Add imports_granularity="Item".

[msmorgan]

This option splits all imports into their own use statement.

[calebcartwright]

Thank you for the PR!

A few important things:

• These changes are causing legitimate test failures, so please take a look at those
• The names of the variants for the new option have largely been finalize after extensive discussion, and the variant name for this style needs to be Item, not Flatten
• Please include thorough tests for this new variant. At a minimum this should include the pre/post formatting files with a variety of imports to be used for the system and idempotence tests (https://github.com/rust-lang/rustfmt/blob/master/Contributing.md#creating-test-cases), but it would be helpful to include the unit level tests as well along the lines of what exists for the other variants (https://github.com/rust-lang/rustfmt/blob/master/src/formatting/imports.rs#L1015)

[msmorgan]

Done! Let me know what you think.

I also filed #4641 after noticing some strange inconsistencies with use statements ending in self or {self}. It depends on this PR.

[jstarks]

Should this transformation be part of merge_use_trees?

[jstarks]

(Although this transformation should be skipped altogether, IIUC)

[msmorgan]

I moved the logic to merge_use_trees, and changed it to rewrite paths ending in ::self into ::{self}. This also allowed me to remove some logic from the start of UseTree::flatten, which did the same thing but only for one-element lists.

Perhaps this should be part of UseTree::normalize, and that should be called again post-merge? Also, I noticed it seems to remove final ::self:

rustfmt/src/formatting/imports.rs

Line 430 in a97fd77

// Remove foo::{} or self without attributes.

[calebcartwright]

Thanks for the updates! Looking good overall, though left some inline feedback to see if there's an opportunity to shuffle the logic around a bit

[msmorgan]

@calebcartwright

Something like this?

The logic to make self into {self} is duplicated in UseTree::flatten and flatten_use_trees now though.

[calebcartwright]

Something like this?

Excellent! I think this is a better approach 👍

The logic to make self into {self} is duplicated in UseTree::flatten and flatten_use_trees now though

Yeah, though I'm happy to accept that tradeoff all things considered. It's a tiny piece of code and the implementation for Item reads more clearly now IMO.

[calebcartwright]

Do you want to squash up the commits a bit? Otherwise I can just squash on merging

[msmorgan]

Squashed and rebased onto master. Ready to go!

[calebcartwright]

Squashed and rebased onto master. Ready to go!

Fantastic, and thanks again for this! A lot of folks seemed quite keen on having this style available so I anticipate there will be many ready to utilize this addition!

[karyon]

Backported in #4674