Implement RFC 1861: Extern types

6 files changed, 55 insertions, 8 deletions

diff --git a/src/libsyntax/ast.rs b/src/libsyntax/ast.rs
index 090fc193b38..d3995d95792 100644
--- a/src/libsyntax/ast.rs
+++ b/src/libsyntax/ast.rs
@@ -2007,13 +2007,16 @@ pub enum ForeignItemKind {
     /// A foreign static item (`static ext: u8`), with optional mutability
     /// (the boolean is true when mutable)
     Static(P<Ty>, bool),
+    /// A foreign type
+    Ty,
 }
 
 impl ForeignItemKind {
     pub fn descriptive_variant(&self) -> &str {
         match *self {
             ForeignItemKind::Fn(..) => "foreign function",
-            ForeignItemKind::Static(..) => "foreign static item"
+            ForeignItemKind::Static(..) => "foreign static item",
+            ForeignItemKind::Ty => "foreign type",
         }
     }
 }
diff --git a/src/libsyntax/feature_gate.rs b/src/libsyntax/feature_gate.rs
index 02aba8a3612..30451ec757a 100644
--- a/src/libsyntax/feature_gate.rs
+++ b/src/libsyntax/feature_gate.rs
@@ -404,6 +404,9 @@ declare_features! (
 
     // `crate` as visibility modifier, synonymous to `pub(crate)`
     (active, crate_visibility_modifier, "1.23.0", Some(45388)),
+
+    // extern types
+    (active, extern_types, "1.23.0", Some(43467)),
 );
 
 declare_features! (
@@ -1398,13 +1401,23 @@ impl<'a> Visitor<'a> for PostExpansionVisitor<'a> {
     }
 
     fn visit_foreign_item(&mut self, i: &'a ast::ForeignItem) {
-        let links_to_llvm = match attr::first_attr_value_str_by_name(&i.attrs, "link_name") {
-            Some(val) => val.as_str().starts_with("llvm."),
-            _ => false
-        };
-        if links_to_llvm {
-            gate_feature_post!(&self, link_llvm_intrinsics, i.span,
-                              "linking to LLVM intrinsics is experimental");
+        match i.node {
+            ast::ForeignItemKind::Fn(..) |
+            ast::ForeignItemKind::Static(..) => {
+                let link_name = attr::first_attr_value_str_by_name(&i.attrs, "link_name");
+                let links_to_llvm = match link_name {
+                    Some(val) => val.as_str().starts_with("llvm."),
+                    _ => false
+                };
+                if links_to_llvm {
+                    gate_feature_post!(&self, link_llvm_intrinsics, i.span,
+                                       "linking to LLVM intrinsics is experimental");
+                }
+            }
+            ast::ForeignItemKind::Ty => {
+                    gate_feature_post!(&self, extern_types, i.span,
+                                       "extern types are experimental");
+            }
         }
 
         visit::walk_foreign_item(self, i)
diff --git a/src/libsyntax/fold.rs b/src/libsyntax/fold.rs
index 518386a2ad2..fea49424dc8 100644
--- a/src/libsyntax/fold.rs
+++ b/src/libsyntax/fold.rs
@@ -1069,6 +1069,7 @@ pub fn noop_fold_foreign_item<T: Folder>(ni: ForeignItem, folder: &mut T) -> For
             ForeignItemKind::Static(t, m) => {
                 ForeignItemKind::Static(folder.fold_ty(t), m)
             }
+            ForeignItemKind::Ty => ForeignItemKind::Ty,
         },
         span: folder.new_span(ni.span)
     }
diff --git a/src/libsyntax/parse/parser.rs b/src/libsyntax/parse/parser.rs
index a2c431dc8b1..1d990f16ac9 100644
--- a/src/libsyntax/parse/parser.rs
+++ b/src/libsyntax/parse/parser.rs
@@ -5671,6 +5671,24 @@ impl<'a> Parser<'a> {
         })
     }
 
+    /// Parse a type from a foreign module
+    fn parse_item_foreign_type(&mut self, vis: ast::Visibility, lo: Span, attrs: Vec<Attribute>)
+                             -> PResult<'a, ForeignItem> {
+        self.expect_keyword(keywords::Type)?;
+
+        let ident = self.parse_ident()?;
+        let hi = self.span;
+        self.expect(&token::Semi)?;
+        Ok(ast::ForeignItem {
+            ident: ident,
+            attrs: attrs,
+            node: ForeignItemKind::Ty,
+            id: ast::DUMMY_NODE_ID,
+            span: lo.to(hi),
+            vis: vis
+        })
+    }
+
     /// Parse extern crate links
     ///
     /// # Examples
@@ -6145,6 +6163,10 @@ impl<'a> Parser<'a> {
         if self.check_keyword(keywords::Fn) {
             return Ok(Some(self.parse_item_foreign_fn(visibility, lo, attrs)?));
         }
+        // FOREIGN TYPE ITEM
+        if self.check_keyword(keywords::Type) {
+            return Ok(Some(self.parse_item_foreign_type(visibility, lo, attrs)?));
+        }
 
         // FIXME #5668: this will occur for a macro invocation:
         match self.parse_macro_use_or_failure(attrs, true, false, lo, visibility)? {
diff --git a/src/libsyntax/print/pprust.rs b/src/libsyntax/print/pprust.rs
index 656a51c6637..8a970fd4098 100644
--- a/src/libsyntax/print/pprust.rs
+++ b/src/libsyntax/print/pprust.rs
@@ -1112,6 +1112,13 @@ impl<'a> State<'a> {
                 self.end()?; // end the head-ibox
                 self.end() // end the outer cbox
             }
+            ast::ForeignItemKind::Ty => {
+                self.head(&visibility_qualified(&item.vis, "type"))?;
+                self.print_ident(item.ident)?;
+                self.s.word(";")?;
+                self.end()?; // end the head-ibox
+                self.end() // end the outer cbox
+            }
         }
     }
 
diff --git a/src/libsyntax/visit.rs b/src/libsyntax/visit.rs
index 4198055f670..96e47a6cc0f 100644
--- a/src/libsyntax/visit.rs
+++ b/src/libsyntax/visit.rs
@@ -477,6 +477,7 @@ pub fn walk_foreign_item<'a, V: Visitor<'a>>(visitor: &mut V, foreign_item: &'a
             visitor.visit_generics(generics)
         }
         ForeignItemKind::Static(ref typ, _) => visitor.visit_ty(typ),
+        ForeignItemKind::Ty => (),
     }
 
     walk_list!(visitor, visit_attribute, &foreign_item.attrs);