NLL should identify and respect the lifetime annotations that the user wrote

src/librustc/ich/impls_mir.rs

@@ -277,6 +277,10 @@ for mir::StatementKind<'gcx> {
                 op.hash_stable(hcx, hasher);
                 places.hash_stable(hcx, hasher);
             }
+            mir::StatementKind::UserAssertTy(ref c_ty, ref local) => {
+                c_ty.hash_stable(hcx, hasher);
+                local.hash_stable(hcx, hasher);
+            }
             mir::StatementKind::Nop => {}
             mir::StatementKind::InlineAsm { ref asm, ref outputs, ref inputs } => {
                 asm.hash_stable(hcx, hasher);

src/librustc/infer/canonical.rs

@@ -33,6 +33,7 @@
 
 use infer::{InferCtxt, InferOk, InferResult, RegionVariableOrigin, TypeVariableOrigin};
 use rustc_data_structures::indexed_vec::Idx;
+use serialize::UseSpecializedDecodable;
 use std::fmt::Debug;
 use std::ops::Index;
 use syntax::codemap::Span;
@@ -49,14 +50,16 @@ use rustc_data_structures::fx::FxHashMap;
 /// A "canonicalized" type `V` is one where all free inference
 /// variables have been rewriten to "canonical vars". These are
 /// numbered starting from 0 in order of first appearance.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcDecodable, RustcEncodable)]
 pub struct Canonical<'gcx, V> {
     pub variables: CanonicalVarInfos<'gcx>,
     pub value: V,
 }
 
 pub type CanonicalVarInfos<'gcx> = &'gcx Slice<CanonicalVarInfo>;
 
+impl<'gcx> UseSpecializedDecodable for CanonicalVarInfos<'gcx> { }
+
 /// A set of values corresponding to the canonical variables from some
 /// `Canonical`. You can give these values to
 /// `canonical_value.substitute` to substitute them into the canonical
@@ -69,7 +72,7 @@ pub type CanonicalVarInfos<'gcx> = &'gcx Slice<CanonicalVarInfo>;
 /// You can also use `infcx.fresh_inference_vars_for_canonical_vars`
 /// to get back a `CanonicalVarValues` containing fresh inference
 /// variables.
-#[derive(Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Clone, Debug, PartialEq, Eq, Hash, RustcDecodable, RustcEncodable)]
 pub struct CanonicalVarValues<'tcx> {
     pub var_values: IndexVec<CanonicalVar, Kind<'tcx>>,
 }
@@ -78,15 +81,15 @@ pub struct CanonicalVarValues<'tcx> {
 /// canonical value. This is sufficient information for code to create
 /// a copy of the canonical value in some other inference context,
 /// with fresh inference variables replacing the canonical values.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcDecodable, RustcEncodable)]
 pub struct CanonicalVarInfo {
     pub kind: CanonicalVarKind,
 }
 
 /// Describes the "kind" of the canonical variable. This is a "kind"
 /// in the type-theory sense of the term -- i.e., a "meta" type system
 /// that analyzes type-like values.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcDecodable, RustcEncodable)]
 pub enum CanonicalVarKind {
     /// Some kind of type inference variable.
     Ty(CanonicalTyVarKind),
@@ -100,7 +103,7 @@ pub enum CanonicalVarKind {
 /// 22.) can only be instantiated with integral/float types (e.g.,
 /// usize or f32). In order to faithfully reproduce a type, we need to
 /// know what set of types a given type variable can be unified with.
-#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash)]
+#[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcDecodable, RustcEncodable)]
 pub enum CanonicalTyVarKind {
     /// General type variable `?T` that can be unified with arbitrary types.
     General,
@@ -855,11 +858,14 @@ impl<'cx, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for CanonicalVarValuesSubst<'cx, 'g
 }
 
 CloneTypeFoldableAndLiftImpls! {
+    ::infer::canonical::Certainty,
+    ::infer::canonical::CanonicalVarInfo,
+    ::infer::canonical::CanonicalVarKind,
+}
+
+CloneTypeFoldableImpls! {
     for <'tcx> {
-        ::infer::canonical::Certainty,
-        ::infer::canonical::CanonicalVarInfo,
         ::infer::canonical::CanonicalVarInfos<'tcx>,
-        ::infer::canonical::CanonicalVarKind,
     }
 }
 
@@ -870,6 +876,13 @@ BraceStructTypeFoldableImpl! {
     } where C: TypeFoldable<'tcx>
 }
 
+BraceStructLiftImpl! {
+    impl<'a, 'tcx, T> Lift<'tcx> for Canonical<'a, T> {
+        type Lifted = Canonical<'tcx, T::Lifted>;
+        variables, value
+    } where T: Lift<'tcx>
+}
+
 impl<'tcx> CanonicalVarValues<'tcx> {
     fn iter<'a>(&'a self) -> impl Iterator<Item = Kind<'tcx>> + 'a {
         self.var_values.iter().cloned()

src/librustc/mir/mod.rs

@@ -27,7 +27,7 @@ use hir::def_id::DefId;
 use mir::visit::MirVisitable;
 use mir::interpret::{Value, PrimVal};
 use ty::subst::{Subst, Substs};
-use ty::{self, AdtDef, ClosureSubsts, Region, Ty, TyCtxt, GeneratorInterior};
+use ty::{self, AdtDef, CanonicalTy, ClosureSubsts, Region, Ty, TyCtxt, GeneratorInterior};
 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use ty::TypeAndMut;
 use util::ppaux;
@@ -1253,6 +1253,23 @@ pub enum StatementKind<'tcx> {
     /// (The starting point(s) arise implicitly from borrows.)
     EndRegion(region::Scope),
 
+    /// Encodes a user's type assertion. These need to be preserved intact so that NLL can respect
+    /// them. For example:
+    ///
+    ///     let (a, b): (T, U) = y;
+    ///
+    /// Here we would insert a `UserAssertTy<(T, U)>(y)` instruction to check that the type of `y`
+    /// is the right thing.
+    ///
+    /// `CanonicalTy` is used to capture "inference variables" from the user's types. For example:
+    ///
+    ///     let x: Vec<_> = ...;
+    ///     let y: &u32 = ...;
+    ///
+    /// would result in `Vec<?0>` and `&'?0 u32` respectively (where `?0` is a canonicalized
+    /// variable).
+    UserAssertTy(CanonicalTy<'tcx>, Local),
+
     /// No-op. Useful for deleting instructions without affecting statement indices.
     Nop,
 }
@@ -1324,6 +1341,8 @@ impl<'tcx> Debug for Statement<'tcx> {
             InlineAsm { ref asm, ref outputs, ref inputs } => {
                 write!(fmt, "asm!({:?} : {:?} : {:?})", asm, outputs, inputs)
             },
+            UserAssertTy(ref c_ty, ref local) => write!(fmt, "UserAssertTy({:?}, {:?})",
+                                                        c_ty, local),
             Nop => write!(fmt, "nop"),
         }
     }
@@ -2184,6 +2203,7 @@ EnumTypeFoldableImpl! {
         (StatementKind::InlineAsm) { asm, outputs, inputs },
         (StatementKind::Validate)(a, b),
         (StatementKind::EndRegion)(a),
+        (StatementKind::UserAssertTy)(a, b),
         (StatementKind::Nop),
     }
 }

src/librustc/mir/visit.rs

@@ -10,7 +10,7 @@
 
 use hir::def_id::DefId;
 use ty::subst::Substs;
-use ty::{ClosureSubsts, Region, Ty, GeneratorInterior};
+use ty::{CanonicalTy, ClosureSubsts, Region, Ty, GeneratorInterior};
 use mir::*;
 use syntax_pos::Span;
 
@@ -144,6 +144,13 @@ macro_rules! make_mir_visitor {
                 self.super_operand(operand, location);
             }
 
+            fn visit_user_assert_ty(&mut self,
+                                    c_ty: & $($mutability)* CanonicalTy<'tcx>,
+                                    local: & $($mutability)* Local,
+                                    location: Location) {
+                self.super_user_assert_ty(c_ty, local, location);
+            }
+
             fn visit_place(&mut self,
                             place: & $($mutability)* Place<'tcx>,
                             context: PlaceContext<'tcx>,
@@ -376,6 +383,10 @@ macro_rules! make_mir_visitor {
                             self.visit_operand(input, location);
                         }
                     }
+                    StatementKind::UserAssertTy(ref $($mutability)* c_ty,
+                                                ref $($mutability)* local) => {
+                        self.visit_user_assert_ty(c_ty, local, location);
+                    }
                     StatementKind::Nop => {}
                 }
             }
@@ -619,6 +630,13 @@ macro_rules! make_mir_visitor {
                 }
             }
 
+            fn super_user_assert_ty(&mut self,
+                                    _c_ty: & $($mutability)* CanonicalTy<'tcx>,
+                                    local: & $($mutability)* Local,
+                                    location: Location) {
+                self.visit_local(local, PlaceContext::Validate, location);
+            }
+
             fn super_place(&mut self,
                             place: & $($mutability)* Place<'tcx>,
                             context: PlaceContext<'tcx>,

src/librustc/session/config.rs

@@ -1251,6 +1251,8 @@ options! {DebuggingOptions, DebuggingSetter, basic_debugging_options,
         "choose which RELRO level to use"),
     nll: bool = (false, parse_bool, [UNTRACKED],
                  "run the non-lexical lifetimes MIR pass"),
+    disable_nll_user_type_assert: bool = (false, parse_bool, [UNTRACKED],
+        "disable user provided type assertion in NLL"),
     trans_time_graph: bool = (false, parse_bool, [UNTRACKED],
         "generate a graphical HTML report of time spent in trans and LLVM"),
     thinlto: Option<bool> = (None, parse_opt_bool, [TRACKED],

src/librustc/ty/codec.rs

@@ -17,6 +17,7 @@
 // persisting to incr. comp. caches.
 
 use hir::def_id::{DefId, CrateNum};
+use infer::canonical::{CanonicalVarInfo, CanonicalVarInfos};
 use rustc_data_structures::fx::FxHashMap;
 use rustc_serialize::{Decodable, Decoder, Encoder, Encodable, opaque};
 use std::hash::Hash;
@@ -239,6 +240,19 @@ pub fn decode_existential_predicate_slice<'a, 'tcx, D>(decoder: &mut D)
               .mk_existential_predicates((0..len).map(|_| Decodable::decode(decoder)))?)
 }
 
+#[inline]
+pub fn decode_canonical_var_infos<'a, 'tcx, D>(decoder: &mut D)
+    -> Result<CanonicalVarInfos<'tcx>, D::Error>
+    where D: TyDecoder<'a, 'tcx>,
+          'tcx: 'a,
+{
+    let len = decoder.read_usize()?;
+    let interned: Result<Vec<CanonicalVarInfo>, _> = (0..len).map(|_| Decodable::decode(decoder))
+                                                             .collect();
+    Ok(decoder.tcx()
+              .intern_canonical_var_infos(interned?.as_slice()))
+}
+
 #[inline]
 pub fn decode_const<'a, 'tcx, D>(decoder: &mut D)
                                  -> Result<&'tcx ty::Const<'tcx>, D::Error>
@@ -262,6 +276,7 @@ macro_rules! implement_ty_decoder {
     ($DecoderName:ident <$($typaram:tt),*>) => {
         mod __ty_decoder_impl {
             use super::$DecoderName;
+            use $crate::infer::canonical::CanonicalVarInfos;
             use $crate::ty;
             use $crate::ty::codec::*;
             use $crate::ty::subst::Substs;
@@ -364,6 +379,14 @@ macro_rules! implement_ty_decoder {
                 }
             }
 
+            impl<$($typaram),*> SpecializedDecoder<CanonicalVarInfos<'tcx>>
+                for $DecoderName<$($typaram),*> {
+                fn specialized_decode(&mut self)
+                    -> Result<CanonicalVarInfos<'tcx>, Self::Error> {
+                    decode_canonical_var_infos(self)
+                }
+            }
+
             impl<$($typaram),*> SpecializedDecoder<&'tcx $crate::ty::Const<'tcx>>
             for $DecoderName<$($typaram),*> {
                 fn specialized_decode(&mut self) -> Result<&'tcx ty::Const<'tcx>, Self::Error> {

src/librustc/ty/context.rs

@@ -48,6 +48,7 @@ use ty::layout::{LayoutDetails, TargetDataLayout};
 use ty::maps;
 use ty::steal::Steal;
 use ty::BindingMode;
+use ty::CanonicalTy;
 use util::nodemap::{NodeMap, DefIdSet, ItemLocalMap};
 use util::nodemap::{FxHashMap, FxHashSet};
 use rustc_data_structures::accumulate_vec::AccumulateVec;
@@ -344,6 +345,10 @@ pub struct TypeckTables<'tcx> {
     /// method calls, including those of overloaded operators.
     type_dependent_defs: ItemLocalMap<Def>,
 
+    /// Stores the canonicalized types provided by the user. See also `UserAssertTy` statement in
+    /// MIR.
+    user_provided_tys: ItemLocalMap<CanonicalTy<'tcx>>,
+
     /// Stores the types for various nodes in the AST.  Note that this table
     /// is not guaranteed to be populated until after typeck.  See
     /// typeck::check::fn_ctxt for details.
@@ -420,6 +425,7 @@ impl<'tcx> TypeckTables<'tcx> {
         TypeckTables {
             local_id_root,
             type_dependent_defs: ItemLocalMap(),
+            user_provided_tys: ItemLocalMap(),
             node_types: ItemLocalMap(),
             node_substs: ItemLocalMap(),
             adjustments: ItemLocalMap(),
@@ -461,6 +467,20 @@ impl<'tcx> TypeckTables<'tcx> {
         }
     }
 
+    pub fn user_provided_tys(&self) -> LocalTableInContext<CanonicalTy<'tcx>> {
+        LocalTableInContext {
+            local_id_root: self.local_id_root,
+            data: &self.user_provided_tys
+        }
+    }
+
+    pub fn user_provided_tys_mut(&mut self) -> LocalTableInContextMut<CanonicalTy<'tcx>> {
+        LocalTableInContextMut {
+            local_id_root: self.local_id_root,
+            data: &mut self.user_provided_tys
+        }
+    }
+
     pub fn node_types(&self) -> LocalTableInContext<Ty<'tcx>> {
         LocalTableInContext {
             local_id_root: self.local_id_root,
@@ -685,6 +705,7 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for TypeckTables<'gcx> {
         let ty::TypeckTables {
             local_id_root,
             ref type_dependent_defs,
+            ref user_provided_tys,
             ref node_types,
             ref node_substs,
             ref adjustments,
@@ -704,6 +725,7 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for TypeckTables<'gcx> {
 
         hcx.with_node_id_hashing_mode(NodeIdHashingMode::HashDefPath, |hcx| {
             type_dependent_defs.hash_stable(hcx, hasher);
+            user_provided_tys.hash_stable(hcx, hasher);
             node_types.hash_stable(hcx, hasher);
             node_substs.hash_stable(hcx, hasher);
             adjustments.hash_stable(hcx, hasher);
@@ -1635,6 +1657,24 @@ impl<'a, 'tcx> Lift<'tcx> for &'a Slice<Predicate<'a>> {
     }
 }
 
+impl<'a, 'tcx> Lift<'tcx> for &'a Slice<CanonicalVarInfo> {
+    type Lifted = &'tcx Slice<CanonicalVarInfo>;
+    fn lift_to_tcx<'b, 'gcx>(&self, tcx: TyCtxt<'b, 'gcx, 'tcx>) -> Option<Self::Lifted> {
+        if self.len() == 0 {
+            return Some(Slice::empty());
+        }
+        if tcx.interners.arena.in_arena(*self as *const _) {
+            return Some(unsafe { mem::transmute(*self) });
+        }
+        // Also try in the global tcx if we're not that.
+        if !tcx.is_global() {
+            self.lift_to_tcx(tcx.global_tcx())
+        } else {
+            None
+        }
+    }
+}
+
 pub mod tls {
     use super::{CtxtInterners, GlobalCtxt, TyCtxt};
 

src/librustc/ty/mod.rs

@@ -21,6 +21,7 @@ use hir::map::DefPathData;
 use hir::svh::Svh;
 use ich::Fingerprint;
 use ich::StableHashingContext;
+use infer::canonical::{Canonical, Canonicalize};
 use middle::const_val::ConstVal;
 use middle::lang_items::{FnTraitLangItem, FnMutTraitLangItem, FnOnceTraitLangItem};
 use middle::privacy::AccessLevels;
@@ -554,6 +555,17 @@ pub type Ty<'tcx> = &'tcx TyS<'tcx>;
 impl<'tcx> serialize::UseSpecializedEncodable for Ty<'tcx> {}
 impl<'tcx> serialize::UseSpecializedDecodable for Ty<'tcx> {}
 
+pub type CanonicalTy<'gcx> = Canonical<'gcx, Ty<'gcx>>;
+
+impl <'gcx: 'tcx, 'tcx> Canonicalize<'gcx, 'tcx> for Ty<'tcx> {
+    type Canonicalized = CanonicalTy<'gcx>;
+
+    fn intern(_gcx: TyCtxt<'_, 'gcx, 'gcx>,
+              value: Canonical<'gcx, Self::Lifted>) -> Self::Canonicalized {
+        value
+    }
+}
+
 /// A wrapper for slices with the additional invariant
 /// that the slice is interned and no other slice with
 /// the same contents can exist in the same context.

src/librustc_mir/borrow_check/mod.rs

@@ -392,11 +392,13 @@ impl<'cx, 'gcx, 'tcx> DataflowResultsConsumer<'cx, 'tcx> for MirBorrowckCtxt<'cx
                 // ignored when consuming results (update to
                 // flow_state already handled).
             }
-            StatementKind::Nop | StatementKind::Validate(..) | StatementKind::StorageLive(..) => {
-                // `Nop`, `Validate`, and `StorageLive` are irrelevant
+            StatementKind::Nop |
+            StatementKind::UserAssertTy(..) |
+            StatementKind::Validate(..) |
+            StatementKind::StorageLive(..) => {
+                // `Nop`, `UserAssertTy`, `Validate`, and `StorageLive` are irrelevant
                 // to borrow check.
             }
-
             StatementKind::StorageDead(local) => {
                 self.access_place(
                     ContextKind::StorageDead.new(location),