rust-lang / rust-lang/rust-clippy

fp uninlined-format-args + ref-binding-to-reference

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C-bug I-false-positive I-suggestion-causes-error
Dominant language
Rust
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Description

Summary

These lints together break the code

Lint Name

No response

Reproducer

I tried this code:

#![allow(dead_code)]

struct ST3<'a>(&'a i32); // With lifetime parameter

impl<'a> ST3<'a> {

    fn ctor(v: &'a i32) -> Self {
        Self(v)
    }

    fn pattern(self) {
        let Self(ref v) = self;
        println!("{}", v);
    }
}

fn main() {}

I saw this happen:
cargo clippy --fix -- -Wclippy::uninlined-format-args -Wclippy::ref-binding-to-reference

after fixes were automatically applied the compiler reported errors within these files:

  * src/main.rs

This likely indicates a bug in either rustc or cargo itself,
and we would appreciate a bug report! You're likely to see
a number of compiler warnings after this message which cargo
attempted to fix but failed. If you could open an issue at
https://github.com/rust-lang/rust/issues
quoting the full output of this command we'd be very appreciative!
Note that you may be able to make some more progress in the near-term
fixing code with the `--broken-code` flag

The following errors were reported:
error: argument never used
  --> src/main.rs:13:25
   |
13 |         println!("{v}", &v);
   |                  -----  ^^ argument never used
   |                  |
   |                  formatting specifier missing

error: aborting due to previous error

Original diagnostics will follow.

warning: variables can be used directly in the `format!` string
  --> src/main.rs:13:9
   |
13 |         println!("{}", v);
   |         ^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#uninlined_format_args
   = note: requested on the command line with `-W clippy::uninlined-format-args`
help: change this to
   |
13 -         println!("{}", v);
13 +         println!("{v}");
   |

warning: this pattern creates a reference to a reference
  --> src/main.rs:12:18
   |
12 |         let Self(ref v) = self;
   |                  ^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#ref_binding_to_reference
   = note: requested on the command line with `-W clippy::ref-binding-to-reference`
help: try this
   |
12 ~         let Self(v) = self;
13 ~         println!("{}", &v);
   |
Version
rustc 1.67.0-nightly (e0098a5cc 2022-11-29)
binary: rustc
commit-hash: e0098a5cc3a87d857e597af824d0ce1ed1ad85e0
commit-date: 2022-11-29
host: x86_64-unknown-linux-gnu
release: 1.67.0-nightly
LLVM version: 15.0.4
Additional Labels

No response

Contributor guide

Open the contributing guide

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Start with the reproducer in src/main.rs and run the shown cargo clippy command with both uninlined-format-args and ref-binding-to-reference enabled. Compare the individual fixes with the combined --fix result; done means the automatic fixes preserve valid formatting arguments and the example compiles without the reported error.

Written by the indexing model from the issue text.

Assessment

Tech stack
rust
Domain
devtools
Issue type
Bug
Difficulty
4/5
Estimated time
3-5 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
35/100

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