False positive branches_sharing_code: trailing expression in else of if-let

[dtolnay]

fn main() {
    let string;
    let _x = if let true = true {
        ""
    } else if true {
        string = "x".to_owned();
        &string
    } else {
        string = "y".to_owned();
        &string
    };
}

$ cargo clippy
warning: all if blocks contain the same code at the end
  --> src/main.rs:10:5
   |
10 | /         &string
11 | |     };
   | |_____^
   |
   = note: `#[warn(clippy::branches_sharing_code)]` on by default
   = note: The end suggestion probably needs some adjustments to use the expression result correctly
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#branches_sharing_code
help: consider moving the end statements out like this
   |
10 |     }
11 |     &string;
   |

Clippy's preferred code is the following, which does not compile.

fn main() {
    let string;
    let _x = if let true = true {
        ""
    } else if true {
        string = "x".to_owned();
    } else {
        string = "y".to_owned();
    }
    &string;
}

error[E0308]: `if` and `else` have incompatible types
 --> src/main.rs:5:12
  |
3 |        let _x = if let true = true {
  |   ______________-
4 |  |         ""
  |  |         -- expected because of this
5 |  |     } else if true {
  |  |____________^
6 | ||         string = "x".to_owned();
7 | ||     } else {
8 | ||         string = "y".to_owned();
9 | ||     }
  | ||     ^
  | ||_____|
  | |______`if` and `else` have incompatible types
  |        expected `&str`, found `()`

It's possible that clippy means the following, but I still consider this a false positive because I find the original code clearer than this.

fn main() {
    let string;
    let _x = if let true = true {
        ""
    } else {
        if true {
            string = "x".to_owned();
        } else {
            string = "y".to_owned();
        }
        &string
    };
}

Meta

• cargo clippy -V: clippy 0.1.53 (2e495d2 2021-04-08)
• rustc -Vv:

  rustc 1.53.0-nightly (2e495d2e8 2021-04-08)
  binary: rustc
  commit-hash: 2e495d2e845cf27740e3665f718acfd3aa17253e
  commit-date: 2021-04-08
  host: x86_64-unknown-linux-gnu
  release: 1.53.0-nightly
  LLVM version: 12.0.0
  

Mentioning @xFrednet @phansch #6463

[xFrednet]

This is also a FP. We've decided in the PR that only whole if blocks should be linted (not single else ifs). My guess is that it's caused by the same problem like your other issue but I'll have to dig into it. :)

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