Update rustfmt

[alshdavid]

This PR adds

imports_granularity = "Item"
group_imports = "StdExternalCrate"

to the Rustfmt.

https://rust-lang.github.io/rustfmt/?version=v1.7.0&search=imports_granularity#imports_granularity
https://rust-lang.github.io/rustfmt/?version=v1.7.0&search=#group_imports

This will change Rust imports so that they are split into individual line items that are grouped (in order) as std, extern and crate

example:

use swc_core::ecma::ast::{Atom, Span};
crate::{Baz, Buzz};
use std::foo::{Foo, Bar};

becomes

use std::foo::Bar;
use std::foo::Foo;

use swc_core::ecma::ast::Atom;
use swc_core::ecma::ast::Span;

use crate::Baz;
use crate::Buzz;

The import groupings rule enforces the import grouping convention used by the Rust community whist the import granularity rule makes it easier to read/tidy-up Rust imports and makes it easier to see changes in PRs

Most of the code changes are the formatting rules being applied.

Notable changes in the PR are:

• package.json
• rustfmt.toml

An example case where the applied rule improves readability

[yamadapc]

I don't think we should change default formatting settings.

Most rust code that exists will use the default settings. This is great because it means a lot of rust code has consistent style.

For example, the following projects do not change these settings

• rust standard library https://github.com/rust-lang/rust/blob/master/rustfmt.toml
• linux https://github.com/torvalds/linux/blob/e67572cd2204894179d89bd7b984072f19313b03/rust/alloc/boxed.rs
• tokio asynchronous runtime https://github.com/tokio-rs/tokio/

[alshdavid]

This is great because it means a lot of rust code has consistent style.

I agree in general however in this case - with the import style - we have inconsistent usage throughout the codebase.

I believe that the addition of these style rules will improve code consistency within our codebase in a way that remains congruent with the styling and conventions used broadly by the Rust community.

[mischnic]

Apart from causing loads of merge conflicts, this is also not being enforced with the current setup

Warning: can't set `imports_granularity = Item`, unstable features are only available in nightly channel.
Warning: can't set `group_imports = StdExternalCrate`, unstable features are only available in nightly channel.

because we have it set to stable

parcel/rust-toolchain

Line 1 in 3ff10bc

stable