Add support for edition 2021.

[m-ou-se]

This adds initial support for Rust 2021, by making it behave the same as Rust 2018. It simply changes == Edition2018 to >= Edition2018. (And adds a PartialOrd implementation to Edition to make that possible.)

[calebcartwright]

Thanks for this, we've triggered an early publish of the rustc-ap* crates so v697 is now available, and we should be able to proceed a bit earlier than Tue

[m-ou-se]

Updated.

This now fails on a change in how rustfmt formats macro arguments:

-macro foo($type_name: ident, $docs: expr) {
+macro foo($type_name:ident, $docs:expr) {

Trying to find out which rustc change caused this.

Edit: This changed between rustc-ap 693 and 694.

Edit 2: git bisect points at rust-lang/rust@31d72c2 of rust-lang/rust#78837.

[m-ou-se]

Looks like this is a bug that is now fixed by that change.

Before that change, format_snippet inside MacroBranch::rewrite would return None for that test case. After that change, it returns Some(..) with the newly formatted macro definition with the two spaces removed.

[m-ou-se]

Ah, the problem was that rustfmt skipped formatting of the entire macro definition because of #[doc=$docs] inside the body, which was solved by that change in rustc_parse. See rust-lang/rust#78837 (comment)

I'll update the expected test output, as this seems simply a bug that is now fixed.

[calebcartwright]

Changes LGTM, thank you! Would you mind adding a test that has the Edition set to 2021?

Something as simple as adding a single file (perhaps tests/target/imports_2021_edition.rs) with a snippet like the one below would suffice

// rustfmt-edition: 2021

use ::foo::Bar;

[m-ou-se]

Done!

[calebcartwright]

😆 love it

[karyon]

Backported in #4623