Merge ref 'f605b57042ff' from rust-lang/rust

Pull recent changes from https://github.com/rust-lang/rust via Josh.

Upstream ref: f605b57042ffeb320d7ae44490113a827139b766
Filtered ref: c69d2743ed4676c4529ebb60b258f6c1273c9145

This merge was created using https://github.com/rust-lang/josh-sync.

1 files changed, 9 insertions, 0 deletions

diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index f111fcb4a47..ab417b6c72f 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -330,6 +330,7 @@
 #![feature(bstr)]
 #![feature(bstr_internals)]
 #![feature(cast_maybe_uninit)]
+#![feature(cfg_select)]
 #![feature(char_internals)]
 #![feature(clone_to_uninit)]
 #![feature(const_cmp)]
@@ -737,6 +738,14 @@ pub use core::{
     unreachable, write, writeln,
 };
 
+// Re-export unstable derive macro defined through core.
+#[unstable(feature = "derive_from", issue = "144889")]
+/// Unstable module containing the unstable `From` derive macro.
+pub mod from {
+    #[unstable(feature = "derive_from", issue = "144889")]
+    pub use core::from::From;
+}
+
 // Include a number of private modules that exist solely to provide
 // the rustdoc documentation for primitive types. Using `include!`
 // because rustdoc only looks for these modules at the crate level.