len_without_is_empty triggers when both len and is_empty have non-standard signatures #9520
Description
Summary
I have a proxy type (a symbol from a string interner) which has len and is_empty method which:
- are fallible
- take the interner as a method parameter
len_without_is_empty triggers with these methods, which is unexpected since neither method matches the method signature the lint looks for.
Lint Name
len_without_is_empty
Reproducer
I tried this code:
#[warn(clippy::len_without_is_empty)]
pub trait Intern {
type Symbol: Copy;
fn lookup_symbol(&self, sym: Self::Symbol) -> Result<Option<&[u8]>, String>;
}
#[derive(Debug, Clone, Copy, Hash, PartialEq, Eq, PartialOrd, Ord)]
pub struct Symbol(u32);
impl Symbol {
#[inline]
#[must_use]
pub fn is_empty<T, U>(self, interner: &T) -> bool
where
T: Intern<Symbol = U>,
U: Copy + From<Symbol>,
{
if let Ok(Some(bytes)) = interner.lookup_symbol(self.into()) {
bytes.is_empty()
} else {
true
}
}
#[inline]
#[must_use]
// #[allow(clippy::len_without_is_empty)]
pub fn len<T, U>(self, interner: &T) -> usize
where
T: Intern<Symbol = U>,
U: Copy + From<Symbol>,
{
if let Ok(Some(bytes)) = interner.lookup_symbol(self.into()) {
bytes.len()
} else {
0_usize
}
}
}I saw this happen:
Checking playground v0.0.1 (/playground)
warning: struct `Symbol` has a public `len` method, but the `is_empty` method has an unexpected signature
--> src/lib.rs:31:5
|
31 | / pub fn len<T, U>(self, interner: &T) -> usize
32 | | where
33 | | T: Intern<Symbol = U>,
34 | | U: Copy + From<Symbol>,
| |_______________________________^
|
= note: `#[warn(clippy::len_without_is_empty)]` on by default
note: `is_empty` defined here
--> src/lib.rs:16:5
|
16 | / pub fn is_empty<T, U>(self, interner: &T) -> bool
17 | | where
18 | | T: Intern<Symbol = U>,
19 | | U: Copy + From<Symbol>,
| |_______________________________^
= note: expected signature: `(self) -> bool`
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#len_without_is_empty
warning: `playground` (lib) generated 1 warning
Finished dev [unoptimized + debuginfo] target(s) in 0.48s
I expected to see this happen: No error because neither len nor is_empty has the expected signature.
Version
rustc 1.64.0 (a55dd71d5 2022-09-19)
binary: rustc
commit-hash: a55dd71d5fb0ec5a6a3a9e8c27b2127ba491ce52
commit-date: 2022-09-19
host: x86_64-apple-darwin
release: 1.64.0
LLVM version: 14.0.6
Additional Labels
No response