branches_sharing_code reporting a false positive

[MGlolenstine]

I tried this code:

fn test() {
    let v = vec![1, 2, 3, 4, 5, 6, 7, 8, 9, 0];
    let mut counter = 0;
    for i in v {
        if counter == 0 {
            counter += 1;
            println!("first");
        } else if counter == 1 {
            counter += 1;
            println!("second");
        } else {
            counter += 1;
            println!("other: {}", i);
        }
    }
}

I expected to see this happen: I expected the lint to pass without a hitch, as the counter is used in the if statement.

Instead, this happened:
I got a lint report, that I could change the if statements, as they all start with the same line of code, but doing that makes the code invalid.

warning: all if blocks contain the same code at the start
 --> src/lib.rs:5:9
  |
5 | /         if counter == 0 {
6 | |             counter += 1;
  | |_________________________^
  |
  = note: `#[warn(clippy::branches_sharing_code)]` on by default
  = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#branches_sharing_code
help: consider moving the start statements out like this
  |
5 |         counter += 1;
6 |         if counter == 0 {
  |

Meta

• cargo clippy -V: clippy 0.1.53 (53cb7b0 2021-06-17)
• rustc -Vv:

rustc 1.53.0 (53cb7b09b 2021-06-17)
binary: rustc
commit-hash: 53cb7b09b00cbea8754ffb78e7e3cb521cb8af4b
commit-date: 2021-06-17
host: x86_64-unknown-linux-gnu
release: 1.53.0
LLVM version: 12.0.1

[MGlolenstine]

Suggesting label change to I-suggestion-causes-error, as it's correctly detected the case, but the fix causes a problem.

[xFrednet]

@rustbot label +I-suggestion-causes-error -I-false-positive

[xFrednet]

This kind of fits both labels, I'm going over a possible solution in my head and might claim this issue :)

[MGlolenstine]

@xFrednet Can this issue be closed now that the #7462 has been merged?
Thanks for the great work!

[xFrednet]

#7462 only documented this as a known issue. It's possible to actually fix this issue to not trigger the lint at all. I would keep this issue open until that is done, or it's decided that it's not worth it.

You're welcome, thank you for the report. 🙃

[youknowone]

Similar false positive happens when the shared code is locking. Moving lock to outside of if statement may cause different behaviour.