Add `default` as contextual keyword, and parse it for impl items.

src/librustc_front/fold.rs

@@ -839,6 +839,7 @@ pub fn noop_fold_impl_item<T: Folder>(i: ImplItem, folder: &mut T) -> ImplItem {
         name: folder.fold_name(i.name),
         attrs: fold_attrs(i.attrs, folder),
         vis: i.vis,
+        defaultness: i.defaultness,
         node: match i.node {
             ImplItemKind::Const(ty, expr) => {
                 ImplItemKind::Const(folder.fold_ty(ty), folder.fold_expr(expr))

src/librustc_front/hir.rs

@@ -864,10 +864,10 @@ pub struct MethodSig {
     pub explicit_self: ExplicitSelf,
 }
 
-/// Represents a method declaration in a trait declaration, possibly including
-/// a default implementation A trait method is either required (meaning it
-/// doesn't have an implementation, just a signature) or provided (meaning it
-/// has a default implementation).
+/// Represents an item declaration within a trait declaration,
+/// possibly including a default implementation. A trait item is
+/// either required (meaning it doesn't have an implementation, just a
+/// signature) or provided (meaning it has a default implementation).
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub struct TraitItem {
     pub id: NodeId,
@@ -889,6 +889,7 @@ pub struct ImplItem {
     pub id: NodeId,
     pub name: Name,
     pub vis: Visibility,
+    pub defaultness: Defaultness,
     pub attrs: HirVec<Attribute>,
     pub node: ImplItemKind,
     pub span: Span,
@@ -1046,6 +1047,12 @@ pub enum Constness {
     NotConst,
 }
 
+#[derive(Copy, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
+pub enum Defaultness {
+    Default,
+    Final,
+}
+
 impl fmt::Display for Unsafety {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Display::fmt(match *self {

src/librustc_front/lowering.rs

@@ -756,6 +756,7 @@ pub fn lower_impl_item(lctx: &LoweringContext, i: &ImplItem) -> hir::ImplItem {
         name: i.ident.name,
         attrs: lower_attrs(lctx, &i.attrs),
         vis: lower_visibility(lctx, i.vis),
+        defaultness: lower_defaultness(lctx, i.defaultness),
         node: match i.node {
             ImplItemKind::Const(ref ty, ref expr) => {
                 hir::ImplItemKind::Const(lower_ty(lctx, ty), lower_expr(lctx, expr))
@@ -1707,6 +1708,13 @@ pub fn lower_visibility(_lctx: &LoweringContext, v: Visibility) -> hir::Visibili
     }
 }
 
+pub fn lower_defaultness(_lctx: &LoweringContext, d: Defaultness) -> hir::Defaultness {
+    match d {
+        Defaultness::Default => hir::Defaultness::Default,
+        Defaultness::Final => hir::Defaultness::Final,
+    }
+}
+
 pub fn lower_block_check_mode(lctx: &LoweringContext, b: &BlockCheckMode) -> hir::BlockCheckMode {
     match *b {
         BlockCheckMode::Default => hir::DefaultBlock,

src/libsyntax/ast.rs

@@ -1328,10 +1328,10 @@ pub struct MethodSig {
     pub explicit_self: ExplicitSelf,
 }
 
-/// Represents a method declaration in a trait declaration, possibly including
-/// a default implementation. A trait method is either required (meaning it
-/// doesn't have an implementation, just a signature) or provided (meaning it
-/// has a default implementation).
+/// Represents an item declaration within a trait declaration,
+/// possibly including a default implementation. A trait item is
+/// either required (meaning it doesn't have an implementation, just a
+/// signature) or provided (meaning it has a default implementation).
 #[derive(Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
 pub struct TraitItem {
     pub id: NodeId,
@@ -1353,6 +1353,7 @@ pub struct ImplItem {
     pub id: NodeId,
     pub ident: Ident,
     pub vis: Visibility,
+    pub defaultness: Defaultness,
     pub attrs: Vec<Attribute>,
     pub node: ImplItemKind,
     pub span: Span,
@@ -1654,6 +1655,12 @@ pub enum Constness {
     NotConst,
 }
 
+#[derive(Copy, Clone, PartialEq, Eq, RustcEncodable, RustcDecodable, Hash, Debug)]
+pub enum Defaultness {
+    Default,
+    Final,
+}
+
 impl fmt::Display for Unsafety {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Display::fmt(match *self {

src/libsyntax/ext/expand.rs

@@ -1061,6 +1061,7 @@ fn expand_impl_item(ii: ast::ImplItem, fld: &mut MacroExpander)
             ident: ii.ident,
             attrs: ii.attrs,
             vis: ii.vis,
+            defaultness: ii.defaultness,
             node: match ii.node  {
                 ast::ImplItemKind::Method(sig, body) => {
                     let (sig, body) = expand_and_rename_method(sig, body, fld);

src/libsyntax/fold.rs

@@ -993,6 +993,7 @@ pub fn noop_fold_impl_item<T: Folder>(i: ImplItem, folder: &mut T)
         ident: folder.fold_ident(i.ident),
         attrs: fold_attrs(i.attrs, folder),
         vis: i.vis,
+        defaultness: i.defaultness,
         node: match i.node  {
             ast::ImplItemKind::Const(ty, expr) => {
                 ast::ImplItemKind::Const(folder.fold_ty(ty), folder.fold_expr(expr))

src/libsyntax/parse/parser.rs

@@ -18,7 +18,7 @@
 use ast::Block;
 use ast::{BlockCheckMode, CaptureBy};
 use ast::{Constness, Crate, CrateConfig};
-use ast::{Decl, DeclKind};
+use ast::{Decl, DeclKind, Defaultness};
 use ast::{EMPTY_CTXT, EnumDef, ExplicitSelf};
 use ast::{Expr, ExprKind, RangeLimits};
 use ast::{Field, FnDecl};
@@ -644,6 +644,25 @@ pub fn eat_keyword_noexpect(&mut self, kw: keywords::Keyword) -> bool {
         }
     }
 
+    pub fn check_contextual_keyword(&mut self, ident: Ident) -> bool {
+        let tok = token::Ident(ident, token::Plain);
+        self.expected_tokens.push(TokenType::Token(tok));
+        if let token::Ident(ref cur_ident, _) = self.token {
+            cur_ident.name == ident.name
+        } else {
+            false
+        }
+    }
+
+    pub fn eat_contextual_keyword(&mut self, ident: Ident) -> PResult<bool> {
+        if self.check_contextual_keyword(ident) {
+            try!(self.bump());
+            Ok(true)
+        } else {
+            Ok(false)
+        }
+    }
+
     /// If the given word is not a keyword, signal an error.
     /// If the next token is not the given word, signal an error.
     /// Otherwise, eat it.
@@ -705,7 +724,6 @@ pub fn expect_no_suffix(&self, sp: Span, kind: &str, suffix: Option<ast::Name>)
         }
     }
 
-
     /// Attempt to consume a `<`. If `<<` is seen, replace it with a single
     /// `<` and continue. If a `<` is not seen, return false.
     ///
@@ -4846,6 +4864,7 @@ pub fn parse_impl_item(&mut self) -> PResult<'a, ImplItem> {
         let mut attrs = try!(self.parse_outer_attributes());
         let lo = self.span.lo;
         let vis = try!(self.parse_visibility());
+        let defaultness = try!(self.parse_defaultness());
         let (name, node) = if self.eat_keyword(keywords::Type) {
             let name = try!(self.parse_ident());
             try!(self.expect(&token::Eq));
@@ -4872,6 +4891,7 @@ pub fn parse_impl_item(&mut self) -> PResult<'a, ImplItem> {
             span: mk_sp(lo, self.last_span.hi),
             ident: name,
             vis: vis,
+            defaultness: defaultness,
             attrs: attrs,
             node: node
         })
@@ -5208,6 +5228,15 @@ fn parse_visibility(&mut self) -> PResult<'a, Visibility> {
         else { Ok(Visibility::Inherited) }
     }
 
+    /// Parse defaultness: DEFAULT or nothing
+    fn parse_defaultness(&mut self) -> PResult<Defaultness> {
+        if try!(self.eat_contextual_keyword(special_idents::DEFAULT)) {
+            Ok(Defaultness::Default)
+        } else {
+            Ok(Defaultness::Final)
+        }
+    }
+
     /// Given a termination token, parse all of the items in a module
     fn parse_mod_items(&mut self, term: &token::Token, inner_lo: BytePos) -> PResult<'a, Mod> {
         let mut items = vec![];

src/libsyntax/parse/token.rs

@@ -545,66 +545,67 @@ pub mod special_idents {
         (9,                          __unused1,              "<__unused1>");
         (super::SELF_TYPE_KEYWORD_NAME_NUM, type_self,       "Self");
         (11,                         prelude_import,         "prelude_import");
+        (12,                         DEFAULT,                "default");
     }
 
     pub mod keywords {
         // These ones are variants of the Keyword enum
 
         'strict:
-        (12,                         As,         "as");
-        (13,                         Break,      "break");
-        (14,                         Crate,      "crate");
-        (15,                         Else,       "else");
-        (16,                         Enum,       "enum");
-        (17,                         Extern,     "extern");
-        (18,                         False,      "false");
-        (19,                         Fn,         "fn");
-        (20,                         For,        "for");
-        (21,                         If,         "if");
-        (22,                         Impl,       "impl");
-        (23,                         In,         "in");
-        (24,                         Let,        "let");
-        (25,                         Loop,       "loop");
-        (26,                         Match,      "match");
-        (27,                         Mod,        "mod");
-        (28,                         Move,       "move");
-        (29,                         Mut,        "mut");
-        (30,                         Pub,        "pub");
-        (31,                         Ref,        "ref");
-        (32,                         Return,     "return");
+        (13,                         As,         "as");
+        (14,                         Break,      "break");
+        (15,                         Crate,      "crate");
+        (16,                         Else,       "else");
+        (17,                         Enum,       "enum");
+        (18,                         Extern,     "extern");
+        (19,                         False,      "false");
+        (20,                         Fn,         "fn");
+        (21,                         For,        "for");
+        (22,                         If,         "if");
+        (23,                         Impl,       "impl");
+        (24,                         In,         "in");
+        (25,                         Let,        "let");
+        (26,                         Loop,       "loop");
+        (27,                         Match,      "match");
+        (28,                         Mod,        "mod");
+        (29,                         Move,       "move");
+        (30,                         Mut,        "mut");
+        (31,                         Pub,        "pub");
+        (32,                         Ref,        "ref");
+        (33,                         Return,     "return");
         // Static and Self are also special idents (prefill de-dupes)
         (super::STATIC_KEYWORD_NAME_NUM, Static, "static");
         (super::SELF_KEYWORD_NAME_NUM, SelfValue, "self");
         (super::SELF_TYPE_KEYWORD_NAME_NUM, SelfType, "Self");
-        (33,                         Struct,     "struct");
+        (34,                         Struct,     "struct");
         (super::SUPER_KEYWORD_NAME_NUM, Super,   "super");
-        (34,                         True,       "true");
-        (35,                         Trait,      "trait");
-        (36,                         Type,       "type");
-        (37,                         Unsafe,     "unsafe");
-        (38,                         Use,        "use");
-        (39,                         While,      "while");
-        (40,                         Continue,   "continue");
-        (41,                         Box,        "box");
-        (42,                         Const,      "const");
-        (43,                         Where,      "where");
+        (35,                         True,       "true");
+        (36,                         Trait,      "trait");
+        (37,                         Type,       "type");
+        (38,                         Unsafe,     "unsafe");
+        (39,                         Use,        "use");
+        (40,                         While,      "while");
+        (41,                         Continue,   "continue");
+        (42,                         Box,        "box");
+        (43,                         Const,      "const");
+        (44,                         Where,      "where");
         'reserved:
-        (44,                         Virtual,    "virtual");
-        (45,                         Proc,       "proc");
-        (46,                         Alignof,    "alignof");
-        (47,                         Become,     "become");
-        (48,                         Offsetof,   "offsetof");
-        (49,                         Priv,       "priv");
-        (50,                         Pure,       "pure");
-        (51,                         Sizeof,     "sizeof");
-        (52,                         Typeof,     "typeof");
-        (53,                         Unsized,    "unsized");
-        (54,                         Yield,      "yield");
-        (55,                         Do,         "do");
-        (56,                         Abstract,   "abstract");
-        (57,                         Final,      "final");
-        (58,                         Override,   "override");
-        (59,                         Macro,      "macro");
+        (45,                         Virtual,    "virtual");
+        (46,                         Proc,       "proc");
+        (47,                         Alignof,    "alignof");
+        (48,                         Become,     "become");
+        (49,                         Offsetof,   "offsetof");
+        (50,                         Priv,       "priv");
+        (51,                         Pure,       "pure");
+        (52,                         Sizeof,     "sizeof");
+        (53,                         Typeof,     "typeof");
+        (54,                         Unsized,    "unsized");
+        (55,                         Yield,      "yield");
+        (56,                         Do,         "do");
+        (57,                         Abstract,   "abstract");
+        (58,                         Final,      "final");
+        (59,                         Override,   "override");
+        (60,                         Macro,      "macro");
     }
 }
 

src/libsyntax_ext/deriving/generic/mod.rs

@@ -476,6 +476,7 @@ fn create_derived_impl(&self,
                 span: self.span,
                 ident: ident,
                 vis: ast::Visibility::Inherited,
+                defaultness: ast::Defaultness::Final,
                 attrs: Vec::new(),
                 node: ast::ImplItemKind::Type(type_def.to_ty(cx,
                     self.span,
@@ -893,6 +894,7 @@ fn create_method(&self,
             attrs: self.attributes.clone(),
             span: trait_.span,
             vis: ast::Visibility::Inherited,
+            defaultness: ast::Defaultness::Final,
             ident: method_ident,
             node: ast::ImplItemKind::Method(ast::MethodSig {
                 generics: fn_generics,

src/test/parse-fail/default.rs

+// Copyright 2015 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-flags: -Z parse-only
+
+// Test successful and unsucessful parsing of the `default` contextual keyword
+
+trait Foo {
+    fn foo<T: Default>() -> T;
+}
+
+impl Foo for u8 {
+    default fn foo<T: Default>() -> T {
+        T::default()
+    }
+}
+
+impl Foo for u16 {
+    pub default fn foo<T: Default>() -> T {
+        T::default()
+    }
+}
+
+impl Foo for u32 {
+    default pub fn foo<T: Default>() -> T { T::default() } //~ ERROR expected one of
+}
+
+fn main() {}