Stabilise ?

cc [`?` tracking issue](#31436)

Author: nrc

src/libcore/lib.rs

@@ -89,7 +89,7 @@
 #![feature(specialization)]
 #![feature(staged_api)]
 #![feature(unboxed_closures)]
-#![feature(question_mark)]
+#![cfg_attr(stage0, feature(question_mark))]
 #![feature(never_type)]
 #![feature(prelude_import)]
 

src/libcore/macros.rs

@@ -255,6 +255,9 @@ macro_rules! debug_assert_ne {
 /// Helper macro for reducing boilerplate code for matching `Result` together
 /// with converting downstream errors.
 ///
+/// Prefer using `?` syntax to `try!`. `?` is built in to the language and is
+/// more succinct than `try!`, it is the standard method for error propogation.
+///
 /// `try!` matches the given `Result`. In case of the `Ok` variant, the
 /// expression has the value of the wrapped value.
 ///

src/libgraphviz/lib.rs

@@ -295,7 +295,7 @@
 #![cfg_attr(not(stage0), deny(warnings))]
 
 #![feature(str_escape)]
-#![feature(question_mark)]
+#![cfg_attr(stage0, feature(question_mark))]
 
 use self::LabelText::*;
 

src/librustc/diagnostics.rs

@@ -1327,30 +1327,6 @@ let x: i32 = "I am not a number!";
 //      |
 //    type `i32` assigned to variable `x`
 ```
-
-Another situation in which this occurs is when you attempt to use the `try!`
-macro inside a function that does not return a `Result<T, E>`:
-
-```compile_fail,E0308
-use std::fs::File;
-
-fn main() {
-    let mut f = try!(File::create("foo.txt"));
-}
-```
-
-This code gives an error like this:
-
-```text
-<std macros>:5:8: 6:42 error: mismatched types:
- expected `()`,
-     found `core::result::Result<_, _>`
- (expected (),
-     found enum `core::result::Result`) [E0308]
-```
-
-`try!` returns a `Result<T, E>`, and so the function must. But `main()` has
-`()` as its return type, hence the error.
 "##,
 
 E0309: r##"

src/librustc/lib.rs

@@ -40,7 +40,7 @@
 #![feature(rustc_private)]
 #![feature(slice_patterns)]
 #![feature(staged_api)]
-#![feature(question_mark)]
+#![cfg_attr(stage0, feature(question_mark))]
 #![cfg_attr(test, feature(test))]
 
 extern crate arena;

src/librustc_back/lib.rs

@@ -37,7 +37,7 @@
 #![feature(rustc_private)]
 #![feature(staged_api)]
 #![feature(step_by)]
-#![feature(question_mark)]
+#![cfg_attr(stage0, feature(question_mark))]
 #![cfg_attr(test, feature(test, rand))]
 
 extern crate syntax;

src/librustc_borrowck/lib.rs

@@ -26,7 +26,7 @@
 #![feature(staged_api)]
 #![feature(associated_consts)]
 #![feature(nonzero)]
-#![feature(question_mark)]
+#![cfg_attr(stage0, feature(question_mark))]
 #[macro_use] extern crate log;
 #[macro_use] extern crate syntax;
 extern crate syntax_pos;

src/librustc_const_eval/lib.rs

@@ -27,7 +27,7 @@
 #![feature(staged_api)]
 #![feature(rustc_diagnostic_macros)]
 #![feature(slice_patterns)]
-#![feature(question_mark)]
+#![cfg_attr(stage0, feature(question_mark))]
 #![feature(box_patterns)]
 #![feature(box_syntax)]
 

src/librustc_const_math/lib.rs

@@ -25,7 +25,7 @@
 
 #![feature(rustc_private)]
 #![feature(staged_api)]
-#![feature(question_mark)]
+#![cfg_attr(stage0, feature(question_mark))]
 
 #[macro_use] extern crate log;
 #[macro_use] extern crate syntax;

src/librustc_driver/lib.rs

@@ -31,7 +31,7 @@
 #![feature(rustc_private)]
 #![feature(set_stdio)]
 #![feature(staged_api)]
-#![feature(question_mark)]
+#![cfg_attr(stage0, feature(question_mark))]
 
 extern crate arena;
 extern crate flate;