A new lint for imports ending in `::{self};`

What it does

It detects imports that end in ::{self}; and emits a warning for them.

Categories (optional)

• Kind: Perhaps clippy::style.

The advantage of the recommended code over the original code is that it's shorter and simpler.

Drawbacks

None.

Example

use std::io::{self};

Could be written as:

use std::io;

[camsteffen]

I think this is a rustfmt bug. rustfmt does the following:

• use std::io::{Write}; -> use std::io::Write;
• use std::io::self; -> use std::io;
• use std::io::{self}; -> use std::io::{self}; 😲😲😲

[camsteffen]

I take it back. See rust-lang/rustfmt#3568. For this lint, clippy would need to check if changing the import will break it.

[ebobrow]

This looks interesting! I'd like to give it a try.

@rustbot claim

[ebobrow]

I'm just about done with this, but I've run into an issue. As far as I can tell, there's no way to see what items are exported from an external crate, meaning that I can't check if removing ::{self} from an import would bring in anything else with the same name. I could skip that check for imports from external crates and risk false positives or negatives. Or, am I wrong and there is a way to check?

[camsteffen]

For use a::b::{self}, I think you should be able to do tcx.item_children(b_def_id).

[ebobrow]

Thank you! That works for external crates, but checking a local mod gives:

error: internal compiler error: compiler/rustc_middle/src/ty/query/mod.rs:282:1: `tcx.item_children(DefId(0:3 ~ unnecessary_self_imports[317d]::a))` unsupported by its crate; perhaps the `item_children` query was never assigned a provider function

thread 'rustc' panicked at 'Box<Any>', /rustc/07e0e2ec268c140e607e1ac7f49f145612d0f597/library/std/src/panic.rs:59:5
note: run with `RUST_BACKTRACE=1` environment variable to display a backtrace

Do you know what that is? If it isn't fixable I can use tcx.hir().get_if_local() for local mods, but I would prefer to have the same check for all imports, if possible.

[camsteffen]

Hmm, looks like item_children is an "extern" query (codez).

I can use tcx.hir().get_if_local() for local mods

Seems like a good solution.

[ebobrow]

Thanks for your help!