Infer default static/Owned bounds for unbounded heap fns/traits (#7264)

Author: bblum

src/librustc/metadata/encoder.rs

@@ -959,7 +959,7 @@ fn encode_info_for_item(ecx: &EncodeContext,
         encode_attributes(ebml_w, item.attrs);
         match ty.node {
             ast::ty_path(path, bounds, _) if path.idents.len() == 1 => {
-                assert!(bounds.is_empty());
+                assert!(bounds.is_none());
                 encode_impl_type_basename(ecx, ebml_w,
                                           ast_util::path_to_ident(path));
             }

src/librustc/middle/kind.rs

@@ -128,7 +128,7 @@ fn check_item(item: @item, (cx, visitor): (Context, visit::vt<Context>)) {
                             // Yes, it's a destructor.
                             match self_type.node {
                                 ty_path(_, bounds, path_node_id) => {
-                                    assert!(bounds.is_empty());
+                                    assert!(bounds.is_none());
                                     let struct_def = cx.tcx.def_map.get_copy(
                                         &path_node_id);
                                     let struct_did =

src/librustc/middle/resolve.rs

@@ -4195,15 +4195,19 @@ impl Resolver {
                     }
                 }
 
-                for bounds.iter().advance |bound| {
-                    self.resolve_type_parameter_bound(bound, visitor);
-                }
+                do bounds.map |bound_vec| {
+                    for bound_vec.iter().advance |bound| {
+                        self.resolve_type_parameter_bound(bound, visitor);
+                    }
+                };
             }
 
             ty_closure(c) => {
-                for c.bounds.iter().advance |bound| {
-                    self.resolve_type_parameter_bound(bound, visitor);
-                }
+                do c.bounds.map |bounds| {
+                    for bounds.iter().advance |bound| {
+                        self.resolve_type_parameter_bound(bound, visitor);
+                    }
+                };
                 visit_ty(ty, ((), visitor));
             }
 

src/librustc/middle/ty.rs

@@ -4497,7 +4497,9 @@ pub fn visitor_object_ty(tcx: ctxt) -> (@TraitRef, t) {
     };
     let trait_lang_item = tcx.lang_items.ty_visitor();
     let trait_ref = @TraitRef { def_id: trait_lang_item, substs: substs };
+    let mut static_trait_bound = EmptyBuiltinBounds();
+    static_trait_bound.add(BoundStatic);
     (trait_ref,
      mk_trait(tcx, trait_ref.def_id, copy trait_ref.substs,
-              BoxTraitStore, ast::m_imm, EmptyBuiltinBounds()))
+              BoxTraitStore, ast::m_imm, static_trait_bound))
 }

src/librustc/middle/typeck/astconv.rs

@@ -303,7 +303,7 @@ pub fn ast_ty_to_ty<AC:AstConv, RS:region_scope + Copy + 'static>(
                                 ty::BoxTraitStore
                             }
                         };
-                        let bounds = conv_builtin_bounds(this.tcx(), bounds);
+                        let bounds = conv_builtin_bounds(this.tcx(), bounds, trait_store);
                         return ty::mk_trait(tcx,
                                             result.def_id,
                                             copy result.substs,
@@ -386,7 +386,13 @@ pub fn ast_ty_to_ty<AC:AstConv, RS:region_scope + Copy + 'static>(
                                             bf.abis, &bf.lifetimes, &bf.decl))
       }
       ast::ty_closure(ref f) => {
-          let bounds = conv_builtin_bounds(this.tcx(), &f.bounds);
+          let bounds = conv_builtin_bounds(this.tcx(), &f.bounds, match f.sigil {
+              // Use corresponding trait store to figure out default bounds
+              // if none were specified.
+              ast::BorrowedSigil => ty::RegionTraitStore(ty::re_empty), // dummy region
+              ast::OwnedSigil    => ty::UniqTraitStore,
+              ast::ManagedSigil  => ty::BoxTraitStore,
+          });
           let fn_decl = ty_of_closure(this,
                                       rscope,
                                       f.sigil,
@@ -411,7 +417,7 @@ pub fn ast_ty_to_ty<AC:AstConv, RS:region_scope + Copy + 'static>(
         match a_def {
             // But don't emit the error if the user meant to do a trait anyway.
             ast::def_trait(*) => { },
-            _ if !bounds.is_empty() =>
+            _ if bounds.is_some() =>
                 tcx.sess.span_err(ast_ty.span,
                     "kind bounds can only be used on trait types"),
             _ => { },
@@ -741,41 +747,60 @@ pub fn ty_of_closure<AC:AstConv,RS:region_scope + Copy + 'static>(
     }
 }
 
-fn conv_builtin_bounds(tcx: ty::ctxt,
-                       ast_bounds: &OptVec<ast::TyParamBound>)
+fn conv_builtin_bounds(tcx: ty::ctxt, ast_bounds: &Option<OptVec<ast::TyParamBound>>,
+                       store: ty::TraitStore)
                        -> ty::BuiltinBounds {
     //! Converts a list of bounds from the AST into a `BuiltinBounds`
     //! struct. Reports an error if any of the bounds that appear
     //! in the AST refer to general traits and not the built-in traits
     //! like `Copy` or `Owned`. Used to translate the bounds that
     //! appear in closure and trait types, where only builtin bounds are
     //! legal.
-
-    let mut builtin_bounds = ty::EmptyBuiltinBounds();
-    for ast_bounds.iter().advance |ast_bound| {
-        match *ast_bound {
-            ast::TraitTyParamBound(b) => {
-                match lookup_def_tcx(tcx, b.path.span, b.ref_id) {
-                    ast::def_trait(trait_did) => {
-                        if try_add_builtin_trait(tcx,
-                                                 trait_did,
-                                                 &mut builtin_bounds) {
-                            loop; // success
+    //! If no bounds were specified, we choose a "default" bound based on
+    //! the allocation type of the fn/trait, as per issue #7264. The user can
+    //! override this with an empty bounds list, e.g. "~fn:()" or "~Trait:".
+
+    match (ast_bounds, store) {
+        (&Some(ref bound_vec), _) => {
+            let mut builtin_bounds = ty::EmptyBuiltinBounds();
+            for bound_vec.iter().advance |ast_bound| {
+                match *ast_bound {
+                    ast::TraitTyParamBound(b) => {
+                        match lookup_def_tcx(tcx, b.path.span, b.ref_id) {
+                            ast::def_trait(trait_did) => {
+                                if try_add_builtin_trait(tcx,
+                                                         trait_did,
+                                                         &mut builtin_bounds) {
+                                    loop; // success
+                                }
+                            }
+                            _ => { }
                         }
+                        tcx.sess.span_fatal(
+                            b.path.span,
+                            fmt!("only the builtin traits can be used \
+                                  as closure or object bounds"));
+                    }
+                    ast::RegionTyParamBound => {
+                        builtin_bounds.add(ty::BoundStatic);
                     }
-                    _ => { }
                 }
-                tcx.sess.span_fatal(
-                    b.path.span,
-                    fmt!("only the builtin traits can be used \
-                          as closure or object bounds"));
-            }
-            ast::RegionTyParamBound => {
-                builtin_bounds.add(ty::BoundStatic);
             }
+            builtin_bounds
+        },
+        // ~Trait is sugar for ~Trait:Owned.
+        (&None, ty::UniqTraitStore) => {
+            let mut set = ty::EmptyBuiltinBounds(); set.add(ty::BoundOwned); set
+        }
+        // @Trait is sugar for @Trait:'static.
+        // &'static Trait is sugar for &'static Trait:'static.
+        (&None, ty::BoxTraitStore) |
+        (&None, ty::RegionTraitStore(ty::re_static)) => {
+            let mut set = ty::EmptyBuiltinBounds(); set.add(ty::BoundStatic); set
         }
+        // &'r Trait is sugar for &'r Trait:<no-bounds>.
+        (&None, ty::RegionTraitStore(*)) => ty::EmptyBuiltinBounds(),
     }
-    builtin_bounds
 }
 
 pub fn try_add_builtin_trait(tcx: ty::ctxt,

src/libsyntax/ast.rs

@@ -771,7 +771,11 @@ pub struct TyClosure {
     purity: purity,
     onceness: Onceness,
     decl: fn_decl,
-    bounds: OptVec<TyParamBound>
+    // Optional optvec distinguishes between "fn()" and "fn:()" so we can
+    // implement issue #7264. None means "fn()", which means infer a default
+    // bound based on pointer sigil during typeck. Some(Empty) means "fn:()",
+    // which means use no bounds (e.g., not even Owned on a ~fn()).
+    bounds: Option<OptVec<TyParamBound>>,
 }
 
 #[deriving(Eq, Encodable, Decodable)]
@@ -795,7 +799,7 @@ pub enum ty_ {
     ty_closure(@TyClosure),
     ty_bare_fn(@TyBareFn),
     ty_tup(~[@Ty]),
-    ty_path(@Path, @OptVec<TyParamBound>, node_id),
+    ty_path(@Path, @Option<OptVec<TyParamBound>>, node_id), // for #7264; see above
     ty_mac(mac),
     // ty_infer means the type should be inferred instead of it having been
     // specified. This should only appear at the "top level" of a type and not

src/libsyntax/ext/build.rs

@@ -46,7 +46,7 @@ pub trait AstBuilder {
     fn ty_mt(&self, ty: @ast::Ty, mutbl: ast::mutability) -> ast::mt;
 
     fn ty(&self, span: span, ty: ast::ty_) -> @ast::Ty;
-    fn ty_path(&self, @ast::Path, @OptVec<ast::TyParamBound>) -> @ast::Ty;
+    fn ty_path(&self, @ast::Path, @Option<OptVec<ast::TyParamBound>>) -> @ast::Ty;
     fn ty_ident(&self, span: span, idents: ast::ident) -> @ast::Ty;
 
     fn ty_rptr(&self, span: span,
@@ -265,7 +265,7 @@ impl AstBuilder for @ExtCtxt {
         }
     }
 
-    fn ty_path(&self, path: @ast::Path, bounds: @OptVec<ast::TyParamBound>)
+    fn ty_path(&self, path: @ast::Path, bounds: @Option<OptVec<ast::TyParamBound>>)
               -> @ast::Ty {
         self.ty(path.span,
                 ast::ty_path(path, bounds, self.next_id()))
@@ -275,7 +275,7 @@ impl AstBuilder for @ExtCtxt {
     // to generate a bounded existential trait type.
     fn ty_ident(&self, span: span, ident: ast::ident)
         -> @ast::Ty {
-        self.ty_path(self.path_ident(span, ident), @opt_vec::Empty)
+        self.ty_path(self.path_ident(span, ident), @None)
     }
 
     fn ty_rptr(&self,
@@ -306,7 +306,7 @@ impl AstBuilder for @ExtCtxt {
                           ],
                           None,
                           ~[ ty ]),
-            @opt_vec::Empty)
+            @None)
     }
 
     fn ty_field_imm(&self, span: span, name: ident, ty: @ast::Ty) -> ast::ty_field {
@@ -344,7 +344,7 @@ impl AstBuilder for @ExtCtxt {
     fn ty_vars_global(&self, ty_params: &OptVec<ast::TyParam>) -> ~[@ast::Ty] {
         opt_vec::take_vec(
             ty_params.map(|p| self.ty_path(
-                self.path_global(dummy_sp(), ~[p.ident]), @opt_vec::Empty)))
+                self.path_global(dummy_sp(), ~[p.ident]), @None)))
     }
 
     fn strip_bounds(&self, generics: &Generics) -> Generics {

src/libsyntax/ext/deriving/generic.rs

@@ -357,7 +357,7 @@ impl<'self> TraitDef<'self> {
         // Create the type of `self`.
         let self_type = cx.ty_path(cx.path_all(span, false, ~[ type_ident ], self_lifetime,
                                                opt_vec::take_vec(self_ty_params)),
-                                   @opt_vec::Empty);
+                                   @None);
 
         let doc_attr = cx.attribute(
             span,

src/libsyntax/ext/deriving/ty.rs

@@ -63,7 +63,7 @@ impl<'self> Path<'self> {
                  self_generics: &Generics)
                  -> @ast::Ty {
         cx.ty_path(self.to_path(cx, span,
-                                self_ty, self_generics), @opt_vec::Empty)
+                                self_ty, self_generics), @None)
     }
     pub fn to_path(&self,
                    cx: @ExtCtxt,
@@ -143,7 +143,7 @@ impl<'self> Ty<'self> {
             Literal(ref p) => { p.to_ty(cx, span, self_ty, self_generics) }
             Self  => {
                 cx.ty_path(self.to_path(cx, span, self_ty, self_generics),
-                           @opt_vec::Empty)
+                           @None)
             }
             Tuple(ref fields) => {
                 let ty = if fields.is_empty() {

src/libsyntax/ext/pipes/pipec.rs

@@ -59,7 +59,7 @@ impl gen_send for message {
 
             let pipe_ty = cx.ty_path(
                 path(~[this.data_name()], span)
-                .add_tys(cx.ty_vars(&this.generics.ty_params)), @opt_vec::Empty);
+                .add_tys(cx.ty_vars(&this.generics.ty_params)), @None);
             let args_ast = vec::append(
                 ~[cx.arg(span, cx.ident_of("pipe"), pipe_ty)],
                 args_ast);
@@ -115,7 +115,7 @@ impl gen_send for message {
 
             let mut rty = cx.ty_path(path(~[next.data_name()],
                                           span)
-                                     .add_tys(copy next_state.tys), @opt_vec::Empty);
+                                     .add_tys(copy next_state.tys), @None);
             if try {
                 rty = cx.ty_option(rty);
             }
@@ -144,7 +144,7 @@ impl gen_send for message {
                              cx.ty_path(
                                  path(~[this.data_name()], span)
                                  .add_tys(cx.ty_vars(
-                                     &this.generics.ty_params)), @opt_vec::Empty))],
+                                     &this.generics.ty_params)), @None))],
                     args_ast);
 
                 let message_args = if arg_names.len() == 0 {
@@ -190,7 +190,7 @@ impl gen_send for message {
 
     fn to_ty(&mut self, cx: @ExtCtxt) -> @ast::Ty {
         cx.ty_path(path(~[cx.ident_of(self.name())], self.span())
-          .add_tys(cx.ty_vars(&self.get_generics().ty_params)), @opt_vec::Empty)
+          .add_tys(cx.ty_vars(&self.get_generics().ty_params)), @None)
     }
 }
 
@@ -224,7 +224,7 @@ impl to_type_decls for state {
                                 cx.ty_path(
                                     path(~[cx.ident_of(dir),
                                            cx.ident_of(next_name)], span)
-                                    .add_tys(copy next_state.tys), @opt_vec::Empty))
+                                    .add_tys(copy next_state.tys), @None))
               }
               None => tys
             };
@@ -277,8 +277,8 @@ impl to_type_decls for state {
                                    self.data_name()],
                                  dummy_sp())
                             .add_tys(cx.ty_vars(
-                                &self.generics.ty_params)), @opt_vec::Empty)),
-                        @opt_vec::Empty),
+                                &self.generics.ty_params)), @None)),
+                        @None),
                     cx.strip_bounds(&self.generics)));
         }
         else {
@@ -297,8 +297,8 @@ impl to_type_decls for state {
                                    self.data_name()],
                                         dummy_sp())
                             .add_tys(cx.ty_vars_global(
-                                &self.generics.ty_params)), @opt_vec::Empty),
-                                   self.proto.buffer_ty_path(cx)]), @opt_vec::Empty),
+                                &self.generics.ty_params)), @None),
+                                   self.proto.buffer_ty_path(cx)]), @None),
                     cx.strip_bounds(&self.generics)));
         };
         items
@@ -383,7 +383,7 @@ impl gen_init for protocol {
         cx.ty_path(path(~[cx.ident_of("super"),
                           cx.ident_of("__Buffer")],
                         copy self.span)
-                   .add_tys(cx.ty_vars_global(&params)), @opt_vec::Empty)
+                   .add_tys(cx.ty_vars_global(&params)), @None)
     }
 
     fn gen_buffer_type(&self, cx: @ExtCtxt) -> @ast::item {