initial draft of 'testing rust 2018'

Author: steveklabnik

_posts/2018-10-29-help-test-rust-2018.md

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+---
+title: "Help test Rust 2018"
+---
+
+Back in July, we talked about ["Rust 2018"]. In short, we're adding a new
+concept to Rust, "Editions." Editions are a way of showing larger progress
+than our six-week release cycle, and will happen on a roughly three-year
+cycle. Rust 1.0 was "Rust 2015," and Rust 1.31 will be "Rust 2018."
+
+We've been [testing Rust 2018 for a while already], and things are looking
+pretty good! We have just under six weeks until Rust 1.31 ships, and so
+we'd appreciate it if you could give the beta a try.
+
+There's two ways to try out Rust 2018: updating an existing project, and
+starting a new one. For full details, please check out the [Edition Guide],
+but the rest of this post is a quickstart to make it even easier. In
+addition, we have some new lints we'd like you to try; they're described at
+the very end of the post.
+
+If anything goes wrong, or is confusing, please [file an issue] and let us
+know. We want to make sure this is an extra-awesome release! Thank you for
+helping us make Rust even better. <3
+
+["Rust 2018"]: https://blog.rust-lang.org/2018/07/27/what-is-rust-2018.html
+[testing Rust 2018 for a while already]: https://internals.rust-lang.org/t/rust-2018-release-schedule-and-extended-beta/8076
+[Edition Guide]: https://rust-lang-nursery.github.io/edition-guide/
+[file an issue]: https://github.com/rust-lang/rust/issues/new
+
+## Setup: install Rust beta
+
+First things first, you'll need to install the beta release channel of Rust.
+With Rustup, it's as easy as:
+
+```console
+$ rustup install beta
+```
+
+To use this channel of Rust instead of your default, you can append a `+beta`
+to any `rustc` or cargo commands:
+
+```console
+$ rustc +beta --version
+$ cargo +beta build
+```
+
+This lets you stick to stable as the default, while using beta for your
+experiments.
+
+## Start a new project
+
+To start a new project with Rust 2018:
+
+```console
+$ cargo +beta new my-sample-project
+```
+
+Nothing changes! Well, something changed. Check out `Cargo.toml`:
+
+```toml
+[package]
+name = "my-sample-project"
+version = "0.1.0"
+authors = ["Your Name <[email protected]>"]
+edition = "2018"
+
+[dependencies]
+```
+
+That new `edition = "2018"` key/value pair means you're working with Rust 2018.
+If it doesn't exist, it's the same as `edition = "2015"`, so all
+existing projects keep working.
+
+## Convert an existing project
+
+You can also convert an existing project to Rust 2018. Remember, none of your
+dependencies need to be updated for this to work; Rust 2018 and 2015
+interoperate seamlessly!
+
+The first step is to run `cargo fix`:
+
+```console
+$ cargo fix --edition
+```
+
+This will check your code, and automatically fix any issues that it can.
+`cargo fix` is still pretty new, and so it can't always fix your code
+automatically. If `cargo fix` can't fix something, it will print the warning
+that it cannot fix to the console. If you see one of these warnings, you'll
+have to update your code manually. See the corresponding section of the
+edition guide for help, and if you have problems, please seek help at the
+user's forums.
+
+Keep running `cargo fix --edition` until you have no more warnings.
+
+Congrats! Your code is now valid in both Rust 2015 and Rust 2018!
+
+Once this is done, you can commit to Rust 2018 by updating
+your `Cargo.toml`:
+
+```toml
+[package]
+name = "my-sample-project"
+version = "0.1.0"
+authors = ["Your Name <[email protected]>"]
+edition = "2018"
+
+[dependencies]
+```
+
+See that `edition = "2018"`? That's what opts you in to the new features.
+Set it, `cargo +beta build`, and you should be good to go!
+
+## Writing idiomatic code
+
+We have some new lints that suggest using certain idioms in your Rust 2018
+code. We don't have them turned on by default yet. To see what your code would
+look like, you can use `cargo fix`:
+
+```console
+$ cargo +beta fix --edition-idioms
+```
+
+If things look great, or things look terrible, please let us know! We hope to make
+these lints warn by default after gaining some experience with them and working
+out the bugs.
+
+> The `--edition-idioms` flag applies only to the "current crate"; if you want
+> to run it against a workspace is necessary to use a workaround with `RUSTFLAGS`
+> in order to execute it in all the workspace members.
+> 
+>     $ RUSTFLAGS='-Wrust_2018_idioms' cargo fix --all