Auto merge of #52024 - oli-obk:existential_parse, r=nikomatsakis

Implement existential types

(not for associated types yet)

r? @nikomatsakis

cc @Centril @varkor @alexreg

src/librustc/hir/def.rs

@@ -37,11 +37,15 @@ pub enum Def {
     Enum(DefId),
     Variant(DefId),
     Trait(DefId),
+    /// `existential type Foo: Bar;`
     Existential(DefId),
+    /// `type Foo = Bar;`
     TyAlias(DefId),
     TyForeign(DefId),
     TraitAlias(DefId),
     AssociatedTy(DefId),
+    /// `existential type Foo: Bar;`
+    AssociatedExistential(DefId),
     PrimTy(hir::PrimTy),
     TyParam(DefId),
     SelfTy(Option<DefId> /* trait */, Option<DefId> /* impl */),
@@ -245,7 +249,7 @@ impl Def {
             Def::AssociatedTy(id) | Def::TyParam(id) | Def::Struct(id) | Def::StructCtor(id, ..) |
             Def::Union(id) | Def::Trait(id) | Def::Method(id) | Def::Const(id) |
             Def::AssociatedConst(id) | Def::Macro(id, ..) |
-            Def::Existential(id) |
+            Def::Existential(id) | Def::AssociatedExistential(id) |
             Def::GlobalAsm(id) | Def::TyForeign(id) => {
                 id
             }
@@ -276,6 +280,7 @@ impl Def {
             Def::TyAlias(..) => "type alias",
             Def::TraitAlias(..) => "trait alias",
             Def::AssociatedTy(..) => "associated type",
+            Def::AssociatedExistential(..) => "associated existential type",
             Def::Struct(..) => "struct",
             Def::StructCtor(.., CtorKind::Fn) => "tuple struct",
             Def::StructCtor(.., CtorKind::Const) => "unit struct",

src/librustc/hir/intravisit.rs

@@ -907,6 +907,10 @@ pub fn walk_impl_item<'v, V: Visitor<'v>>(visitor: &mut V, impl_item: &'v ImplIt
             visitor.visit_id(impl_item.id);
             visitor.visit_ty(ty);
         }
+        ImplItemKind::Existential(ref bounds) => {
+            visitor.visit_id(impl_item.id);
+            walk_list!(visitor, visit_param_bound, bounds);
+        }
     }
 }
 

src/librustc/hir/lowering.rs

@@ -323,6 +323,7 @@ impl<'a> LoweringContext<'a> {
                     | ItemKind::Union(_, ref generics)
                     | ItemKind::Enum(_, ref generics)
                     | ItemKind::Ty(_, ref generics)
+                    | ItemKind::Existential(_, ref generics)
                     | ItemKind::Trait(_, _, ref generics, ..) => {
                         let def_id = self.lctx.resolver.definitions().local_def_id(item.id);
                         let count = generics
@@ -2632,6 +2633,11 @@ impl<'a> LoweringContext<'a> {
                 self.lower_ty(t, ImplTraitContext::Disallowed),
                 self.lower_generics(generics, ImplTraitContext::Disallowed),
             ),
+            ItemKind::Existential(ref b, ref generics) => hir::ItemKind::Existential(hir::ExistTy {
+                generics: self.lower_generics(generics, ImplTraitContext::Disallowed),
+                bounds: self.lower_param_bounds(b, ImplTraitContext::Disallowed),
+                impl_trait_fn: None,
+            }),
             ItemKind::Enum(ref enum_definition, ref generics) => hir::ItemKind::Enum(
                 hir::EnumDef {
                     variants: enum_definition
@@ -3037,6 +3043,12 @@ impl<'a> LoweringContext<'a> {
                 self.lower_generics(&i.generics, ImplTraitContext::Disallowed),
                 hir::ImplItemKind::Type(self.lower_ty(ty, ImplTraitContext::Disallowed)),
             ),
+            ImplItemKind::Existential(ref bounds) => (
+                self.lower_generics(&i.generics, ImplTraitContext::Disallowed),
+                hir::ImplItemKind::Existential(
+                    self.lower_param_bounds(bounds, ImplTraitContext::Disallowed),
+                ),
+            ),
             ImplItemKind::Macro(..) => panic!("Shouldn't exist any more"),
         };
 
@@ -3065,6 +3077,7 @@ impl<'a> LoweringContext<'a> {
             kind: match i.node {
                 ImplItemKind::Const(..) => hir::AssociatedItemKind::Const,
                 ImplItemKind::Type(..) => hir::AssociatedItemKind::Type,
+                ImplItemKind::Existential(..) => hir::AssociatedItemKind::Existential,
                 ImplItemKind::Method(ref sig, _) => hir::AssociatedItemKind::Method {
                     has_self: sig.decl.has_self(),
                 },
@@ -4335,7 +4348,7 @@ impl<'a> LoweringContext<'a> {
         respan(v.span, node)
     }
 
-    fn lower_defaultness(&mut self, d: Defaultness, has_value: bool) -> hir::Defaultness {
+    fn lower_defaultness(&self, d: Defaultness, has_value: bool) -> hir::Defaultness {
         match d {
             Defaultness::Default => hir::Defaultness::Default {
                 has_value: has_value,

src/librustc/hir/map/def_collector.rs

@@ -116,7 +116,7 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
             ItemKind::Impl(..) => DefPathData::Impl,
             ItemKind::Trait(..) => DefPathData::Trait(i.ident.as_interned_str()),
             ItemKind::Enum(..) | ItemKind::Struct(..) | ItemKind::Union(..) |
-            ItemKind::TraitAlias(..) |
+            ItemKind::TraitAlias(..) | ItemKind::Existential(..) |
             ItemKind::ExternCrate(..) | ItemKind::ForeignMod(..) | ItemKind::Ty(..) =>
                 DefPathData::TypeNs(i.ident.as_interned_str()),
             ItemKind::Mod(..) if i.ident == keywords::Invalid.ident() => {
@@ -250,6 +250,9 @@ impl<'a> visit::Visitor<'a> for DefCollector<'a> {
             ImplItemKind::Method(..) | ImplItemKind::Const(..) =>
                 DefPathData::ValueNs(ii.ident.as_interned_str()),
             ImplItemKind::Type(..) => DefPathData::AssocTypeInImpl(ii.ident.as_interned_str()),
+            ImplItemKind::Existential(..) => {
+                DefPathData::AssocExistentialInImpl(ii.ident.as_interned_str())
+            },
             ImplItemKind::Macro(..) => return self.visit_macro_invoc(ii.id),
         };
 

src/librustc/hir/map/definitions.rs

@@ -330,6 +330,8 @@ pub enum DefPathData {
     AssocTypeInTrait(InternedString),
     /// An associated type **value** (i.e., in an impl)
     AssocTypeInImpl(InternedString),
+    /// An existential associated type **value** (i.e., in an impl)
+    AssocExistentialInImpl(InternedString),
     /// Something in the type NS
     TypeNs(InternedString),
     /// Something in the value NS
@@ -605,6 +607,7 @@ impl DefPathData {
             Trait(name) |
             AssocTypeInTrait(name) |
             AssocTypeInImpl(name) |
+            AssocExistentialInImpl(name) |
             ValueNs(name) |
             Module(name) |
             MacroDef(name) |
@@ -631,6 +634,7 @@ impl DefPathData {
             Trait(name) |
             AssocTypeInTrait(name) |
             AssocTypeInImpl(name) |
+            AssocExistentialInImpl(name) |
             ValueNs(name) |
             Module(name) |
             MacroDef(name) |

src/librustc/hir/map/mod.rs

@@ -470,6 +470,7 @@ impl<'hir> Map<'hir> {
                     ImplItemKind::Const(..) => Some(Def::AssociatedConst(def_id)),
                     ImplItemKind::Method(..) => Some(Def::Method(def_id)),
                     ImplItemKind::Type(..) => Some(Def::AssociatedTy(def_id)),
+                    ImplItemKind::Existential(..) => Some(Def::AssociatedExistential(def_id)),
                 }
             }
             NodeVariant(variant) => {
@@ -1323,7 +1324,7 @@ fn node_id_to_string(map: &Map, id: NodeId, include_id: bool) -> String {
                 ItemKind::ForeignMod(..) => "foreign mod",
                 ItemKind::GlobalAsm(..) => "global asm",
                 ItemKind::Ty(..) => "ty",
-                ItemKind::Existential(..) => "existential",
+                ItemKind::Existential(..) => "existential type",
                 ItemKind::Enum(..) => "enum",
                 ItemKind::Struct(..) => "struct",
                 ItemKind::Union(..) => "union",
@@ -1347,6 +1348,9 @@ fn node_id_to_string(map: &Map, id: NodeId, include_id: bool) -> String {
                 ImplItemKind::Type(_) => {
                     format!("assoc type {} in {}{}", ii.ident, path_str(), id_str)
                 }
+                ImplItemKind::Existential(_) => {
+                    format!("assoc existential type {} in {}{}", ii.ident, path_str(), id_str)
+                }
             }
         }
         Some(NodeTraitItem(ti)) => {

src/librustc/hir/mod.rs

@@ -1620,6 +1620,8 @@ pub enum ImplItemKind {
     Method(MethodSig, BodyId),
     /// An associated type
     Type(P<Ty>),
+    /// An associated existential type
+    Existential(GenericBounds),
 }
 
 // Bind a type to an associated type: `A=Foo`.
@@ -2080,7 +2082,7 @@ pub enum ItemKind {
     GlobalAsm(P<GlobalAsm>),
     /// A type alias, e.g. `type Foo = Bar<u8>`
     Ty(P<Ty>, Generics),
-    /// A type alias, e.g. `type Foo = Bar<u8>`
+    /// An existential type definition, e.g. `existential type Foo: Bar;`
     Existential(ExistTy),
     /// An enum definition, e.g. `enum Foo<A, B> {C<A>, D<B>}`
     Enum(EnumDef, Generics),
@@ -2138,6 +2140,7 @@ impl ItemKind {
         Some(match *self {
             ItemKind::Fn(_, _, ref generics, _) |
             ItemKind::Ty(_, ref generics) |
+            ItemKind::Existential(ExistTy { ref generics, impl_trait_fn: None, .. }) |
             ItemKind::Enum(_, ref generics) |
             ItemKind::Struct(_, ref generics) |
             ItemKind::Union(_, ref generics) |
@@ -2184,6 +2187,7 @@ pub enum AssociatedItemKind {
     Const,
     Method { has_self: bool },
     Type,
+    Existential,
 }
 
 #[derive(Clone, RustcEncodable, RustcDecodable, Debug)]

src/librustc/hir/print.rs

@@ -627,9 +627,7 @@ impl<'a> State<'a> {
                 self.end()?
             }
             hir::ItemKind::Ty(ref ty, ref generics) => {
-                self.ibox(indent_unit)?;
-                self.ibox(0)?;
-                self.word_nbsp(&visibility_qualified(&item.vis, "type"))?;
+                self.head(&visibility_qualified(&item.vis, "type"))?;
                 self.print_name(item.name)?;
                 self.print_generic_params(&generics.params)?;
                 self.end()?; // end the inner ibox
@@ -642,9 +640,7 @@ impl<'a> State<'a> {
                 self.end()?; // end the outer ibox
             }
             hir::ItemKind::Existential(ref exist) => {
-                self.ibox(indent_unit)?;
-                self.ibox(0)?;
-                self.word_nbsp(&visibility_qualified(&item.vis, "existential type"))?;
+                self.head(&visibility_qualified(&item.vis, "existential type"))?;
                 self.print_name(item.name)?;
                 self.print_generic_params(&exist.generics.params)?;
                 self.end()?; // end the inner ibox
@@ -994,6 +990,10 @@ impl<'a> State<'a> {
             hir::ImplItemKind::Type(ref ty) => {
                 self.print_associated_type(ii.ident, None, Some(ty))?;
             }
+            hir::ImplItemKind::Existential(ref bounds) => {
+                self.word_space("existential")?;
+                self.print_associated_type(ii.ident, Some(bounds), None)?;
+            }
         }
         self.ann.post(self, NodeSubItem(ii.id))
     }

src/librustc/ich/impls_hir.rs

@@ -701,6 +701,7 @@ impl<'a> HashStable<StableHashingContext<'a>> for hir::ImplItem {
 impl_stable_hash_for!(enum hir::ImplItemKind {
     Const(t, body),
     Method(sig, body),
+    Existential(bounds),
     Type(t)
 });
 
@@ -890,6 +891,7 @@ impl<'a> HashStable<StableHashingContext<'a>> for hir::AssociatedItemKind {
         mem::discriminant(self).hash_stable(hcx, hasher);
         match *self {
             hir::AssociatedItemKind::Const |
+            hir::AssociatedItemKind::Existential |
             hir::AssociatedItemKind::Type => {
                 // No fields to hash.
             }
@@ -997,6 +999,7 @@ impl_stable_hash_for!(enum hir::def::Def {
     TyAlias(def_id),
     TraitAlias(def_id),
     AssociatedTy(def_id),
+    AssociatedExistential(def_id),
     PrimTy(prim_ty),
     TyParam(def_id),
     SelfTy(trait_def_id, impl_def_id),

src/librustc/ich/impls_ty.rs

@@ -1055,6 +1055,7 @@ impl_stable_hash_for!(struct ty::AssociatedItem {
 impl_stable_hash_for!(enum ty::AssociatedKind {
     Const,
     Method,
+    Existential,
     Type
 });
 

src/librustc/infer/anon_types/mod.rs

@@ -653,6 +653,7 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> {
         let tcx = self.infcx.tcx;
         value.fold_with(&mut BottomUpFolder {
             tcx,
+            reg_op: |reg| reg,
             fldop: |ty| {
                 if let ty::TyAnon(def_id, substs) = ty.sty {
                     // Check that this is `impl Trait` type is
@@ -690,26 +691,35 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> {
                     // }
                     // ```
                     if let Some(anon_node_id) = tcx.hir.as_local_node_id(def_id) {
-                        let anon_parent_def_id = match tcx.hir.expect_item(anon_node_id).node {
+                        let in_definition_scope = match tcx.hir.expect_item(anon_node_id).node {
+                            // impl trait
                             hir::ItemKind::Existential(hir::ExistTy {
                                 impl_trait_fn: Some(parent),
                                 ..
-                            }) => parent,
+                            }) => parent == self.parent_def_id,
+                            // named existential types
+                            hir::ItemKind::Existential(hir::ExistTy {
+                                impl_trait_fn: None,
+                                ..
+                            }) => may_define_existential_type(
+                                tcx,
+                                self.parent_def_id,
+                                anon_node_id,
+                            ),
                             _ => {
                                 let anon_parent_node_id = tcx.hir.get_parent(anon_node_id);
-                                tcx.hir.local_def_id(anon_parent_node_id)
+                                self.parent_def_id == tcx.hir.local_def_id(anon_parent_node_id)
                             },
                         };
-                        if self.parent_def_id == anon_parent_def_id {
+                        if in_definition_scope {
                             return self.fold_anon_ty(ty, def_id, substs);
                         }
 
                         debug!(
                             "instantiate_anon_types_in_map: \
-                             encountered anon with wrong parent \
-                             def_id={:?} \
-                             anon_parent_def_id={:?}",
-                            def_id, anon_parent_def_id
+                             encountered anon outside it's definition scope \
+                             def_id={:?}",
+                            def_id,
                         );
                     }
                 }
@@ -742,6 +752,10 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> {
         let ty_var = infcx.next_ty_var(TypeVariableOrigin::TypeInference(span));
 
         let predicates_of = tcx.predicates_of(def_id);
+        debug!(
+            "instantiate_anon_types: predicates: {:#?}",
+            predicates_of,
+        );
         let bounds = predicates_of.instantiate(tcx, substs);
         debug!("instantiate_anon_types: bounds={:?}", bounds);
 
@@ -751,6 +765,18 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> {
             required_region_bounds
         );
 
+        // make sure that we are in fact defining the *entire* type
+        // e.g. `existential type Foo<T: Bound>: Bar;` needs to be
+        // defined by a function like `fn foo<T: Bound>() -> Foo<T>`.
+        debug!(
+            "instantiate_anon_types: param_env: {:#?}",
+            self.param_env,
+        );
+        debug!(
+            "instantiate_anon_types: generics: {:#?}",
+            tcx.generics_of(def_id),
+        );
+
         self.anon_types.insert(
             def_id,
             AnonTypeDecl {
@@ -778,3 +804,42 @@ impl<'a, 'gcx, 'tcx> Instantiator<'a, 'gcx, 'tcx> {
         ty_var
     }
 }
+
+/// Whether `anon_node_id` is a sibling or a child of a sibling of `def_id`
+///
+/// ```rust
+/// pub mod foo {
+///     pub mod bar {
+///         pub existential type Baz;
+///
+///         fn f1() -> Baz { .. }
+///     }
+///
+///     fn f2() -> bar::Baz { .. }
+/// }
+/// ```
+///
+/// Here, `def_id` will be the `DefId` of the existential type `Baz`.
+/// `anon_node_id` is the `NodeId` of the reference to Baz -- so either the return type of f1 or f2.
+/// We will return true if the reference is within the same module as the existential type
+/// So true for f1, false for f2.
+pub fn may_define_existential_type(
+    tcx: TyCtxt,
+    def_id: DefId,
+    anon_node_id: ast::NodeId,
+) -> bool {
+    let mut node_id = tcx
+        .hir
+        .as_local_node_id(def_id)
+        .unwrap();
+    // named existential types can be defined by any siblings or
+    // children of siblings
+    let mod_id = tcx.hir.get_parent(anon_node_id);
+    // so we walk up the node tree until we hit the root or the parent
+    // of the anon type
+    while node_id != mod_id && node_id != ast::CRATE_NODE_ID {
+        node_id = tcx.hir.get_parent(node_id);
+    }
+    // syntactically we are allowed to define the concrete type
+    node_id == mod_id
+}

src/librustc/infer/error_reporting/mod.rs

@@ -279,7 +279,9 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> {
     fn impl_item_scope_tag(item: &hir::ImplItem) -> &'static str {
         match item.node {
             hir::ImplItemKind::Method(..) => "method body",
-            hir::ImplItemKind::Const(..) | hir::ImplItemKind::Type(_) => "associated item",
+            hir::ImplItemKind::Const(..) |
+            hir::ImplItemKind::Existential(..) |
+            hir::ImplItemKind::Type(..) => "associated item",
         }
     }