wrong_self_convention: FN with is_* taking &mut self

[jendrikw]

Summary

My interpretation of the table at https://rust-lang.github.io/rust-clippy/master/index.html#wrong_self_convention is that a method called is_* is allowed to take no self, or &self, but not self or &mut self. In reality, only self produces a warning. Is this intentional?

Lint Name

wrong_self_convention

Reproducer

I tried this code:

#![allow(unused)]
struct S { field: String }

impl S {
    fn is_foo(&mut self) -> bool { todo!() }
}

fn main() {}

I expected to see this happen:

warning: methods called `is_*` usually take `self` by reference or no `self`
  --> src/main.rs:16:15
   |
16 |     fn is_foo(&mut self) -> bool {
   |               ^^^^

Instead, this happened:

No warning

Version

rustc 1.57.0 (f1edd0429 2021-11-29)
binary: rustc
commit-hash: f1edd0429582dd29cccacaf50fd134b05593bd9c
commit-date: 2021-11-29
host: x86_64-unknown-linux-gnu
release: 1.57.0
LLVM version: 13.0.0

[jendrikw]

This issue was filed because intellij-rust warns for both &mut self and self and it wants to be consistent with clippy. See intellij-rust/intellij-rust#7557.

(The yellow background is a warning from intellij-rust, the yellow underline is from clippy.)

[ghost]

I agree. It should warn on &mut self.

[nmathewson]

This one looks neat, and I think I can see what the trouble is; I'll try writing a patch for this in the next day or two. (If I haven't written a PR by 5 January, I have probably given up or forgotten this.)