Auto merge of #46479 - bkchr:termination_trait, r=arielb1

Implements RFC 1937: `?` in `main`

This is the first part of the RFC 1937 that supports new
`Termination` trait in the rust `main` function.

Thanks @nikomatsakis, @arielb1 and all other people in the gitter channel for all your help!

The support for doctest and `#[test]` is still missing, bu as @nikomatsakis said, smaller pull requests are better :)

1 files changed, 6 insertions, 0 deletions

diff --git a/src/libstd/lib.rs b/src/libstd/lib.rs
index 12e6231136e..171c108e3aa 100644
--- a/src/libstd/lib.rs
+++ b/src/libstd/lib.rs
@@ -308,6 +308,7 @@
 #![feature(str_char)]
 #![feature(str_internals)]
 #![feature(str_utf16)]
+#![feature(termination_trait)]
 #![feature(test, rustc_private)]
 #![feature(thread_local)]
 #![feature(toowned_clone_into)]
@@ -499,6 +500,11 @@ mod memchr;
 // The runtime entry point and a few unstable public functions used by the
 // compiler
 pub mod rt;
+// The trait to support returning arbitrary types in the main function
+mod termination;
+
+#[unstable(feature = "termination_trait", issue = "43301")]
+pub use self::termination::Termination;
 
 // Include a number of private modules that exist solely to provide
 // the rustdoc documentation for primitive types. Using `include!`