Make various fixes:

- add feature gate
- add basic tests
- adjust parser to eliminate conflict between `const fn` and associated
constants
- allow `const fn` in traits/trait-impls, but forbid later in type check
- correct some merge conflicts

src/test/compile-fail/check-static-values-constraints.rs

@@ -117,7 +117,7 @@ static mut STATIC14: SafeStruct = SafeStruct {
 //~^ ERROR mutable statics are not allowed to have destructors
     field1: SafeEnum::Variant1,
     field2: SafeEnum::Variant4("str".to_string())
-//~^ ERROR static contains unimplemented expression type
+//~^ ERROR method calls in statics are limited to constant inherent methods
 };
 
 static STATIC15: &'static [Box<MyOwned>] = &[

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

@@ -0,0 +1,26 @@
+// 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.
+
+// Test that we can't declare a const fn in an impl -- right now it's
+// just not allowed at all, though eventually it'd make sense to allow
+// it if the trait fn is const (but right now no trait fns can be
+// const).
+
+#![feature(const_fn)]
+
+trait Foo {
+    fn f() -> u32;
+}
+
+impl Foo for u32 {
+    const fn f() -> u32 { 22 } //~ ERROR E0379
+}
+
+fn main() { }

src/test/compile-fail/const-fn-not-in-trait.rs

@@ -0,0 +1,21 @@
+// 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.
+
+// Test that const fn is illegal in a trait declaration, whether or
+// not a default is provided.
+
+#![feature(const_fn)]
+
+trait Foo {
+    const fn f() -> u32; //~ ERROR trait fns cannot be declared const
+    const fn g() -> u32 { 0 } //~ ERROR trait fns cannot be declared const
+}
+
+fn main() { }

src/test/compile-fail/const-fn-not-safe-for-const.rs

@@ -0,0 +1,47 @@
+// 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.
+
+// Test that we can't call random fns in a const fn or do other bad things.
+
+#![feature(const_fn)]
+
+use std::mem::transmute;
+
+fn random() -> u32 { 0 }
+
+const fn sub(x: &u32) -> usize {
+    unsafe { transmute(x) } //~ ERROR E0015
+}
+
+const fn sub1() -> u32 {
+    random() //~ ERROR E0015
+}
+
+static Y: u32 = 0;
+
+const fn get_Y() -> u32 {
+    Y
+        //~^ ERROR E0013
+        //~| ERROR cannot refer to other statics by value
+}
+
+const fn get_Y_addr() -> &'static u32 {
+    &Y
+        //~^ ERROR E0013
+}
+
+const fn get() -> u32 {
+    let x = 22; //~ ERROR E0016
+    let y = 44; //~ ERROR E0016
+    x + y
+}
+
+fn main() {
+}

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

@@ -0,0 +1,28 @@
+// 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.
+
+// Test use of const fn without feature gate.
+
+const fn foo() -> usize { 0 } //~ ERROR const fn is unstable
+
+trait Foo {
+    const fn foo() -> u32; //~ ERROR const fn is unstable
+    const fn bar() -> u32 { 0 } //~ ERROR const fn is unstable
+}
+
+impl Foo {
+    const fn baz() -> u32 { 0 } //~ ERROR const fn is unstable
+}
+
+impl Foo for u32 {
+    const fn foo() -> u32 { 0 } //~ ERROR const fn is unstable
+}
+
+fn main() { }

src/test/compile-fail/issue-16538.rs

@@ -20,6 +20,6 @@ mod Y {
 
 static foo: *const Y::X = Y::foo(Y::x as *const Y::X);
 //~^ ERROR the trait `core::marker::Sync` is not implemented for the type
-//~| ERROR function calls in statics are limited to struct and enum constructors
+//~| ERROR E0015
 
 fn main() {}

src/test/compile-fail/issue-7364.rs

@@ -17,6 +17,6 @@ static boxed: Box<RefCell<isize>> = box RefCell::new(0);
 //~^ ERROR allocations are not allowed in statics
 //~| ERROR the trait `core::marker::Sync` is not implemented for the type
 //~| ERROR the trait `core::marker::Sync` is not implemented for the type
-//~| ERROR function calls in statics are limited to struct and enum constructors
+//~| ERROR E0015
 
 fn main() { }

src/test/compile-fail/static-vec-repeat-not-constant.rs

@@ -11,6 +11,6 @@
 fn foo() -> isize { 23 }
 
 static a: [isize; 2] = [foo(); 2];
-//~^ ERROR: function calls in statics are limited to struct and enum constructors
+//~^ ERROR: E0015
 
 fn main() {}

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

@@ -0,0 +1,23 @@
+// 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.
+
+// Test a call whose argument is the result of another call.
+
+#![feature(const_fn)]
+
+const fn sub(x: u32, y: u32) -> u32 {
+    x - y
+}
+
+const X: u32 = sub(sub(88, 44), 22);
+
+fn main() {
+    assert_eq!(X, 22);
+}

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

@@ -0,0 +1,32 @@
+// 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 very basic test of const fn functionality.
+
+#![feature(const_fn)]
+
+const fn add(x: u32, y: u32) -> u32 {
+    x + y
+}
+
+const fn sub(x: u32, y: u32) -> u32 {
+    x - y
+}
+
+const SUM: u32 = add(44, 22);
+const DIFF: u32 = sub(44, 22);
+
+fn main() {
+    assert_eq!(SUM, 66);
+    assert!(SUM != 88);
+
+    assert_eq!(DIFF, 22);
+
+}