable)]
 pub struct ClosureSubsts<'tcx> {
     /// Lifetime and type parameters from the enclosing function,
     /// concatenated with the types of the upvars.
@@ -392,8 +391,7 @@ impl<'tcx> ClosureSubsts<'tcx> {
 }
 
 /// Similar to `ClosureSubsts`; see the above documentation for more.
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, Debug,
+#[derive(Copy, Clone, Debug)]
-         RustcEncodable, RustcDecodable, HashStable)]
 pub struct GeneratorSubsts<'tcx> {
     pub substs: SubstsRef<'tcx>,
 }
@@ -1035,7 +1033,7 @@ impl<'tcx> ProjectionTy<'tcx> {
     }
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, HashStable)]
+#[derive(Clone, Debug)]
 pub struct GenSig<'tcx> {
     pub yield_ty: Ty<'tcx>,
     pub return_ty: Ty<'tcx>,
@@ -2373,6 +2371,4 @@ pub enum InferConst<'tcx> {
     Var(ConstVid<'tcx>),
     /// A fresh const variable. See `infer::freshen` for more details.
     Fresh(u32),
-    /// Canonicalized const variable, used only when preparing a trait query.
-    Canonical(DebruijnIndex, BoundVar),
 }

src/librustc/ty/subst.rs

@@ -2,7 +2,7 @@
 
 use crate::hir::def_id::DefId;
 use crate::infer::canonical::Canonical;
-use crate::ty::{self, Lift, List, Ty, TyCtxt, InferConst, ParamConst};
+use crate::ty::{self, Lift, List, Ty, TyCtxt, ParamConst};
 use crate::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use crate::mir::interpret::ConstValue;
 use crate::ty::sty::{ClosureSubsts, GeneratorSubsts};
@@ -234,9 +234,7 @@ impl<'a, 'tcx> InternalSubsts<'tcx> {
 
                 ty::GenericParamDefKind::Const => {
                     tcx.mk_const(ty::Const {
-                        val: ConstValue::Infer(
+                        val: ConstValue::Bound(ty::INNERMOST, ty::BoundVar::from(param.index)),
-                            InferConst::Canonical(ty::INNERMOST, ty::BoundVar::from(param.index))
-                        ),
                         ty: tcx.type_of(def_id),
                     }).into()
                 }

src/librustc/ty/util.rs

@@ -818,6 +818,8 @@ impl<'tcx> ty::TyS<'tcx> {
     ///
     /// (Note that this implies that if `ty` has a destructor attached,
     /// then `needs_drop` will definitely return `true` for `ty`.)
+    ///
+    /// Note that this method is used to check eligible types in unions.
     #[inline]
     pub fn needs_drop(&'tcx self, tcx: TyCtxt<'tcx>, param_env: ty::ParamEnv<'tcx>) -> bool {
         tcx.needs_drop_raw(param_env.and(self)).0

src/librustc_codegen_llvm/llvm/ffi.rs

@@ -50,7 +50,7 @@ pub enum CallConv {
 }
 
 /// LLVMRustLinkage
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(PartialEq)]
 #[repr(C)]
 pub enum Linkage {
     ExternalLinkage = 0,
@@ -67,7 +67,6 @@ pub enum Linkage {
 }
 
 // LLVMRustVisibility
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
 #[repr(C)]
 pub enum Visibility {
     Default = 0,

src/librustc_codegen_ssa/mir/operand.rs

@@ -79,6 +79,7 @@ impl<'a, 'tcx, V: CodegenObject> OperandRef<'tcx, V> {
             ConstValue::Unevaluated(..) => bug!("unevaluated constant in `OperandRef::from_const`"),
             ConstValue::Param(_) => bug!("encountered a ConstValue::Param in codegen"),
             ConstValue::Infer(_) => bug!("encountered a ConstValue::Infer in codegen"),
+            ConstValue::Bound(..) => bug!("encountered a ConstValue::Bound in codegen"),
             ConstValue::Placeholder(_) => bug!("encountered a ConstValue::Placeholder in codegen"),
             ConstValue::Scalar(x) => {
                 let scalar = match layout.abi {

src/librustc_data_structures/graph/implementation/mod.rs

@@ -60,10 +60,10 @@ impl<N> SnapshotVecDelegate for Edge<N> {
     fn reverse(_: &mut Vec<Edge<N>>, _: ()) {}
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
+#[derive(Copy, Clone, PartialEq, Debug)]
 pub struct NodeIndex(pub usize);
 
-#[derive(Copy, Clone, PartialEq, Eq, Debug, Hash)]
+#[derive(Copy, Clone, PartialEq, Debug)]
 pub struct EdgeIndex(pub usize);
 
 pub const INVALID_EDGE_INDEX: EdgeIndex = EdgeIndex(usize::MAX);

src/librustc_data_structures/sharded.rs

@@ -90,7 +90,7 @@ impl<T> Sharded<T> {
 
 pub type ShardedHashMap<K, V> = Sharded<FxHashMap<K, V>>;
 
-impl<K: Eq + Hash, V> ShardedHashMap<K, V> {
+impl<K: Eq, V> ShardedHashMap<K, V> {
     pub fn len(&self) -> usize {
         self.lock_shards().iter().map(|shard| shard.len()).sum()
     }

src/librustc_data_structures/snapshot_map/mod.rs

@@ -7,7 +7,7 @@ use std::mem;
 mod tests;
 
 pub struct SnapshotMap<K, V>
-    where K: Hash + Clone + Eq
+    where K: Clone + Eq
 {
     map: FxHashMap<K, V>,
     undo_log: Vec<UndoLog<K, V>>,

src/librustc_data_structures/stable_hasher.rs

@@ -169,7 +169,7 @@ pub trait HashStable<CTX> {
 /// example, for DefId that can be converted to a DefPathHash. This is used for
 /// bringing maps into a predictable order before hashing them.
 pub trait ToStableHashKey<HCX> {
-    type KeyType: Ord + Clone + Sized + HashStable<HCX>;
+    type KeyType: Ord + Sized + HashStable<HCX>;
     fn to_stable_hash_key(&self, hcx: &HCX) -> Self::KeyType;
 }
 
@@ -460,7 +460,7 @@ impl_stable_hash_via_hash!(::std::path::Path);
 impl_stable_hash_via_hash!(::std::path::PathBuf);
 
 impl<K, V, R, HCX> HashStable<HCX> for ::std::collections::HashMap<K, V, R>
-    where K: ToStableHashKey<HCX> + Eq + Hash,
+    where K: ToStableHashKey<HCX> + Eq,
           V: HashStable<HCX>,
           R: BuildHasher,
 {
@@ -471,7 +471,7 @@ impl<K, V, R, HCX> HashStable<HCX> for ::std::collections::HashMap<K, V, R>
 }
 
 impl<K, R, HCX> HashStable<HCX> for ::std::collections::HashSet<K, R>
-    where K: ToStableHashKey<HCX> + Eq + Hash,
+    where K: ToStableHashKey<HCX> + Eq,
           R: BuildHasher,
 {
     fn hash_stable(&self, hcx: &mut HCX, hasher: &mut StableHasher) {
@@ -513,10 +513,10 @@ pub fn hash_stable_hashmap<HCX, K, V, R, SK, F>(
     hasher: &mut StableHasher,
     map: &::std::collections::HashMap<K, V, R>,
     to_stable_hash_key: F)
-    where K: Eq + Hash,
+    where K: Eq,
           V: HashStable<HCX>,
           R: BuildHasher,
-          SK: HashStable<HCX> + Ord + Clone,
+          SK: HashStable<HCX> + Ord,
           F: Fn(&K, &HCX) -> SK,
 {
     let mut entries: Vec<_> = map.iter()

src/librustc_data_structures/sync.rs

@@ -738,7 +738,7 @@ impl<T: Clone> Clone for RwLock<T> {
 
 /// A type which only allows its inner value to be used in one thread.
 /// It will panic if it is used on multiple threads.
-#[derive(Copy, Clone, Hash, Debug, Eq, PartialEq)]
+#[derive(Debug)]
 pub struct OneThread<T> {
     #[cfg(parallel_compiler)]
     thread: thread::ThreadId,

src/librustc_data_structures/thin_vec.rs

@@ -3,7 +3,7 @@ use crate::stable_hasher::{StableHasher, HashStable};
 /// A vector type optimized for cases where this size is usually 0 (cf. `SmallVector`).
 /// The `Option<Box<..>>` wrapping allows us to represent a zero sized vector with `None`,
 /// which uses only a single (null) pointer.
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub struct ThinVec<T>(Option<Box<Vec<T>>>);
 
 impl<T> ThinVec<T> {

src/librustc_data_structures/tiny_list.rs

@@ -14,7 +14,7 @@
 #[cfg(test)]
 mod tests;
 
-#[derive(Clone, Hash, Debug, PartialEq)]
+#[derive(Clone)]
 pub struct TinyList<T: PartialEq> {
     head: Option<Element<T>>
 }
@@ -80,7 +80,7 @@ impl<T: PartialEq> TinyList<T> {
     }
 }
 
-#[derive(Clone, Hash, Debug, PartialEq)]
+#[derive(Clone)]
 struct Element<T: PartialEq> {
     data: T,
     next: Option<Box<Element<T>>>,

src/librustc_data_structures/transitive_relation.rs

@@ -11,7 +11,7 @@ use std::mem;
 mod tests;
 
 #[derive(Clone, Debug)]
-pub struct TransitiveRelation<T: Clone + Debug + Eq + Hash> {
+pub struct TransitiveRelation<T: Eq + Hash> {
     // List of elements. This is used to map from a T to a usize.
     elements: Vec<T>,
 
@@ -35,7 +35,7 @@ pub struct TransitiveRelation<T: Clone + Debug + Eq + Hash> {
 }
 
 // HACK(eddyb) manual impl avoids `Default` bound on `T`.
-impl<T: Clone + Debug + Eq + Hash> Default for TransitiveRelation<T> {
+impl<T: Eq + Hash> Default for TransitiveRelation<T> {
     fn default() -> Self {
         TransitiveRelation {
             elements: Default::default(),
@@ -46,7 +46,7 @@ impl<T: Clone + Debug + Eq + Hash> Default for TransitiveRelation<T> {
     }
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash, RustcEncodable, RustcDecodable, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, RustcEncodable, RustcDecodable, Debug)]
 struct Index(usize);
 
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Debug)]

src/librustc_lint/builtin.rs

@@ -980,35 +980,6 @@ impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnstableFeatures {
     }
 }
 
-declare_lint! {
-    UNIONS_WITH_DROP_FIELDS,
-    Warn,
-    "use of unions that contain fields with possibly non-trivial drop code"
-}
-
-declare_lint_pass!(
-    /// Lint for unions that contain fields with possibly non-trivial destructors.
-    UnionsWithDropFields => [UNIONS_WITH_DROP_FIELDS]
-);
-
-impl<'a, 'tcx> LateLintPass<'a, 'tcx> for UnionsWithDropFields {
-    fn check_item(&mut self, ctx: &LateContext<'_, '_>, item: &hir::Item) {
-        if let hir::ItemKind::Union(ref vdata, _) = item.kind {
-            for field in vdata.fields() {
-                let field_ty = ctx.tcx.type_of(
-                    ctx.tcx.hir().local_def_id(field.hir_id));
-                if field_ty.needs_drop(ctx.tcx, ctx.param_env) {
-                    ctx.span_lint(UNIONS_WITH_DROP_FIELDS,
-                                  field.span,
-                                  "union contains a field with possibly non-trivial drop code, \
-                                   drop code of union fields is ignored when dropping the union");
-                    return;
-                }
-            }
-        }
-    }
-}
-
 declare_lint! {
     pub UNREACHABLE_PUB,
     Allow,
@@ -1288,7 +1259,6 @@ declare_lint_pass!(
         NO_MANGLE_GENERIC_ITEMS,
         MUTABLE_TRANSMUTES,
         UNSTABLE_FEATURES,
-        UNIONS_WITH_DROP_FIELDS,
         UNREACHABLE_PUB,
         TYPE_ALIAS_BOUNDS,
         TRIVIAL_BOUNDS

src/librustc_lint/lib.rs

@@ -164,9 +164,6 @@ macro_rules! late_lint_mod_passes {
             // Depends on referenced function signatures in expressions
             MutableTransmutes: MutableTransmutes,
 
-            // Depends on types of fields, checks if they implement Drop
-            UnionsWithDropFields: UnionsWithDropFields,
-
             TypeAliasBounds: TypeAliasBounds,
 
             TrivialConstraints: TrivialConstraints,

src/librustc_mir/borrow_check/nll/constraints/mod.rs

@@ -71,7 +71,7 @@ impl Index<OutlivesConstraintIndex> for OutlivesConstraintSet {
     }
 }
 
-#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Hash)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord)]
 pub struct OutlivesConstraint {
     // NB. The ordering here is not significant for correctness, but
     // it is for convenience. Before we dump the constraints in the

src/librustc_mir/borrow_check/nll/member_constraints.rs

@@ -11,7 +11,7 @@ use syntax_pos::Span;
 /// indexed by the region `R0`.
 crate struct MemberConstraintSet<'tcx, R>
 where
-    R: Copy + Hash + Eq,
+    R: Copy + Eq,
 {
     /// Stores the first "member" constraint for a given `R0`. This is an
     /// index into the `constraints` vector below.
@@ -191,7 +191,7 @@ where
 
 impl<'tcx, R> Index<NllMemberConstraintIndex> for MemberConstraintSet<'tcx, R>
 where
-    R: Copy + Hash + Eq,
+    R: Copy + Eq,
 {
     type Output = NllMemberConstraint<'tcx>;
 

src/librustc_mir/borrow_check/nll/region_infer/values.rs

@@ -129,7 +129,7 @@ rustc_index::newtype_index! {
 
 /// An individual element in a region value -- the value of a
 /// particular region variable consists of a set of these elements.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Debug)]
 crate enum RegionElement {
     /// A point in the control-flow graph.
     Location(Location),

src/librustc_mir/borrow_check/nll/universal_regions.rs

@@ -146,7 +146,7 @@ struct UniversalRegionIndices<'tcx> {
     indices: FxHashMap<ty::Region<'tcx>, RegionVid>,
 }
 
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Debug, PartialEq)]
 pub enum RegionClassification {
     /// A **global** region is one that can be named from
     /// anywhere. There is only one, `'static`.

src/librustc_mir/interpret/eval_context.rs

@@ -91,7 +91,7 @@ pub struct Frame<'mir, 'tcx, Tag=(), Extra=()> {
     pub extra: Extra,
 }
 
-#[derive(Clone, Debug, Eq, PartialEq, Hash)]
+#[derive(Clone, Eq, PartialEq)]
 pub enum StackPopCleanup {
     /// Jump to the next block in the caller, or cause UB if None (that's a function
     /// that may never return). Also store layout of return place so
@@ -113,7 +113,7 @@ pub struct LocalState<'tcx, Tag=(), Id=AllocId> {
 }
 
 /// Current value of a local variable
-#[derive(Copy, Clone, PartialEq, Eq, Hash, Debug)]
+#[derive(Clone, PartialEq, Eq)]
 pub enum LocalValue<Tag=(), Id=AllocId> {
     /// This local is not currently alive, and cannot be used at all.
     Dead,

src/librustc_mir/interpret/memory.rs

@@ -7,7 +7,7 @@
 //! short-circuiting the empty case!
 
 use std::collections::VecDeque;
-use std::ptr;
+use std::{ptr, iter};
 use std::borrow::Cow;
 
 use rustc::ty::{self, Instance, ParamEnv, query::TyCtxtAt};
@@ -22,7 +22,7 @@ use super::{
     Machine, AllocMap, MayLeak, ErrorHandled, CheckInAllocMsg,
 };
 
-#[derive(Debug, PartialEq, Eq, Copy, Clone, Hash)]
+#[derive(Debug, PartialEq, Copy, Clone)]
 pub enum MemoryKind<T> {
     /// Error if deallocated except during a stack pop
     Stack,
@@ -785,6 +785,25 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> Memory<'mir, 'tcx, M> {
         self.get(ptr.alloc_id)?.read_c_str(self, ptr)
     }
 
+    /// Writes the given stream of bytes into memory.
+    ///
+    /// Performs appropriate bounds checks.
+    pub fn write_bytes(
+        &mut self,
+        ptr: Scalar<M::PointerTag>,
+        src: impl IntoIterator<Item=u8, IntoIter: iter::ExactSizeIterator>,
+    ) -> InterpResult<'tcx>
+    {
+        let src = src.into_iter();
+        let size = Size::from_bytes(src.len() as u64);
+        let ptr = match self.check_ptr_access(ptr, size, Align::from_bytes(1).unwrap())? {
+            Some(ptr) => ptr,
+            None => return Ok(()), // zero-sized access
+        };
+        let tcx = self.tcx.tcx;
+        self.get_mut(ptr.alloc_id)?.write_bytes(&tcx, ptr, src)
+    }
+
     /// Expects the caller to have checked bounds and alignment.
     pub fn copy(
         &mut self,

src/librustc_mir/interpret/operand.rs

@@ -26,7 +26,7 @@ pub use rustc::mir::interpret::ScalarMaybeUndef;
 /// operations and fat pointers. This idea was taken from rustc's codegen.
 /// In particular, thanks to `ScalarPair`, arithmetic operations and casts can be entirely
 /// defined on `Immediate`, and do not have to work with a `Place`.
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum Immediate<Tag=(), Id=AllocId> {
     Scalar(ScalarMaybeUndef<Tag, Id>),
     ScalarPair(ScalarMaybeUndef<Tag, Id>, ScalarMaybeUndef<Tag, Id>),
@@ -123,7 +123,7 @@ impl<'tcx, Tag> ::std::ops::Deref for ImmTy<'tcx, Tag> {
 /// An `Operand` is the result of computing a `mir::Operand`. It can be immediate,
 /// or still in memory. The latter is an optimization, to delay reading that chunk of
 /// memory and to avoid having to store arbitrary-sized data here.
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq)]
 pub enum Operand<Tag=(), Id=AllocId> {
     Immediate(Immediate<Tag, Id>),
     Indirect(MemPlace<Tag, Id>),
@@ -153,7 +153,7 @@ impl<Tag> Operand<Tag> {
     }
 }
 
-#[derive(Copy, Clone, Debug, Hash, PartialEq, Eq)]
+#[derive(Copy, Clone, Debug, PartialEq)]
 pub struct OpTy<'tcx, Tag=()> {
     op: Operand<Tag>, // Keep this private, it helps enforce invariants
     pub layout: TyLayout<'tcx>,
@@ -589,8 +589,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
                 let ptr = self.tag_static_base_pointer(Pointer::new(id, offset));
                 Operand::Indirect(MemPlace::from_ptr(ptr, layout.align.abi))
             },
-            ConstValue::Scalar(x) =>
+            ConstValue::Scalar(x) => Operand::Immediate(tag_scalar(x).into()),
-                Operand::Immediate(tag_scalar(x).into()),
             ConstValue::Slice { data, start, end } => {
                 // We rely on mutability being set correctly in `data` to prevent writes
                 // where none should happen.
@@ -606,6 +605,7 @@ impl<'mir, 'tcx, M: Machine<'mir, 'tcx>> InterpCx<'mir, 'tcx, M> {
             }
             ConstValue::Param(..) |
             ConstValue::Infer(..) |
+            ConstValue::Bound(..) |
             ConstValue::Placeholder(..) |
             ConstValue::Unevaluated(..) =>
                 bug!("eval_const_to_op: Unexpected ConstValue {:?}", val),

src/librustc_mir/monomorphize/collector.rs

@@ -199,7 +199,7 @@ use rustc_data_structures::sync::{MTRef, MTLock, ParallelIterator, par_iter};
 
 use std::iter;
 
-#[derive(PartialEq, Eq, Hash, Clone, Copy, Debug)]
+#[derive(PartialEq)]
 pub enum MonoItemCollectionMode {
     Eager,
     Lazy

src/librustc_target/spec/mod.rs

@@ -71,8 +71,7 @@ mod riscv_base;
 mod wasm32_base;
 mod vxworks_base;
 
-#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd, Hash,
+#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
-         RustcEncodable, RustcDecodable)]
 pub enum LinkerFlavor {
     Em,
     Gcc,
@@ -82,8 +81,7 @@ pub enum LinkerFlavor {
     PtxLinker,
 }
 
-#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd, Hash,
+#[derive(Clone, Copy, Debug, Eq, Ord, PartialEq, PartialOrd)]
-         RustcEncodable, RustcDecodable)]
 pub enum LldFlavor {
     Wasm,
     Ld64,

src/librustc_traits/chalk_context/mod.rs

@@ -33,7 +33,7 @@ use rustc::traits::{
     InEnvironment,
     ChalkCanonicalGoal,
 };
-use rustc::ty::{self, TyCtxt, InferConst};
+use rustc::ty::{self, TyCtxt};
 use rustc::ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use rustc::ty::query::Providers;
 use rustc::ty::subst::{GenericArg, GenericArgKind};
@@ -286,7 +286,7 @@ impl context::ContextOps<ChalkArenas<'tcx>> for ChalkContext<'tcx> {
                     _ => false,
                 },
                 GenericArgKind::Const(ct) => match ct.val {
-                    ConstValue::Infer(InferConst::Canonical(debruijn, bound_ct)) => {
+                    ConstValue::Bound(debruijn, bound_ct) => {
                         debug_assert_eq!(debruijn, ty::INNERMOST);
                         cvar == bound_ct
                     }

src/librustc_traits/chalk_context/resolvent_ops.rs

@@ -16,7 +16,7 @@ use rustc::traits::{
     Environment,
     InEnvironment,
 };
-use rustc::ty::{self, Ty, TyCtxt, InferConst};
+use rustc::ty::{self, Ty, TyCtxt};
 use rustc::ty::subst::GenericArg;
 use rustc::ty::relate::{Relate, RelateResult, TypeRelation};
 use rustc::mir::interpret::ConstValue;
@@ -287,10 +287,7 @@ impl TypeRelation<'tcx> for AnswerSubstitutor<'cx, 'tcx> {
         a: &'tcx ty::Const<'tcx>,
         b: &'tcx ty::Const<'tcx>,
     ) -> RelateResult<'tcx, &'tcx ty::Const<'tcx>> {
-        if let ty::Const {
+        if let ty::Const { val: ConstValue::Bound(debruijn, bound_ct), .. } = a {
-            val: ConstValue::Infer(InferConst::Canonical(debruijn, bound_ct)),
-            ..
-        } = a {
             if *debruijn == self.binder_index {
                 self.unify_free_answer_var(*bound_ct, b.into())?;
                 return Ok(b);
@@ -299,14 +296,8 @@ impl TypeRelation<'tcx> for AnswerSubstitutor<'cx, 'tcx> {
 
         match (a, b) {
             (
-                ty::Const {
+                ty::Const { val: ConstValue::Bound(a_debruijn, a_bound), .. },
-                    val: ConstValue::Infer(InferConst::Canonical(a_debruijn, a_bound)),
+                ty::Const { val: ConstValue::Bound(b_debruijn, b_bound), .. },
-                    ..
-                },
-                ty::Const {
-                    val: ConstValue::Infer(InferConst::Canonical(b_debruijn, b_bound)),
-                    ..
-                },
             ) => {
                 assert_eq!(a_debruijn, b_debruijn);
                 assert_eq!(a_bound, b_bound);

src/librustc_typeck/check/mod.rs

@@ -1387,9 +1387,37 @@ fn check_union(tcx: TyCtxt<'_>, id: hir::HirId, span: Span) {
     def.destructor(tcx); // force the destructor to be evaluated
     check_representable(tcx, span, def_id);
     check_transparent(tcx, span, def_id);
+    check_union_fields(tcx, span, def_id);
     check_packed(tcx, span, def_id);
 }
 
+/// When the `#![feature(untagged_unions)]` gate is active,
+/// check that the fields of the `union` does not contain fields that need dropping.
+fn check_union_fields(tcx: TyCtxt<'_>, span: Span, item_def_id: DefId) -> bool {
+    let item_type = tcx.type_of(item_def_id);
+    if let ty::Adt(def, substs) = item_type.kind {
+        assert!(def.is_union());
+        let fields = &def.non_enum_variant().fields;
+        for field in fields {
+            let field_ty = field.ty(tcx, substs);
+            // We are currently checking the type this field came from, so it must be local.
+            let field_span = tcx.hir().span_if_local(field.did).unwrap();
+            let param_env = tcx.param_env(field.did);
+            if field_ty.needs_drop(tcx, param_env) {
+                struct_span_err!(tcx.sess, field_span, E0740,
+                                    "unions may not contain fields that need dropping")
+                            .span_note(field_span,
+                                        "`std::mem::ManuallyDrop` can be used to wrap the type")
+                            .emit();
+                return false;
+            }
+        }
+    } else {
+        span_bug!(span, "unions must be ty::Adt, but got {:?}", item_type.kind);
+    }
+    return true;
+}
+
 /// Checks that an opaque type does not contain cycles and does not use `Self` or `T::Foo`
 /// projections that would result in "inheriting lifetimes".
 fn check_opaque<'tcx>(

src/librustc_typeck/error_codes.rs

@@ -4863,6 +4863,10 @@ assert_eq!(1, discriminant(&Enum::Struct{a: 7, b: 11}));
 ```
 "##,
 
+E0740: r##"
+A `union` cannot have fields with destructors.
+"##,
+
 E0733: r##"
 Recursion in an `async fn` requires boxing. For example, this will not compile:
 

src/librustdoc/clean/mod.rs

@@ -1307,7 +1307,7 @@ impl Clean<Option<Lifetime>> for ty::RegionKind {
     }
 }
 
-#[derive(Clone, PartialEq, Eq, Debug, Hash)]
+#[derive(Clone, Debug)]
 pub enum WherePredicate {
     BoundPredicate { ty: Type, bounds: Vec<GenericBound> },
     RegionPredicate { lifetime: Lifetime, bounds: Vec<GenericBound> },
@@ -1589,7 +1589,7 @@ impl Clean<GenericParamDef> for hir::GenericParam {
 }
 
 // maybe use a Generic enum and use Vec<Generic>?
-#[derive(Clone, PartialEq, Eq, Debug, Default, Hash)]
+#[derive(Clone, Debug, Default)]
 pub struct Generics {
     pub params: Vec<GenericParamDef>,
     pub where_predicates: Vec<WherePredicate>,
@@ -3847,7 +3847,7 @@ impl Clean<Mutability> for hir::Mutability {
     }
 }
 
-#[derive(Clone, PartialEq, Eq, Copy, Debug, Hash)]
+#[derive(Clone, PartialEq, Debug)]
 pub enum ImplPolarity {
     Positive,
     Negative,
@@ -4506,7 +4506,6 @@ struct RegionDeps<'tcx> {
     smaller: FxHashSet<RegionTarget<'tcx>>
 }
 
-#[derive(Eq, PartialEq, Hash, Debug)]
 enum SimpleBound {
     TraitBound(Vec<PathSegment>, Vec<SimpleBound>, Vec<GenericParamDef>, hir::TraitBoundModifier),
     Outlives(Lifetime),

src/libserialize/collection_impls.rs

@@ -143,7 +143,7 @@ impl<T> Decodable for BTreeSet<T>
 }
 
 impl<K, V, S> Encodable for HashMap<K, V, S>
-    where K: Encodable + Hash + Eq,
+    where K: Encodable + Eq,
           V: Encodable,
           S: BuildHasher,
 {
@@ -180,7 +180,7 @@ impl<K, V, S> Decodable for HashMap<K, V, S>
 }
 
 impl<T, S> Encodable for HashSet<T, S>
-    where T: Encodable + Hash + Eq,
+    where T: Encodable + Eq,
           S: BuildHasher,
 {
     fn encode<E: Encoder>(&self, s: &mut E) -> Result<(), E::Error> {

src/libstd/lib.rs

@@ -275,6 +275,7 @@
 #![feature(link_args)]
 #![feature(linkage)]
 #![feature(log_syntax)]
+#![feature(manually_drop_take)]
 #![feature(maybe_uninit_ref)]
 #![feature(maybe_uninit_slice)]
 #![feature(needs_panic_runtime)]

src/libstd/panic.rs

@@ -264,7 +264,7 @@ impl RefUnwindSafe for atomic::AtomicI128 {}
 #[cfg(target_has_atomic_load_store = "ptr")]
 #[stable(feature = "unwind_safe_atomic_refs", since = "1.14.0")]
 impl RefUnwindSafe for atomic::AtomicUsize {}
-#[cfg(target_hastarget_has_atomic_load_store_atomic = "8")]
+#[cfg(target_has_atomic_load_store = "8")]
 #[unstable(feature = "integer_atomics", issue = "32976")]
 impl RefUnwindSafe for atomic::AtomicU8 {}
 #[cfg(target_has_atomic_load_store = "16")]

src/libstd/panicking.rs

@@ -12,8 +12,7 @@ use core::panic::{BoxMeUp, PanicInfo, Location};
 use crate::any::Any;
 use crate::fmt;
 use crate::intrinsics;
-use crate::mem;
+use crate::mem::{self, ManuallyDrop};
-use crate::ptr;
 use crate::raw;
 use crate::sync::atomic::{AtomicBool, Ordering};
 use crate::sys::stdio::panic_output;
@@ -227,10 +226,9 @@ pub use realstd::rt::update_panic_count;
 
 /// Invoke a closure, capturing the cause of an unwinding panic if one occurs.
 pub unsafe fn r#try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>> {
-    #[allow(unions_with_drop_fields)]
     union Data<F, R> {
-        f: F,
+        f: ManuallyDrop<F>,
-        r: R,
+        r: ManuallyDrop<R>,
     }
 
     // We do some sketchy operations with ownership here for the sake of
@@ -261,7 +259,7 @@ pub unsafe fn r#try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>>
     let mut any_data = 0;
     let mut any_vtable = 0;
     let mut data = Data {
-        f,
+        f: ManuallyDrop::new(f)
     };
 
     let r = __rust_maybe_catch_panic(do_call::<F, R>,
@@ -271,7 +269,7 @@ pub unsafe fn r#try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>>
 
     return if r == 0 {
         debug_assert!(update_panic_count(0) == 0);
-        Ok(data.r)
+        Ok(ManuallyDrop::into_inner(data.r))
     } else {
         update_panic_count(-1);
         debug_assert!(update_panic_count(0) == 0);
@@ -284,8 +282,9 @@ pub unsafe fn r#try<R, F: FnOnce() -> R>(f: F) -> Result<R, Box<dyn Any + Send>>
     fn do_call<F: FnOnce() -> R, R>(data: *mut u8) {
         unsafe {
             let data = data as *mut Data<F, R>;
-            let f = ptr::read(&mut (*data).f);
+            let data = &mut (*data);
-            ptr::write(&mut (*data).r, f());
+            let f = ManuallyDrop::take(&mut data.f);
+            data.r = ManuallyDrop::new(f());
         }
     }
 }

src/libsyntax/ast.rs

@@ -1305,7 +1305,7 @@ impl MacroDef {
     }
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug, Copy, Hash, PartialEq)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug, Copy)]
 pub enum StrStyle {
     /// A regular string, like `"foo"`.
     Cooked,
@@ -1327,7 +1327,7 @@ pub struct Lit {
     pub span: Span,
 }
 
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug, Copy, Hash, PartialEq)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug, Copy)]
 pub enum LitIntType {
     Signed(IntTy),
     Unsigned(UintTy),
@@ -1337,7 +1337,7 @@ pub enum LitIntType {
 /// Literal kind.
 ///
 /// E.g., `"foo"`, `42`, `12.34`, or `bool`.
-#[derive(Clone, RustcEncodable, RustcDecodable, Debug, Hash, PartialEq)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug)]
 pub enum LitKind {
     /// A string literal (`"foo"`).
     Str(Symbol, StrStyle),

src/libsyntax/attr/builtin.rs

@@ -84,7 +84,7 @@ fn handle_errors(sess: &ParseSess, span: Span, error: AttrError) {
     }
 }
 
-#[derive(Copy, Clone, Hash, PartialEq, RustcEncodable, RustcDecodable)]
+#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable)]
 pub enum InlineAttr {
     None,
     Hint,
@@ -92,7 +92,7 @@ pub enum InlineAttr {
     Never,
 }
 
-#[derive(Copy, Clone, Hash, PartialEq, RustcEncodable, RustcDecodable)]
+#[derive(Clone, RustcEncodable, RustcDecodable)]
 pub enum OptimizeAttr {
     None,
     Speed,
@@ -624,8 +624,7 @@ pub fn eval_condition<F>(cfg: &ast::MetaItem, sess: &ParseSess, eval: &mut F)
     }
 }
 
-
+#[derive(RustcEncodable, RustcDecodable, Clone)]
-#[derive(RustcEncodable, RustcDecodable, PartialEq, PartialOrd, Clone, Debug, Eq, Hash)]
 pub struct Deprecation {
     pub since: Option<Symbol>,
     pub note: Option<Symbol>,
@@ -749,7 +748,7 @@ pub enum ReprAttr {
     ReprAlign(u32),
 }
 
-#[derive(Eq, Hash, PartialEq, Debug, RustcEncodable, RustcDecodable, Copy, Clone)]
+#[derive(Eq, PartialEq, Debug, RustcEncodable, RustcDecodable, Copy, Clone)]
 pub enum IntType {
     SignedInt(ast::IntTy),
     UnsignedInt(ast::UintTy)

src/libsyntax/ptr.rs

@@ -35,7 +35,6 @@ use rustc_serialize::{Encodable, Decodable, Encoder, Decoder};
 
 use rustc_data_structures::stable_hasher::{StableHasher, HashStable};
 /// An owned smart pointer.
-#[derive(Hash, PartialEq, Eq)]
 pub struct P<T: ?Sized> {
     ptr: Box<T>
 }

src/libsyntax/source_map.rs

@@ -41,7 +41,7 @@ pub fn original_sp(sp: Span, enclosing_sp: Span) -> Span {
     }
 }
 
-#[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
+#[derive(Clone, RustcEncodable, RustcDecodable, Debug, Copy)]
 pub struct Spanned<T> {
     pub node: T,
     pub span: Span,

src/libsyntax_expand/mbe.rs

@@ -73,7 +73,7 @@ impl KleeneToken {
 
 /// A Kleene-style [repetition operator](http://en.wikipedia.org/wiki/Kleene_star)
 /// for token sequences.
-#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Hash, Debug, Copy)]
+#[derive(Clone, PartialEq, RustcEncodable, RustcDecodable, Debug, Copy)]
 enum KleeneOp {
     /// Kleene star (`*`) for zero or more repetitions
     ZeroOrMore,

src/libsyntax_pos/lib.rs

@@ -1311,7 +1311,7 @@ pub struct BytePos(pub u32);
 /// A character offset. Because of multibyte UTF-8 characters, a byte offset
 /// is not equivalent to a character offset. The `SourceMap` will convert `BytePos`
 /// values to `CharPos` values as necessary.
-#[derive(Copy, Clone, PartialEq, Eq, Hash, PartialOrd, Ord, Debug)]
+#[derive(Copy, Clone, PartialEq, Eq, PartialOrd, Ord, Debug)]
 pub struct CharPos(pub usize);
 
 // FIXME: lots of boilerplate in these impls, but so far my attempts to fix

src/test/ui/associated-type-bounds/union-bounds.rs

@@ -3,13 +3,13 @@
 #![feature(associated_type_bounds)]
 #![feature(untagged_unions)]
 
-#![allow(unions_with_drop_fields, unused_assignments)]
+#![allow(unused_assignments)]
 
-trait Tr1 { type As1; }
+trait Tr1: Copy { type As1: Copy; }
-trait Tr2 { type As2; }
+trait Tr2: Copy { type As2: Copy; }
-trait Tr3 { type As3; }
+trait Tr3: Copy { type As3: Copy; }
-trait Tr4<'a> { type As4; }
+trait Tr4<'a>: Copy { type As4: Copy; }
-trait Tr5 { type As5; }
+trait Tr5: Copy { type As5: Copy; }
 
 impl Tr1 for &str { type As1 = bool; }
 impl Tr2 for bool { type As2 = u8; }
@@ -71,7 +71,8 @@ where
     let _: &'a T = &x.f0;
 }
 
-union UnSelf<T> where Self: Tr1<As1: Tr2> {
+#[derive(Copy, Clone)]
+union UnSelf<T> where Self: Tr1<As1: Tr2>, T: Copy {
     f0: T,
     f1: <Self as Tr1>::As1,
     f2: <<Self as Tr1>::As1 as Tr2>::As2,

src/test/ui/consts/const-int-pow-rpass.rs

@@ -0,0 +1,11 @@
+// run-pass
+
+const IS_POWER_OF_TWO_A: bool = 0u32.is_power_of_two();
+const IS_POWER_OF_TWO_B: bool = 32u32.is_power_of_two();
+const IS_POWER_OF_TWO_C: bool = 33u32.is_power_of_two();
+
+fn main() {
+    assert!(!IS_POWER_OF_TWO_A);
+    assert!(IS_POWER_OF_TWO_B);
+    assert!(!IS_POWER_OF_TWO_C);
+}

src/test/ui/drop/dynamic-drop.rs

@@ -8,6 +8,7 @@
 #![feature(slice_patterns)]
 
 use std::cell::{Cell, RefCell};
+use std::mem::ManuallyDrop;
 use std::ops::Generator;
 use std::panic;
 use std::pin::Pin;
@@ -152,17 +153,16 @@ fn assignment1(a: &Allocator, c0: bool) {
     _v = _w;
 }
 
-#[allow(unions_with_drop_fields)]
 union Boxy<T> {
-    a: T,
+    a: ManuallyDrop<T>,
-    b: T,
+    b: ManuallyDrop<T>,
 }
 
 fn union1(a: &Allocator) {
     unsafe {
-        let mut u = Boxy { a: a.alloc() };
+        let mut u = Boxy { a: ManuallyDrop::new(a.alloc()) };
-        u.b = a.alloc();
+        *u.b = a.alloc(); // drops first alloc
-        drop(u.a);
+        drop(ManuallyDrop::into_inner(u.a));
     }
 }
 

src/test/ui/feature-gates/feature-gate-associated_type_bounds.rs

@@ -1,7 +1,7 @@
 #![feature(untagged_unions)]
 
-trait Tr1 { type As1; }
+trait Tr1 { type As1: Copy; }
-trait Tr2 { type As2; }
+trait Tr2 { type As2: Copy; }
 
 struct S1;
 #[derive(Copy, Clone)]
@@ -32,7 +32,7 @@ enum _En1<T: Tr1<As1: Tr2>> {
 
 union _Un1<T: Tr1<As1: Tr2>> {
 //~^ ERROR associated type bounds are unstable
-    outest: T,
+    outest: std::mem::ManuallyDrop<T>,
     outer: T::As1,
     inner: <T::As1 as Tr2>::As2,
 }

src/test/ui/feature-gates/feature-gate-untagged_unions.rs

@@ -7,11 +7,11 @@ union U2<T: Copy> { // OK
 }
 
 union U3 { //~ ERROR unions with non-`Copy` fields are unstable
-    a: String,
+    a: String, //~ ERROR unions may not contain fields that need dropping
 }
 
 union U4<T> { //~ ERROR unions with non-`Copy` fields are unstable
-    a: T,
+    a: T, //~ ERROR unions may not contain fields that need dropping
 }
 
 union U5 { //~ ERROR unions with `Drop` implementations are unstable

src/test/ui/feature-gates/feature-gate-untagged_unions.stderr

@@ -31,6 +31,31 @@ LL | | }
    = note: for more information, see https://github.com/rust-lang/rust/issues/32836
    = help: add `#![feature(untagged_unions)]` to the crate attributes to enable
 
-error: aborting due to 3 previous errors
+error[E0740]: unions may not contain fields that need dropping
+  --> $DIR/feature-gate-untagged_unions.rs:10:5
+   |
+LL |     a: String,
+   |     ^^^^^^^^^
+   |
+note: `std::mem::ManuallyDrop` can be used to wrap the type
+  --> $DIR/feature-gate-untagged_unions.rs:10:5
+   |
+LL |     a: String,
+   |     ^^^^^^^^^
 
-For more information about this error, try `rustc --explain E0658`.
+error[E0740]: unions may not contain fields that need dropping
+  --> $DIR/feature-gate-untagged_unions.rs:14:5
+   |
+LL |     a: T,
+   |     ^^^^
+   |
+note: `std::mem::ManuallyDrop` can be used to wrap the type
+  --> $DIR/feature-gate-untagged_unions.rs:14:5
+   |
+LL |     a: T,
+   |     ^^^^
+
+error: aborting due to 5 previous errors
+
+Some errors have detailed explanations: E0658, E0740.
+For more information about an error, try `rustc --explain E0658`.

src/test/ui/rfc-2093-infer-outlives/explicit-union.rs

@@ -1,13 +1,12 @@
 #![feature(rustc_attrs)]
 #![feature(untagged_unions)]
-#![allow(unions_with_drop_fields)]
 
 #[rustc_outlives]
-union Foo<'b, U> { //~ ERROR rustc_outlives
+union Foo<'b, U: Copy> { //~ ERROR rustc_outlives
     bar: Bar<'b, U>
 }
 
-union Bar<'a, T> where T: 'a {
+union Bar<'a, T: Copy> where T: 'a {
     x: &'a (),
     y: T,
 }

src/test/ui/rfc-2093-infer-outlives/explicit-union.stderr

@@ -1,7 +1,7 @@
 error: rustc_outlives
-  --> $DIR/explicit-union.rs:6:1
+  --> $DIR/explicit-union.rs:5:1
    |
-LL | / union Foo<'b, U> {
+LL | / union Foo<'b, U: Copy> {
 LL | |     bar: Bar<'b, U>
 LL | | }
    | |_^

src/test/ui/rfc-2093-infer-outlives/nested-union.rs

@@ -1,14 +1,13 @@
 #![feature(rustc_attrs)]
 #![feature(untagged_unions)]
-#![allow(unions_with_drop_fields)]
 
 #[rustc_outlives]
-union Foo<'a, T> { //~ ERROR rustc_outlives
+union Foo<'a, T: Copy> { //~ ERROR rustc_outlives
     field1: Bar<'a, T>
 }
 
 // Type U needs to outlive lifetime 'b
-union Bar<'b, U> {
+union Bar<'b, U: Copy> {
     field2: &'b U
 }
 

src/test/ui/rfc-2093-infer-outlives/nested-union.stderr

@@ -1,7 +1,7 @@
 error: rustc_outlives
-  --> $DIR/nested-union.rs:6:1
+  --> $DIR/nested-union.rs:5:1
    |
-LL | / union Foo<'a, T> {
+LL | / union Foo<'a, T: Copy> {
 LL | |     field1: Bar<'a, T>
 LL | | }
    | |_^

src/test/ui/self/self-in-typedefs.rs

@@ -3,7 +3,8 @@
 #![feature(untagged_unions)]
 
 #![allow(dead_code)]
-#![allow(unions_with_drop_fields)]
+
+use std::mem::ManuallyDrop;
 
 enum A<'a, T: 'a>
 where
@@ -24,6 +25,14 @@ where
 union C<'a, T: 'a>
 where
     Self: Send, T: PartialEq<Self>
+{
+    foo: &'a Self,
+    bar: ManuallyDrop<T>,
+}
+
+union D<'a, T: 'a>
+where
+    Self: Send, T: PartialEq<Self> + Copy
 {
     foo: &'a Self,
     bar: T,

src/test/ui/symbol-names/impl1.legacy.stderr

@@ -46,13 +46,13 @@ error: def-path(bar::<impl foo::Foo>::baz)
 LL |         #[rustc_def_path]
    |         ^^^^^^^^^^^^^^^^^
 
-error: symbol-name(_ZN209_$LT$$u5b$$RF$dyn$u20$impl1..Foo$u2b$Assoc$u20$$u3d$$u20$extern$u20$$u22$C$u22$$u20$fn$LP$$RF$u8$C$$u20$...$RP$$u2b$impl1..AutoTrait$u3b$$u20$_$u5d$$u20$as$u20$impl1..main..$u7b$$u7b$closure$u7d$$u7d$..Bar$GT$6method17h059bf53000885489E)
+error: symbol-name(_ZN209_$LT$$u5b$$RF$dyn$u20$impl1..Foo$u2b$Assoc$u20$$u3d$$u20$extern$u20$$u22$C$u22$$u20$fn$LP$$RF$u8$C$$u20$...$RP$$u2b$impl1..AutoTrait$u3b$$u20$_$u5d$$u20$as$u20$impl1..main..$u7b$$u7b$closure$u7d$$u7d$..Bar$GT$6method17h636bc933fc62ee2fE)
   --> $DIR/impl1.rs:61:13
    |
 LL |             #[rustc_symbol_name]
    |             ^^^^^^^^^^^^^^^^^^^^
 
-error: demangling(<[&dyn impl1::Foo+Assoc = extern "C" fn(&u8, ::.)+impl1::AutoTrait; _] as impl1::main::{{closure}}::Bar>::method::h059bf53000885489)
+error: demangling(<[&dyn impl1::Foo+Assoc = extern "C" fn(&u8, ::.)+impl1::AutoTrait; _] as impl1::main::{{closure}}::Bar>::method::h636bc933fc62ee2f)
   --> $DIR/impl1.rs:61:13
    |
 LL |             #[rustc_symbol_name]

src/test/ui/union/issue-41073.rs

@@ -0,0 +1,24 @@
+#![feature(untagged_unions)]
+
+union Test {
+    a: A, //~ ERROR unions may not contain fields that need dropping
+    b: B
+}
+
+#[derive(Debug)]
+struct A(i32);
+impl Drop for A {
+    fn drop(&mut self) { println!("A"); }
+}
+
+#[derive(Debug)]
+struct B(f32);
+impl Drop for B {
+    fn drop(&mut self) { println!("B"); }
+}
+
+fn main() {
+    let mut test = Test { a: A(3) };
+    println!("{:?}", unsafe { test.b });
+    unsafe { test.b = B(0.5); }
+}

src/test/ui/union/issue-41073.stderr

@@ -0,0 +1,15 @@
+error[E0740]: unions may not contain fields that need dropping
+  --> $DIR/issue-41073.rs:4:5
+   |
+LL |     a: A,
+   |     ^^^^
+   |
+note: `std::mem::ManuallyDrop` can be used to wrap the type
+  --> $DIR/issue-41073.rs:4:5
+   |
+LL |     a: A,
+   |     ^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0740`.

src/test/ui/union/union-borrow-move-parent-sibling.rs

@@ -1,51 +1,90 @@
 #![feature(untagged_unions)]
 #![allow(unused)]
 
-#[allow(unions_with_drop_fields)]
+use std::ops::{Deref, DerefMut};
+
+#[derive(Default)]
+struct MockBox<T> {
+    value: [T; 1],
+}
+
+impl<T> MockBox<T> {
+    fn new(value: T) -> Self { MockBox { value: [value] } }
+}
+
+impl<T> Deref for MockBox<T> {
+    type Target = T;
+    fn deref(&self) -> &T { &self.value[0] }
+}
+
+impl<T> DerefMut for MockBox<T> {
+    fn deref_mut(&mut self) -> &mut T { &mut self.value[0] }
+}
+
+#[derive(Default)]
+struct MockVec<T> {
+    value: [T; 0],
+}
+
+impl<T> MockVec<T> {
+    fn new() -> Self { MockVec { value: [] } }
+}
+
+impl<T> Deref for MockVec<T> {
+    type Target = [T];
+    fn deref(&self) -> &[T] { &self.value }
+}
+
+impl<T> DerefMut for MockVec<T> {
+    fn deref_mut(&mut self) -> &mut [T] { &mut self.value }
+}
+
+
 union U {
-    x: ((Vec<u8>, Vec<u8>), Vec<u8>),
+    x: ((MockVec<u8>, MockVec<u8>), MockVec<u8>),
-    y: Box<Vec<u8>>,
+    y: MockBox<MockVec<u8>>,
 }
 
 fn use_borrow<T>(_: &T) {}
 
 unsafe fn parent_sibling_borrow() {
-    let mut u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+    let mut u = U { x: ((MockVec::new(), MockVec::new()), MockVec::new()) };
     let a = &mut u.x.0;
     let b = &u.y; //~ ERROR cannot borrow `u` (via `u.y`)
     use_borrow(a);
 }
 
 unsafe fn parent_sibling_move() {
-    let u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+    let u = U { x: ((MockVec::new(), MockVec::new()), MockVec::new()) };
     let a = u.x.0;
     let b = u.y; //~ ERROR use of moved value: `u`
 }
 
 unsafe fn grandparent_sibling_borrow() {
-    let mut u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+    let mut u = U { x: ((MockVec::new(), MockVec::new()), MockVec::new()) };
     let a = &mut (u.x.0).0;
     let b = &u.y; //~ ERROR cannot borrow `u` (via `u.y`)
     use_borrow(a);
 }
 
 unsafe fn grandparent_sibling_move() {
-    let u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+    let u = U { x: ((MockVec::new(), MockVec::new()), MockVec::new()) };
     let a = (u.x.0).0;
     let b = u.y; //~ ERROR use of moved value: `u`
 }
 
 unsafe fn deref_sibling_borrow() {
-    let mut u = U { y: Box::default() };
+    let mut u = U { y: MockBox::default() };
     let a = &mut *u.y;
     let b = &u.x; //~ ERROR cannot borrow `u` (via `u.x`)
     use_borrow(a);
 }
 
 unsafe fn deref_sibling_move() {
-    let u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+    let u = U { x: ((MockVec::new(), MockVec::new()), MockVec::new()) };
-    let a = *u.y;
+    // No way to test deref-move without Box in union
-    let b = u.x; //~ ERROR use of moved value: `u`
+    // let a = *u.y;
+    // let b = u.x; ERROR use of moved value: `u`
 }
 
 

src/test/ui/union/union-borrow-move-parent-sibling.stderr

@@ -1,5 +1,5 @@
 error[E0502]: cannot borrow `u` (via `u.y`) as immutable because it is also borrowed as mutable (via `u.x.0`)
-  --> $DIR/union-borrow-move-parent-sibling.rs:15:13
+  --> $DIR/union-borrow-move-parent-sibling.rs:53:13
    |
 LL |     let a = &mut u.x.0;
    |             ---------- mutable borrow occurs here (via `u.x.0`)
@@ -11,9 +11,9 @@ LL |     use_borrow(a);
    = note: `u.y` is a field of the union `U`, so it overlaps the field `u.x.0`
 
 error[E0382]: use of moved value: `u`
-  --> $DIR/union-borrow-move-parent-sibling.rs:22:13
+  --> $DIR/union-borrow-move-parent-sibling.rs:60:13
    |
-LL |     let u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+LL |     let u = U { x: ((MockVec::new(), MockVec::new()), MockVec::new()) };
    |         - move occurs because `u` has type `U`, which does not implement the `Copy` trait
 LL |     let a = u.x.0;
    |             ----- value moved here
@@ -21,7 +21,7 @@ LL |     let b = u.y;
    |             ^^^ value used here after move
 
 error[E0502]: cannot borrow `u` (via `u.y`) as immutable because it is also borrowed as mutable (via `u.x.0.0`)
-  --> $DIR/union-borrow-move-parent-sibling.rs:28:13
+  --> $DIR/union-borrow-move-parent-sibling.rs:66:13
    |
 LL |     let a = &mut (u.x.0).0;
    |             -------------- mutable borrow occurs here (via `u.x.0.0`)
@@ -33,38 +33,28 @@ LL |     use_borrow(a);
    = note: `u.y` is a field of the union `U`, so it overlaps the field `u.x.0.0`
 
 error[E0382]: use of moved value: `u`
-  --> $DIR/union-borrow-move-parent-sibling.rs:35:13
+  --> $DIR/union-borrow-move-parent-sibling.rs:73:13
    |
-LL |     let u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
+LL |     let u = U { x: ((MockVec::new(), MockVec::new()), MockVec::new()) };
    |         - move occurs because `u` has type `U`, which does not implement the `Copy` trait
 LL |     let a = (u.x.0).0;
    |             --------- value moved here
 LL |     let b = u.y;
    |             ^^^ value used here after move
 
-error[E0502]: cannot borrow `u` (via `u.x`) as immutable because it is also borrowed as mutable (via `*u.y`)
+error[E0502]: cannot borrow `u` (via `u.x`) as immutable because it is also borrowed as mutable (via `u.y`)
-  --> $DIR/union-borrow-move-parent-sibling.rs:41:13
+  --> $DIR/union-borrow-move-parent-sibling.rs:79:13
    |
 LL |     let a = &mut *u.y;
-   |             --------- mutable borrow occurs here (via `*u.y`)
+   |                   --- mutable borrow occurs here (via `u.y`)
 LL |     let b = &u.x;
-   |             ^^^^ immutable borrow of `u.x` -- which overlaps with `*u.y` -- occurs here
+   |             ^^^^ immutable borrow of `u.x` -- which overlaps with `u.y` -- occurs here
 LL |     use_borrow(a);
    |                - mutable borrow later used here
    |
-   = note: `u.x` is a field of the union `U`, so it overlaps the field `*u.y`
+   = note: `u.x` is a field of the union `U`, so it overlaps the field `u.y`
 
-error[E0382]: use of moved value: `u`
+error: aborting due to 5 previous errors
-  --> $DIR/union-borrow-move-parent-sibling.rs:48:13
-   |
-LL |     let u = U { x: ((Vec::new(), Vec::new()), Vec::new()) };
-   |         - move occurs because `u` has type `U`, which does not implement the `Copy` trait
-LL |     let a = *u.y;
-   |             ---- value moved here
-LL |     let b = u.x;
-   |             ^^^ value used here after move
-
-error: aborting due to 6 previous errors
 
 Some errors have detailed explanations: E0382, E0502.
 For more information about an error, try `rustc --explain E0382`.

src/test/ui/union/union-custom-drop.rs

@@ -0,0 +1,19 @@
+// test for a union with a field that's a union with a manual impl Drop
+// Ensures we do not treat all unions as not having any drop glue.
+
+#![feature(untagged_unions)]
+
+union Foo {
+    bar: Bar, //~ ERROR unions may not contain fields that need dropping
+}
+
+union Bar {
+    a: i32,
+    b: u32,
+}
+
+impl Drop for Bar {
+    fn drop(&mut self) {}
+}
+
+fn main() {}

src/test/ui/union/union-custom-drop.stderr

@@ -0,0 +1,15 @@
+error[E0740]: unions may not contain fields that need dropping
+  --> $DIR/union-custom-drop.rs:7:5
+   |
+LL |     bar: Bar,
+   |     ^^^^^^^^
+   |
+note: `std::mem::ManuallyDrop` can be used to wrap the type
+  --> $DIR/union-custom-drop.rs:7:5
+   |
+LL |     bar: Bar,
+   |     ^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0740`.

src/test/ui/union/union-derive-clone.rs

@@ -1,5 +1,7 @@
 #![feature(untagged_unions)]
 
+use std::mem::ManuallyDrop;
+
 #[derive(Clone)] //~ ERROR the trait bound `U1: std::marker::Copy` is not satisfied
 union U1 {
     a: u8,
@@ -18,14 +20,19 @@ union U3 {
 }
 
 #[derive(Clone, Copy)]
-union U4<T> {
+union U4<T: Copy> {
     a: T, // OK
 }
 
+#[derive(Clone, Copy)]
+union U5<T> {
+    a: ManuallyDrop<T>, // OK
+}
+
 #[derive(Clone)]
 struct CloneNoCopy;
 
 fn main() {
-    let u = U4 { a: CloneNoCopy };
+    let u = U5 { a: ManuallyDrop::new(CloneNoCopy) };
-    let w = u.clone(); //~ ERROR no method named `clone` found for type `U4<CloneNoCopy>`
+    let w = u.clone(); //~ ERROR no method named `clone` found for type `U5<CloneNoCopy>`
 }

src/test/ui/union/union-derive-clone.stderr

@@ -1,22 +1,22 @@
 error[E0277]: the trait bound `U1: std::marker::Copy` is not satisfied
-  --> $DIR/union-derive-clone.rs:3:10
+  --> $DIR/union-derive-clone.rs:5:10
    |
 LL | #[derive(Clone)]
    |          ^^^^^ the trait `std::marker::Copy` is not implemented for `U1`
    |
    = note: required by `std::clone::AssertParamIsCopy`
 
-error[E0599]: no method named `clone` found for type `U4<CloneNoCopy>` in the current scope
+error[E0599]: no method named `clone` found for type `U5<CloneNoCopy>` in the current scope
-  --> $DIR/union-derive-clone.rs:30:15
+  --> $DIR/union-derive-clone.rs:37:15
    |
-LL | union U4<T> {
+LL | union U5<T> {
    | ----------- method `clone` not found for this
 ...
 LL |     let w = u.clone();
-   |               ^^^^^ method not found in `U4<CloneNoCopy>`
+   |               ^^^^^ method not found in `U5<CloneNoCopy>`
    |
    = note: the method `clone` exists but the following trait bounds were not satisfied:
-           `U4<CloneNoCopy> : std::clone::Clone`
+           `U5<CloneNoCopy> : std::clone::Clone`
    = help: items from traits can only be used if the trait is implemented and in scope
    = note: the following trait defines an item `clone`, perhaps you need to implement it:
            candidate #1: `std::clone::Clone`

src/test/ui/union/union-derive-rpass.rs

@@ -1,7 +1,6 @@
 // run-pass
 #![allow(dead_code)]
 #![allow(unused_variables)]
-#![allow(unions_with_drop_fields)]
 
 // Some traits can be derived for unions.
 
@@ -24,11 +23,11 @@ impl PartialEq for U { fn eq(&self, rhs: &Self) -> bool { true } }
     Copy,
     Eq
 )]
-union W<T> {
+union W<T: Copy> {
     a: T,
 }
 
-impl<T> PartialEq for W<T> { fn eq(&self, rhs: &Self) -> bool { true } }
+impl<T: Copy> PartialEq for W<T> { fn eq(&self, rhs: &Self) -> bool { true } }
 
 fn main() {
     let u = U { b: 0 };