Distinguish between placeholder kinds

Author: scalexm

src/librustc/infer/canonical/mod.rs

@@ -142,7 +142,7 @@ pub enum CanonicalVarKind {
     /// A "placeholder" that represents "any region". Created when you
     /// are solving a goal like `for<'a> T: Foo<'a>` to represent the
     /// bound region `'a`.
-    PlaceholderRegion(ty::Placeholder),
+    PlaceholderRegion(ty::PlaceholderRegion),
 }
 
 impl CanonicalVarKind {
@@ -374,9 +374,9 @@ impl<'cx, 'gcx, 'tcx> InferCtxt<'cx, 'gcx, 'tcx> {
                 universe_map(ui),
             ).into(),
 
-            CanonicalVarKind::PlaceholderRegion(ty::Placeholder { universe, name }) => {
+            CanonicalVarKind::PlaceholderRegion(ty::PlaceholderRegion { universe, name }) => {
                 let universe_mapped = universe_map(universe);
-                let placeholder_mapped = ty::Placeholder {
+                let placeholder_mapped = ty::PlaceholderRegion {
                     universe: universe_mapped,
                     name,
                 };

src/librustc/infer/higher_ranked/mod.rs

@@ -340,7 +340,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         let next_universe = self.create_next_universe();
 
         let (result, map) = self.tcx.replace_late_bound_regions(binder, |br| {
-            self.tcx.mk_region(ty::RePlaceholder(ty::Placeholder {
+            self.tcx.mk_region(ty::RePlaceholder(ty::PlaceholderRegion {
                 universe: next_universe,
                 name: br,
             }))

src/librustc/infer/mod.rs

@@ -411,7 +411,7 @@ pub enum NLLRegionVariableOrigin {
 
     /// "Universal" instantiation of a higher-ranked region (e.g.,
     /// from a `for<'a> T` binder). Meant to represent "any region".
-    Placeholder(ty::Placeholder),
+    Placeholder(ty::PlaceholderRegion),
 
     Existential,
 }

src/librustc/infer/nll_relate/mod.rs

@@ -95,7 +95,7 @@ pub trait TypeRelatingDelegate<'tcx> {
     /// So e.g. if you have `for<'a> fn(..) <: for<'b> fn(..)`, then
     /// we will invoke this method to instantiate `'b` with a
     /// placeholder region.
-    fn next_placeholder_region(&mut self, placeholder: ty::Placeholder) -> ty::Region<'tcx>;
+    fn next_placeholder_region(&mut self, placeholder: ty::PlaceholderRegion) -> ty::Region<'tcx>;
 
     /// Creates a new existential region in the given universe. This
     /// is used when handling subtyping and type variables -- if we
@@ -176,7 +176,7 @@ where
                         universe
                     });
 
-                    let placeholder = ty::Placeholder { universe, name: br };
+                    let placeholder = ty::PlaceholderRegion { universe, name: br };
                     delegate.next_placeholder_region(placeholder)
                 } else {
                     delegate.next_existential_region_var()

src/librustc/ty/mod.rs

@@ -1587,12 +1587,27 @@ impl UniverseIndex {
 /// universe are just two regions with an unknown relationship to one
 /// another.
 #[derive(Copy, Clone, Debug, PartialEq, Eq, Hash, RustcEncodable, RustcDecodable, PartialOrd, Ord)]
-pub struct Placeholder {
+pub struct Placeholder<T> {
     pub universe: UniverseIndex,
-    pub name: BoundRegion,
+    pub name: T,
 }
 
-impl_stable_hash_for!(struct Placeholder { universe, name });
+impl<'a, 'gcx, T> HashStable<StableHashingContext<'a>> for Placeholder<T>
+    where T: HashStable<StableHashingContext<'a>>
+{
+    fn hash_stable<W: StableHasherResult>(
+        &self,
+        hcx: &mut StableHashingContext<'a>,
+        hasher: &mut StableHasher<W>
+    ) {
+        self.universe.hash_stable(hcx, hasher);
+        self.name.hash_stable(hcx, hasher);
+    }
+}
+
+pub type PlaceholderRegion = Placeholder<BoundRegion>;
+
+pub type PlaceholderType = Placeholder<BoundVar>;
 
 /// When type checking, we use the `ParamEnv` to track
 /// details about the set of where-clauses that are in scope at this

src/librustc/ty/sty.rs

@@ -1165,7 +1165,7 @@ pub enum RegionKind {
 
     /// A placeholder region - basically the higher-ranked version of ReFree.
     /// Should not exist after typeck.
-    RePlaceholder(ty::Placeholder),
+    RePlaceholder(ty::PlaceholderRegion),
 
     /// Empty lifetime is for data that is never accessed.
     /// Bottom in the region lattice. We treat ReEmpty somewhat

src/librustc/util/ppaux.rs

@@ -792,7 +792,7 @@ define_print! {
                 }
                 ty::ReLateBound(_, br) |
                 ty::ReFree(ty::FreeRegion { bound_region: br, .. }) |
-                ty::RePlaceholder(ty::Placeholder { name: br, .. }) => {
+                ty::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
                     write!(f, "{}", br)
                 }
                 ty::ReScope(scope) if cx.identify_regions => {

src/librustc_mir/borrow_check/error_reporting.rs

@@ -2193,7 +2193,7 @@ impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
         match ty.sty {
             ty::TyKind::Ref(ty::RegionKind::ReLateBound(_, br), _, _)
             | ty::TyKind::Ref(
-                ty::RegionKind::RePlaceholder(ty::Placeholder { name: br, .. }),
+                ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }),
                 _,
                 _,
             ) => with_highlight_region_for_bound_region(*br, counter, || ty.to_string()),
@@ -2207,7 +2207,7 @@ impl<'tcx> AnnotatedBorrowFnSignature<'tcx> {
         match ty.sty {
             ty::TyKind::Ref(region, _, _) => match region {
                 ty::RegionKind::ReLateBound(_, br)
-                | ty::RegionKind::RePlaceholder(ty::Placeholder { name: br, .. }) => {
+                | ty::RegionKind::RePlaceholder(ty::PlaceholderRegion { name: br, .. }) => {
                     with_highlight_region_for_bound_region(*br, counter, || region.to_string())
                 }
                 _ => region.to_string(),

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

@@ -1230,7 +1230,7 @@ impl<'tcx> RegionInferenceContext<'tcx> {
         mir: &Mir<'tcx>,
         _mir_def_id: DefId,
         longer_fr: RegionVid,
-        placeholder: ty::Placeholder,
+        placeholder: ty::PlaceholderRegion,
     ) {
         debug!(
             "check_bound_universal_region(fr={:?}, placeholder={:?})",

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

@@ -150,7 +150,7 @@ crate enum RegionElement {
 
     /// A placeholder (e.g., instantiated from a `for<'a> fn(&'a u32)`
     /// type).
-    PlaceholderRegion(ty::Placeholder),
+    PlaceholderRegion(ty::PlaceholderRegion),
 }
 
 /// When we initially compute liveness, we use a bit matrix storing
@@ -219,17 +219,17 @@ impl<N: Idx> LivenessValues<N> {
     }
 }
 
-/// Maps from `ty::Placeholder` values that are used in the rest of
+/// Maps from `ty::PlaceholderRegion` values that are used in the rest of
 /// rustc to the internal `PlaceholderIndex` values that are used in
 /// NLL.
 #[derive(Default)]
 crate struct PlaceholderIndices {
-    to_index: FxHashMap<ty::Placeholder, PlaceholderIndex>,
-    from_index: IndexVec<PlaceholderIndex, ty::Placeholder>,
+    to_index: FxHashMap<ty::PlaceholderRegion, PlaceholderIndex>,
+    from_index: IndexVec<PlaceholderIndex, ty::PlaceholderRegion>,
 }
 
 impl PlaceholderIndices {
-    crate fn insert(&mut self, placeholder: ty::Placeholder) -> PlaceholderIndex {
+    crate fn insert(&mut self, placeholder: ty::PlaceholderRegion) -> PlaceholderIndex {
         let PlaceholderIndices {
             to_index,
             from_index,
@@ -239,11 +239,11 @@ impl PlaceholderIndices {
             .or_insert_with(|| from_index.push(placeholder))
     }
 
-    crate fn lookup_index(&self, placeholder: ty::Placeholder) -> PlaceholderIndex {
+    crate fn lookup_index(&self, placeholder: ty::PlaceholderRegion) -> PlaceholderIndex {
         self.to_index[&placeholder]
     }
 
-    crate fn lookup_placeholder(&self, placeholder: PlaceholderIndex) -> ty::Placeholder {
+    crate fn lookup_placeholder(&self, placeholder: PlaceholderIndex) -> ty::PlaceholderRegion {
         self.from_index[placeholder]
     }
 
@@ -375,7 +375,7 @@ impl<N: Idx> RegionValues<N> {
     crate fn placeholders_contained_in<'a>(
         &'a self,
         r: N,
-    ) -> impl Iterator<Item = ty::Placeholder> + 'a {
+    ) -> impl Iterator<Item = ty::PlaceholderRegion> + 'a {
         self.placeholders
             .row(r)
             .into_iter()
@@ -432,7 +432,7 @@ impl ToElementIndex for RegionVid {
     }
 }
 
-impl ToElementIndex for ty::Placeholder {
+impl ToElementIndex for ty::PlaceholderRegion {
     fn add_to_row<N: Idx>(self, values: &mut RegionValues<N>, row: N) -> bool {
         let index = values.placeholder_indices.lookup_index(self);
         values.placeholders.insert(row, index)

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

@@ -777,7 +777,7 @@ impl MirTypeckRegionConstraints<'tcx> {
     fn placeholder_region(
         &mut self,
         infcx: &InferCtxt<'_, '_, 'tcx>,
-        placeholder: ty::Placeholder,
+        placeholder: ty::PlaceholderRegion,
     ) -> ty::Region<'tcx> {
         let placeholder_index = self.placeholder_indices.insert(placeholder);
         match self.placeholder_index_to_region.get(placeholder_index) {

src/librustc_mir/borrow_check/nll/type_check/relate_tys.rs

@@ -84,7 +84,10 @@ impl TypeRelatingDelegate<'tcx> for NllTypeRelatingDelegate<'_, '_, '_, 'tcx> {
         }
     }
 
-    fn next_placeholder_region(&mut self, placeholder: ty::Placeholder) -> ty::Region<'tcx> {
+    fn next_placeholder_region(
+        &mut self,
+        placeholder: ty::PlaceholderRegion
+    ) -> ty::Region<'tcx> {
         if let Some(borrowck_context) = &mut self.borrowck_context {
             borrowck_context.constraints.placeholder_region(self.infcx, placeholder)
         } else {