Update for 2021 stabilization.

Author: ehuss

src/SUMMARY.md

@@ -24,7 +24,7 @@
 
 ## Rust 2021
 
-- [Rust 2021 🚧](rust-2021/index.md)
+- [Rust 2021](rust-2021/index.md)
   - [Additions to the prelude](rust-2021/prelude.md)
   - [Default Cargo feature resolver](rust-2021/default-cargo-resolver.md)
   - [IntoIterator for arrays](rust-2021/IntoIterator-for-arrays.md)

src/editions/transitioning-an-existing-project-to-a-new-edition.md

@@ -8,15 +8,6 @@ Briefly, the steps to update to the next edition are:
 2. Edit `Cargo.toml` and set the `edition` field to the next edition, for example `edition = "2021"`
 3. Run `cargo build` or `cargo test` to verify the fixes worked.
 
-<!-- remove this when 2021 is stabilized -->
-> If you are migrating from 2018 to 2021, the steps are slightly different because 2021 is not yet stabilized, and is only available on the [nightly channel].
-> The steps to follow are:
->
-> 1. Install the most recent nightly: `rustup update nightly`.
-> 2. Run `cargo +nightly fix --edition`.
-> 3. Edit `Cargo.toml` and place `cargo-features = ["edition2021"]` at the top (above `[package]`), and change the edition field to say `edition = "2021"`.
-> 4. Run `cargo +nightly check` to verify it now works in the new edition.
-
 The following sections dig into the details of these steps, and some of the issues you may encounter along the way.
 
 > It's our intention that the migration to new editions is as smooth an

src/rust-2021/index.md

@@ -1,22 +1,11 @@
 # Rust 2021
 
-🚧 The 2021 Edition has not yet been released and hence this section is still "under construction".
-You can [read more about our plans in this blog post](https://blog.rust-lang.org/2021/05/11/edition-2021.html).
-
 | Info | |
 | --- | --- |
 | RFC | [#3085](https://github.com/rust-lang/rfcs/pull/3085) |
-| Release version | 1.56.0 (anticipated) |
-
-The Rust 2021 Edition is currently slated for release in Rust 1.56.0.
-Rust 1.56.0 will then be in beta for six weeks,
-after which it is released as stable on October 21st.
-
-However, note that Rust is a project run by volunteers.
-We prioritize the personal well-being of everyone working on Rust
-over any deadlines and expectations we might have set.
-This could mean delaying the edition a version if necessary,
-or dropping a feature that turns out to be too difficult or stressful to finish in time.
+| Release version | 1.56.0 |
 
-That said, we are on schedule and many of the difficult problems are already tackled,
-thanks to all the people contributing to Rust 2021! 💛
+The Rust 2021 Edition contains several changes that bring new capabilities and more consistency to the language,
+and opens up room for expansion in the future.
+The following chapters dive into the details of each change,
+and they include guidance on migrating your existing code.