feat: add rustfmt imports_granularity

[qiweiii]

What was wrong?

resolve #1046

How was it fixed?

• add rustfmt.toml
• run cargo +nightly fmt --all
• update ci to use nightly toolchain

[qiweiii]

the lint ci failed, not very familiar with circleci, please help😁

[ogenev]

The new rustlang/rust:nightly-slim image seems to break the CircleCI lint job because the sudo command is not included.

I'm not sure what the slim version contains compared to the regular nightly but I guess we can get away with the regular image.

[ogenev]

We need also to update the fmt command in book/src/developers/contributing/git/pull_requests.md.

[ogenev]

The lint is still failing, it looks like we don't need the sudo command for the nightly image lint used inside the install-depends step. But this step is also used in other jobs.

Creating an install-depends-nighly step without sudo and adding this step for the lint (instead of the default install-depends) is a reasonable solution.

[qiweiii]

Nice, lint works now, I also added a rust-toolchain file so developers don't need to manually switch toolchain

[ogenev]

Nice, lint works now, I also added a rust-toolchain file so developers don't need to manually switch toolchain

Great but we don't want to pin Trin to the latest nightly version (at least we need to have a discussion about that with the rest of the team).

The current workflow is to use nightly only for fmt, so let's remove the rust-toolchain file for now. In the future, if we decide, we can pin Trin to a nightly specific version (for example nightly-2023-01-04) and this will not require to manually set nighly fmt with +nighlty.

[ogenev]

By the way, while we are still here, could you also add those configs to the rustfmt.toml file:

comment_width = 100
wrap_comments = true
format_code_in_doc_comments = true
doc_comment_code_block_width = 100

[ogenev]

Looking at this now, I assume here clippy is running with the nightly version, but because we don't pin Trin to nightly there may be some discrepancies between nightly clippy and stable clippy in the future.

It would be better if we split the lint job to cargo-fmt and cargo-clippy and run clippy with the default stable toolchain.

If you don't feel like doing it in this PR, we can leave it for a future fix (this will not be a blocker for merging this PR).

[qiweiii]

I could try it in this PR, seems like a simple change

[qiweiii]

all done!

[ogenev]

Looks good to me 💯 !. Thank you for this contribution, really happy to see some structure to our imports. ❤️