Implement RFC #1245 : unsafe const fn

src/libsyntax/parse/parser.rs

@@ -4380,11 +4380,11 @@ impl<'a> Parser<'a> {
     /// - `extern fn`
     /// - etc
     pub fn parse_fn_front_matter(&mut self) -> PResult<(ast::Constness, ast::Unsafety, abi::Abi)> {
+        let unsafety = try!(self.parse_unsafety());
         let is_const_fn = try!(self.eat_keyword(keywords::Const));
         let (constness, unsafety, abi) = if is_const_fn {
-            (Constness::Const, Unsafety::Normal, abi::Rust)
+            (Constness::Const, unsafety, abi::Rust)
         } else {
-            let unsafety = try!(self.parse_unsafety());
             let abi = if try!(self.eat_keyword(keywords::Extern)) {
                 try!(self.parse_opt_abi()).unwrap_or(abi::C)
             } else {
@@ -5399,9 +5399,14 @@ impl<'a> Parser<'a> {
             } else {
                 abi::Rust
             };
+            let constness = if abi == abi::Rust && try!(self.eat_keyword(keywords::Const) ){
+                Constness::Const
+            } else {
+                Constness::NotConst
+            };
             try!(self.expect_keyword(keywords::Fn));
             let (ident, item_, extra_attrs) =
-                try!(self.parse_item_fn(Unsafety::Unsafe, Constness::NotConst, abi));
+                try!(self.parse_item_fn(Unsafety::Unsafe, constness, abi));
             let last_span = self.last_span;
             let item = self.mk_item(lo,
                                     last_span.hi,

src/test/compile-fail/unsafe-const-fn.rs

@@ -0,0 +1,24 @@
+// 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.
+
+// A quick test of 'unsafe const fn' functionality
+
+#![feature(const_fn)]
+
+unsafe const fn dummy(v: u32) -> u32 {
+    !v
+}
+
+const VAL: u32 = dummy(0xFFFF); //~ ERROR E0133
+
+fn main() {
+    assert_eq!(VAL, 0xFFFF0000);
+}
+

src/test/run-pass/unsafe-const-fn.rs

@@ -0,0 +1,31 @@
+// 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.
+
+// A quick test of 'unsafe const fn' functionality
+
+#![feature(const_fn)]
+
+unsafe const fn dummy(v: u32) -> u32 {
+    !v
+}
+
+struct Type;
+impl Type {
+    unsafe const fn new() -> Type {
+        Type
+    }
+}
+
+const VAL: u32 = unsafe { dummy(0xFFFF) };
+const TYPE_INST: Type = unsafe { Type::new() };
+
+fn main() {
+    assert_eq!(VAL, 0xFFFF0000);
+}