Update to new bootstrap compiler

src/doc/unstable-book/src/library-features/try-trait.md

@@ -1,50 +0,0 @@
-# `try_trait`
-
-The tracking issue for this feature is: [#42327]
-
-[#42327]: https://github.com/rust-lang/rust/issues/42327
-
-------------------------
-
-This introduces a new trait `Try` for extending the `?` operator to types
-other than `Result` (a part of [RFC 1859]).  The trait provides the canonical
-way to _view_ a type in terms of a success/failure dichotomy.  This will
-allow `?` to supplant the `try_opt!` macro on `Option` and the `try_ready!`
-macro on `Poll`, among other things.
-
-[RFC 1859]: https://github.com/rust-lang/rfcs/pull/1859
-
-Here's an example implementation of the trait:
-
-```rust,ignore (cannot-reimpl-Try)
-/// A distinct type to represent the `None` value of an `Option`.
-///
-/// This enables using the `?` operator on `Option`; it's rarely useful alone.
-#[derive(Debug)]
-#[unstable(feature = "try_trait", issue = "42327")]
-pub struct None { _priv: () }
-
-#[unstable(feature = "try_trait", issue = "42327")]
-impl<T> ops::Try for Option<T>  {
-    type Ok = T;
-    type Error = None;
-
-    fn into_result(self) -> Result<T, None> {
-        self.ok_or(None { _priv: () })
-    }
-
-    fn from_ok(v: T) -> Self {
-        Some(v)
-    }
-
-    fn from_error(_: None) -> Self {
-        None
-    }
-}
-```
-
-Note the `Error` associated type here is a new marker.  The `?` operator
-allows interconversion between different `Try` implementers only when
-the error type can be converted `Into` the error type of the enclosing
-function (or catch block).  Having a distinct error type (as opposed to
-just `()`, or similar) restricts this to where it's semantically meaningful.