How to help test the 2018 edition
An edition brings together the features that have landed into a clear package, with fully updated documentation and tooling. By the end of the year we are planning to release the 2018 edition, our first since the Rust 1.0 release. You can currently opt-in to a preview of the 2018 edition to try it out and help test it.
In fact, we really need help testing it out! Once you’ve turned it on and seen its wonderful new features, what then? Here we’ve got some specific things we’d like you to test.
How to use the 2018 edition
- You’ll first need a nightly toolchain (compiler, etc). If you’re not using nightly, install it with
rustup install nightly
#![feature(rust_2018_preview)]to your crate (at the top of any
main.rsfiles, or any other root files)
cargo-features = ["edition"]to the top of your Cargo.toml
edition = '2018``'to the
[package]section of your Cargo.toml
How to report issues
- File an issue, adding the ‘A-rust-2018-preview’ label (if you can, and if you can’t, note in the issue that it should be labeled as such). Please search the existing issues first to avoid duplication (start with the A-rust-2018-preview and A-2018-edition-lints labels). If you find a duplicate, leave a comment explaining how this also applied to your situation.
- Tell someone in the rust-edition channel on irc, or on Discord, they might ask you to file an issue instead 🙂
What to test
Here are some suggestions for things you can do that would be extra-helpful to test. It’s also great if you can just use Rust like you normally would, but using the new language features and idioms of the 2018 edition. In either case, please report any crashes, bugs, or any rough edges.
Make sure you make a backup or commit your code before experimenting - some of these tools are at the ‘might eat your laundry’ stage.
Transition an existing crate
Use Rustfix, report any mistakes it makes, anything it can’t transition, bugs when compiling the transitioned code, anything surprising that happens. If you have a good time and things worked well, please also tell us!
To install Rustfix, use
cargo install --force cargo-fix
To use Rustfix before transitioning to the 2018 edition, you can run
cargo +nightly fix --prepare-for 2018
If you want to use it after you’ve transitioned, use
cargo +nightly fix
The latter may give you more warnings to fix up.
You don’t need
+nightly if nightly is your default toolchain. You can use
--all-targets to run Rustfix on all configurations (e.g., this includes tests).
Test the tools
Once you’ve transitioned the crate to the 2018 edition, try running rustdoc, Clippy, Rustfmt, or your favorite IDE on the crate and see if it works. Report any bugs that occur (either as issues in the Rust repo (or the specific tool’s repo if you know where to go) or on irc or Discord).
Use some new language features
Are there any bugs in the compiler or tools? Did the feature feel good? Did you hit any surprising edge cases? The new features are listed in the guide.
The module system changes include no longer requiring
extern crate statements, absolute paths always starting with a crate name or
crate for the current crate, using
crate instead of
pub(crate), and permitting
foo/ subdirectories to coexist. We’re interested in how these changes make the module system feel as a whole, especially once you’ve adjusted to the new mental model.
In-band lifetimes allow the programmer to write lifetimes in function signatures without declaring them, e.g.,
fn two_args(foo: &Foo, bar: &'b Bar) -> &'b Baz instead of
fn two_args<'b>(foo: &Foo, bar: &'b Bar) -> &'b
Some resources if you’re looking for more information about the 2018 edition:
Thanks to centril, marksimulacrum, and steveklabnik for feedback on this post.