rustc: Enable writing "unsafe extern fn() {}"

Previously, the parser would not allow you to simultaneously implement a
function with a different abi as well as being unsafe at the same time. This
extends the parser to allow functions of the form:

    unsafe extern fn foo() {
        // ...
    }

The closure type grammar was also changed to reflect this reversal, types
previously written as "extern unsafe fn()" must now be written as
"unsafe extern fn()". The parser currently has a hack which allows the old
style, but this will go away once a snapshot has landed.

Closes #10025

[breaking-change]

src/librustc/metadata/decoder.rs

@@ -110,7 +110,6 @@ enum Family {
     UnsafeFn,              // u
     StaticMethod,          // F
     UnsafeStaticMethod,    // U
-    ForeignFn,             // e
     Type,                  // y
     ForeignType,           // T
     Mod,                   // m
@@ -134,7 +133,6 @@ fn item_family(item: ebml::Doc) -> Family {
       'u' => UnsafeFn,
       'F' => StaticMethod,
       'U' => UnsafeStaticMethod,
-      'e' => ForeignFn,
       'y' => Type,
       'T' => ForeignType,
       'm' => Mod,
@@ -339,7 +337,6 @@ fn item_to_def_like(item: ebml::Doc, did: ast::DefId, cnum: ast::CrateNum)
         Struct    => DlDef(ast::DefStruct(did)),
         UnsafeFn  => DlDef(ast::DefFn(did, ast::UnsafeFn)),
         Fn        => DlDef(ast::DefFn(did, ast::NormalFn)),
-        ForeignFn => DlDef(ast::DefFn(did, ast::ExternFn)),
         StaticMethod | UnsafeStaticMethod => {
             let fn_style = if fam == UnsafeStaticMethod { ast::UnsafeFn } else
                 { ast::NormalFn };

src/librustc/metadata/encoder.rs

@@ -787,7 +787,6 @@ fn style_fn_family(s: FnStyle) -> char {
     match s {
         UnsafeFn => 'u',
         NormalFn => 'f',
-        ExternFn => 'e'
     }
 }
 
@@ -795,7 +794,6 @@ fn fn_style_static_method_family(s: FnStyle) -> char {
     match s {
         UnsafeFn => 'U',
         NormalFn => 'F',
-        _ => fail!("extern fn can't be static")
     }
 }
 

src/librustc/metadata/tydecode.rs

@@ -441,7 +441,6 @@ fn parse_fn_style(c: char) -> FnStyle {
     match c {
         'u' => UnsafeFn,
         'n' => NormalFn,
-        'c' => ExternFn,
         _ => fail!("parse_fn_style: bad fn_style {}", c)
     }
 }

src/librustc/metadata/tyencode.rs

@@ -293,7 +293,6 @@ fn enc_fn_style(w: &mut MemWriter, p: FnStyle) {
     match p {
         NormalFn => mywrite!(w, "n"),
         UnsafeFn => mywrite!(w, "u"),
-        ExternFn => mywrite!(w, "c")
     }
 }
 

src/librustc/middle/reachable.rs

@@ -22,6 +22,7 @@ use middle::privacy;
 use util::nodemap::NodeSet;
 
 use collections::HashSet;
+use syntax::abi;
 use syntax::ast;
 use syntax::ast_map;
 use syntax::ast_util::{def_id_of_def, is_local};
@@ -250,8 +251,10 @@ impl<'a> ReachableContext<'a> {
             match *node {
                 ast_map::NodeItem(item) => {
                     match item.node {
-                        ast::ItemFn(_, ast::ExternFn, _, _, _) => {
+                        ast::ItemFn(_, _, abi, _, _) => {
-                            self.reachable_symbols.insert(search_item);
+                            if abi != abi::Rust {
+                                self.reachable_symbols.insert(search_item);
+                            }
                         }
                         _ => {}
                     }

src/librustc/middle/trans/base.rs

@@ -1594,8 +1594,8 @@ impl<'a> Visitor<()> for TransItemVisitor<'a> {
 pub fn trans_item(ccx: &CrateContext, item: &ast::Item) {
     let _icx = push_ctxt("trans_item");
     match item.node {
-      ast::ItemFn(decl, fn_style, _abi, ref generics, body) => {
+      ast::ItemFn(decl, _fn_style, abi, ref generics, body) => {
-        if fn_style == ast::ExternFn  {
+        if abi != Rust  {
             let llfndecl = get_item_val(ccx, item.id);
             foreign::trans_rust_fn_with_foreign_abi(
                 ccx, decl, body, item.attrs.as_slice(), llfndecl, item.id);
@@ -1939,8 +1939,8 @@ pub fn get_item_val(ccx: &CrateContext, id: ast::NodeId) -> ValueRef {
                     }
                 }
 
-                ast::ItemFn(_, fn_style, _, _, _) => {
+                ast::ItemFn(_, _, abi, _, _) => {
-                    let llfn = if fn_style != ast::ExternFn {
+                    let llfn = if abi == Rust {
                         register_fn(ccx, i.span, sym, i.id, ty)
                     } else {
                         foreign::register_rust_fn_with_foreign_abi(ccx,

src/librustc/middle/trans/reflect.rs

@@ -403,6 +403,5 @@ pub fn ast_fn_style_constant(fn_style: ast::FnStyle) -> uint {
     match fn_style {
         ast::UnsafeFn => 1u,
         ast::NormalFn => 2u,
-        ast::ExternFn => 3u
     }
 }

src/librustc/middle/typeck/infer/glb.rs

@@ -22,7 +22,7 @@ use middle::typeck::infer::{cres, InferCtxt};
 use middle::typeck::infer::{TypeTrace, Subtype};
 use middle::typeck::infer::fold_regions_in_sig;
 use syntax::ast::{Many, Once, MutImmutable, MutMutable};
-use syntax::ast::{ExternFn, NormalFn, UnsafeFn, NodeId};
+use syntax::ast::{NormalFn, UnsafeFn, NodeId};
 use syntax::ast::{Onceness, FnStyle};
 use collections::HashMap;
 use util::common::{indenter};
@@ -83,7 +83,6 @@ impl<'f> Combine for Glb<'f> {
 
     fn fn_styles(&self, a: FnStyle, b: FnStyle) -> cres<FnStyle> {
         match (a, b) {
-          (ExternFn, _) | (_, ExternFn) => Ok(ExternFn),
           (NormalFn, _) | (_, NormalFn) => Ok(NormalFn),
           (UnsafeFn, UnsafeFn) => Ok(UnsafeFn)
         }

src/librustc/middle/typeck/infer/lub.rs

@@ -23,7 +23,7 @@ use middle::typeck::infer::fold_regions_in_sig;
 use middle::typeck::infer::{TypeTrace, Subtype};
 use collections::HashMap;
 use syntax::ast::{Many, Once, NodeId};
-use syntax::ast::{ExternFn, NormalFn, UnsafeFn};
+use syntax::ast::{NormalFn, UnsafeFn};
 use syntax::ast::{Onceness, FnStyle};
 use util::ppaux::mt_to_str;
 
@@ -78,8 +78,7 @@ impl<'f> Combine for Lub<'f> {
     fn fn_styles(&self, a: FnStyle, b: FnStyle) -> cres<FnStyle> {
         match (a, b) {
           (UnsafeFn, _) | (_, UnsafeFn) => Ok(UnsafeFn),
-          (NormalFn, _) | (_, NormalFn) => Ok(NormalFn),
+          (NormalFn, NormalFn) => Ok(NormalFn),
-          (ExternFn, ExternFn) => Ok(ExternFn),
         }
     }
 

src/librustdoc/clean.rs

@@ -1200,7 +1200,7 @@ impl Clean<Item> for ast::ForeignItem {
                 ForeignFunctionItem(Function {
                     decl: decl.clean(),
                     generics: generics.clean(),
-                    fn_style: ast::ExternFn,
+                    fn_style: ast::NormalFn,
                 })
             }
             ast::ForeignItemStatic(ref ty, mutbl) => {

src/librustdoc/html/format.rs

@@ -397,10 +397,10 @@ impl fmt::Show for clean::Type {
             clean::BareFunction(ref decl) => {
                 write!(f.buf, "{}{}fn{}{}",
                        FnStyleSpace(decl.fn_style),
-                       match decl.abi {
+                       match decl.abi.as_slice() {
-                           ref x if "" == *x => "".to_owned(),
+                           "" => " extern ".to_owned(),
-                           ref x if "\"Rust\"" == *x => "".to_owned(),
+                           "\"Rust\"" => "".to_owned(),
-                           ref s => " " + *s + " ",
+                           s => format!(" extern {} ", s)
                        },
                        decl.generics,
                        decl.decl)
@@ -517,7 +517,6 @@ impl fmt::Show for FnStyleSpace {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         match self.get() {
             ast::UnsafeFn => write!(f.buf, "unsafe "),
-            ast::ExternFn => write!(f.buf, "extern "),
             ast::NormalFn => Ok(())
         }
     }

src/libsyntax/ast.rs

@@ -876,7 +876,6 @@ pub struct FnDecl {
 pub enum FnStyle {
     UnsafeFn, // declared with "unsafe fn"
     NormalFn, // declared with "fn"
-    ExternFn, // declared with "extern fn"
 }
 
 impl fmt::Show for FnStyle {
@@ -884,7 +883,6 @@ impl fmt::Show for FnStyle {
         match *self {
             NormalFn => "normal".fmt(f),
             UnsafeFn => "unsafe".fmt(f),
-            ExternFn => "extern".fmt(f),
         }
     }
 }

src/libsyntax/parse/parser.rs

@@ -27,7 +27,7 @@ use ast::{ExprLit, ExprLoop, ExprMac};
 use ast::{ExprMethodCall, ExprParen, ExprPath, ExprProc};
 use ast::{ExprRepeat, ExprRet, ExprStruct, ExprTup, ExprUnary};
 use ast::{ExprVec, ExprVstore, ExprVstoreSlice};
-use ast::{ExprVstoreMutSlice, ExprWhile, ExprForLoop, ExternFn, Field, FnDecl};
+use ast::{ExprVstoreMutSlice, ExprWhile, ExprForLoop, Field, FnDecl};
 use ast::{ExprVstoreUniq, Once, Many};
 use ast::{ForeignItem, ForeignItemStatic, ForeignItemFn, ForeignMod};
 use ast::{Ident, NormalFn, Inherited, Item, Item_, ItemStatic};
@@ -881,25 +881,29 @@ impl<'a> Parser<'a> {
     pub fn parse_ty_bare_fn(&mut self) -> Ty_ {
         /*
 
-        [extern "ABI"] [unsafe] fn <'lt> (S) -> T
+        [unsafe] [extern "ABI"] fn <'lt> (S) -> T
-                ^~~~^  ^~~~~~~^    ^~~~^ ^~^    ^
+         ^~~~^           ^~~~^     ^~~~^ ^~^    ^
-                  |      |           |    |     |
+           |               |         |    |     |
-                  |      |           |    |   Return type
+           |               |         |    |   Return type
-                  |      |           |  Argument types
+           |               |         |  Argument types
-                  |      |       Lifetimes
+           |               |     Lifetimes
-                  |      |
+           |              ABI
-                  |    Function Style
+        Function Style
-                 ABI
-
         */
 
+        let fn_style = self.parse_unsafety();
         let abi = if self.eat_keyword(keywords::Extern) {
             self.parse_opt_abi().unwrap_or(abi::C)
         } else {
             abi::Rust
         };
 
-        let fn_style = self.parse_unsafety();
+        // NOTE: remove after a stage0 snapshot
+        let fn_style = match self.parse_unsafety() {
+            UnsafeFn => UnsafeFn,
+            NormalFn => fn_style,
+        };
+
         self.expect_keyword(keywords::Fn);
         let (decl, lifetimes) = self.parse_ty_fn_decl(true);
         return TyBareFn(@BareFnTy {
@@ -1245,6 +1249,7 @@ impl<'a> Parser<'a> {
             self.expect_and();
             self.parse_borrowed_pointee()
         } else if self.is_keyword(keywords::Extern) ||
+                  self.is_keyword(keywords::Unsafe) ||
                 self.token_is_bare_fn_keyword() {
             // BARE FUNCTION
             self.parse_ty_bare_fn()
@@ -4551,7 +4556,7 @@ impl<'a> Parser<'a> {
                 // EXTERN FUNCTION ITEM
                 let abi = opt_abi.unwrap_or(abi::C);
                 let (ident, item_, extra_attrs) =
-                    self.parse_item_fn(ExternFn, abi);
+                    self.parse_item_fn(NormalFn, abi);
                 let item = self.mk_item(lo,
                                         self.last_span.hi,
                                         ident,
@@ -4605,9 +4610,14 @@ impl<'a> Parser<'a> {
             && self.look_ahead(1u, |t| *t != token::LBRACE) {
             // UNSAFE FUNCTION ITEM
             self.bump();
+            let abi = if self.eat_keyword(keywords::Extern) {
+                self.parse_opt_abi().unwrap_or(abi::C)
+            } else {
+                abi::Rust
+            };
             self.expect_keyword(keywords::Fn);
             let (ident, item_, extra_attrs) =
-                self.parse_item_fn(UnsafeFn, abi::Rust);
+                self.parse_item_fn(UnsafeFn, abi);
             let item = self.mk_item(lo,
                                     self.last_span.hi,
                                     ident,

src/libsyntax/print/pprust.rs

@@ -2372,16 +2372,10 @@ impl<'a> State<'a> {
                                 abi: abi::Abi,
                                 vis: ast::Visibility) -> IoResult<()> {
         try!(word(&mut self.s, visibility_qualified(vis, "")));
-
+        try!(self.print_opt_fn_style(opt_fn_style));
         if abi != abi::Rust {
             try!(self.word_nbsp("extern"));
             try!(self.word_nbsp(abi.to_str()));
-
-            if opt_fn_style != Some(ast::ExternFn) {
-                try!(self.print_opt_fn_style(opt_fn_style));
-            }
-        } else {
-            try!(self.print_opt_fn_style(opt_fn_style));
         }
 
         word(&mut self.s, "fn")
@@ -2391,7 +2385,6 @@ impl<'a> State<'a> {
         match s {
             ast::NormalFn => Ok(()),
             ast::UnsafeFn => self.word_nbsp("unsafe"),
-            ast::ExternFn => self.word_nbsp("extern")
         }
     }
 

src/test/run-pass/issue-10025.rs

@@ -0,0 +1,17 @@
+// Copyright 2014 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.
+
+unsafe extern fn foo() {}
+unsafe extern "C" fn bar() {}
+
+fn main() {
+    let _a: unsafe extern fn() = foo;
+    let _a: unsafe extern "C" fn() = foo;
+}