Suggest removing `self` import when not in a list

[varkor]

use std::self; // error[E0429]: `self` imports are only allowed within a { } list

we should offer the suggestion to remove ::self, as this is likely what the user intended.

This issue has been assigned to @mibac138 via this comment.

[Centril]

@petrochenkov Would it simplify or complicate things if we simply allowed this instead of rejecting it?

[petrochenkov]

~Simplify.

[Centril]

Might be worth doing that in that case.

(Although use foo::bar::self; is less clean from a readability perspective but perhaps that should merely be a lint.)

[petrochenkov]

It needs some amount design work though (not large).

The idea is to treat self and super in Rust paths as . and .. in filesystem paths.
Some questions arise in the process, e.g. if bar is an import (symlink), then whose parent bar::super refers too, or whether use foo::super [as name]; is allowed without the as name part and what name it introduces (use foo::self; needs to be allowed for compatibility and introduces foo).

Also cc #48067 (path concatenation in macros).

[nikomatsakis]

Visited in compiler triage. I think this is medium priority, clearly, but I am guessing that @Centril intended the nomination for the lang team.

Wearing my lang team hat, I think I'd expect this to compile, but I don't have strong opinions about it.

[nikomatsakis]

We discussed this in the lang team meeting last week. We decided that there were some reasons to tread carefully here: in particular, we didn't really want to admit the possibility of "non-canonical" paths like use foo::bar::self::super::bar. Moreover, there isn't a strong reason to accept this pattern -- it would definitely be linted against, and if you have some kind of tooling that wishes to emit self for simplicity, they can always emit things like use foo::bar::{self}.

So the conclusion was "probably better to just leave it alone for now" from a language perspective.

If we were to accept foo::self, we'd want some conditions:

• always the last item in a path
• do not accept super in that position, just self

[comex]

In addition to a suggestion, the compiler could have better error recovery. Currently, the following produces errors on both the first and second line; it should only error on the first line:

use std::mem; // `self` imports are only allowed within a { } list
fn main() { mem::drop(42); } // use of undeclared type or module `mem`

[mibac138]

@rustbot claim