Const-stabilize String::new.

Author: Centril

src/liballoc/string.rs

@@ -369,7 +369,7 @@ impl String {
     /// ```
     #[inline]
     #[stable(feature = "rust1", since = "1.0.0")]
-    #[rustc_const_unstable(feature = "const_string_new")]
+    #[cfg_attr(bootstrap, rustc_const_unstable(feature = "const_string_new"))]
     pub const fn new() -> String {
         String { vec: Vec::new() }
     }

src/test/ui/collections-const-new.rs

@@ -1,11 +1,9 @@
-// run-pass
+// check-pass
 
 // Test several functions can be used for constants
 // 1. Vec::new()
 // 2. String::new()
 
-#![feature(const_string_new)]
-
 const MY_VEC: Vec<usize> = Vec::new();
 
 const MY_STRING: String = String::new();