Rust-clippy: if_same_then_else false positive on 'else if'

[Wilfred]

I tried this code:

pub fn demo(net_loop_movement: i64) -> i64 {
    if net_loop_movement == 0 {
        0
    } else if net_loop_movement < 0 {
        // Net movement was negative, so conservatively assume
        // it was zero (e.g. the loop may run zero times).
        0
    } else {
        // Net loop movement was positive, so we can't
        // assume any bounds.
        1
    }
}

I wouldn't expect if_same_then_else to fire in this case. I'm explicitly documenting why the second case is a fallback. This is a reduced reproduction from this original source code.

It produces the following message:

error: this `if` has identical blocks
   --> src/bounds.rs:99:37
    |
99  |       } else if net_loop_movement < 0 {
    |  _____________________________________^
100 | |         // Net movement was negative, so conservatively assume
101 | |         // it was zero (e.g. the loop may run zero times).
102 | |         0
103 | |     } else {
    | |_____^
    |
    = note: `#[deny(clippy::if_same_then_else)]` on by default
note: same as this
   --> src/bounds.rs:97:31
    |
97  |       if net_loop_movement == 0 {
    |  _______________________________^
98  | |         0
99  | |     } else if net_loop_movement < 0 {
    | |_____^
    = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#if_same_then_else

Could the check be more conservative? Perhaps not firing if there's an additional else later, or considering blocks to be different based on trivia like comments?

Meta

• cargo clippy -V: clippy 0.0.212 (623fb90 2020-09-26)
• rustc -Vv:

$ rustc -Vv
rustc 1.48.0-nightly (623fb90b5 2020-09-26)
binary: rustc
commit-hash: 623fb90b5a1f324e0ec44085116bf858cef19a00
commit-date: 2020-09-26
host: x86_64-unknown-linux-gnu
release: 1.48.0-nightly
LLVM version: 11.0

[MTRNord]

Can reproduce with this tree:

else if msg_body.contains("!in") || msg_body.contains("!i") {

            } else if msg_body.contains("!out") || msg_body.contains("!o") {

            } else if msg_body.contains("!record") || msg_body.contains("!r") {

            } else if msg_body.contains("!break") || msg_body.contains("!b") {

            } else if msg_body.contains("!setTimeZoneDefault") {

            } else if msg_body.contains("!stats") || msg_body.contains("!s") {

            }

[ebroto]

Duplicate of #3770, specifically this comment refering to the existence of comments in the blocks, and this other comment with a possible resolution.

Thanks for taking the time to report this in any case!