Auto merge of rust-lang#53225 - nikomatsakis:nll-type-annot, r=pnkfelix

MIR: support user-given type annotations on fns, structs, and enums

This branch adds tooling to track user-given type annotations on functions, structs, and enum variant expressions. The user-given types are passed onto NLL which then enforces them.

cc rust-lang#47184 — not a complete fix, as there are more cases to cover

r? @eddyb
cc @rust-lang/wg-compiler-nll

Author: bors

src/librustc/hir/def.rs

@@ -68,7 +68,7 @@ pub enum Def {
     Const(DefId),
     Static(DefId, bool /* is_mutbl */),
     StructCtor(DefId, CtorKind), // DefId refers to NodeId of the struct's constructor
-    VariantCtor(DefId, CtorKind),
+    VariantCtor(DefId, CtorKind), // DefId refers to the enum variant
     Method(DefId),
     AssociatedConst(DefId),
 

src/librustc/ich/impls_mir.rs

@@ -479,10 +479,11 @@ for mir::AggregateKind<'gcx> {
             mir::AggregateKind::Array(t) => {
                 t.hash_stable(hcx, hasher);
             }
-            mir::AggregateKind::Adt(adt_def, idx, substs, active_field) => {
+            mir::AggregateKind::Adt(adt_def, idx, substs, user_substs, active_field) => {
                 adt_def.hash_stable(hcx, hasher);
                 idx.hash_stable(hcx, hasher);
                 substs.hash_stable(hcx, hasher);
+                user_substs.hash_stable(hcx, hasher);
                 active_field.hash_stable(hcx, hasher);
             }
             mir::AggregateKind::Closure(def_id, ref substs) => {
@@ -528,7 +529,7 @@ impl_stable_hash_for!(enum mir::NullOp {
     SizeOf
 });
 
-impl_stable_hash_for!(struct mir::Constant<'tcx> { span, ty, literal });
+impl_stable_hash_for!(struct mir::Constant<'tcx> { span, ty, user_ty, literal });
 
 impl_stable_hash_for!(struct mir::Location { block, statement_index });
 

src/librustc/infer/canonical/mod.rs

@@ -188,6 +188,36 @@ impl<'tcx, R> Canonical<'tcx, QueryResult<'tcx, R>> {
     }
 }
 
+impl<'gcx, V> Canonical<'gcx, V> {
+    /// Allows you to map the `value` of a canonical while keeping the
+    /// same set of bound variables.
+    ///
+    /// **WARNING:** This function is very easy to mis-use, hence the
+    /// name!  In particular, the new value `W` must use all **the
+    /// same type/region variables** in **precisely the same order**
+    /// as the original! (The ordering is defined by the
+    /// `TypeFoldable` implementation of the type in question.)
+    ///
+    /// An example of a **correct** use of this:
+    ///
+    /// ```rust,ignore (not real code)
+    /// let a: Canonical<'_, T> = ...;
+    /// let b: Canonical<'_, (T,)> = a.unchecked_map(|v| (v, ));
+    /// ```
+    ///
+    /// An example of an **incorrect** use of this:
+    ///
+    /// ```rust,ignore (not real code)
+    /// let a: Canonical<'tcx, T> = ...;
+    /// let ty: Ty<'tcx> = ...;
+    /// let b: Canonical<'tcx, (T, Ty<'tcx>)> = a.unchecked_map(|v| (v, ty));
+    /// ```
+    pub fn unchecked_map<W>(self, map_op: impl FnOnce(V) -> W) -> Canonical<'gcx, W> {
+        let Canonical { variables, value } = self;
+        Canonical { variables, value: map_op(value) }
+    }
+}
+
 pub type QueryRegionConstraint<'tcx> = ty::Binder<ty::OutlivesPredicate<Kind<'tcx>, Region<'tcx>>>;
 
 impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {

src/librustc/mir/mod.rs

@@ -1888,12 +1888,15 @@ pub enum Operand<'tcx> {
     /// This implies that the type of the place must be `Copy`; this is true
     /// by construction during build, but also checked by the MIR type checker.
     Copy(Place<'tcx>),
+
     /// Move: The value (including old borrows of it) will not be used again.
     ///
     /// Safe for values of all types (modulo future developments towards `?Move`).
     /// Correct usage patterns are enforced by the borrow checker for safe code.
     /// `Copy` may be converted to `Move` to enable "last-use" optimizations.
     Move(Place<'tcx>),
+
+    /// Synthesizes a constant value.
     Constant(Box<Constant<'tcx>>),
 }
 
@@ -1909,6 +1912,9 @@ impl<'tcx> Debug for Operand<'tcx> {
 }
 
 impl<'tcx> Operand<'tcx> {
+    /// Convenience helper to make a constant that refers to the fn
+    /// with given def-id and substs. Since this is used to synthesize
+    /// MIR, assumes `user_ty` is None.
     pub fn function_handle<'a>(
         tcx: TyCtxt<'a, 'tcx, 'tcx>,
         def_id: DefId,
@@ -1919,6 +1925,7 @@ impl<'tcx> Operand<'tcx> {
         Operand::Constant(box Constant {
             span,
             ty,
+            user_ty: None,
             literal: ty::Const::zero_sized(tcx, ty),
         })
     }
@@ -2002,7 +2009,7 @@ pub enum AggregateKind<'tcx> {
     /// active field number and is present only for union expressions
     /// -- e.g. for a union expression `SomeUnion { c: .. }`, the
     /// active field index would identity the field `c`
-    Adt(&'tcx AdtDef, usize, &'tcx Substs<'tcx>, Option<usize>),
+    Adt(&'tcx AdtDef, usize, &'tcx Substs<'tcx>, Option<CanonicalTy<'tcx>>, Option<usize>),
 
     Closure(DefId, ClosureSubsts<'tcx>),
     Generator(DefId, GeneratorSubsts<'tcx>, hir::GeneratorMovability),
@@ -2128,7 +2135,7 @@ impl<'tcx> Debug for Rvalue<'tcx> {
                         _ => fmt_tuple(fmt, places),
                     },
 
-                    AggregateKind::Adt(adt_def, variant, substs, _) => {
+                    AggregateKind::Adt(adt_def, variant, substs, _user_ty, _) => {
                         let variant_def = &adt_def.variants[variant];
 
                         ppaux::parameterized(fmt, substs, variant_def.did, &[])?;
@@ -2207,6 +2214,14 @@ impl<'tcx> Debug for Rvalue<'tcx> {
 pub struct Constant<'tcx> {
     pub span: Span,
     pub ty: Ty<'tcx>,
+
+    /// Optional user-given type: for something like
+    /// `collect::<Vec<_>>`, this would be present and would
+    /// indicate that `Vec<_>` was explicitly specified.
+    ///
+    /// Needed for NLL to impose user-given type constraints.
+    pub user_ty: Option<CanonicalTy<'tcx>>,
+
     pub literal: &'tcx ty::Const<'tcx>,
 }
 
@@ -2798,8 +2813,14 @@ impl<'tcx> TypeFoldable<'tcx> for Rvalue<'tcx> {
                 let kind = box match **kind {
                     AggregateKind::Array(ty) => AggregateKind::Array(ty.fold_with(folder)),
                     AggregateKind::Tuple => AggregateKind::Tuple,
-                    AggregateKind::Adt(def, v, substs, n) => {
-                        AggregateKind::Adt(def, v, substs.fold_with(folder), n)
+                    AggregateKind::Adt(def, v, substs, user_ty, n) => {
+                        AggregateKind::Adt(
+                            def,
+                            v,
+                            substs.fold_with(folder),
+                            user_ty.fold_with(folder),
+                            n,
+                        )
                     }
                     AggregateKind::Closure(id, substs) => {
                         AggregateKind::Closure(id, substs.fold_with(folder))
@@ -2831,7 +2852,8 @@ impl<'tcx> TypeFoldable<'tcx> for Rvalue<'tcx> {
                 (match **kind {
                     AggregateKind::Array(ty) => ty.visit_with(visitor),
                     AggregateKind::Tuple => false,
-                    AggregateKind::Adt(_, _, substs, _) => substs.visit_with(visitor),
+                    AggregateKind::Adt(_, _, substs, user_ty, _) =>
+                        substs.visit_with(visitor) || user_ty.visit_with(visitor),
                     AggregateKind::Closure(_, substs) => substs.visit_with(visitor),
                     AggregateKind::Generator(_, substs, _) => substs.visit_with(visitor),
                 }) || fields.visit_with(visitor)
@@ -2902,6 +2924,7 @@ impl<'tcx> TypeFoldable<'tcx> for Constant<'tcx> {
         Constant {
             span: self.span.clone(),
             ty: self.ty.fold_with(folder),
+            user_ty: self.user_ty.fold_with(folder),
             literal: self.literal.fold_with(folder),
         }
     }

src/librustc/mir/tcx.rs

@@ -216,7 +216,7 @@ impl<'tcx> Rvalue<'tcx> {
                     AggregateKind::Tuple => {
                         tcx.mk_tup(ops.iter().map(|op| op.ty(local_decls, tcx)))
                     }
-                    AggregateKind::Adt(def, _, substs, _) => {
+                    AggregateKind::Adt(def, _, substs, _, _) => {
                         tcx.type_of(def.did).subst(tcx, substs)
                     }
                     AggregateKind::Closure(did, substs) => {

src/librustc/mir/visit.rs

@@ -213,6 +213,10 @@ macro_rules! make_mir_visitor {
                 self.super_ty(ty);
             }
 
+            fn visit_canonical_ty(&mut self, ty: & $($mutability)* CanonicalTy<'tcx>) {
+                self.super_canonical_ty(ty);
+            }
+
             fn visit_region(&mut self,
                             region: & $($mutability)* ty::Region<'tcx>,
                             _: Location) {
@@ -585,6 +589,7 @@ macro_rules! make_mir_visitor {
                             AggregateKind::Adt(_adt_def,
                                                _variant_index,
                                                ref $($mutability)* substs,
+                                               _user_substs,
                                                _active_field_index) => {
                                 self.visit_substs(substs, location);
                             }
@@ -625,9 +630,10 @@ macro_rules! make_mir_visitor {
             }
 
             fn super_user_assert_ty(&mut self,
-                                    _c_ty: & $($mutability)* CanonicalTy<'tcx>,
+                                    c_ty: & $($mutability)* CanonicalTy<'tcx>,
                                     local: & $($mutability)* Local,
                                     location: Location) {
+                self.visit_canonical_ty(c_ty);
                 self.visit_local(local, PlaceContext::Validate, location);
             }
 
@@ -740,11 +746,13 @@ macro_rules! make_mir_visitor {
                 let Constant {
                     ref $($mutability)* span,
                     ref $($mutability)* ty,
+                    ref $($mutability)* user_ty,
                     ref $($mutability)* literal,
                 } = *constant;
 
                 self.visit_span(span);
                 self.visit_ty(ty, TyContext::Location(location));
+                drop(user_ty); // no visit method for this
                 self.visit_const(literal, location);
             }
 
@@ -764,6 +772,9 @@ macro_rules! make_mir_visitor {
                 self.visit_source_scope(scope);
             }
 
+            fn super_canonical_ty(&mut self, _ty: & $($mutability)* CanonicalTy<'tcx>) {
+            }
+
             fn super_ty(&mut self, _ty: & $($mutability)* Ty<'tcx>) {
             }
 

src/librustc/ty/context.rs

@@ -33,7 +33,7 @@ use middle::resolve_lifetime::{self, ObjectLifetimeDefault};
 use middle::stability;
 use mir::{self, Mir, interpret};
 use mir::interpret::Allocation;
-use ty::subst::{Kind, Substs, Subst};
+use ty::subst::{CanonicalSubsts, Kind, Substs, Subst};
 use ty::ReprOptions;
 use traits;
 use traits::{Clause, Clauses, Goal, Goals};
@@ -371,6 +371,18 @@ pub struct TypeckTables<'tcx> {
     /// other items.
     node_substs: ItemLocalMap<&'tcx Substs<'tcx>>,
 
+    /// Stores the substitutions that the user explicitly gave (if any)
+    /// attached to `id`. These will not include any inferred
+    /// values. The canonical form is used to capture things like `_`
+    /// or other unspecified values.
+    ///
+    /// Example:
+    ///
+    /// If the user wrote `foo.collect::<Vec<_>>()`, then the
+    /// canonical substitutions would include only `for<X> { Vec<X>
+    /// }`.
+    user_substs: ItemLocalMap<CanonicalSubsts<'tcx>>,
+
     adjustments: ItemLocalMap<Vec<ty::adjustment::Adjustment<'tcx>>>,
 
     /// Stores the actual binding mode for all instances of hir::BindingAnnotation.
@@ -444,6 +456,7 @@ impl<'tcx> TypeckTables<'tcx> {
             user_provided_tys: ItemLocalMap(),
             node_types: ItemLocalMap(),
             node_substs: ItemLocalMap(),
+            user_substs: ItemLocalMap(),
             adjustments: ItemLocalMap(),
             pat_binding_modes: ItemLocalMap(),
             pat_adjustments: ItemLocalMap(),
@@ -561,6 +574,18 @@ impl<'tcx> TypeckTables<'tcx> {
         self.node_substs.get(&id.local_id).cloned()
     }
 
+    pub fn user_substs_mut(&mut self) -> LocalTableInContextMut<CanonicalSubsts<'tcx>> {
+        LocalTableInContextMut {
+            local_id_root: self.local_id_root,
+            data: &mut self.user_substs
+        }
+    }
+
+    pub fn user_substs(&self, id: hir::HirId) -> Option<CanonicalSubsts<'tcx>> {
+        validate_hir_id_for_typeck_tables(self.local_id_root, id, false);
+        self.user_substs.get(&id.local_id).cloned()
+    }
+
     // Returns the type of a pattern as a monotype. Like @expr_ty, this function
     // doesn't provide type parameter substitutions.
     pub fn pat_ty(&self, pat: &hir::Pat) -> Ty<'tcx> {
@@ -740,6 +765,7 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for TypeckTables<'gcx> {
             ref user_provided_tys,
             ref node_types,
             ref node_substs,
+            ref user_substs,
             ref adjustments,
             ref pat_binding_modes,
             ref pat_adjustments,
@@ -762,6 +788,7 @@ impl<'a, 'gcx> HashStable<StableHashingContext<'a>> for TypeckTables<'gcx> {
             user_provided_tys.hash_stable(hcx, hasher);
             node_types.hash_stable(hcx, hasher);
             node_substs.hash_stable(hcx, hasher);
+            user_substs.hash_stable(hcx, hasher);
             adjustments.hash_stable(hcx, hasher);
             pat_binding_modes.hash_stable(hcx, hasher);
             pat_adjustments.hash_stable(hcx, hasher);

src/librustc/ty/subst.rs

@@ -11,13 +11,15 @@
 // Type substitutions.
 
 use hir::def_id::DefId;
-use ty::{self, Lift, List, Ty, TyCtxt};
+use infer::canonical::Canonical;
+use ty::{self, CanonicalVar, Lift, List, Ty, TyCtxt};
 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 
 use serialize::{self, Encodable, Encoder, Decodable, Decoder};
 use syntax_pos::{Span, DUMMY_SP};
 use rustc_data_structures::accumulate_vec::AccumulateVec;
 use rustc_data_structures::array_vec::ArrayVec;
+use rustc_data_structures::indexed_vec::Idx;
 
 use core::intrinsics;
 use std::cmp::Ordering;
@@ -339,6 +341,33 @@ impl<'tcx> TypeFoldable<'tcx> for &'tcx Substs<'tcx> {
     }
 }
 
+pub type CanonicalSubsts<'gcx> = Canonical<'gcx, &'gcx Substs<'gcx>>;
+
+impl<'gcx> CanonicalSubsts<'gcx> {
+    /// True if this represents a substitution like
+    ///
+    /// ```text
+    /// [?0, ?1, ?2]
+    /// ```
+    ///
+    /// i.e., each thing is mapped to a canonical variable with the same index.
+    pub fn is_identity(&self) -> bool {
+        self.value.iter().zip(CanonicalVar::new(0)..).all(|(kind, cvar)| {
+            match kind.unpack() {
+                UnpackedKind::Type(ty) => match ty.sty {
+                    ty::Infer(ty::CanonicalTy(cvar1)) => cvar == cvar1,
+                    _ => false,
+                },
+
+                UnpackedKind::Lifetime(r) => match r {
+                    ty::ReCanonical(cvar1) => cvar == *cvar1,
+                    _ => false,
+                },
+            }
+        })
+    }
+}
+
 impl<'tcx> serialize::UseSpecializedDecodable for &'tcx Substs<'tcx> {}
 
 ///////////////////////////////////////////////////////////////////////////

src/librustc_codegen_llvm/mir/rvalue.rs

@@ -148,7 +148,7 @@ impl FunctionCx<'a, 'll, 'tcx> {
 
             mir::Rvalue::Aggregate(ref kind, ref operands) => {
                 let (dest, active_field_index) = match **kind {
-                    mir::AggregateKind::Adt(adt_def, variant_index, _, active_field_index) => {
+                    mir::AggregateKind::Adt(adt_def, variant_index, _, _, active_field_index) => {
                         dest.codegen_set_discr(&bx, variant_index);
                         if adt_def.is_enum() {
                             (dest.project_downcast(&bx, variant_index), active_field_index)