Implement impl Trait in return type position by anonymization.

src/librustc/hir/fold.rs

@@ -375,6 +375,9 @@ pub fn noop_fold_ty<T: Folder>(t: P<Ty>, fld: &mut T) -> P<Ty> {
                 TyPolyTraitRef(bounds) => {
                     TyPolyTraitRef(bounds.move_map(|b| fld.fold_ty_param_bound(b)))
                 }
+                TyImplTrait(bounds) => {
+                    TyImplTrait(bounds.move_map(|b| fld.fold_ty_param_bound(b)))
+                }
             },
             span: fld.new_span(span),
         }

src/librustc/hir/intravisit.rs

@@ -427,6 +427,9 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty) {
         TyPolyTraitRef(ref bounds) => {
             walk_list!(visitor, visit_ty_param_bound, bounds);
         }
+        TyImplTrait(ref bounds) => {
+            walk_list!(visitor, visit_ty_param_bound, bounds);
+        }
         TyTypeof(ref expression) => {
             visitor.visit_expr(expression)
         }

src/librustc/hir/lowering.rs

@@ -293,8 +293,10 @@ impl<'a> LoweringContext<'a> {
                     hir::TyTypeof(self.lower_expr(expr))
                 }
                 PolyTraitRef(ref bounds) => {
-                    let bounds = bounds.iter().map(|b| self.lower_ty_param_bound(b)).collect();
-                    hir::TyPolyTraitRef(bounds)
+                    hir::TyPolyTraitRef(self.lower_bounds(bounds))
+                }
+                ImplTrait(ref bounds) => {
+                    hir::TyImplTrait(self.lower_bounds(bounds))
                 }
                 Mac(_) => panic!("TyMac should have been expanded by now."),
             },

src/librustc/hir/map/collector.rs

@@ -194,6 +194,14 @@ impl<'ast> Visitor<'ast> for NodeCollector<'ast> {
         });
     }
 
+    fn visit_ty(&mut self, ty: &'ast Ty) {
+        self.insert(ty.id, NodeTy(ty));
+
+        self.with_parent(ty.id, |this| {
+            intravisit::walk_ty(this, ty);
+        });
+    }
+
     fn visit_fn(&mut self, fk: intravisit::FnKind<'ast>, fd: &'ast FnDecl,
                 b: &'ast Block, s: Span, id: NodeId) {
         assert_eq!(self.parent_node, id);

src/librustc/hir/map/def_collector.rs

@@ -268,6 +268,9 @@ impl<'ast> visit::Visitor for DefCollector<'ast> {
         if let TyKind::FixedLengthVec(_, ref length) = ty.node {
             self.visit_ast_const_integer(length);
         }
+        if let TyKind::ImplTrait(..) = ty.node {
+            self.create_def(ty.id, DefPathData::ImplTrait);
+        }
         visit::walk_ty(self, ty);
     }
 
@@ -428,6 +431,9 @@ impl<'ast> intravisit::Visitor<'ast> for DefCollector<'ast> {
         if let hir::TyFixedLengthVec(_, ref length) = ty.node {
             self.visit_hir_const_integer(length);
         }
+        if let hir::TyImplTrait(..) = ty.node {
+            self.create_def(ty.id, DefPathData::ImplTrait);
+        }
         intravisit::walk_ty(self, ty);
     }
 

src/librustc/hir/map/definitions.rs

@@ -215,6 +215,8 @@ pub enum DefPathData {
     Initializer,
     /// Pattern binding
     Binding(InternedString),
+    /// An `impl Trait` type node.
+    ImplTrait
 }
 
 impl Definitions {
@@ -369,6 +371,10 @@ impl DefPathData {
             Initializer => {
                 InternedString::new("{{initializer}}")
             }
+
+            ImplTrait => {
+                InternedString::new("{{impl-Trait}}")
+            }
         }
     }
 

src/librustc/hir/map/mod.rs

@@ -50,6 +50,7 @@ pub enum Node<'ast> {
     NodeVariant(&'ast Variant),
     NodeExpr(&'ast Expr),
     NodeStmt(&'ast Stmt),
+    NodeTy(&'ast Ty),
     NodeLocal(&'ast Pat),
     NodePat(&'ast Pat),
     NodeBlock(&'ast Block),
@@ -76,6 +77,7 @@ pub enum MapEntry<'ast> {
     EntryVariant(NodeId, &'ast Variant),
     EntryExpr(NodeId, &'ast Expr),
     EntryStmt(NodeId, &'ast Stmt),
+    EntryTy(NodeId, &'ast Ty),
     EntryLocal(NodeId, &'ast Pat),
     EntryPat(NodeId, &'ast Pat),
     EntryBlock(NodeId, &'ast Block),
@@ -104,6 +106,7 @@ impl<'ast> MapEntry<'ast> {
             NodeVariant(n) => EntryVariant(p, n),
             NodeExpr(n) => EntryExpr(p, n),
             NodeStmt(n) => EntryStmt(p, n),
+            NodeTy(n) => EntryTy(p, n),
             NodeLocal(n) => EntryLocal(p, n),
             NodePat(n) => EntryPat(p, n),
             NodeBlock(n) => EntryBlock(p, n),
@@ -122,6 +125,7 @@ impl<'ast> MapEntry<'ast> {
             EntryVariant(id, _) => id,
             EntryExpr(id, _) => id,
             EntryStmt(id, _) => id,
+            EntryTy(id, _) => id,
             EntryLocal(id, _) => id,
             EntryPat(id, _) => id,
             EntryBlock(id, _) => id,
@@ -144,6 +148,7 @@ impl<'ast> MapEntry<'ast> {
             EntryVariant(_, n) => NodeVariant(n),
             EntryExpr(_, n) => NodeExpr(n),
             EntryStmt(_, n) => NodeStmt(n),
+            EntryTy(_, n) => NodeTy(n),
             EntryLocal(_, n) => NodeLocal(n),
             EntryPat(_, n) => NodePat(n),
             EntryBlock(_, n) => NodeBlock(n),
@@ -257,6 +262,7 @@ impl<'ast> Map<'ast> {
                     EntryVariant(p, _) |
                     EntryExpr(p, _) |
                     EntryStmt(p, _) |
+                EntryTy(p, _) |
                     EntryLocal(p, _) |
                     EntryPat(p, _) |
                     EntryBlock(p, _) |
@@ -297,6 +303,7 @@ impl<'ast> Map<'ast> {
                     EntryVariant(p, _) |
                     EntryExpr(p, _) |
                     EntryStmt(p, _) |
+                    EntryTy(p, _) |
                     EntryLocal(p, _) |
                     EntryPat(p, _) |
                     EntryBlock(p, _) |
@@ -680,6 +687,7 @@ impl<'ast> Map<'ast> {
             Some(NodeVariant(variant)) => variant.span,
             Some(NodeExpr(expr)) => expr.span,
             Some(NodeStmt(stmt)) => stmt.span,
+            Some(NodeTy(ty)) => ty.span,
             Some(NodeLocal(pat)) => pat.span,
             Some(NodePat(pat)) => pat.span,
             Some(NodeBlock(block)) => block.span,
@@ -971,6 +979,7 @@ impl<'a> NodePrinter for pprust::State<'a> {
             NodeVariant(a)     => self.print_variant(&a),
             NodeExpr(a)        => self.print_expr(&a),
             NodeStmt(a)        => self.print_stmt(&a),
+            NodeTy(a)          => self.print_type(&a),
             NodePat(a)         => self.print_pat(&a),
             NodeBlock(a)       => self.print_block(&a),
             NodeLifetime(a)    => self.print_lifetime(&a),
@@ -1059,6 +1068,9 @@ fn node_id_to_string(map: &Map, id: NodeId, include_id: bool) -> String {
         Some(NodeStmt(ref stmt)) => {
             format!("stmt {}{}", pprust::stmt_to_string(&stmt), id_str)
         }
+        Some(NodeTy(ref ty)) => {
+            format!("type {}{}", pprust::ty_to_string(&ty), id_str)
+        }
         Some(NodeLocal(ref pat)) => {
             format!("local {}{}", pprust::pat_to_string(&pat), id_str)
         }

src/librustc/hir/mod.rs

@@ -1132,6 +1132,8 @@ pub enum Ty_ {
     TyObjectSum(P<Ty>, TyParamBounds),
     /// A type like `for<'a> Foo<&'a Bar>`
     TyPolyTraitRef(TyParamBounds),
+    /// An `impl TraitA+TraitB` type.
+    TyImplTrait(TyParamBounds),
     /// Unused for now
     TyTypeof(P<Expr>),
     /// TyInfer means the type should be inferred instead of it having been

src/librustc/hir/print.rs

@@ -536,6 +536,9 @@ impl<'a> State<'a> {
             hir::TyPolyTraitRef(ref bounds) => {
                 self.print_bounds("", &bounds[..])?;
             }
+            hir::TyImplTrait(ref bounds) => {
+                self.print_bounds("impl ", &bounds[..])?;
+            }
             hir::TyFixedLengthVec(ref ty, ref v) => {
                 word(&mut self.s, "[")?;
                 self.print_type(&ty)?;

src/librustc/infer/freshen.rs

@@ -170,7 +170,8 @@ impl<'a, 'gcx, 'tcx> TypeFolder<'gcx, 'tcx> for TypeFreshener<'a, 'gcx, 'tcx> {
             ty::TyClosure(..) |
             ty::TyTuple(..) |
             ty::TyProjection(..) |
-            ty::TyParam(..) => {
+            ty::TyParam(..) |
+            ty::TyAnon(..) => {
                 t.super_fold_with(self)
             }
         }

src/librustc/infer/mod.rs

@@ -34,7 +34,7 @@ use ty::{self, Ty, TyCtxt};
 use ty::error::{ExpectedFound, TypeError, UnconstrainedNumeric};
 use ty::fold::{TypeFoldable, TypeFolder, TypeVisitor};
 use ty::relate::{Relate, RelateResult, TypeRelation};
-use traits::{self, PredicateObligations, ProjectionMode};
+use traits::{self, PredicateObligations, Reveal};
 use rustc_data_structures::unify::{self, UnificationTable};
 use std::cell::{Cell, RefCell, Ref, RefMut};
 use std::fmt;
@@ -147,8 +147,8 @@ pub struct InferCtxt<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
 
     // Sadly, the behavior of projection varies a bit depending on the
     // stage of compilation. The specifics are given in the
-    // documentation for `ProjectionMode`.
-    projection_mode: ProjectionMode,
+    // documentation for `Reveal`.
+    projection_mode: Reveal,
 
     // When an error occurs, we want to avoid reporting "derived"
     // errors that are due to this original failure. Normally, we
@@ -459,15 +459,15 @@ pub struct InferCtxtBuilder<'a, 'gcx: 'a+'tcx, 'tcx: 'a> {
     arenas: ty::CtxtArenas<'tcx>,
     tables: Option<RefCell<ty::Tables<'tcx>>>,
     param_env: Option<ty::ParameterEnvironment<'gcx>>,
-    projection_mode: ProjectionMode,
+    projection_mode: Reveal,
     normalize: bool
 }
 
 impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
     pub fn infer_ctxt(self,
                       tables: Option<ty::Tables<'tcx>>,
                       param_env: Option<ty::ParameterEnvironment<'gcx>>,
-                      projection_mode: ProjectionMode)
+                      projection_mode: Reveal)
                       -> InferCtxtBuilder<'a, 'gcx, 'tcx> {
         InferCtxtBuilder {
             global_tcx: self,
@@ -479,7 +479,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
         }
     }
 
-    pub fn normalizing_infer_ctxt(self, projection_mode: ProjectionMode)
+    pub fn normalizing_infer_ctxt(self, projection_mode: Reveal)
                                   -> InferCtxtBuilder<'a, 'gcx, 'tcx> {
         InferCtxtBuilder {
             global_tcx: self,
@@ -509,7 +509,7 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'gcx> {
             projection_cache: RefCell::new(traits::ProjectionCache::new()),
             reported_trait_errors: RefCell::new(FnvHashSet()),
             normalize: false,
-            projection_mode: ProjectionMode::AnyFinal,
+            projection_mode: Reveal::NotSpecializable,
             tainted_by_errors_flag: Cell::new(false),
             err_count_on_creation: self.sess.err_count(),
             obligations_in_snapshot: Cell::new(false),
@@ -641,7 +641,7 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
             return value;
         }
 
-        self.infer_ctxt(None, None, ProjectionMode::Any).enter(|infcx| {
+        self.infer_ctxt(None, None, Reveal::All).enter(|infcx| {
             value.trans_normalize(&infcx)
         })
     }
@@ -659,7 +659,7 @@ impl<'a, 'tcx> TyCtxt<'a, 'tcx, 'tcx> {
             return value;
         }
 
-        self.infer_ctxt(None, Some(env.clone()), ProjectionMode::Any).enter(|infcx| {
+        self.infer_ctxt(None, Some(env.clone()), Reveal::All).enter(|infcx| {
             value.trans_normalize(&infcx)
        })
     }
@@ -736,7 +736,7 @@ impl<'a, 'gcx, 'tcx> InferCtxt<'a, 'gcx, 'tcx> {
         Ok(self.tcx.erase_regions(&result))
     }
 
-    pub fn projection_mode(&self) -> ProjectionMode {
+    pub fn projection_mode(&self) -> Reveal {
         self.projection_mode
     }
 

src/librustc/middle/intrinsicck.rs

@@ -12,7 +12,7 @@ use dep_graph::DepNode;
 use hir::def::Def;
 use hir::def_id::DefId;
 use infer::InferCtxt;
-use traits::ProjectionMode;
+use traits::Reveal;
 use ty::{self, Ty, TyCtxt};
 use ty::layout::{LayoutError, Pointer, SizeSkeleton};
 
@@ -36,7 +36,7 @@ struct ItemVisitor<'a, 'tcx: 'a> {
 impl<'a, 'tcx> ItemVisitor<'a, 'tcx> {
     fn visit_const(&mut self, item_id: ast::NodeId, expr: &hir::Expr) {
         let param_env = ty::ParameterEnvironment::for_item(self.tcx, item_id);
-        self.tcx.infer_ctxt(None, Some(param_env), ProjectionMode::Any).enter(|infcx| {
+        self.tcx.infer_ctxt(None, Some(param_env), Reveal::All).enter(|infcx| {
             let mut visitor = ExprVisitor {
                 infcx: &infcx
             };
@@ -114,7 +114,7 @@ impl<'a, 'gcx, 'tcx> ExprVisitor<'a, 'gcx, 'tcx> {
 impl<'a, 'tcx, 'v> Visitor<'v> for ItemVisitor<'a, 'tcx> {
     // const, static and N in [T; N].
     fn visit_expr(&mut self, expr: &hir::Expr) {
-        self.tcx.infer_ctxt(None, None, ProjectionMode::Any).enter(|infcx| {
+        self.tcx.infer_ctxt(None, None, Reveal::All).enter(|infcx| {
             let mut visitor = ExprVisitor {
                 infcx: &infcx
             };
@@ -144,7 +144,7 @@ impl<'a, 'tcx, 'v> Visitor<'v> for ItemVisitor<'a, 'tcx> {
             span_bug!(s, "intrinsicck: closure outside of function")
         }
         let param_env = ty::ParameterEnvironment::for_item(self.tcx, id);
-        self.tcx.infer_ctxt(None, Some(param_env), ProjectionMode::Any).enter(|infcx| {
+        self.tcx.infer_ctxt(None, Some(param_env), Reveal::All).enter(|infcx| {
             let mut visitor = ExprVisitor {
                 infcx: &infcx
             };

src/librustc/middle/liveness.rs

@@ -113,7 +113,7 @@ use dep_graph::DepNode;
 use hir::def::*;
 use hir::pat_util;
 use ty::{self, TyCtxt, ParameterEnvironment};
-use traits::{self, ProjectionMode};
+use traits::{self, Reveal};
 use ty::subst::Subst;
 use lint;
 use util::nodemap::NodeMap;
@@ -1484,7 +1484,7 @@ impl<'a, 'tcx> Liveness<'a, 'tcx> {
                 let param_env = ParameterEnvironment::for_item(self.ir.tcx, id);
                 let t_ret_subst = t_ret.subst(self.ir.tcx, &param_env.free_substs);
                 let is_nil = self.ir.tcx.infer_ctxt(None, Some(param_env),
-                                                    ProjectionMode::Any).enter(|infcx| {
+                                                    Reveal::All).enter(|infcx| {
                     let cause = traits::ObligationCause::dummy();
                     traits::fully_normalize(&infcx, cause, &t_ret_subst).unwrap().is_nil()
                 });

src/librustc/middle/resolve_lifetime.rs

@@ -832,7 +832,10 @@ fn insert_late_bound_lifetimes(map: &mut NamedRegionMap,
         constrained_by_input.visit_ty(&arg.ty);
     }
 
-    let mut appears_in_output = AllCollector { regions: FnvHashSet() };
+    let mut appears_in_output = AllCollector {
+        regions: FnvHashSet(),
+        impl_trait: false
+    };
     intravisit::walk_fn_ret_ty(&mut appears_in_output, &decl.output);
 
     debug!("insert_late_bound_lifetimes: constrained_by_input={:?}",
@@ -842,7 +845,10 @@ fn insert_late_bound_lifetimes(map: &mut NamedRegionMap,
     //
     // Subtle point: because we disallow nested bindings, we can just
     // ignore binders here and scrape up all names we see.
-    let mut appears_in_where_clause = AllCollector { regions: FnvHashSet() };
+    let mut appears_in_where_clause = AllCollector {
+        regions: FnvHashSet(),
+        impl_trait: false
+    };
     for ty_param in generics.ty_params.iter() {
         walk_list!(&mut appears_in_where_clause,
                    visit_ty_param_bound,
@@ -864,12 +870,16 @@ fn insert_late_bound_lifetimes(map: &mut NamedRegionMap,
     // Late bound regions are those that:
     // - appear in the inputs
     // - do not appear in the where-clauses
+    // - are not implicitly captured by `impl Trait`
     for lifetime in &generics.lifetimes {
         let name = lifetime.lifetime.name;
 
         // appears in the where clauses? early-bound.
         if appears_in_where_clause.regions.contains(&name) { continue; }
 
+        // any `impl Trait` in the return type? early-bound.
+        if appears_in_output.impl_trait { continue; }
+
         // does not appear in the inputs, but appears in the return
         // type? eventually this will be early-bound, but for now we
         // just mark it so we can issue warnings.
@@ -932,12 +942,20 @@ fn insert_late_bound_lifetimes(map: &mut NamedRegionMap,
 
     struct AllCollector {
         regions: FnvHashSet<ast::Name>,
+        impl_trait: bool
     }
 
     impl<'v> Visitor<'v> for AllCollector {
         fn visit_lifetime(&mut self, lifetime_ref: &'v hir::Lifetime) {
             self.regions.insert(lifetime_ref.name);
         }
+
+        fn visit_ty(&mut self, ty: &hir::Ty) {
+            if let hir::TyImplTrait(_) = ty.node {
+                self.impl_trait = true;
+            }
+            intravisit::walk_ty(self, ty);
+        }
     }
 }