rust-lang / rust-lang/rust-clippy
`needless_borrow` suggestion causes error when removing `ref` in match
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Description
Summary
I was running clippy on rustc and ended up with this error
Lint Name
needless_borrow
Reproducer
I tried this code:
pub struct Impl<'a> {generics: &'a Generics<'a> }
pub struct Generics<'a>(&'a String);
pub enum ItemKind<'hir> {
Impl(&'hir Impl<'hir>),
Fn(&'hir Generics<'hir>),
}
impl ItemKind<'_> {
pub fn generics(&self) -> &Generics<'_> {
match *self {
ItemKind::Fn(ref generics)
| ItemKind::Impl(Impl { ref generics }) => generics,
}
}
}
fn main() {}
I saw this happen:
warning: this pattern creates a reference to a reference
--> src/main.rs:12:26
|
12 | ItemKind::Fn(ref generics)
| ^^^^^^^^^^^^
13 | | ItemKind::Impl(Impl { ref generics }) => generics,
| ^^^^^^^^^^^^
|
= note: `#[warn(clippy::needless_borrow)]` on by default
= help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#needless_borrow
help: try this
|
12 ~ ItemKind::Fn(generics)
13 ~ | ItemKind::Impl(Impl { generics }) => generics,
|
I expected to see this happen:
Nothing. You can't remove the ref here without causing a compile error. (Or, suggest the correct thing to do here, I'm not too familiar with ref patterns so there might be a correct thing here.)
Version
rustc 1.63.0-nightly (fdca237d5 2022-06-24)
binary: rustc
commit-hash: fdca237d5194bf8a1c9b437ebd2114d1c2ba6195
commit-date: 2022-06-24
host: x86_64-unknown-linux-gnu
release: 1.63.0-nightly
LLVM version: 14.0.5
Additional Labels
@rustbot label +I-suggestion-causes-error
Contributor guide
First steps
- Read the whole issue, then the project's contributing guide.
- Comment on the issue to say you are picking it up — it saves two people doing the same work.
- Fork the repository and make your change on a branch.
- Open a pull request that references the issue number.
Research direction
Start by reproducing the issue from the provided example in src/main.rs with Clippy and the needless_borrow lint. Then locate the lint implementation and its existing tests; done means the lint no longer suggests removing ref when that suggestion causes a compile error, with a regression test covering the match patterns.
Written by the indexing model from the issue text.
Assessment
- Tech stack
- rust
- Domain
- devtools, tooling
- Issue type
- Bug
- Difficulty
- 3/5
- Estimated time
- 1-2 days
- Activity status
- Stale
- Clarity
- Mostly clear
- Newbie friendliness
- 48/100